HBSC1203 BIOLOGY I

� INTRODUCTION

Life comprises living and non-living things. There are millions of living things on Earth, consisting of plants and animal species. The species range from simple to complex organisms. Before we go any further, let us take a look at Figure 1.1. What common characteristics do these living organisms have?

Figure 1.1: Living organisms

TTooppiicc

11�� Characteristics

of Living Things

LEARNING OUTCOMES By the end of this topic, you should be able to:

1. List the seven basic living processes;

2. Explain the life processes in humans and animals;

3. Explain the life processes in plants;

4. Describe the basic needs of humans and animals; and

5. Describe the basic needs of plants.

� TOPIC 1 CHARACTERISTICS OF LIVING THINGS

2

This is what we are going to learn in this topic. We will discuss their common characteristics and also differences. Due to their characteristics as living organisms, they need basic things in order to survive. What are they? LetÊs read more.

BASIC LIVING PROCESSES

Living things comprise animals and plants. Although all living things look different from each other, they all have seven things in common. These seven things are called life processes. You must be wondering, what are the seven basic life processes? These seven basic life processes are shown in Figure 1.2.

Figure 1.2: Seven basic life processes

Things are only alive if they engage in all the seven processes as shown in Figure 1.1. When they have the capacity to carry out these seven life processes, they are characterised as living organisms. Some non-living things may have one or two of these characteristics but living things will have all the seven characteristics.

1.1

SELF-CHECK 1.1

List the basic seven life processes in living organisms.

TOPIC 1 CHARACTERISTICS OF LIVING THINGS � 3

LIFE PROCESSES IN HUMANS AND ANIMALS

As mentioned previously, living organisms have the capacity to carry out the seven life processes as shown in Figure 1.1. Firstly, letÊs take a look at the life processes that happen specifically in humans and animals.

1.2.1 Nutrition

Animals and human beings are in the animal group. They feed or eat from the day they are born until they die. Right after birth, they are fed by their mothers with the simplest form of food. Many of them feed on their mothersÊ milk. However, as they develop and grow up, they eat different kinds of foods. Some animals feed on plants only, some eat meat of other animals and others eat both meat and plants. Animals that eat only plants, algae and photosynthesising bacteria like fungi, belong to the class called herbivores. On the other hand, animals that feed on the meat of other animals are called carnivores. Animals that consume both animals and plants as their primary food source are in the group called omnivores.

1.2.2 Movement

The second characteristic of animals is that they can move. They move from one place to another for many reasons, namely in search of living places, food, safety, breeding, and escaping from predators. Some of them move just like human beings do, because of occupation; finding a place that is safer or suitable for living; or other reasons. Animals move in one of various ways. The various types of movement are walking, running, leaping, hopping, slithering, burrowing, swimming and flying.

1.2.3 Respiration

The third characteristic of living things is that they breathe. Human beings and animals breathe oxygen into their lungs and then breathe out carbon dioxide through a process called breathing. Therefore, breathing refers to the process that brings about an exchange of gases between an� organism and its environment. The oxygen from the lungs is then transported to each cell via the circulatory system and then is used to oxidise glucose through the process of respiration in every cell.

1.2

� TOPIC 1 CHARACTERISTICS OF LIVING THINGS 4

1.2.4 Excretion

The fourth characteristic of living things is that they must eliminate the waste products of metabolism and other non-useful materials from their bodies. The way of removing this waste is called excretion. If this waste is to remain in the body, it may be poisonous and harm them. Humans and animals produce liquid waste called urine. Both of them also excrete waste when they exhale. Thus, all living things have to remove waste from their bodies.

1.2.5 Growth

Human beings and animals are small in size when they are newborn. They need energy from food and water to develop and grow. With food, they become bigger and taller because this energy is used in growth. Living things develop and become larger and more complicated as they grow. Look at how small a baby elephant is when it was born (Figure 1.3). Then look at its size some years later! If you have a younger sibling, can you remember how small he or she was at birth? How tall or big he or she is now? What do you know about this phenomenon? �

�Figure 1.3: A baby elephant and its mother

Source: http://www.saburchill.com


1.2.6 Sensitivity

The other characteristic of living things is that they are sensitive. They can react or respond to the conditions around them through light, touch, pain, heat, cold, sound and others. Animals and humans can respond to stimuli as they possess sense organs that are made up of nerve cells. Certain microbes curl into tiny balls when something touches them. Human beings blink when light shines into their eyes. Some people become disturbed if the environment around them is too noisy.

1.2.7 Reproduction

Living things are capable of multiplying or reproducing themselves. If one organism fails to reproduce, the population will decrease and finally become extinct. Several factors can affect the existing number of living things. They may become fewer, then disappear because their members die due to old age, get infected by diseases or involved in accidents, are hunted by others (man or animals), get killed in territorial disputes, wars, power struggles and so on. It is a fundamental law of biology that living things can only be reproduced by other living things to survive. Almost every living organism exists due to the reproductive activities of other organisms. There are two types of reproduction for living things. They are: (a) AAsexual Asexual reproduction involves no exchange of genetic material between

organisms. It is a simple replication to produce a new organism. An organism reproduced in this way has little or no genetic variation from the parent organism. Single celled-animals like Protozoa and Hydra (Figure 1.4 and 1.5) are examples of animals that reproduce asexually. �


�Figure 1.4: Protozoa

Source: http://www.microimaging.ca

�Figure 1.5: Hydra

Source: http://www.saburchill.com �

(b) SSexual Sexual reproduction involves two organisms, male and female. Human

beings make babies, kangaroos produce joeys, and chickens and ducks lay eggs. The process involves the combining of genetic materials from the two parent organisms during mating. The offspring or babies from the sexual reproduction generally will have some of the characteristics of both parents. Sexual reproduction from the parent organisms gives rise to reproductive cells called gametes. Sexual reproduction ensures that a high degree of variation occurs within populations.


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SELF-CHECK 1.2

Explain living processes in humans and animals.

1. Name five examples of animals (apart from Protozoa and Hydra) that reproduce asexually.

2. Do research on how a baby in its motherÊs womb excretes its

waste. Share the information with your classmates. 3. Look at Figures 1.6 to 1.8. Which animal is a herbivore, carnivore

and omnivore?

Figure 1.6: Horse

Figure 1.7: Lion

Figure 1.8: Crow

ACTIVITY 1.1

� TOPIC 1 CHARACTERISTICS OF LIVING THINGS

8

Activity 1.1

1. Figures 1.9 to 1.16 show different kinds of animal movement. Can you name other examples of animals that move according to this type of movement?

Figure 1.9: People walking

Source: http://www.li

fetrek-slovenia.com

Figure 1.10: A running fox

Source: http://artfiles.art

.com

Figure 1.11: A leaping lemur

Source: http://www.magma.nationalgeographi

c.com

Figure 1.12: A hopping kangaroo Source:

http://www.bio.davidson.edu

Figure 1.13: A flying eagle

Source: http://www.h

ickerphoto. com

Figure 1.14: A burrowing owl

Source: http://members.

cox.net

Figure 1.15: A slithering snake

Source: http://coolinsights.

blogspot.com

Figure 1.16: A swimming tiger

Source: http://www.mc

cullagh.org

ACTIVITY 1.2


LIFE PROCESSES IN PLANTS

Plants also carry out the seven life processes but they differ in some aspects when compared to animals and humans. Now, let us learn about the life processes in plants.

1.3.1 Nutrition

Plants make their own food through the process of photosynthesis. They are able to do so because they have chlorophyll that capture sunlight and the energy needed to start photosynthesis. The end product of photosynthesis is glucose which is then stored as starch.��

1.3.2 Movement

Unlike animals, only certain parts of the plants move. Plants move slowly, usually by growing in one direction, such as towards a source of light. Plant movement occurs both above ground, in the form of leaves and shoots, and below ground, where roots spread out and move deeper into the earth in order to provide stronger support and get a greater supply of nutrients.

1.3.3 Respiration

Just as humans and animals breathe, plants use respiration as a means of releasing energy, using up nutrients and oxygen and producing water and carbon dioxide. Respiration is essentially the opposite of photosynthesis, the process by which plants create food and matter.

1.3.4 Excretion

Plants have no special organs for the removal of wastes. The waste products of respiration and photosynthesis are used as raw materials for each other. Oxygen, produced as a by-product of photosynthesis, is used up during respiration and carbon dioxide (produced during respiration) is used up during photosynthesis. �

1.3


Excretion is carried out in the plants in the following ways:

(a) The gaseous wastes, oxygen, carbon dioxide and water vapour are removed through stomata of leaves and lenticels of stems.

(b) Some waste products collect in the leaves and bark of trees. When the leaves and bark are shed, the wastes are eliminated.

(c) Some waste products are rendered harmless and then stored in the stem as solid bodies. Raphides, tannins, resins, gum, rubber and essential oils are some such wastes.

1.3.5 Growth

Growth in plants occurs chiefly at mmeristems where rapid mmitosis provides new cells. In sstems, mitosis in the aapical meristem (Figure 1.17) of the shoot apex (also called the tterminal bud) produces cells that enable the stem to grow longer and periodically produces cells that will give rise to leaves. The point on the stem where leaves develop is called a nnode. The region between a pair of adjacent nodes is called the iinternode. �

�Figure 1.17: Apical meristem

Source: http://www.doctortee.com The internodes in the tterminal bud are very short so that the developing leaves grow above the apical meristem that produced them and thus protect it. New meristems, the llateral buds, develop at the nodes, each just above the point where a leaf is attached. When the lateral buds develop, they produce new stem tissues, thus bbranches are formed. �


Growth also occurs at the root tip as can be seen in Figure 1.18. The root tip consists of a:

(a) MMeristem � a region of rapid mitosis, which produces the new cells for root growth; and

(b) RRoot cap � a sheath of cells that protects the meristem from abrasion and damage as the root tip grows through the soil.

�

�Figure 1.18: Growth at root tip of plants

Source: http://www.doctortee.com

1.3.6 Sensitivity

Like animals, plants sense changes in their surroundings and respond to them. Plants are able to detect and respond to light, gravity, changes in temperature, chemicals, and even touch. Unlike animals, plants do not have nerves or muscles, so they cannot move very fast. A plant usually responds to change by gradually altering its growth rate or its direction of growth. The slow movements that plants make towards or away from a stimulus, such as light, are known as tropisms. Tropisms are controlled with the help of special chemicals called plant growth regulators. Roots push down through soil because of the effect of gravity. They may also be drawn towards water, or away from bright light as illustrated in Figure 1.19.


�Figure 1.19: PlantsÊ sensitivity

Did you notice that sunflowers face east in the morning but west by the evening? This is called phototropism, which means the movement of part of a body towards light (Figure 1.20). �

�Figure 1.20: Sunflowers respond towards light

�


1.3.7 Reproduction

Plants also reproduce in two ways; asexual and sexually. The process of reproduction is the same as in animals. Plants growing from tubers or bulbs, such as sweet potatoes and onions, are examples of plants that reproduce asexually. This can be seen in Figure 1.21. �

�Figure 1.21: Asexual reproduction in plants

Sexual reproduction is the formation of offspring by the fusion of ggametes. In higher plants, the offspring are packaged in protective seeds, which are long-lived and can be dispersed farther away from the parents. In flowering plants (angiosperms), the seeds themselves are contained inside the fruit, which may protect the developing seeds and aid in their dispersal. �


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BASIC NEEDS OF HUMANS AND ANIMALS

You have learned the basic life processes of humans, animals and plants. Now, letÊs go through the basic needs of humans and animals first. Then, we will go through the basic needs of plants. But bear in mind that the basic needs of animals and humans are quite similar to plants and differ only in certain things.

1.4.1 Water

The most important nutrient for survival is water. Water is the medium in which all chemical reactions take place within an animal's body. If an animal loses one-tenth of its water for any reason, the results are fatal. Water also functions in excretion of wastes, regulating body temperature and transporting food.

1.4

SELF-CHECK 1.3

Tick [�] the following statements that are true.

1. Green leaves have chlorophyll that can capture sunlight, the energy needed to start photosynthesis.

2. Shoots of plants move away from sunlight while the roots move downward.

3. Plants carry out photosynthesis but not respiration.

4. Plants take in carbon dioxide as well as oxygen.

5. Tannin, resin and gum are the waste products of plants.

6. Growth only happens at the shoot tip and root tip.

7. Plants respond to sunlight for growth.

8. Bulb, tuber and rhizome are examples of asexual reproduction in plants.

9. Flowers enable plants to reproduce sexually.

10. Plants can also reproduce sexually through spores.

�


Animals get water from streams, lakes, ponds or even puddles. Others drink water that collects on leaves after a rainfall. But do you know that some animals do not drink water? Instead, they get water from the food that they eat.

1.4.2 Food

Animals and humans get their food by eating other animals or plants or both. Different classes of food have different functions on the animals. For example, protein is needed for building and repairing cells, carbohydrate and fats provide energy. Energy is needed for bodily functions such as respiration, movement and growth. Food, or lack of it, often affects animals in dramatic ways. Food scarcity can trigger great migrations such as the year round movements of caribou and the winter migrations of many birds. Adaptation enables all animals to get food. Toothed herbivores, for example, have large, flat, round teeth that help them grind plant leaves and grasses. Some carnivorous animals, such as bears, dogs and the big cats have sharp canines and incisors for chewing through meat with ease. The digestive systems of animals have proteins known as enzymes that break down food and convert it into energy. Some animals eat insects as their food.

1.4.3 Air

All animals must breathe in oxygen in order to survive. Land-dwelling species receive oxygen from the air, which they inhale directly to their lungs. Marine and freshwater species filter oxygen from water by using their gills. Oxygen is much needed in respiration that provides energy for animals and humans. It is also important in destroying harmful bacteria in an animal's body without sacrificing the body's necessary bacteria.

1.4.4 Temperature

External temperature is a major factor in the survival of animals. The vertebrate groups, amphibians, reptiles and fish are said to be cold-blooded � they take on the temperature of their environment. Most have thin skin. On the other hand, birds and mammals, which are termed warm-blooded, can regulate their own body temperature. � Let us take a look at an example of the Monarch butterflies (Figure 1.22). They are unable to survive the cold winters. In order to escape the cold weather, they will migrate to the south.


�Figure 1.22: Monarch butterfly

Source: http://animals.nationalgeographic.com �However, some mammals, such as bears, gophers (Figure 1.23) and bats, hibernate during winter and live off their body fat. They can drop their body temperature to about 50 degrees Fahrenheit. �

�Figure 1.23: Gopher

Source: http://animal-wildlife.blogspot.com/2011/10/gopher.htm

1.4.5 Shelter

Every animal needs a place to live · a place where it can find food, water, oxygen and the proper temperature. Shelter provides cover from adverse weather, protection from predators and a place to rest and have their young. It is also a place to prevent death due to exposure that directly affects the reproductive success. Good sites greatly increase the chance of survival for young animals. Animals live in various types of shelter as illustrated in Figure 1.24.


Figure 1.24: Examples of shelters

Source: http://marzukitm.edublogs.org

Animals also depend on their physical features to help them obtain food, keep safe, build homes, withstand weather and attract mates. These physical features are called physical adaptations. Physical adaptations do not develop during an animalÊs life but over many generations. The shape of a birdÊs beak, the number of fingers, colour of the fur, the thickness or thinness of the fur, the shape of the nose or ears are all examples of physical adaptations which help different animals to survive. You could read more about animal adaptations at:

(a) http://www.oaklandzoo.org/atoz/azhgehog.html; and

(b) http://www.pbs.org/kratts/world/index.html.

SELF-CHECK 1.4

1. Explain the basic needs of humans and animals. 2. Is mating a basic need for an animal?

ACTIVITY 1.3

List a few animals that eat insects.


1.5 BASIC NEEDS OF PLANTS

Plants are living things that have needs in order to stay alive. Do you know what are the basic needs of plants? LetÊs read further in order to know the basic needs of plants.

1.5.1 Sunlight

Why do you think sunlight is important to plants? Sunlight is very important for plants as it supplies the energy required for photosynthesis to take place. Photosynthesis depends upon the absorption of light by pigments in the leaves of plants. The most important of these is chlorophyll-a. Figure 1.25 shows the spectra of sunlight before and after its journey of being absorbed by a green leaf. �

�Figure 1.25: Spectrum of light being absorbed by plants

Source: http://www.tomatosphere.org As can be seen in Figure 1.25, when sunlight falls on a green leaf, some of the sunlight is absorbed by chlorophyll.


1.5.2 Carbon Dioxide

Without sufficient quantities of dissolved carbon dioxide, photosynthesis cannot take place. Some plants do not need much carbon dioxide (CO2) and some plants like Cryptocorynes seemed to worsen with higher levels of CO2. Typical levels of CO2 in a non-CO2 injected aquarium are in the range of 1�3 ppm. Most plants will flourish at the levels of 10�20 ppm but this requires some types of CO2 injection. With lower levels of CO2, the plants will not be able to utilise high levels of light and nutrients. Figure 1.26 shows how CO2 concentration affects the rate of photosynthesis. �

��

Figure 1.26: The effect of CO2 concentration upon rate of photosynthesis Source: http://science.halleyhosting.com/�

1.5.3 Nutrients

The minerals available in soil is absorbed by roots and transported to other parts of the plants along with water in the xylem vessel. Essential plant elements include, carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulphur, calcium, iron, magnesium sodium, chlorine, copper, manganese, cobalt, zinc, molybdenum and boron to name the most common. Other minerals are also required, but they vary greatly from plant to plant. For example, some algae need large amounts of iodine and silicon, while some locoweed species need selenium.


When any of these elements are lacking in the soil and the deficiencies are not compensated for by adding fertiliser compounds of compost, the plant will demonstrate symptoms characteristic of mineral deficiencies. Most commercial fertilisers contain some ratio of nitrogen, phosphorus and potassium. Thus, they are able to compensate for a wide variety of insufficiency.

1.5.4 Water

All living things need water to stay alive, but plants use much more water than animals do. Plants are 90 percent water, compared to animals with as little as 75 percent water by weight. Plants use water directly when they capture light energy from the sun and transform it into useful food molecules. Water is also needed to support the stem of plants. Plants need water to maintain turgor pressure. Turgor pressure helps to keep the plant erect and is accomplished when the plasma membrane pushes against the cell wall. Without water, the plantÊs cells will shrink and the stem will wilt. Water is also used to cool down a plant through evaporation. Plants absorb water and minerals from soil through roots and transport them to cells through xylem.

1.5.5 Oxygen

Plants need oxygen for their respiration process. During the day, plants produce far more oxygen from photosynthesis than the production of carbon dioxide from respiration. During the night, plants actually use the leftover oxygen produced from the daylight photosynthesis or take in oxygen from the air surrounding the plants to meet their energy needs. The exchange of oxygen and carbon dioxide in the leaves occurs through pores called stomata as can be seen in Figure 1.27(a), while in roots and stems through lenticels as can be seen in Figure 1.27(b).


� (a) (b)

Figure 1.27: Stoma (a) and lenticel (b) Source: http://users.rcn.com

SELF-CHECK 1.5

Describe the basic needs of plants. Is soil a basic need for a plant?

ACTIVITY 1.4

In groups, surf the Internet or other resources to find out experiments that you can do to show that plants need oxygen, sunlight and water to live. Try the experiments and share your findings with the other groups.


� Living things can be categorised into humans, plants and animals.

� Living things undergo seven basic living processes such as nutrition, movement, respiration, excretion, growth, sensitivity and reproduction.

� Plants make their own food through photosynthesis while animals and humans have to rely on the plants or other animals for food.

� Animals and humans move their whole bodies from one place to another while only certain parts of the plants move.

� Both plants and animals undergo cellular respiration in the same way.

� Both plants and animals experience changes in size and mass when they grow.

� Both plants and animals reproduce asexually and sexually.

� Both plants and animals can respond to external stimuli.

� Both plants and animals excrete their wastes but the waste products of animals and plants are different.

� The basic needs of animals are food, water, air, temperature and shelter.

� The basic needs of plants are sunlight, water, nutrients, carbon dioxide and oxygen. �

Basic needs

Excretion

Growth

Living processes

Movement

Nutrition

Reproduction

Respiration

Sensitivity


�

Ainslie, K. (1994). Why do my plants need so much water?. Retrieved March 20, 2012, from http://www.pa.msu.edu/sciencet/ask_st/092194.html

Allen, J. (2012). Seven life processes of a plant. Retrieved March 20, 2012, from http://www.ehow.com/list_6731235_seven-life-processes-plant.html Campbell, N. A., Reece, J. B., Mitchell, L. G., & Taylor, M. R. (2003). Biology

(4th ed.). San Francisco, CA: Benjamin Cummings. Green, N. P., Stout, G. W, & Taylor, D. J. (1993). Biological science (2nd ed.).

Oxford, UK: Oxford University Press. Johnson, G. B. (2000). The living world (2nd ed.). Boston, MA: McGraw Hill Higher

Education. Kindersley, D. (2007). Plant sensitivity. Retrieved March 20, 2012, from http://www.teachervision.fen.com/dk/science/encyclopedia/plant-

sensitivity.html RCN.(2011). Roots. Retrieved March 20, 2012, from http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/Roots.html Schultz, S. T. (2012). Reproduction in plants. Retrieved March 20, 2012, from http://www.biologyreference.com/Re-Se/Reproduction-in-Plants.html

� INTRODUCTION A living thing is called an organism. Life on earth is represented by a great variety of organisms. There are single-cell organisms called prokaryotes and multicellular organisms called eukaryotes. The general structure of an animal cell and a plant cell is quite similar with some differences between them. In this topic, we will be looking at the levels of organisation of life, prokaryotes and eukaryotes, the structure of the animal and plant cells, its parts and the organelles in them. Lastly we will look at the different methods of movement of substances across the cell membranes.

By the end of this topic, you should be able to:

1. Describe the levels of organisation of life;

2. Differentiate prokaryotic and eukaryotic cells;

3. Describe animal cell structures and their functions;

4. Describe plant cell structures and their functions; and

5. Explain the movement of substances across the membranes.

LEARNING OUTCOMES

TTooppiicc

22 � Cell Structure

and Organisation

TOPIC 2 CELL STRUCTURE AND ORGANISATION � 25

INTRODUCTION TO LIFE AND LEVELS OF ORGANISATION

Life on earth started as a unicellular organism. Later, some evolved into multicellular organisms. In unicellular (single-celled) organisms, the single cell performs all life functions. It functions independently. However, multicellular (many celled) organisms have various levels of organisation within them. Individual cells may perform specific functions and also work together for the good of the entire organism. The cells become dependent on one another. Multicellular organisms have the following five levels of organisation ranging from the simplest to the most complex. This can be seen in Figure 2.1.

Figure 2.1: Levels of organisation

Now, let us take a look at Table 2.1 to learn more about each level. There are also examples for each level of organisation.

2.1

� TOPIC 2 CELL STRUCTURE AND ORGANISATION

26

Table 2.1: Levels of Organisation

Level Description Example

Cells � The basic unit of structure and function in living things.

� May serve a specific function within the organism.

Blood cells, nerve cells, bone cells.

Tissues � Made up of cells that are similar in structure and function which work together to perform a specific activity.

Connective, epithelial, muscle and nerve.

Organs � Made up of tissues that work together to perform a specific activity

Heart, brain, skin.

Systems � Groups of two or more tissues that work together to perform a specific function for the organism.

Circulatory system, nervous system, skeletal system.

Organism � Entire living things that can carry out all basic life processes. Meaning, they can take in materials, release energy from food, release wastes, grow, respond to the environment and reproduce.

� Usually made up of organ systems, but an organism may be made up of only one cell such as bacteria or protist.

Bacteria, amoeba, mushroom.

SELF-CHECK 2.1

1. Describe the five levels of organisation in an organism.

2. Does this sequence represent the levels of organisation from the simplest to the most complex?


PROKARYOTIC AND EUKARYOTIC CELLS

We have learned that a cell is the basic unit of life. It is the basic unit of an organism and consists of a jelly-like material surrounded by a cell membrane. In the cell itself, there are structures or organelles that have different functions for the cell. According to the organisation of their structures, living cells come in two basic types, pprokaryotic (also spelt as procaryotic) and eeukaryotic (also spelt as eucaryotic) cells. These two cells can be seen in Figure 2.2.

(a) (b)

Figure 2.2: Prokaryote (a) and eukaryote (b) Source: http://www.daviddarling.info

2.2.1 Prokaryotic Cells

The Greek word ÂkaryoseÊ means ÂkernelÊ, as in a kernel of grain. In biology, this root word is used to refer to the nucleus of a cell. ÂProÊ means ÂbeforeÊ, and ÂeuÊ means ÂtrueÊ, or ÂgoodÊ. Thus,ÊProkaryoticÊ means Âbefore a nucleusÊ. Bacteria and other ssingle or uunicellular organisms are in the prokaryotic class.

2.2

The levels of organisation also happen in multicellular plants. Can you name some examples of cells, tissues, organs and systems in plants? Post your answer in the forum.

ACTIVITY 2.1


28

Prokaryotic cells are smaller and simpler compared to eukaryotic. The cell is structurally simple because of its small size. In many single organisms, the smaller a cell is, the greater is its surface-to-volume ratio (the surface area of a cell compared to its volume). This can be seen in a prokaryotic spherical cell of 2 micrometers (�m) in diameter. It has a surface-to-volume ratio of approximately 3:1, while a spherical cell having a diameter of 20 �m has a surface-to-volume ratio of around 0.3:1. A large surface-to-volume ratio, as seen in smaller prokaryotic cells, means that nutrients can be easily and rapidly transferred and sent to any interior part of the cells.

2.2.2 Eukaryotic Cells

Eukaryotic, on the other hand, means Âpossessing a true nucleusÂ. Human beings, animals, plants, fungi, protozoans and algae cells are all eukaryotic cells. This is a big clue on the differences between these two cell types. Prokaryotic cells have no nuclei, while eukaryotic cells have true nuclei. Eukaryotic cell is much bigger in size compared to the prokaryotic cell. Due to the large size, it has a limited surface area when compared to its volume. It means that nutrients cannot rapidly diffuse to all interior parts of the cell easily. Thus, the eukaryotic organism cells require a variety of specialised internal structures or organelles to carry out metabolism, provide energy and transport chemicals throughout the cell. However, both Prokaryote and Eukaryote cells must carry out the same functions for life processes.

2.2.3 Prokaryotic versus Eukaryotic Cells

Both Prokaryote and Eukaryote cells have some similarities and differences. Learning these terms will help us understand a cell better by recognising them in terms of these elements:

(a) Structural (cytoskeleton, flagella and cilia);

(b) Endomembrane (plasma membrane, nucleus, Golgi apparatus, lysosome);

(c) Energy-producing organelles (mitochondria, chloroplasts); and

(d) Genetic materials (chromosomes, nucleolus, ribosomes).


Unfortunately, not all elements mentioned are present in all type of cells. It means that if one particular element is present in the prokaryotic organism, that element may not be found in the eukaryotic cells and vice-versa. Let us examine these features of elements of the type of cells in Table 2.2.

Table 2.2: Prokaryotic versus Eukaryotic Cells

Prokaryotic Eukaryotic

Features Bacteria Plant Animal

Size (diameter) 0.5�5 �m 40 �m 15 �m

Cell wall Yes (contains peptidoglycan)

Yes (contains cellulose)

No

Genetic material A single circular molecule and DNA is naked.

DNA linear, associated with histones (proteins), in a nucleus, surrounded by a nuclear envelope.

Ribosomes 70S ribosomes (smaller) 80S ribosomes (larger)

ER, Golgi apparatus No Yes

Mitochondria No (respiration occurs on an unfolding of the cell membrane called the mesosome.)

Yes

Chloroplasts No Yes No

Source: http://www.dr-sanderson.org

Explain the differences between prokaryotic and eukaryotic cells.

SELF-CHECK 2.2


30

ANIMAL CELLS

Eukaryotic cells are found in two classes of living things. They are aanimals and plants. As indicated in the earlier subtopic, an eukaryotic cell is much bigger in size, more complex and requires a variety of specialised internal structures or organelles to carry out metabolism, provide energy and transport chemicals throughout the cell. In this subtopic, we are going to look at animal cells.

2.3.1 General Structure of Animal Cells

Animal cells are eukaryotes or have true nnuclei. They are bigger compared to prokaryotic cells. This larger size means that there is a lot more space inside the cell like your studio apartment. Eukaryotic cell is like a gigantic warehouse. In order to make this huge space relatively as efficient as the small space, a lot of compartmentalisation and internal specialisation is required. Therefore, the cell has many organelles to do specific functions. However, the majority of the eukaryotic cells, like in the animal cells, will have structures namely:

(a) Plasma membrane;

(b) A nucleus;

(c) Chromosomes;

(d) Numerous membrane-bound cytoplasm organelles: mitochondria, rough endoplasmic reticulum (rer), smooth endoplasmic reticulum (ser);

(e) Lysosomes;

(f) Ribosomes;

(g) Golgi body or apparatus; and

(h) A Cytoskeleton.

2.3


Now, let us have a look at Figure 2.3 which shows a cell of an animal.

Figure 2.3: A cell of an animal

Source: Johnson (2000) You have just learned the features of animal cells. Now you need to conduct an experiment (Activity 2.2) in the Biology laboratory about animal cells taken from your body. In doing this, you need to take a sample from your inner cheek and examine it very carefully using the right procedures under a light microscope. However, before you start the experiment, note that a human cheek cell should look like the one in Figure 2.4.

Figure 2.4: Human cheek cell

Source: http://www.aber.ac.uk


32

ACTIVITY 2.2

Do the following experiment to observe the appearance of your cheek cells under a light microscope.

Title of Experiment: Examining the structure of human cheek cells under a microscope.

Materials Needed: A light microscope, several glass slides and cover slips, forceps, a dropping pipette, 5% iodine methelyne blue solution, cotton, a scalpel for scrapping the upper layer of your cheek and some prepared slides of stained human cheek cells. Procedure:

1. Using a scalpel, scrape your inner cheek and wipe it on a piece of glass slide. Spread it wide to get a large area. Apply a small drop of iodine methelyne blue solution using a dropping pipette.

2. Using forceps, cover the cheek sample with the cover slip

CAUTION: Iodine solution is an irritant poison. Avoid skin/eye contact; do not ingest it. Should this happen, flush the spill and splash it with water for 15 minutes; rinse your mouth with water and call your tutor.

3. Put the slide under the microscope and examine it starting with the low power first and then with the high power.

4. Sketch a few cells as they appear under the high power. How many dimensions do the cells appear to have when viewed under high power? Sketch a cell as it would appear if you could see it in three dimensions.

5. Identify the features of your cheek cells compared to the animal cells that you have learned.

6. Replace your cheek sample slide with the prepared stained human cheek cells.

7. Examine the cheek cells under the low and then the high power of the microscope. Compare the similarities and differences of the cheek cells you prepared with the one purchased. Draw several of the cells seen from both slides.

8. Make an analysis of your experiment.

9. Compare your results with those of your classmates.

10. Extra journey: Browse the Internet for more information, diagrams, pictures and other similar experiments.


2.3.2 Function of Animal Cell Structures

As you have learned previously, an animal cell contains many structures. These structures perform different functions. Let us take a look at the function of each of the structures listed in Table 2.3.

Table 2.3: Function of Animal Cell Structures

Animal Cell Structure Function

Cell Membrane

Among the various membranes of the animal cell, the pplasmalemma is the cell surface membrane (Figure 2.5). It consists of two layers of lipids (phospholipid bilayers) sandwiched between two types of protein layers molecule. It is semi-permeable and controls the exchange of substances between the cell and its environment.

Figure 2.5: Plasmalemma Source: Green, Stout, & Taylor (1993)

Nucleus The nucleusis the largest cell organelle or structure that is enclosed by an envelope of two membranes (Figure 2.6).

Figure 2.6: Nucleus Source: Green, Stout, & Taylor (1993)

As can be seen in Figure 2.6, this envelope is perforated by nuclear pores. It contains cchromatin which is the extended form taken by chromosomes during interphase. The nucleus contains a nnucleolus. In the chromosomes, DNA molecule of inheritance of that particular organism can be found. DNA is organised into genes that control all activities of the cell. During the replication process, nuclear division occurs. Ribosomes containing proteins are manufactured by nucleolus.


34

Endoplasmic Reticulum (ER)

The extensive system of internal membranes is the endoplasmic reticulum (ER) (Figure 2.7). Endoplasmic means Âwithin the cytoplasmÊ, while reticulum is a Latin word meaning Âlittle netÊ.

Figure 2.7: Endoplasmic reticulum Source: Green, Stout, & Taylor (1993)

As can be seen in Figure 2.7, ER is a kind of weaving sacs that creates a series of channels and interconnections to form tubes called cisternae. On the surface of ER is a place where carbohydrates and lipids are manufactured by cells. If rribosomes are found on the surface of endoplasmic reticulum it is called rrough ER. However, if ribosomes are absent, it is called ssmooth ER. Smooth ER is the site of lipid and steroid synthesis.

Ribosomes As mentioned earlier, rribosomes are found on the surface of rough ER and freely suspended in cytoplasm ER (Figure 2.8). They are very small organelles consisting of a large and small subunit, made of protein (polypeptide) and RNA. However, they are slightly smaller ribosomes found in mitochondria (and chloroplasts in plants). Their functions are the sites of protein synthesis.

Figure 2.8: Ribosome Source: Green, Stout, & Taylor (1993)

Mitochondria Mitochondria (singular: mitochondrion) are organelles that convert energy from chemical form to another. They are the ÂpowerhousesÊ of the cell (Figure 2.9). They carry out cellular respiration, where chemical energy of foods (like sugars) are converted into molecules called adenosine triphosphates (ATP). ATP is the main energy source for cellular work.


Figure 2.9: Mitochondria Sources: www.modares.ac.ir

As can be seen in Figure 2.9, a mitochondrion is surrounded by an envelope consisting of two membranes. The inner membrane is in folded form; cristae (singular: crista) which increases the membraneÊs surface area, thus enhancing the mitochondrionÊs ability to produce ATP. It contains a matrix with ribosomes, that is a circular DNA molecule and phosphate granules. The matrix is the site of Krebs cycle enzymes and fatty acid oxidation.

Golgi apparatus

Golgi apparatus was named after the Italian biologist, Camillo Golgi. This apparatus is a stack of flattened, membrane-bound sacs (Figure 2.10). Stacks may form discrete dictyosomes in plant cells or an extensive network as in many animal cells. The Golgi apparatus performs several functions in close partnership with the ER. Golgi apparatus receives and modifies substances made by the ER.

Figure 2.10: Golgi apparatus Sources: www.modares.ac.ir


36

Lysosome A lysosome is a simple spherical sac bound by a single membrane (Figure 2.11).

Figure 2.11: Lysosomes Sources: www.biologie.uni-hamburg.de

It contains digestive enzyme (hydrolytic enzyme). The word ÂlysosomeÊ in Greek means Âbreakdown bodyÊ. Its main function is related to breaking down the enzymes or molecules in the cell. The lysosomal compartments store digestive enzyme safely isolated from the rest of the cytoplasm. In addition, lysosome also helps to destroy harmful bacteria. White blood cells ingest bacteria into vacuoles, the lysosomal enzymes emptied into them and then destroy the bacteria cell walls. Thus, lysosome serves as recycling centres for damaged organelles.

Microbodies The other important organelle in animal cells is microbodies. (Figure 2.12).

Figure 2.12: Microbodies Sources: www.bio.mtu.edu

They possess a single membrane, frequently spherical and typically measure from 20 to 60 nanometres in diameter. These contain fine granules or crystals. MMicrobodies contain catalase, an enzyme that functions to break down hydrogen peroxide. All are associated with oxidation reactions.


PLANT CELLS

Now, let us take a look at plant cells. Plant cells are similar to animal cells.They are eukaryotic and have similar components as animal cells. However, they have three major differences that animal cells do not have. The three differences are:

(a) Plant cell wall is somewhat different from animal cell wall. The cell walls reinforce the structures containing ccellulose and llignin to make them rigid.

(b) Plants are autotrophic. They are energetically self supporting by making their own foods using light energy from the sun. The light energy and chloroplasts (containing cchlorophyll and enzymes) are factors in carrying out photosynthesis to manufacture foods.

(c) Plant cells have very llarge vacuoles. This vacuole is a single membrane organelle used for storing organic acids, salts, etc. in the process of making foods during photosynthesis.

2.4.1 General Structure of Plant Cells

A plant cell is larger in size compared to an animal cell. The cell wall typically consists of more or less rigid cell wall and a protoplast (from the word ÂprotoplasmÊ). A protoplast consists of cytoplasm and a nucleus. In the cytoplasm, there are certain distinct organelles and systems of membranes. In a plant cell, there are plasma membrane, nucleus, plastids, mitochondria, microbodies, vacuoles, ribosomes, endoplasmic reticulum (ER) and microtubules. This can be seen in Figure 2.13.

2.4

SELF-CHECK 2.3

Explain the function of these animal cell structures:

(a) Cell Membrane:________________________________________

(b) Nucleus: ______________________________________________

(c) Mitochondria: _________________________________________


38

Figure 2.13: Eukaryotic cell (Plant)

Source: Johnson (2000)

2.4.2 Structure of Onion Cell

After learning the features of animal and plant cells, you should be able to discuss their similarities and differences in the structures. Do another experiment (Activity 2.3) in the Biology laboratory on plant cells. Bring two bulbs of onions from home. Take an example of a plant cell from the onion skin. You need to examine these very carefully using the right procedures in the lab. See the structures and draw diagrams of the onion cell as you see it using the microscope and then compare it with the prepared stained slide. Before you begin the experiment, here is the structure of an onion cell and its nucleus as shown in Figure 2.14.

(a) (b)

Figure 2.14: Onion cell (a) and its nucleus (b) Source: http://biology.clc.uc.edu


ACTIVITY 2.3

Do the following experiment to observe the appearance of onion cells under a light microscope. Title of Experiment: Examining the structure of onion cells under a microscope. Materials Needed: A light microscope, several glass slides and cover slips, forceps, a dropping pipette, Wright Stain, 5% iodine solution, a razor blade, tissue paper and some prepared slides of the onion cell. Procedure:

1. Scrape the inner side of the onion skin using a razor blade. This membrane is called the epidermis. Using forceps, pull away the epidermis from the inner surface.

CAUTION: Be careful not to wrinkle the membrane.

2. Put it on a glass slide carefully and apply a droplet of water. Cover with the cover slip and place it on the microscope stage. Examine the unstained specimen using the low power and draw diagrams of the cell structure.

3. Remove the specimen from the microscope stage. Apply a little amount of Wright Stain, then re-examine using the low power. Add a drop of iodine to the specimen from the edge of the cover slip. Draw the fluid underneath using a scrap of tissue paper.

4. View the stained onion specimen, first using the low power, then the high power.

5. Look and draw the nucleus, cell wall, vacuole, cytoplasm and other structures as seen.

6. Remove the wet specimen. Now, replace it with the prepared slide of the onion cell specimen. View, first using the low power, then the high power.

7. Draw a table, write the similarities and differences you see for both wet and prepared slides, in terms of their structures.

8. Make an analysis of your experiment.

9. Compare your results with those of your classmates.

10. Extra journey: Browse the Internet for more information, diagrams, pictures and other works of this experiment.


40

2.4.3 Function of Plant Cell Structures

As mentioned earlier, cells of higher plants contain all organelle or structures found and have similar functions as in the animal cells. However, there are exceptions. Certain organelles not found in animals are found in plants of higher order. They are the cell wall, organelle called chloroplast and large vacuoles. Let us take a look at Table 2.3 which shows the function of each plant cell structure.

Table 2.3: Function of Plant Cell Structures

Plant Cell Structure Function

Cell wall Animal cells have plasma membrane. Plant cells have cell walls � thick, rigid membranes surrounding the plant cells (Figure 2.15).

Figure 2.15: Plant cells (cell walls and nuclei are visible) Source: http://www.physicalgeography.net

These plant cell walls are composed totally or partially of a carbohydrate called cellulose that is different from the proteins of prokaryotic cell walls. The function of this cell wall is to support and together with the central vacuole, create stiffness and turgidity in plant structures (in the leaves).


Large vacuole

Plant cells contain a specialised vacuole called the central vacuole or large vacuole (Figure 2.16).

Figure 2.16: Large vacuole Source: http://www.physicalgeography.net

This is a large, fluid-filled sac structure bounded by a single membrane. The vacuole is filled � mostly with water but also some impurities including mineral or protein. Thus, the water concentration is always less than 100%. When the cell is filled with enough water, osmosis causes the central vacuole to swell. This also causes the cell plasma membrane to press against the inside of the cell wall and the leafÊs tissues to be stiff or turgid.

Plastids Plastids are organelles found only in plant cells and in higher plants, develop from small bodies called pproplastids. Proplastids are found in meristematic regions. Plastids are family organelles containing: (a) Chloroplasts � composed of a double layer of modified membrane-

bound (protein, chlorophyll, lipid) like mitochondria (Figure 2.17). The membrane contains chlorophyll and carotenoid pigments. They have a special function, that is, to carry out photosynthesis. Just like mitochondria, their inner membrane is very complicated. In fact, it is formed into many thylakoid structures that perform similar function as performed by the thylakoids in prokaryotic cells.


42

Figure 2.17: Plant cells with visible chloroplasts (granules)

Source: http://news.softpedia.com/ (b) Chromoplasts are non-photosynthetic coloured plastids. These

contain mainly red, orange or yellow pigments (carotenoid). These colours are associated with fruits, such as tomato, pepper, and carrot roots.

(c) Leucoplasts are colourless plastids. They lack pigmentation and are

usually modified for food storage mostly in plant organs like roots, seeds and young leaves.

Chlorophyll Chlorophyll is a green substance pigment in plant cells (Figure 2.18).

Figure 2.18: Chlorophyll, the green substance Source: http://www.nature-education.org

Chlorophyll and enzymes help plants to carry out photosynthesis to manufacture food. During photosynthesis, chlorophyll takes in energy by absorbing light energy from sunlight and breaks down water molecules into hydrogen and oxygen. The hydrogen then combines with carbon dioxide to make sugars or glucose. The oxygen is released back into the atmosphere for us.


MOVEMENT OF SUBSTANCES ACROSS THE MEMBRANE

The plasma membrane is a ssemi-permeable lipid bilayer found in all cells that controls water and certain substances in and out of the cell. Figure 2.19 shows the structure of a cell membrane. Scientists describe the organisation of the phospholipids and proteins usingthe ffluid mosaic model. That model shows that the phospholipids are in the shape of head and a tail. The heads like water (hhydrophilic) and the tails do not like water (hhydrophobic). The tails bump up against each other and the heads are out facing the watery area surrounding the cell. The two layers of cells are called the bilayer.

Figure 2.19: Structure of a cell membrane

Source: http://www.biology4kids.com Do you know why substances moves in and out of the cell? This is to ensure that:

(a) The nutrients can be easily transported into the cells;

(b) The gases can be exchanged;

(c) The metabolic waste from the cell can be got rid of; and

2.5

SELF-CHECK 2.4

1. Do all plant cells contain organelles?

2. Which organelles are found in a plant cell but not in an animal cell? Why?

3. Explain the functions of the different plant cell structures.


44

(d) The ph value and ionic concentration of the cell can be maintained (Figure 2.20).

Figure 2.20: Substances in and out of cells

Source: http://spmbiology403.blogspot.com Substances can be moved in and out through the membrane by different methods; diffusion, facilitated diffusion, osmosis and active transport. Let us take a look at each method in detail.

2.5.1 Diffusion

One method of movement through the membrane is ddiffusion. Diffusion is the movement of molecules from a region of higher concentration to one of lower concentration. This movement occurs because the molecules are constantly colliding with one another. The net movement of the molecules is to move away from the region of high concentration to the region of low concentration. Diffusion is a random movement of molecules down the pathway called the concentration gradient. Molecules are said to move down the concentration gradient because they move from a region of higher concentration to a region of lower concentration. A drop of dye placed in a beaker of water illustrates diffusion as the dye molecules spread out and colour the water. When diffusion between two concentrations is equal, there is no more movement and the system is said to have reached ddiffusion equilibrium.


2.5.2 Facilitated Diffusion

A second mechanism for movement across the plasma membrane is ffacilitated diffusion. Facilitated diffusion is a type of passive transport that allows substances to cross membranes with the assistance of special transport proteins. Some molecules and ions such as glucose, sodium ions and chloride ions are unable to pass through the lipid bilayer of cell membranes. Certain proteins in the membrane assist facilitated diffusion by permitting only certain molecules to pass across the membrane. The proteins encourage movement in the direction that diffusion would normally take place, from a region with a higher concentration of molecules to a region of lower concentration. Through the use of ion channel proteins and carrier proteins that are embedded in the cell membrane these substance can be transported into the cell. Ion channel proteins allow specific ions to pass through the protein channel. The ion channels are regulated by the cell and are either open or closed to control the passage of substances into the cell. Carrier proteins are bound to specific molecules, change shape and then deposit the molecules across the membrane. Once the transaction is completed the proteins return to their original position. Figure 2.21 illustrates facilitated diffusion.

Figure 2.21: Facilitated diffusion

Source: http://biology.about.com

2.5.3 Osmosis

Another method of movement across the membrane is osmosis. OOsmosis is the movement of water from a region of higher concentration of water to one of lower concentration. ItÊs the movement of water from a low concentration of solute to a higher concentration of solute. Osmosis often occurs across a


46

membrane that is semipermeable. A selectively permeable membrane is one that allows unrestricted passage of water, but not solute molecules or ions. Thus,the direction of the movement of water depends on the types of solution as can be seen in Table 2.4.

Table 2.4: Types of Solution

Types of Solution Description

Isotonic � ÂIsoÊ means Âthe sameÊ. If the concentration of solute (salt) is equal on both sides, the water will move back and forth. It will not have any result on the overall amount of water on either side (Figure 2.22).

Figure 2.22: Isotonic solution

Hypotonic � The word ÂhypoÊ means ÂlessÊ. In this case, there are less solute (salt) molecules outside the cell; since salt sucks, water will move into the cell (Figure 2.23). The cell will gain water and grow larger.

Figure 2.23: Hypotonic solution


� In plant cells, the central vacuoles will fill and the plant becomes stiff and rigid, the cell wall keeps the plant from bursting.

� In animal cells, the cell may be in danger of bursting, organelles called ccontractile vacuoles will pump water out of the cell to prevent this.

Hypertonic � The word ÂhyperÊ means ÂmoreÊ. In this case, there are more solute (salt) molecules outside the cell, which causes the water to be sucked out towards that direction (Figure 2.24).

Figure 2.24: Hypertonic solution

� In plant cells, the central vacuole loses water and the cells shrink, causing wilting.

� In animal cells, the cells also shrink. � In both cases, the cells may die. � This is why it is dangerous to drink sea water. There is a myth that

drinking sea water will cause you to go insane and people stranded at sea will speed up dehydration (and death) by drinking sea water.

� This is also why „salting fields‰ was a common tactic used during wars, it would kill the crops in the field, thus causing food shortages.

Source:http://www.biologycorner.com


48

2.5.4 Active Transport

A fourth method for movement across the membrane is active transport. When active transport takes place, a protein moves a certain material across the membrane from a region of lower concentration to a region of higher concentration. Because this movement is against the concentration gradient, the cell must expend energy that is usually derived from a substance called adenosine triphosphate or ATP. An example of active transport occurs in human nerve cells. Here, sodium ions are constantly transported out of the cell into the external fluid bathing it, a region of high concentration of sodium. This transport of sodium sets up the nerve cell for the impulse that will occur within it later.

2.5.5 Endocytosis and Exocytosis

We have discussed the substances movement into and out of the cell membrane through passive or active transport. However, large food particles, whether they be grains of sugar or other organisms, cannot simply diffuse across the membrane; they are just too big. As a cell approaches a food particle, either the food particle pushes into the cell membrane forming an indentation, or pseudopodia which is extended from the cell around the particle. When the two extensions of the cell membrane meet on the other side of the particle, they close and form a vacuole around the food inside the cell. This process is called eendocytosis. Meanwhile, eexocytosis is a very similar process. In fact, it is just endocytosis in a reverse order. A vacuole within the cell moves toward and fuses with the cell membrane. In this manner, the contents of the vacuole are expelled into the external environment. This may occur, for example, after a cell has taken in a large particle through endocytosis, digested it using the enzymes in the lysosome, and then needs to expel the waste products.


Endocytosis and exocytosis are general terms to describe the process by which anything is taken into or expelled from the cell through the action of vacuoles. If the particles are in the form of solid, then the process is called phagocytosis. If the particles are in the form of liquid the process is called pinocytosis. Figure 2.25 illustrates endocytosis and exocytosis.

Figure 2.25: Endocytosis and exocytosis

Source: http://www.kscience.co.uk

SELF-CHECK 2.5

From the list given, circle the passive transport methods.

(a) Osmosis

(b) Diffusion

(c) Facilitated diffusion


50

ACTIVITY 2.4

1. Figure 2.26 shows two containers of equal volume. They are separated by a membrane that allows free passage of water, but totally restricts passage of solute molecules. Solution A has 3 molecules of the protein albumin (molecular weight 66,000) and Solution B contains 15 molecules of glucose (molecular weight 180). Into which compartment will water flow, or will there be no movement of water? Discuss with your classmates.

Figure 2.26:Two containers of equal volume

2. Watch the videos and animations in the links given and draw diagrams to describe the movement of substances across the membrane through the various methods:

(a) http://www.northland.cc.mn.us/biology/biology1111/animations/passive3.swf; and

(b) http://highered.mcgraw-hill.com/sites/dl/free/0072464631/291136/facDiffusion.swf.

3. Active transport is quite difficult to visualise. Surf the Internet to find videos or animation that illustrate this method of transportation. Watch and understand the active transport mechanism. Explain the process to your classmates with the help of diagrams.


� There are five levels of organisation in living things. These levels in sequence are the cells, tissues, organs, organ systems and organisms.

� Organisms are composed of functional structures called cells. Cells are categorised into two: (i) single or unicellular and (ii) multicellular.

� Single or unicellular organisms are prokaryotes while multicellulars are eukaryotes.

� Multicellular organisms are plants and animals.

� Eukaryotic cells, in plants and animals, have similar organelles and functions. However, there are differences between plant and animal cells.

� Substances move across the cell membrane through passive or active transport.

� Passive transport of substances across membrane include diffusion, facilitated diffusion and osmosis.

� Diffusion is the movement of molecules from a region of higher concentration to one of lower concentration

� Facilitated diffusion is a type of passive transport that allows substances to cross membranes with the assistance of special transport proteins.

� Osmosis is the movement of water from a region of higher concentration of water to one of lower concentration

� Active transport takes place when a protein moves a certain material across the membrane from a region of lower concentration to a region of higher concentration.

� Energy is needed in active transport, usually derived from a substance called adenosine triphosphate or ATP.


52

Active transport

Cell membrane

Diffusion

Endoplasmic reticulum

Eukaryo

Facilitated diffusion

Golgi body

Mitochondria

Multicellular

Nucleus

Osmosis

Proka

Ribosomes

Unicellular

Biology-Online. (2005). Movement of substances across membrane. Retrieved March 20, 2012, from http://www.biology-online.org/9/3_movement_ molecules.htm.

Campbell, N. A., Reece, J. B., Mitchell, L. G., & Taylor, M. R. (2003). Biology

(4th ed.). San Francisco, CA: Benjamin Cummings. CikguJes. (2008).What is active transport? Retrieved March 20, 2012, from

http://spmbiology403.blogspot.com/2008/08/active-transport.html. CliffsNotes. (2012). Movement through plasma membrane. Retrieved March 20,

2012, from http://www.cliffsnotes.com/study_guide/Movement-through-the-Plasma-Membrane.topicArticleId-8741,articleId-8588.html.

Fankhauser, D. B. (2011). Cells: the functional units of organisms.. Retrieved

March 20, 2012, from http://biology.clc.uc.edu/fankhauser/ labs/cell_biology/cells_lab/cells.htm Green, N. P., Stout, G. W., & Taylor, D. J. (1993). Biological science (2nd ed.).

Oxford, UK: Oxford University Press. Johnson, G. B. (2000). The living world (2nd ed.). Boston, MA: McGraw Hill Higher

Education.


Neumeyer, R. (2003). Protozoa.Retrieved March 20, 2012, from http://www.microimaging.ca/protozoa.htm. Westbroek, G. (2000). Levels of organization. Retrieved March 20, 2012, from

http://utahscience.oremjr.alpine.k12.ut.us/sciber00/7th/cells/sciber/levelorg.htm.

� ��

� INTRODUCTION

All living things need food to survive. Food provides us with energy for all living processes such as growth and development and also to maintain optimal health. In this topic, you will learn about the different types of nutrition, the classes of food, the concept of a balanced diet, food technology and how to practise a healthy life style. You will also explore nutrition in plants, the process of photosynthesis and the concepts of food chains, food webs and energy pyramids.�

TTooppiicc

33

� Nutrition and Classes of Food

��By the end of this topic, you should be able to:

1. Describe the different types of nutrition;

2. List the characteristics of the different classes of food;

3. Explain the concept of a balanced diet;

4. Define food chains, food webs and energy pyramids;

5. List the various nutrients needed by plants;

6. Explain the process of photosynthesis;

7. Describe food technology, including genetically modified food; and

8. Explain how to practise a healthy lifestyle.

LEARNING OUTCOMES

TOPIC 3 NUTRITION AND CLASSES OF FOOD � 55

TYPES OF NUTRITION

What exactly is nutrition? Nutrition is the process by which organisms obtain energy from food for growth, maintenance and repair of damaged tissues. Nutrients are the useful substances that are present in food. We shall first look at the different types of nutrition. There are two main types of nutrition as can be seen in Table 3.1.

Table 3.1: Types of Nutrition

Autotrophic Nutrition Heterotrophic Nutrition

� It is a process in which organisms make their own food from simple inorganic raw materials such as carbon dioxide, and water by using light or chemical energy.

� In pphotosynthesis, organisms make complex organic compounds from carbon dioxide and water using llight energy in the presence of chlorophyll. Example: all green plants.

� In cchemosynthesis, organisms make complex organic materials from carbon dioxide and water using cchemical energy. Example: certain types of bacteria.

� It is a process in which organisms feed on complex, ready-made organic foods to obtain the nutrients they require.

� The three main types of heterotrophic nutrition are holozoic nutrition, saprophytic nutrition and parasitic nutrition.

� In hholozoic nutrition, organisms feed on solid organic material derived from the bodies of other organisms. Examples: humans and cows.

� In ssaprophytic nutrition, organisms feed on the dead and decaying matter on which they live and grow. Examples: fungi and certain bacteria.

� In pparasitic nutrition, organisms feed on other living organisms known as hosts. Examples: tapeworms and ticks.

3.1

� TOPIC 3 NUTRITION AND CLASSES OF FOOD56

Now, let us take a look at Figure 3.1 which summarises the various types of nutrition.

Figure 3.1: Types of nutrition

3.1.1 Holozoic Nutrition

Let us take a closer look at holozoic nutrition. Can you recall what holozoic nutrition is? Yes. Holozoic organisms feed on solid organic matter which can be either plants or animals. Holozoic organisms may be classified according to their diet; whether their diet is made up of plants, animals or both. Study Figure 3.2 which shows how holozoic animals are classified according to what they eat. �


�

Figure 3.2: Classification of animals according to what they eat


CLASSES OF FOOD

The nutrients in food can be divided into seven classes based on their functions as shown in Figure 3.3. �

�Figure 3.3: Classes of food

Let us look at each of them in detail.�

3.2

SELF-CHECK 3.1�

1. In your own words, explain the term „nutrition‰ and „nutrients‰.

2. Explain each of the following types of nutrition. Give one example for each type:

(a) Autotrophic nutrition;

(b) Heterotropic nutrition; and

(c) Holozoic nutrition.

3. Classify the following animals into herbivores, carnivores or omnivores: eagles, lions, goats, bears, elephants and chickens.

4. Discuss how the animals named in Question 3 have adaptations to suit their diet.


3.2.1 Carbohydrates

Carbohydrates are the main source of energy and should be the major part of our daily intake. Carbohydrates consist of three elements:

(a) Carbon;

(b) Hydrogen; and

(c) Oxygen. There are three main types of carbohydrates based on the number of simple sugars in the molecules. This is shown in Table 3.2. �

Table 3.2: Types of Carbohydrates

Type Number of Simple Sugar Example

Monosaccharide (simple sugars)

One unit Glucose, fructose, galactose.

Disaccharide (complex sugars)

Two units Lactose, maltose, sucrose.

Polysaccharide Many units Starch, glycogen, cellulose.

�Now, let us learn the terms used in Table 3.1. Sugars are sweet crystalline compounds, which can dissolve in water and are found in syrup, honey, sugar cane and fruits. Starch is found in rice, bread and potatoes and is the main energy storage compound in plants. Glycogen is the main storage compound in animals and is stored in the liver and muscle cells. Cellulose is the substance that plant cell walls are made up of. Vegetables and fruits are two examples of food containing cellulose. All carbohydrates are broken down into simple sugars (monosaccharide) by enzymes in the digestive tract. However humans cannot digest cellulose like herbivores because humans do not have the enzyme cellulose. This means that we cannot get energy from cellulose but it still performs a useful function: it forms dietary fibre (roughage). We will learn about the importance of fibre later in this topic.


Before we end the discussion about carbohydrates, let us look at Figure 3.4 which summarises the main characteristics of carbohydrates.

�Figure 3.4: Characteristics of carbohydrates�

3.2.2 Proteins

Proteins are complex organic substances which are made up of carbon, hydrogen, oxygen and nitrogen. Most proteins also contain sulphur and phosphorus. Foods that are rich in protein include fish, meat, milk, nuts, cheese, and eggs as shown in Figure 3.5. �

�Figure 3.5: Sources of protein

Source: http://www.buzzle.com �


The basic unit of protein is amino acid. There are 20 naturally occurring amino acids. These can be divided into two groups: (a) EEssential Amino Acids Essential amino acids are amino acids that cannot be made by the body. We

must get them from our diet. There are altogether nine essential amino acids. They are vital for good health and the absence of just one can have severe consequences.

(b) NNon-essential Amino Acids Non-essential amino acids are amino acids that can be made by the body.

These amino acids are formed from other amino acids. There are eleven non-essential amino acids.

Animal proteins such as meat contain all the essential amino acids and are considered as a „complete protein‰. Animal proteins are known as first class proteins. Plant proteins such as beans are „incomplete proteins‰ in that they do not contain every essential amino acid. Plant proteins are known as second class proteins. The common sources of all essential amino acids are food from animal sources such as eggs and milk while a variety of plant products must be taken together to provide all the other necessary proteins. Proteins form the main structure of our body. Therefore, we need protein for growth of new cells and repairing worn out or damaged body tissues. We also need proteins to produce enzymes, hormones and some components of antibodies. In addition, proteins can provide energy when needed. Figure 3.6 summarises the characteristics of proteins. �

�Figure 3.6: Characteristics of proteins


3.2.3 Fats

Fats are a subgroup of the compound known as lipids. Fats are organic compounds that contain carbon, hydrogen and oxygen, but unlike carbohydrates, they contain much less oxygen. Fats are insoluble in water. Fats are also known as triglycerides. A triglyceride is formed from a molecule of glycerol and three molecules of fatty acids. Figure 3.7 shows the structure of fat. �

�Figure 3.7: Structure of fat

Fatty acids are either saturated or unsaturated. Fats containing saturated fatty acids are called saturated fats while those containing unsaturated fatty acids are called unsaturated fats. Saturated fats are solids at room temperature. Examples of saturated fats are animal fats such as butter. An unsaturated fat is usually liquid at room temperature and is called oil. Examples of unsaturated fats are vegetable oils such as corn oil. Cholesterol which is the major component of the plasma membrane is mostly found in saturated fats. Fats serve as an efficient source of energy. They also act as a solvent for fat-soluble vitamins and other vital substances such as hormones. Fats keep our body warm by building a heat insulator under the skin. This may reduce the rate of heat loss from the skin during the cold season. The oily secretion from certain glands in the skin can reduce the rate of evaporation of water. Fats are also important in forming the cell membrane. Figure 3.8 summarises the characteristics of fats. �


�Figure 3.8: Characteristics of fats

3.2.4 Vitamins

Vitamins are organic compounds needed by the body in small quantities to maintain good health. There are two groups of vitamins: (a) FFat Soluble Vitamins Fat soluble vitamins such as vitamins A, D, E and K can be stored in body

fat. (b) WWater Soluble Vitamins Water soluble vitamins cannot be stored in the body and have to be

continuously supplied in the daily diet. Vitamins B and C are water soluble vitamins.


Figure 3.9 shows the various sources of vitamins. �

Figure 3.9: Various sources of vitamins Source: http://thebest-healthy-foods.com

A varied diet of fresh fruits and vegetables is important to obtain most of the vitamins that we need. The characteristics of vitamins are summarised in Figure 3.10. �

�Figure�3.10:�Characteristics�of�vitamins�

3.2.5 Minerals

Minerals are inorganic chemical elements that are usually found in the body. They are present in the form of ions and are needed in small quantities. They are required to regulate body processes, build bones, form blood cells, maintain health and avoid diseases.


Minerals are divided into two groups: �(a) MMajor Elements Some major elements needed in large quantities are potassium, sodium,

calcium, magnesium, iron, iodine and phosphorus. �(b) TTrace Elements Some trace elements needed in small quantities are fluorine and chlorine. �Figure 3.11 summarises the characteristics of minerals. �

�Figure 3.11: Characteristics of minerals

3.2.6 Fibre

Dietary fibre (roughage) is made up of the indigestible cellulose walls of plant material. Fibre provides bulk to the contents of the large intestine and stimulates peristalsis. This leads to defecation and prevents constipation. The presence of adequate dietary fibre in the diet helps to prevent heart and intestinal disorders. Fibre also absorbs toxic substances in the large intestine and reduces blood cholesterol level. Figure 3.12 summarises the characteristics of fibre. �

�Figure 3.12: Characteristics of fibre

� TOPIC 3 NUTRITION AND CLASSES OF FOOD

66

3.2.7 Water

Water makes up 70% of our body weight. The main sources of water are fruits, vegetables and drinking water. It is a very important compound in our body and mainly acts as a solvent in the transport of wastes and food substances; a medium for enzymatic reactions; to regulate body temperature; and to maintain blood concentration. It is also needed in all metabolic processes. Figure 3.13 summarises the characteristics of water.

Figure 3.13: Characteristics of water

1. Name the different classes of food.

2. Discuss the functions of each of the different classes of foods.

SELF-CHECK 3.2

The diseases shown below are due to the lack of a certain vitamin or mineral. Research these diseases and suggest the vitamin or mineral that is lacking:

Rickets Night-blindness Anaemia Pellagra Goitre Scurvy Beri beri

ACTIVITY 3.1


BALANCED DIET

The food we consume every day makes up our diet. This includes what we drink as well as what we eat. Our diet must include all the seven classes of food described in the previous subtopic. A diet which contains all of these substances in the right quantities is called a balanced diet. The composition of a balanced diet varies from one individual to another according to age, sex, job, size, age, climate and state of health. A balanced diet is important mainly to maintain our body health and growth, to repair or replace old and damaged cells and provide enough energy.

A balanced diet will be able to meet the daily energy requirements of the body. Energy in food is measured in joules (J) or calories (Cal). One calorie equals to 4.2 joules. The amount of heat energy released when one gram of food is completely burnt in the air is known as its calorific value. Each type of food has a different calorific value. Therefore, we should choose the correct types of food to ensure our bodies get sufficient energy. We can use the food pyramid as a guide for a balanced diet as shown in Figure 3.14.

Let us take a look at the food pyramid based on the Malaysian Dietary Guidelines (MDG) 2010 as shown in Figure 3.14.

�Figure 3.14: The food pyramid

3.3


The food pyramid is one way for people to understand how to eat healthily. When choosing a healthy diet, simply follow the food pyramid guidelines. Select the suggested number of servings from the five basic food groups as shown in the previous Figure 3.14. The food pyramid shows you what and how much food you should eat to remain healthy. These are the recommendations according to the food pyramid:

(a) Eat adequately: Rice, noodles, breads, cereals, cereal products and tubers (4�8 servings/day);

(b) Eat plenty: Vegetables (3 servings/day);

(c) Eat plenty: Fruits (2 servings/day);

(d) Eat in moderation: Milk and milk products (1�3 servings/day); and

(e) Eat in moderation: Fish, poultry, meat and legumes (��2 servings of poultry/meat/day, 1 serving of fish/day, ��1 serving of legumes/day).

The sixth group (fats, oil, sugar and salt) consists mostly of items that are pleasing to the palate, but high in fat and calories. These should be eaten in moderation or the intake should be limited. �

�

FOOD CHAINS, FOOD WEBS AND ENERGY PYRAMIDS

The main energy source on earth is the Sun. Solar energy is used by plants to make food. Green plants which are autotrophs store solar energy in carbohydrates during photosynthesis. Green plants are also known as pproducers as they are capable of producing their own food. Heterotrophs are known as consumers as they feed on producers. Herbivores are known as pprimary consumers as they feed on the producer organisms. Carnivores are ssecondary consumers as they eat the primary consumers. What do you think tertiary consumers are?

3.4

ACTIVITY 3.2

Your friend is a champion in bodybuilding sports. Explain to him thereasons bodybuilders need more proteins such as eggs and meat intheir diet.�


3.4.1 Food Chain

Producers and consumers play different roles in a community. The linear feeding relationship which indicates the transfer of energy from producers to consumers is known as a ffood chain. Study Figure 3.15 which shows a food chain.

�Figure 3.15: A food chain

Source: http://www.kidsgeo.com As can be seen in Figure 3.15, notice how all organisms are linked in the food chain. Each stage of a food chain is called a ttrophic level. The arrows in the food chain represent the flow of energy through the ecosystem. Can you identify the herbivore and carnivores in this food chain? Additionally, try to determine the primary, secondary and tertiary consumers as well.


3.4.2 Food Web

In reality, an organism usually feeds on several different types of food. Instead of one simple food chain, there are many food chains which share the same organism. Many food chains interconnect to form a food web. A food web helps to maintain a balanced environment by controlling the number of organisms at each level of the food chain. Study Figure 3.16. How many food chains can you detect from this food web?

�Figure 3.16: A food web

Source: http://ed101.bu.edu

3.4.3 Energy Pyramids

Do you know why there are more herbivores than carnivores in any ecosystem? Energy flows in one direction along a food chain. Energy is transferred along the food chain from the photosynthetic producers through several levels of consumers. The more levels in the food chain, the lesser the energy at the end of the chain. For example, when a herbivore eats, only a fraction of the energy (that it gets from the plant food) becomes new body mass; the rest of the energy is lost as waste or used up by the herbivore to carry out its life processes (e.g., movement, digestion, reproduction). Therefore, when the herbivore is eaten by a carnivore, it passes only a small amount of total energy (that it has received) to the carnivore. Of the energy transferred from the herbivore to the carnivore, some energy will be „wasted‰ or „used up‰ by the carnivore.


An energy pyramid is a graphical representation of the energy at each level in a food chain. They are called pyramids because of the shape of these graphs. An energy pyramid shows maximum energy at the base and steadily diminishing amounts at higher levels. This is shown in Figure 3.17. �

�Figure 3.17: An energy pyramid Source: http://www.vtaide.com

The energy pyramid shown in Figure 3.17 shows many trees and shrubs providing food and energy to giraffes. Note that as we go up, there are fewer giraffes than trees and shrubs and even fewer lions than giraffes. In other words, a large mass of living things at the base is required to support a few at the top. Many herbivores are needed to support a few carnivores. This is why there are more herbivores than carnivores. �

�

�

Define food chains, food webs and energy pyramids. Give examples for each.

SELF-CHECK 3.3

ACTIVITY 3.3

Using producers and consumers from a community near where youlive, draw several interconnecting food chains that form a simple foodweb.


NUTRIENTS IN PLANTS

Plants also need nutrients for healthy growth and development. Plants need carbon, hydrogen, oxygen, phosphorus, sulphur, magnesium, potassium and iron elements in large quantities. For this reason these elements are called major elements or macronutrients. In addition to the major elements, certain other elements are required as well. These are required in small amounts and known as trace elements or micronutrients. Examples of micronutrients are iron, copper, manganese, molybdenum and boron. Carbon, hydrogen and oxygen are macronutrients that can be easily absorbed from carbon dioxide in the atmosphere and water from the soil. Therefore, deficiency in these nutrients rarely occurs. The remaining mineral elements are obtained in the form of inorganic ions from the soil. Table 3.3 shows some essential nutrients in plants. �

Table 3.3: Essential Nutrients in Plants

Nutrients Needed by Plants

Major nutrients from water and CO2 C Carbon

H Hydrogen

O Oxygen

Primary Macronutrients N Nitrogen

P Phosphorus

K Potassium

Secondary Macronutrients Ca Calcium

Mg Magnesium

S Sulphur

Micronutrients Fe Iron

Cu Copper

Mn Manganese

Mo Molybdenum

B Boron

�Macronutrients and micronutrients are involved in the synthesis of chemical substances essential for the healthy growth of plants. They are also required for the various metabolic processes which take place in plants. The absence of one or more of these nutrients can lead to mineral deficiencies in plants. Table 3.4 shows the effects of nutrient deficiencies in plants.

3.5


Table 3.4: Effects of Nutrient Deficiencies in Plants

Type of Nutrients Elements Symptoms

Macronutrients Oxygen Growth retardation

Nitrogen Chlorosis; leaves turn yellow

Potassium Occur in mature tissues, growth retardation, leaves turn to yellowish brown

Calcium Occur in young tissues, drying of the tips of root and leaf, twisted leaf morphology, retardation of root growth and decrease in plant growth rate

Magnesium Chlorosis in veins mainly in young leaves, necrotic at the tip of the leaves, severe deficiency, necrosis occurs in the entire leaves

Phosphorus Old leaves turn to dark green, appearance of dark purple pigment (anthocyanin), delayed maturity

Micronutrients Iron Occur in young tissues

Manganese Appear in young leaves in the form of white spots and interveinal chlorosis

Zinc Spots of necrosis

Copper Necrosis of the leaf margin and reduction in the concentration of plastocynin pigment

Molybdenum Chlorosis and retardation of plant growth

Figure 3.18 shows phosphorus and calcium deficiency in bean plants.

�Figure 3.18: Phosphorus and calcium deficiency in bean plants


�

PHOTOSYNTHESIS

Photosynthesis is derived from two words: ÂphotoÊ which means light, and ÂsynthesisÊ which means making. Therefore, photosynthesis means the making of food with the help of light. Photosynthesis can be defined as a process carried out by green plants to make glucose from carbon dioxide and water in the presence of sunlight and chlorophyll. Oxygen is a by-product of photosynthesis. Here is the equation for photosynthesis. �

�

3.6.1 Requirements of Photosynthesis

Photosynthesis requires carbon dioxide, chlorophyll, sunlight and water. Carbon dioxide is absorbed from the air through stomata into the chloroplast. Chlorophyll is the pigment in chloroplasts which captures sunlight. Sunlight provides the energy needed for photosynthesis. Water is absorbed through the roots.

3.6.2 Importance of Photosynthesis

Photosynthesis is important because it: �(a) PProvides the Basic Food Source Plants use light energy to make their own food. Most organisms depend

directly or indirectly on plants for food. Plants are producers and are very important in providing the basic food source for other life forms on earth.

3.6

SunlightCarbon dioxide + Water Glucose + Oxygen Chlorophyll

1. List all the elements that are needed in large amounts by plants.

2. Name three elements that will result in the yellowing of leaves

(chlorosis) in plants if a deficiency of these elements occurs.

SELF-CHECK 3.4


(b) MMaintains the Oxygen Balance Animals and plants continuously use up oxygen. Combustion (burning of

fuels) and daily human activities (e.g. cooking) also uses up oxygen through respiration. Through photosynthesis, plants release oxygen into the environment and replace the oxygen that has been consumed. �

3.6.3 Experiment to Show that Photosynthesis has Taken Place

How can you determine if photosynthesis has taken place in plants? When the process of photosynthesis takes place, glucose is formed as a product. The glucose produced during photosynthesis is stored in the plant in the form of starch. Iodine reacts with starch to produce a deep dark blue (almost black) colour. The presence of starch in leaves shows that photosynthesis has taken place. Carry out the following experiment to determine whether photosynthesis has taken place in a plant. �

Title: Experiment to determine if photosynthesis has taken place.

Procedure:

1. Pluck a leaf from a plant, which has been exposed to sunlight for a few hours.

2. Immerse the leaf in a beaker of boiling water to kill it.

3. Place the softened leaf inside a boiling tube containing ethanol.

4. Place the boiling tube inside a beaker of hot water to remove chlorophyll.

5. Return the leaf to a beaker of hot water to soften leaf and allow penetration of iodine.

6. Place the leaf on a white tile.

7. Drop iodine solution onto the leaf surface.

8. Record your observation.

Observation:

1. The leaf turns the iodine to dark blue.

2. This shows the presence of starch in the green leaf.

3. This proves that photosynthesis has taken place in the green leaf.�


��

�

FOOD TECHNOLOGY

The increase of the world population means there is a need for greater food supply. The quality and quantity of food production should also be improved to meet the demands of this increasing population. FFood technology is a branch of food science that deals with the production processes to make foods. Development of food technology occurs in two ways: (a) TTechnological Development to Improve Quality and Quantity of Food

Production Various methods are employed to improve the quality and quantity of food

production such as direct seeding for rice, hydroponics and aeroponics, breeding of plants and animals, tissue culture, ggenetic engineering, soil management, and biological control.

(b) TTechnological Development in Food Processing Technology development in ffood processing includes the activities

involved in the preparation and preservation of food. This is to ensure that the food remains safe for consumption whether eaten immediately or later. The main purpose of food processing is to preserve food by overcoming the factors that can cause food spoilage. Examples of food processing and preservation methods are freezing, pickling, fermentation, dehydration, canning, pasteurisation, radiation and sterilisation.

3.7

1. Define photosynthesis.

2. Explain the significance of photosynthesis.

SELF-CHECK 3.5

Draw a flow chart to show the relationship between the following:

water carbohydrates oxygen chlorophyll carbon dioxide chloroplast light

ACTIVITY 3.4


What is genetic engineering? GGenetic engineering is a technique that can increase the quality and quantity of food production. It is a technique that enables the characteristics of an organism to be altered by changing the genetic composition of the organism. For example, genes from plants can be inserted into the DNA of animal cells and vice versa. The ggenetically modified organism (GMO) is called a transgenic organism. Developments in genetic engineering have enabled transgenic crop plants such as wheat, paddy, tomatoes, legumes, soya beans and potatoes to be cultivated commercially. These crop plants contain genes from other organisms to enhance their growth or nutritional properties. Figure 3.19 shows an example of how genetically modified plants are created. �

�Figure 3.19: Creation of a genetically modified pest resistant plant

Source: http://www.gmac.gov.sg

��

ACTIVITY 3.5

Currently there is a controversy over the use of genetically modified(GM) foods. Research this issue and discuss the pros and cons of GMfoods.


DEVELOPING GOOD EATING HABITS

It is important to practise good eating habits. Figure 3.20 shows some guidelines on how to develop good eating habits. �

Figure 3.20: Guidelines on how to develop good eating habits

Do you realise that there are many types of diseases related to imbalanced diets? Table 3.5 shows the different types of nutrient deficiency diseases in humans.

Table 3.5: Nutrient Deficiency Diseases in Humans

Name of Diseases

Nutrient Deficiency Symptoms

Kwashiorkor Protein � Dry and scaly skin. � Hair loss. � Wasting muscles. � Loss of appetite and diarrhoea. � Easily tired � Distended abdomen.

Oedema Protein � Loose muscles and skin. � Some parts of body become swollen.

Marasmus Energy- producing food

� Very thin. � Very weak. � Starvation.

Anaemia Iron � Shortness of breath and headache. � Some parts of body lack oxygen. � Chest pain. � Lips are pale and cracked.

3.8

TOPIC 3 NUTRITION AND CLASSES OF FOOD �

79

Goitre Iodine � Thyroid gland becomes swollen. � Swelling will press the surface of trachea and

oesophagus. � Breathing difficulties.

Cretinism Iodine � Mental retardation and stunted growth. � Rough skin. � Tongue becomes swollen.

Scurvy Vitamin C � Walls of blood vessels break easily. � Bruises appear under skin surface. � Bleeding and swollen gums. � Joints become swollen and painful.

Beri beri Vitamin B � Diarrhoea. � Swelling at ankles and legs. � Numbness of legs and hands. � Stiffness of muscle. � Mental deterioration. � Heartbeats become faster.

Pellagra Vitamin B � Pain in the mouth and tongue. � Dry and reddish skin. � Diarrhoea. � Slow thinking and memory loss.

Rickets Vitamin D � Incomplete development of teeth and bones. � Soft and pliable bones. � Head becomes big.

Figure 3.21 shows a photo of a child suffering from kwashiorkor.

Figure 3.21: A child suffering from Kwashiorkor

Source: http://www.asnom.org


� Nutrition is the process by which organisms obtain energy from food for growth,

maintenance and repair of damaged tissues. � There are two main types of nutrition: autotrophic nutrition and heterotrophic

nutrition. � Autotrophic nutrition is the process by which organisms make their own

food from simple inorganic raw materials such as carbon dioxide and water by using light or chemical energy.

� Heterotrophic nutrition is the process by which organisms feed on complex,

ready-made organic foods to obtain the nutrients they require.

� Heterotrophic nutrition consists of holozoic nutrition, saprophytic nutrition and parasitic nutrition.

� Holozoic organisms may be classified according to their diets. Herbivores eat

only plants, carnivores eat only animals and omnivores eat both animals and plants.

� Food can be divided into seven classes � carbohydrates, proteins, fats,

vitamins, minerals, fibre and water.

SELF-CHECK 3.6

1. Define the term balanced diet. 2. Explain the special food requirements of:

(a) A child;

(b) A pregnant woman; and

(c) A man who does hard physical work. 3. Give examples of nutrient deficiency diseases in plants and

humans.


� Carbohydrates provide energy; proteins provide materials for growth and repair and fats are a source and storage of energy.

� Vitamins and minerals are needed in small quantities for optimal health. � Fibre is required for the proper functioning of the digestive system. � A balanced diet contains all the classes of food in the right quantity and ratio

according to our bodily needs. � A food chain shows the feeding relationships among organisms. � The interconnections of many food chains form a food web. � An energy pyramid is a graphical representation of the energy at each level in

a food chain. � Plants need both macronutrients and micronutrients for healthy growth and

development. � Photosynthesis is a process carried out by green plants to make glucose from

carbon dioxide and water in the presence of sunlight and chlorophyll. � Photosynthesis requires carbon dioxide, chlorophyll, sunlight and water. � Photosynthesis provides the basic source of food and also maintains the

oxygen balance in the atmosphere. � Food technology is a branch of food science that deals with the production

processes to make foods. � Development of food technology occurs in two ways: development in food

production and development in food processing.

� Genetically modified foods are foods that are derived from genetically modified organisms. Genetically modified organisms have had specific changes introduced into their DNA by genetic engineering techniques.

� An imbalanced diet can lead to health problems, mainly deficiency diseases. �


Autotrophic nutrition

Carbohydrates

Carnivore

Chemosynthesis

Deficiency diseases

Energy pyramid

Fats

Fibre

Food chain

Food technology

Food web

Genetically modified foods

Herbivore

Heterotrophic nutrition

Holozoic nutrition

Macronutrients

Micronutrients

Minerals

Nutrition

Omnivore

Parasitic nutrition

Photosynthesis

Primary consumer

Producer

Proteins

Saprophytic nutrition

Secondary consumer

Trophic level

Vitamins

Water

MDG. (2010). Executive summary. Retrieved March 20, 2012 from http://www.nutriweb.org.my/downloads/Executive%20summary.pdf

nutriWEB. (2011). Latest news. Retrieved March 20, 2012 from http://www.nutriweb.org.my/

Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2010).Campbell biology (9th ed.). San Francisco: Pearson - Benjamin Cummings Pub.

Slim With Yoga. (2011). Nutritious food. Retrieved March 20, 2012 from http://slimwithyoga.com/nutritious/index.html

Taylor, D. J., Green, N. P. O., & Stout, G. W. (2004). Biological science 1: Organisms, energy and environment (3rd ed.). R. Soper Editor, New York: Cambridge University Press. �

� INTRODUCTION

In Topic 3, we looked at the various classes of food that are needed by our body. Have you ever wondered about what happens to these foods after we have eaten them? The foods that we eat are in quite a different state from the one that can be used by the cells in our body. Before the foods can be used, they need to be converted into smaller units, so that they can be easily absorbed by our body cells. This process is called ddigestion. Basically, digestion is the process of breaking down food from complex substances into simpler soluble molecules to be absorbed by the body. Starch, protein and fat are large insoluble food molecules. At the end of digestion, starch is broken down into glucose, protein is broken down into amino acids and fats are broken down into fatty acids and glycerol. Glucose, amino acids, fatty acids and glycerol are in the simplest form and are easily absorbed into the body cells. But, how does digestion take place?

TTooppiicc

44

� Digestive System


1. Explain the process of physical digestion and chemical digestion;

2. Describe the structure of the human digestive system;

3. Explain the process of digestion in humans;

4. Describe digestion in ruminants;

5. Describe digestion in rodents; and

6. Explain how excretion occurs in plants.

LEARNING OUTCOMES

� TOPIC 4 DIGESTIVE SYSTEM

84

This is what we are going to learn in this topic. We are going to learn how digestion occurs and also about the digestion in ruminants and rodents. Excretion in plants will also be discussed at the end of this topic.

DIGESTION IN HUMANS

Digestion in humans can be divided into two types. They are: (a) PPhysical or Mechanical Digestion

Physical or mechanical digestion involves physically breaking the food into smaller pieces. By breaking up food into smaller pieces, mechanical digestion increases the surface area of the food available for chemical digestion. For example: teeth chop and grind food; stomach churns (mixes) the food.

(b) CChemical Digestion

Chemical digestion is the breaking down of large molecules, such as starch, proteins and fats into smaller soluble molecules for easy absorption by the body. Chemical digestion involves digestive enzymes. Enzymes break insoluble molecules into smaller molecules. Examples of digestive enzymes are proteases which break up proteins into amino acids; amylases which break up carbohydrates into sugars and lipases which break up fats and other lipids into fatty acids and glycerol.

4.1.1 Stages of Digestion

The digestive system begins with the mouth where the food enters. This stage is called iingestion. After the food enters the alimentary canal, it is digested. This is the breakdown of complex food into the simple subunits. The products of digestion then enter the blood or lymph. This stage is known as aabsorption. After the food is absorbed, the nutrients are brought to the body cells. Here, assimilation occurs where the absorbed nutrients are converted into complex molecules for growth and repair. Finally, the waste products which remain behind must be removed from the body. This stage is called eegestion. These five stages of digestion are shown in Table 4.1.

4.1

TOPIC 4 DIGESTIVE SYSTEM � 85

Table 4.1: The Stages of Human Digestion

Stages of Digestion What Happens

Ingestion Taking of food into the body (eating).

Digestion Breaking down of complex insoluble food into simpler soluble substances. Consists of physical digestion and chemical digestion.

Absorption Absorption of digested food into the blood or lymph.

Assimilation The uptake and use of absorbed food in the body for metabolic activities.

Egestion Undigested food is egested (removed).

4.1.2 The Human Digestive System

The system of organs that carries out digestion is known as the digestive system. The organs involved in the human digestive system can be divided into two main groups: (a) TThe Alimentary Canal The alimentary canal is a continuous muscular tube running from the

mouth to the anus. It is about 10 m long in adults and is further subdivided into organs with specific functions. The alimentary system consists of the mouth, oesophagus, stomach, small intestine, large intestine and anus.

(b) AAccessory Structures of the Digestive System Accessory structures of the digestive system are organs that lie outside the

alimentary canal and either produce or store secretions which aid in the digestion of food. Examples of such organs include the salivary glands, liver, gall bladder and pancreas.


86

Figure 4.1 shows the human digestive system. �

Figure 4.1: Human digestive system Source: http://leavingbio.net

Now, study Table 4.2, which provides the information of the features and functions of organs of our digestive system. �


Table 4.2: The Features and Functions of the Organs of the Digestive System

Organ Features Function

Mouth Teeth and tongue, salivary glands.

� Ingestion and mechanical digestion (chewing of food).

� Digestion of starch.

Oesophagus Long muscular tube which leads from mouth to stomach.

� Moves food from mouth to stomach through peristalsis.

Stomach Thick walled sac that contains gastric glands.

� Acidity kills some bacteria. � Digestion of starch stops. � Digestion of protein starts.

Liver Produces bile which is stored in the gall bladder. Bile enters the duodenum via the bile duct. �

� Bile creates an alkaline environment for the enzyme action in the duodenum.

� Bile salts emulsify lipids.

Pancreas Pancreas secretes pancreatic juice. This is secreted into the duodenum by the pancreas via the pancreatic duct.

� Pancreatic juice contains the enzymes � pancreatic amylase, trypsin and lipase.

Gall bladder

Small sac found on liver. � Stores and concentrates bile from the liver.

Small intestine

Duodenum Receives secretions from the gall bladder (bile) and pancreas (pancreatic juice).

� Digestion of starch, proteins and fats.

Jejunum and Ileum

Produce intestinal juices.

� Completion of digestion and absorption of food.

Large intestine

Caecum Small pouch at the junction of the small and large intestines. Appendix projects from caecum.

� No function in humans.

Colon Consists of three parts: ascending, transverse and descending limb.

� Absorption of water and salts.

Rectum Short and muscular. � Storage of faeces.

Anus External opening surrounded by circular muscles.

� Egestion or defecation.


88

What is the function of salivary glands? Salivary glands secrete saliva which moistens and lubricates food. It also contains amylase enzymes which start the breakdown of starch. Does the appendix have a function? The appendix is a vestigial (functionless) organ in humans, but is large and functional in herbivores. You will be learning more about this later in this topic.

��

SELF-CHECK 4.1

1. Explain the following terms:

(a) Ingestion; and

(b) Digestion. 2. Complete Table 4.3 to show what happens to each class of food as

they pass through the mouth cavity, stomach, duodenum and ileum.

Table 4.3

Nutrient Part of Alimentary Canal

Mouth cavity Stomach Duodenum Ileum

Protein

Fat

Starch


�

4.1.3 The Process of Digestion

Now, let us go through the process of digestion in detail. These are: (a) DDigestion in the Mouth The digestive process starts in the mouth. The chewing action breaks the

food into smaller particles. The presence of food in the mouth stimulates the secretion of saliva by the salivary glands. The tongue manipulates the food while it is being chewed to ensure it is mixed well with the saliva. Saliva contains the enzyme ssalivary amylase which begins the breakdown

3. Describe the parts played in the digestion of food by the following organs:

(a) Pancreas; and

(b) Liver. 4. Label and state the function of each part of the human digestive

system in Figure 4.2.

Figure 4.2: Unlabelled diagram of the human digestive system


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of starch to maltose. The chewed food is rolled into a mass called a bbolus in preparation for swallowing. The food then enters and moves down the oesophagus by a process called pperistalsis, which is a series of wave-like muscular contractions. The food then enters the stomach. This process is illustrated in Figure 4.3.

�Figure 4.3: Peristalsis

Source: http://www.tutorvista.com (a) DDigestion in the Stomach

The stomach is a thick-walled, muscular sac with a highly folded inner wall. The lining of the stomach wall contains gastric glands which secrete gastric juice. Gastric juice contains ddilute hydrochloric acid and the digestive enzymes ppepsin and rrennin. The contents and functions of gastric juice are shown in Table 4.4.


Table 4.4: Contents and Functions of Gastric Juice

Contents of Gastric Juice Functions

Dilute hydrochloric acid

� Stops the action of salivary amylase, which needs an alkaline medium.

� Helps to kill bacteria in food. � Provides an acidic medium for the action of pepsin

and rennin.

Pepsin � Starts the breakdown of large protein molecules to polypeptides.

pepsin Proteins Polypeptides

Rennin � Coagulates liquid milk into a solid form.

Food stays in the stomach for a number of hours. During this period, the food is thoroughly churned and mixed with the gastric juice by the peristaltic contractions of the stomach wall. Eventually, the contents of the stomach become a semi-fluid called cchyme. The food then enters the first part of the small intestine, which is called the dduodenum.

(b) DDigestion in the Small Intestine

The small intestine consists of the duodenum, jejunum and the ileum as shown in Figure 4.4.

Figure 4.4: Parts of the small intestine

Source: http://www.fashion-reply.com


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Let us read about the three parts of the small intestine.

(i) TThe Duodenum The duodenum is the first part of the small intestine and is about 25 cm long. It receives chyme from the stomach and secretions from the gall bladder and pancreas. Study Figure 4.5, which shows the position of the duodenum, pancreas and liver.

Figure 4.5: The position of the duodenum, pancreas and liver

Source: http://digestive.niddk.nih.gov

The liver secretes bile, an alkaline greenish-yellow fluid which is stored in the gall bladder. Bile creates an alkaline environment for the enzyme action in the duodenum. Bile also emulsifies fats, transforming large lumps of fats into tiny droplets. This increases the surface area for lipid digestion. The pancreas secretes pancreatic juice, which contains three types of enzymes: ppancreatic amylase, trypsin and lipase. The digestion of starch, proteins and lipids takes place in the duodenum as shown here:


(ii) TThe Jejunum and Ileum The duodenum leads on to the jejunum and ileum. The jejunum is

about 2 m long. The ileum, which is about 4 m long, is the longest part and is coiled and twisted. Glands in the wall of the ileum secrete intestinal juice, which contains the digestive enzymes: mmaltase, lactase, sucrase and erepsin.These enzymes complete the digestion of proteins and carbohydrates. They require an alkaline medium to act at an optimal rate. The action of the intestinal juice enzymes are shown here:


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4.1.4 Absorption of Digested Food

The final products of digestion are glucose, amino acids, fatty acids and glycerol. The absorption of these digested products takes place in the small intestine. The small intestine has several adaptations to increase its efficiency in the absorption process. These are:

(a) The small intestine is long and coiled. It is about 6�7 m long and is the longest part of the alimentary canal. This increases the time for enzyme action. The surface area for absorption is also increased.

(b) The internal walls of the small intestine are folded to increase the surface area for absorption.

(c) The internal walls of the small intestines are covered with tiny finger-like projections called vvilli (singular: vvillus). The structure of the villus is ideally suited for the function of absorption of food. Figure 4.6 shows the structure of a vvillus.

�

�Figure 4.6: Structure of villus

Source: http://studentbiologist.blogspot.com �


What are the adaptations of the villus for the absorption of food? They are:

(a) Numerous, thus increasing the internal surface area for absorption;

(b) Thin walled (only one cell thick); thus, digested food can be absorbed rapidly;

(c) Contain a network of blood capillaries for the efficient transport of digested food; and

(d) Contain special structures called lacteals for absorbing fatty acids and glycerols.

Simple sugars and amino acids are absorbed directly into the blood capillaries of the villus. Fatty acids and glycerol are absorbed into the lacteal where they are reconverted into lipids and move into the lymphatic system. You will learn more about the lymphatic system in the next topic.

4.1.5 Assimilation of Digested Food

Assimilation refers to what happens to the products of digestion. Absorbed food substances are brought directly to the liver by the blood stream. The liver turns the building materials such as sugars and amino acids into substances that are used by different cells of the body. For an example, amino acids are transformed into proteins. The liver acts as a checkpoint which controls the amount of nutrients released into the blood system. Glucose is oxidised to produce energy during respiration. Excess glucose is changed to glycogen and stored in the liver and muscles. Fats are used to build cell membranes or act as an energy source when required. Excess fats are deposited beneath the skin to reduce heat loss from the body. Amino acids are used to form structural proteins for growth, repair and making of enzymes and antibodies. Excess amino acids undergo a process called deamination where they are broken down and form urea. Urea is carried by the blood to the kidney to be excreted. This process is illustrated in Figure 4.7.


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Figure 4.7: Assimilation in the liver

Source: https://www.cdli.ca

4.1.6 Defaecation or Egestion

After the absorption of nutrients has taken place in the small intestine, the intestinal contents enter the large intestine or colon. The intestinal contents consist of a mixture of water, undigested food substances and indigestible fibre, most of which is cellulose from plant cell walls. The movement of these undigested materials along the colon is slow and helped by peristalsis. The colon reabsorbs almost 90% of water and minerals into the bloodstream. Absorption of water from the undigested that remains in the colon results in the formation of faeces which are a semi-solid waste. After 12�24 hours in the colon, the faeces pass into the rectum for temporary storage. As the faeces accumulate, pressure in the rectum increases, causing a desire to expel the faeces from the body. The elimination of faeces is known as ddefaecation. This process is controlled by muscles around the anus, which is the opening of the rectum. The problems related to defaecation are shown in Table 4.5.


Table 4.5: Problems Related to Defaecation

Problems Explanation

Diarrhoea Food passes through the large intestine too quickly. Not enough water is absorbed by the intestine.

Constipation Faeces move too slowly through the colon. As a result, too much water is reabsorbed making the faeces hard. Taking sufficient amounts of fibre in the diet and drinking a lot of water can prevent constipation.

Haemorrhoids Abnormally swollen veins in the rectum and anus. Caused by too much pressure in the rectum forcing blood veins to stretch, bulge and sometimes rupture.

Colon cancer Malignant tumours of the colon. Believed to be caused by diets high in fats. Breakdown of products of fat metabolism leads to cancer-causing chemicals (carcinogens). A diet high in vegetables and fibre may help to reduce the risk of cancer.

What is the difference between defaecation and excretion? DDefaecation or egestion should not be confused with eexcretion. Defaecation is the elimination of the waste products of digestion from the alimentary canal. Meanwhile, excretion is the removal of waste products of metabolism from excretory organs such as the skin, lungs and kidneys. We will deal with this in Topic 5.

SELF-CHECK 4.2

1. List three ways in which the intestine increases the surface areafor absorption.

2. Name the end products of digestion which are absorbed by:

(a) Blood capillaries of intestinal villi; and

(b) Lacteals. 3. Explain the meaning of assimilation. 4. State the effects of insufficient intake of dietary fibre.


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DIGESTION IN RUMINANTS AND RODENTS

Ruminants and rrodents are herbivores. The plant materials they feed on contain a high percentage of cellulose. In Topic 2, you learnt that cellulose is an insoluble polysaccharide. The digestive systems of ruminants and rodents have unique adaptations that help them to digest cellulose. Ruminants include cattle, sheep, goats, buffalo, deer, antelopes, giraffes and camels. Examples of ruminants are shown in Figure 4.8.

Figure 4.8: Examples of ruminants Examples of rodents are shown in Figure 4.9.

Figure 4.9: Examples of rodents Source: http://visual.merriam-webster.com

Let us now study the digestive systems of ruminants and rodents.

4.2


4.2.1 Digestion in Ruminants

A ruminant is an animal which has a complicated digestive system in which the stomach has several chambers. This unique digestive system allows them to use energy from cellulose plant materials effectively. Ruminant animals like cattle, sheep and goats are hoofed mammals that feed on plants but do not produce cellulase which is needed to digest cellulose. How does digestion of cellulose occur? Ruminant stomachs are made up of four chambers:

(a) Rumen;

(b) Reticulum;

(c) Omasum; and

(d) Abomasum. This adaptation enables ruminants to regurgitate and chew food again. Study Figure 4.10 which shows the digestive tract of a ruminant. �

�Figure 4.10: Digestive tract of a ruminant

As you can see in Figure 4.10, the first two chambers � the rumen and reticulum are specialised compartments which have large communities of bacteria and protozoa. These microorganisms produce cellulase which digests cellulose into simple sugars. The abomasum corresponds to the stomach in humans.


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Still looking at Figure 4.10, partially chewed food is passed into the rrumen. Here, cellulose is broken down by the cellulase produced by the microorganisms. The partially digested food called the „cud‰ is then passed on into the rreticulum. The cud is then regurgitated bit by bit into the mouth to be chewed again. Regurgitation of materials from the reticulum, followed by re-chewing and re-swallowing, is called rrumination. Rumination provides effective mechanical breakdown of cellulose and increases the surface area for microbe action.The food is then re-swallowed and moves to the oomasum. Here, large particles of food are broken down into smaller pieces by peristalsis. The walls of the omasum also reabsorb water from the cud. The food particles finally move into the abomasum, the true stomach of the cow. Here, gastric juices containing the digestive enzymes complete the digestion of the other food substances. The food then passes through the small iintestine to be digested and absorbed.

4.2.2 Digestion in Rodents

Rodents also feed on plants but their digestive systems are different from those of ruminants. Firstly, the ccaecum and aappendix of rodents are enlarged to store cellulase-producing microorganisms (bacteria and protozoa). Secondly rodents rely on ddouble digestion, that is, their food passes through the alimentary canal twice. Rodents eat their own faeces so as to obtain all the nutrients lost with the faeces. The faeces in the first batch are soft and watery. These faeces are eaten again to enable the animals to absorb the products of bacterial breakdown as they pass through the alimentary canal for the second time. The second faeces becomes drier and harder. This adaptation allows rodents to recover the nutrients initially lost with the faeces. This process in illustrated in Figure 4.11.

Figure 4.11: Digestive tract of rodents Source: http://www.petcaregt.com


EXCRETION IN PLANTS

Do you remember what excretion is? Excretion is the process by which an organism removes the waste products of metabolism. Important differences between plant and animal metabolism make the process of excretion in plants less significant than excretion in animals. Plants do not have any specialised organs of excretion as animals do. Most of the waste products diffuse out of the plant through tiny openings called stomata in leaves. Why is plant excretion different from animal excretion? It is because according to Clegg, C. J. & Mackean, D. G (2000):

(a) Plants are stationary so they have a lower metabolic rate and metabolic waste products move more slowly.

(b) Plants are producers and synthesise their own food as raw materials become available. For example, nitrogenous compounds such as ammonia and nitrate are resources for protein production rather than unwanted substances to excrete. Carbon dioxide is used to synthesise sugar.

(c) Plants do not need to break down large molecules as they make their own food.

(d) Much of the structure of plants is based on carbohydrates rather than proteins.

4.3

SELF-CHECK 4.3

1. Cellulose is an insoluble carbohydrate. However, manyherbivorous mammals have special adaptations in their digestivesystems that help them to digest carbohydrates.

(a) Describe the adaptations of ruminants that help in thedigestion of cellulose.

(b) In what ways are the digestive systems of rodents differentfrom ruminants?

(c) Explain what happens to cellulose in the human alimentarycanal.


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What are the waste products of plants? The following are the waste products of plants: (a) CCarbon Dioxide Green plants use carbon dioxide for photosynthesis during the day.

However, in the dark, carbon dioxide produced by respiration becomes a waste product and diffuses out through the stomata in leaves.

(b) OOxygen During the day, oxygen is a waste product of photosynthesis and diffuses

out through the stomata in leaves. (c) WWater Water is produced as a respiratory waste product. Plants get rid of the

excess water by the processes of transpiration and guttation. You will be learning more about transpiration and guttation in Topic 5.

(d) EExcretory Products Plants also excrete products such as secretions, alkaloids, oils and crystals.

Resin, tannin, quinine, nicotine, oil, morphine and latex are examples of plant excretory products. This is shown in Table 4.6.

Table 4.66: Plant Excretory Products and their Uses

Source Excretory Products Uses

Bark of casuarina tree Resin Manufacture of paint and varnish

Bark of mangrove Tannin Manufacture of ink Softening of leather

Bark of cinchona Quinine Medicine of malaria

Tobacco leaf Nicotine Medicine, drug, poison

Flowers/ Leaf Oil Perfume

Poppy leaf Morphine Medicine, drug

Bark of rubber tree Latex Manufacture of rubber goods


� Digestion is the process where food is broken down from complex substances

into simpler soluble molecules. � Digestion can be divided into physical and chemical digestion. � The human digestive system can be divided into the organs of the alimentary

canal and the accessory structures like the salivary glands, liver, gall bladder and pancreas.

� The presence of food in the mouth stimulates the secretion of saliva by the

salivary glands. � Saliva contains the enzyme ssalivary amylase which begins the breakdown of

starch to maltose. � The food then enters and moves down the oesophagus into the stomach by a

process called pperistalsis. � The lining of the stomach wall contains gastric glands which secrete ggastric

juice. � Gastric juice contains ddilute hydrochloric acid and the digestive enzymes

pepsin and rrennin.

SELF-CHECK 4.4

1. Explain why plants do not have specialised excretory organs.

2. State the uses of the following excretory products of plants: latex,resin and tannin.


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� The duodenum receives the contents from the stomach and secretions from the gall bladder and pancreas.

� The liver secretes bile, which is stored in the gall bladder. � Bile also emulsifies fats.

� The pancreas secretes pancreatic juice which contains three types of enzymes:

pancreatic amylase, trypsin and lipase. � Glands in the wall of the ileum secrete intestinal juice which contains the

digestive enzymes: mmaltase, lactase, sucrase and erepsin which complete the digestion of proteins and carbohydrates.

� The final products of digestion, glucose, amino acids, fatty acids and glycerol

are absorbed in the small intestine through the vvilli. � The elimination of faeces known as defaecation is controlled by muscles

around the anus. � Ruminants and rodents are herbivores and need to digest cellulose. � The digestive systems of ruminants and rodents have unique adaptations that

help them to digest cellulose. � Plants do not have any specialised organs of excretion as animals do. � Most of the waste products diffuse out of the plant through tiny openings

called stomata in leaves. � The waste products of plants are carbon dioxide, oxygen, water and excretory

products.


Abomasum

Assimilation

Bolus

Caecum

Digestion

Duodenum

Egestion

Erepsin

Gall bladder

Ileum

Ingestion

Jejunum

Lactase

Lipase

Maltase

Oesophagus

Omasum

Pancreas

Pancreatic amylase

Pepsin

Reticulum

Rectum

Rennin

Rodent

Ruminant

Salivary amylase

Salivary glands

Sucrase

Trypsin

Villus

Clegg, C. J., & Mackean, D. G. (2000). Advanced biology: Principles and

applications (2nd ed.). London: Hodder Murray. Enchanted Learning. (2010). Human digestive system. Retrieved March 20, 2011

from http://www.enchantedlearning.com/subjects/anatomy/digestive/ PBS. (2012). The need for food/the digestive system. Retrieved March 20, 2011

from http://www.hns.org.uk/bio/index.php?option=com_content&view=article&id=123&Itemid=176


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Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., & Jackson, R. B. (2010). Campbell biology (9th ed.). San Francisco: Pearson � Benjamin Cummings Pub

Roberts, M. B. V. (1986). Biology: A functional approach. Surrey: Thomas Neson

& Sons Ltd. Tutor Vista. (2010). Human digestive system � the alimentary canal. Retrieved

March 20, 2011 fromhttp://www.tutorvista.com/content/science/science-ii/nutrition/alimentary-canal.php

� INTRODUCTION

Now, you will learn about the control and maintenance of body fluids such as blood, lymph and water. You will also study the circulatory system, lymphatic system and the osmoregulation as a process that controls and maintains our body fluid, and the body defence system that protects us from the invading pathogens. At the end of the topic, you will learn how plants transport their water and food.

BLOOD AND ITS COMPOSITION

You must be familiar with the sight of blood. It is the red fluid that oozes out of your body when you have had a cut or an injury. But, do you have any idea about the composition of blood?

5.1

LEARNING OUTCOMES


1. Describe the composition of blood;

2. Describe the structure of the human circulatory system;

3. Describe the structure of the lymphatic system;

4. Describe how osmoregulation is being carried out by our body;

5. Discuss the human body defence system; and

6. Explain the transport system in plants through the vascular system.

TTooppiicc

55

� Control and Maintenance of Body Fluids

� TOPIC 5 CONTROL AND MAINTENANCE OF BODY FLUIDS 108

5.1.1 Composition of Blood

The composition of blood is actually quite complex. It is made up of a liquid component and a cellular component. The liquid component of blood is called plasma. Plasma is a straw coloured liquid that is made up of water and soluble substances such as glucose, amino acids, mineral salts, blood proteins, hormones, antibodies, urea and carbon dioxide. The cellular part consists of red blood cells (erythrocytes), white blood cells (leukocytes) and platelets. All these can be seen in Figure 5.1.

Figure 5.1: Composition of blood

Source: http://www.jamesdisabilitylaw.com

TOPIC 5 CONTROL AND MAINTENANCE OF BODY FLUIDS � 109

Now, let us look at Table 5.1 which describes the features of erythrocytes, leukocytes and platelets. Refer to Figure 5.1 to see what these cells look like.

Table 5.1: Features of Erythrocytes, Leukocytes and Platelets

Elements Features

Erythrocytes � Circular, flattened biconcave discs. � Do not have a nucleus. � Have a large surface area to volume ratio. � Contain a pigment known as hhaemoglobin which causes the colour

of erythrocytes to be red. � Produced in bone marrow. � Life span of 90 to 120 days. � Transport oxygen from lungs to all parts of the body and carbon

dioxide from body tissues to lungs.

Leukocytes � Have no colour. � Have a nucleus. � Larger than erythrocytes. � There are two types: ggranulocytes and aagranulocytes (refer to

Table 5.2 and Figure 5.1). � Both types of leukocytes protect the body against disease and fight

infection. � Lymphocytes kill germs by producing antibodies. � Phagocytes kill germs by swallowing and digesting germs (by

phagocytosis). � Life span is about two to four days. � Produced in the bone marrow and lymphatic tissue.

Platelets � Not true cells but bits of cells which have broken off from larger cells in the bone marrow.

� The shape of platelets is inconsistent. � Do not have a nucleus. � Life span of 10 days. � Produced in the bone marrow. � Critical for clotting of blood.

From Table 5.1, we learned that there are two types of leukocytes. Let us look at Figure 5.2 for more details.


Figure 5.2: Types of leucocytes

5.1.2 Functions of Blood

Blood is very important for our survival. It is a medium in which dissolved gases, hormones, nutrients and waste products are being transported. Blood also plays a role in the regulation of body temperature. Blood helps in maintaining balanced conditions within our body. Another function of blood is in the body defence system, which you will be learning later in this topic.

5.1.3 Human Blood Groups

Human blood can be categorised into four groups, which are A, B, AB and O. It is important to know our blood group, especially during blood transfusions. During a blood transfusion, the recipientÊs blood must be compatible with the donorÊs blood. For example, a person in blood group A can only receive blood from blood groups A and O. However, a person in blood group A can donate blood to blood groups A and AB. Table 5.2 shows the compatibility between blood donors and the recipients. Type AB is called „universal acceptor‰ because people with this blood group can accept blood from all other blood groups. Type O is called „universal donor‰ because people with this blood group can donate blood to all other blood groups. � �


Table 5.2: Compatibility of Blood Donors and Recipients

Blood Group Compatibility

A � Can only donate blood to blood groups A and AB. � Can only receive blood from blood groups A and O.

B � Can only donate blood to blood groups B and AB. � Can only receive blood from blood groups B and O.

AB � Can only donate blood to blood group AB. � Can receive blood from blood groups A, B, AB and O.

O � Can donate blood to blood groups A, B, AB and O. � Can only receive blood from blood group O.

�

��

�

SELF-CHECK 5.1

ACTIVITY 5.1

1. In groups, discuss the consequences for a person who has beendiagnosed with a lack of:

(a) Red blood cells

(b) White blood cells

(c) Platelets 2. Discuss also the symptoms of the diseases shown in (1).

1. List the four main components of blood.

2. Name five substances dissolved in plasma.

3. Name two types of leukocytes.

4. Describe the function of leukocytes.

5. Describe the function of platelets.

6. Which types of cells have no nucleus?

7. List the functions of blood.

8. If a person has blood group AB, list the groups from which he/she can receive blood.


THE HUMAN CIRCULATORY SYSTEM

You have studied about blood and its functions. You have also learned that blood needs to reach every cell in the body. How does this happen? You will now learn about the circulatory system which makes it possible. The human blood circulatory system consists of three main parts as shown in Figure 5.3: the heart, blood vessels and blood. �

�Figure 5.3: Parts of the circulatory system

5.2.1 The Heart

Make a fist with your hand. Note its size. Your heart is a bundle of muscles the size of your fist. Heart muscle is called cardiac muscle. The heart is shaped like a cone and is located in the centre of your chest between the lungs. It is tilted to one side and points downward to the left as can be seen in Figure 5.4. �

�Figure 5.4: Location of the heart

�

5.2


The heart never stops beating as long as a person is alive. Can you feel your heart beating now? Before we learn more about the heart, let us take a look at Figure 5.5, which shows the major parts of the heart. �

�Figure 5.5: Structure of the human heart

Source: http://www.interactive-biology.com As shown in Figure 5.5, the human heart has four chambers: two thin walled atria (singular; aatrium) and two thick walled vventricles underneath. The atria receive blood and the ventricles pump blood. Between the atria and the ventricles are aatrioventricular valves, which prevent the back-flow of blood from the ventricles to the atria. The left valve has two flaps and is called the bbicuspid (or mmitral) valve while the right valve has three flaps and is called the ttricuspid valve. There are also two ssemilunar valves: the ppulmonary valve at the base of the ppulmonary artery and the aaortic valve at the base of the aaorta. These valves prevent the backflow of blood into the ventricles. The atrium and the ventricle on the right are separated from the left atrium and ventricle by a thick wall of muscle called the sseptum.


5.2.2 Blood Vessels

How does blood travel throughout the body? There is a network of small tubes that carries blood through the body. These tubes are called blood vessels. Do you know if you were to take out all your blood vessels and line them up end to end, they would be able to go around the earth twice! There are three types of blood vessels in the body; the aarteries, veins and capillaries. Figure 5.6 shows the structure of arteries, veins and capillaries.

Figure 5.6: Structure of arteries, veins and capillaries

Source: http://www.scienceunleashed.ie �Let us learn more about these three types of blood vessels in the body. (a) AArteries Arteries carry blood away from the heart to the tissues of the body. They

have a thick elastic muscular wall that helps them withstand the high pressure of blood pumped from the heart. They also have a small lumen or opening. All arteries carry oxygenated blood except for the pulmonary artery. The largest artery is the aorta. This is the artery which carries oxygenated blood from the heart to the rest of the body. The smallest branch of an artery is called an aarteriole.


(b) VVeins Veins carry blood from the body tissues to the heart. They have relatively

thinner and less muscular walls than arteries. They have larger lumen compared to arteries. Veins also have valves that prevent the back-flow of blood. All veins carry deoxygenated blood except for the pulmonary veins. The smallest branch of a vein is called a vvenule. You can see some of your veins as they lie just under the surface of the skin.

(c) CCapillaries Capillaries are tiny vessels that connect arteries to veins as shown in

Figure 5.7. Capillary walls are only one cell thick which allow diffusion of materials between capillaries and body cells. At the capillaries oxygen and nutrients pass from the blood to the cells while carbon dioxide and waste products pass from the cells to the blood.

�

�Figure 5.7: Relationship between arteries, veins and capillaries

Source: http://www.factmonster.com


5.2.3 The Circulatory System

On average, your body has about five litres of blood travelling continuously through the circulatory system. The pumping of the heart forces the blood onto its journey. The human circulatory system consists of two parts: (a) TThe Pulmonary Circulation The pulmonary circulation involves the flow of blood from the heart to the

lungs and back to the heart. (b) TThe Systemic Circulation The systematic circulation involves the flow of the blood from the heart to

all parts of the body and back to the heart. Since there are two circulations, the human circulatory system is also known as a double circulatory system. This means blood passes through the heart twice on one circuit of the body. How does this happen? Refer to Figure 5.8 as you read the following explanation.

��

�

THE DOUBLE CIRCULATION SYSTEM Pulmonary Circulation

� Deoxygenated blood from all parts of the body flows into the right atrium through the anterior and posterior vena cava.

� Contraction of the right atrium forces blood into the left ventricle and out through the pulmonary artery.

� The pulmonary artery carries the deoxygenated blood to the lungs where carbon dioxide diffuses out and oxygen enters the blood.

� Oxygenated blood flows back to the heart through the pulmonary veins. Systemic Circulation

� The left atrium receives oxygenated blood, rich in oxygen from the lungs.

� The left atrium contracts and pushes blood through the valves into the ventricles.

� The left ventricle contracts and pumps the oxygenated blood into the aorta.

� The aorta carries the oxygenated blood to all parts of the body.


�Figure 5.8: The human circulatory system

5.2.4 Heartbeat and Pulse

The heart beats as the cardiac muscle in its walls contracts and relaxes. This alternate contraction and relaxation of the heart muscle gives the impression of a beat. The time of contraction is called ssystole and that of relaxation is called diastole. During systole, the heart contracts to squeeze blood out. During diastole, the heart relaxes to allow blood to flow into the atria and ventricles. One complete systole and diastole is called a heartbeat. The heart usually beats about 70 times a minute. �Have you listened to your heartbeat? Your heart makes a „lub-dub‰ sound. These sounds are caused by the closing of the valves. The „lub‰ is caused when the ventricles contract and the bicuspid and tricuspid valves close. The „dub‰ sound is caused by the semi lunar valves closing. A normal heart repeats the „lub-dub‰ sound over and over again in perfect rhythm.


Every time the heart muscles contract to push blood out into the arteries, there is an increase of pressure on the wall of the arteries. When the heart relaxes, this pressure decreases. This is felt as the ppulse. Your pulse rate is an indication of the rate of your heart beat. You can easily feel your pulse by placing a finger over an artery which lies near the body surface. A good example is the radial artery in your wrist. You can also take your pulse at your neck as in Figure 5.9.

Figure 5.9: How to take your pulse

Source: http://www.cchs.net What is the common procedure to measure our pulse rate? It is quite simple and easy. You just need a watch. Just count the pulse that you can feel under your skin either at your wrist or neck for 15 seconds and multiply this by 4 to get the number of beats per minute. If you are not doing any activity (resting), your pulse rate should range from 70 to 100 beats per minute (BPM). However, if you are jogging, the range of the pulse rate may increase to as high as 150 to 200 BPM. Another important circulation is called the ccoronary circulation as can be seen in Figure 5.10. �

�Figure 5.10: Coronary circulation

Source: http://www.squidoo.com


The coronary circulation refers to the flow of blood through the heart. Since the heart is a very active organ, it has a high demand for oxygen and nutrients. Serious heart damage may occur if the heart tissue does not receive a normal supply of nutrients and oxygen. When this happens, it is called a heart attack. �

�

SELF-CHECK 5.2

1. Name the parts of the circulatory system.

2. The muscular organ that pumps blood to all parts of the body is called the __________.

3. Name the upper and lower chambers of the heart.

4. Which ventricle has the thickest wall and why?

5. What prevents backflow to the heart?

Arteries take blood ______ from the heart. The walls of an artery are made up of thick _________ walls and elastic fibres. Veins carry blood ________ the heart and also have valves. The _________ link arteries and veins, and have a one cell thick wall.

6. Which side of the heart contains oxygenated blood?

7. After the ventricles, where does the blood go?

8. Name the blood vessel that returns blood to the heart.

9. Name the blood vessel that takes oxygenated blood to the body.

10. Why does the blood go to the lungs?

11. What does double circulation mean?

12. What is a heartbeat?

13. What causes your heart rate to increase.? Discuss why this is so.


THE LYMPHATIC SYSTEM

Besides blood, our body contains two other important fluids called tissue fluid and lymph. We shall first look at what tissue fluid is and then discuss the lymphatic system of which the lymph is a part.

5.3.1 Tissue Fluid

Tissue fluid, which is also known as interstitial fluid or intracellular fluid, is the medium surrounding body cells. It is the immediate environment of the cells. The cells get all the substances they need from the bloodstream through the tissue fluid. The tissue fluid also removes waste products. It is an essential link between blood and body cells as can be seen in Figure 5.11.

5.3

In this activity, you will take your pulse rate for each of the following physical activities.

Activity Beats Per Minute (BPM)

At rest (when you are sitting down completely relaxed)

Walking for 30 seconds

Running for 10 seconds

Running for 30 seconds

Running for 1 minute

Jumping 15 times

Jumping 30 times

What is the conclusion you can make about heart rate and exercise?

ACTIVITY 5.2


Figure 5.11: Relationship of blood, tissue and lymph Source: http://mol-biol4masters.masters.grkraj.org

How is tissue fluid formed? Tissue fluid is derived from blood. Some of the plasma (remember the part of the blood that is a clear liquid?) leaks out and bathes the cells surrounding the capillaries. The blood cells and plasma proteins are too large to go through the capillary walls, so they stay in the blood. What passes through is therefore a colourless fluid consisting of blood plasma minus the proteins. This fluid is known as tissue fluid or interstitial fluid. Once formed, the tissue fluid seeps around the cells. If there is too much of it, it either returns to the capillaries, or is drained into a system of narrow tubes called the lymph capillaries. Once it enters the lymph capillaries, the fluid is called lymph.

5.3.2 Lymphatic System

The lymphatic system consists of a network of lymphatic vessels, numerous small lymph nodes, colourless or pale yellow fluid called lymph and lymphatic organs. This is shown in Figure 5.12. �

�Figure 5.12: The parts of the lymphatic system

�


Let us take a look at each part in detail. (a) LLymphatic Vessels The lymphatic vessels which resemble blood capillaries merge into larger

vessels that form a network around the body. Look at Figure 5.13, which illustrates the lymphatic system.

�

�Figure 5.13: The lymphatic system

Source: http://labspace.open.ac.uk

The lymphatic vessels as can be seen in Figure 5.13 contain valves, which help to keep the lymph flowing in the right direction. Unlike blood capillaries, which form a continuous connected network, lymph capillaries face dead-end in the bodyÊs tissues. The lymph is pushed along the lymph vessels by the contractions of the muscles of the body. All the lymphatic vessels join up and empty their contents into two large veins just above the heart.


(b) LLymph Lymph is a colourless or pale yellow fluid. Lymph has a composition

similar to tissue fluid, but it contains more fatty substances. It also contains more white blood cells.

(c) LLymph Nodes Look closely at Figure 5.13. You will see little swellings at intervals along

the length of the lymph vessels. These are called lymph nodes or lymph glands. The lymph has to filter through these lymph nodes on its journey. The lymph nodes help us to fight diseases. They produce white blood cells, which help to protect the body from diseases. These cells are the same as the leukocytes mentioned earlier in this topic. Some of them are phagocytes and ingest bacteria while others produce antibodies. Lymph nodes are abundant in the neck region, arm pit, groin, breast and stomach.

Suppose you have a severe throat infection. The bacteria get trapped in the

nearby lymph nodes in your neck where your phagocytes and lymph cells do their best to kill them and prevent them from getting to the rest of your body. This causes the glands to swell up and become tender and painful.

(d) LLymphatic Organs The largest organ of the lymphatic system is the sppleen, located to the left of

and just behind the stomach. The spleen stores an emergency supply of blood and also contains white blood cells.

The tthymus is located above the heart and is responsible for the production

of lymphocytes. The thymus is active in infants and young children but decreases in size and importance by early adulthood. It is important in the maturation of certain lymphocytes called T-cells, which play a major role in the immune system.

Do you know that AAIDS (Acquired Immune Deficiency Syndrome) is caused by a virus called HHIV (Human Immunodeficiency Virus)? HIV is a virus of the lymphatic system. HIV enters the body and kills off all the lymphocytes. A person infected with HIV usually dies from the diseases that the lymphocytes usually would have fought off.


5.3.3 Functions of the Lymphatic System�

The lymphatic system has several important functions. These functions include:

(a) Removing excess tissue fluid and direct it back to the blood vessels;

(b) Transporting fatty acids and glycerol (the products of lipid digestion) which are absorbed from lacteals in the villi of the small intestine;

(c) Producing and storing white blood cells;

(d) Fighting foreign substances during an infection. White blood cells which are produced engulf bacteria or secrete antibodies.

(e) Filtering bacteria and foreign matter in the lymph nodes and thus preventing them from entering the blood circulatory system.

5.3.4 The Differences

Now, we have come to the end of this subtopic. Before we go into the next subtopic, let us take a look at Table 5.2, which shows the difference among blood, plasma, tissue fluid and lymph.

Table 5.2: The Differences among Blood, Plasma, Tissue Fluid and Lymph

Body Fluid Differences

Blood Consists of a liquid component called plasma and a cellular component. It transports substances around the body and defends it against diseases.

Plasma: The liquid part of blood. It contains dissolved nutrients, proteins, hormones, urea and carbon dioxide.

Tissue fluid The fluid surrounding the cells. Its composition is similar to plasma, but without the proteins (which stay in the blood capillaries).

Lymph The fluid inside the lymphatic vessels. Its composition is similar to tissue fluid, but with more fat (from the digestive system). Contains white blood cells.


OSMOREGULATION

Animals need to keep its internal condition such as water concentration, temperature and glucose concentration as constant as possible. The control systems that help to maintain this is called hhomeostasis. The liver, the kidneys and the brain (hypothalamus, the autonomic nervous system and the endocrine system) help maintain homeostasis. The liver is responsible for metabolising toxic substances and maintaining carbohydrate metabolism. The kidneys are responsible for regulating blood water levels, re-absorption of substances into the blood, maintenance of salt and ion levels in the blood, regulation of blood pH, and excretion of urea and other wastes.

5.4

SELF-CHECK 5.3

1. Complete the table below to compare blood and lymph:

Blood Lymph

Presence of cells

Location

Moved by

Direction of flow

Function 2. The fluid that travels inside the lymph vessels is called _________. 3. What is the function of:

(a) Thymus � ____________________________________________

(b) Spleen � _____________________________________________

(c) Lymph nodes � _______________________________________


An inability to maintain homeostasis may lead to death or a disease, a condition known as hhomeostatic imbalance. For instance, heart failure may occur when negative feedback mechanisms become overwhelmed and destructive positive feedback mechanisms take over. Other diseases which result from a homeostatic imbalance include ddiabetes, dehydration, hypoglycemia, hyperglycemia, gout and any diseases caused by the presence of a toxin in the bloodstream. Negative feedback is an important type of control that is found in homeostasis. A negative feedback control system responds when conditions change from the ideal or set point and returns conditions to this set point. There is a continuous cycle of events in negative feedback. This can be seen in Figure 5.14.

�Figure 5.14: General cycle in a negative feedback mechanism�

Osmoregulation is an example of negative feedback system. Figure 5.15 shows the steps involved in osmoregulation.


Figure 5.15: Osmoregulation

Source: http://www.jirvine.co.uk Osmoregulation is the active regulation of the osmotic pressure of bodily fluids to maintain the homeostasis of the bodyÊs water content; that is, it keeps the bodyÊs fluids from becoming too dilute or too concentrated. Osmotic pressure is a measure of the tendency of water to move into one solution from another through osmosis. The higher the osmotic pressure of a solution, the more water tends to go into the solution. The hormones, anti-diuretic hormone (AADH) and Aldosterone, play a major role in this. If the body is becoming fluid-deficient, there will be an increase in the secretion of these hormones (ADH), causing fluid to be retained by the kidneys and urine output to be reduced. Conversely, if fluid levels are excessive, secretion of these hormones (aldosterone) is suppressed, resulting in less retention of fluid by the kidneys and a subsequent increase in the volume of urine produced.

SELF-CHECK 5.4

Describe the relationship between the terms homeostasis, osmorelationand negative feedback.


BODY DEFENCE SYSTEM

In the first part of this topic, you have studied blood composition. You have seen that leucocytes are cells that make up the defence system in order to fight invaders or pathogens that attack the body. In this subtopic, we are going to discuss them in detail.

5.5.1 The Physical Barrier

The first parts of our defence system is really the physical barriers that stop the pathogens from entering the body. These first parts of our defence system is as shown in Table 5.3.

Table 5.3: The First Parts of Our Defence System

The Physical Barrier Description

Skin The largest organ in our body that also acts as a physical barrier that stops pathogens.

Clotting If the skin is broken, the blood clot stops the entry of pathogens.

Sebaceous and sweat glands

These produce chemicals that kill bacteria.

Lysozyme This is in the saliva and the tear glands. It kills bacteria.

Mucous membranes These secrete mucus which lines many body parts. The mucous traps pathogens and prevents them from entering the body.

Nasal hairs These remove suspended micro-organisms from the air.

Cilia These small hairs beat to force mucus to the pharynx for swallowing then to the stomach. Coughing helps in this process.

Hydrochloric acid This is found in the stomach. It kills micro-organisms.

Lactic acid produced by bacteria in the vagina

Prevent the growth of pathogens. Vagina has a low pH to kill bacteria as well as mucous membranes.

5.5


5.5.2 The General Defence System

If pathogens do get past the physical barriers, our ssecond line of defence takes over. This is our ggeneral defence system. The major components of the ggeneral defence system are shown in Table 5.4:

Table 5.4: The General Defence System

General Defence System Description

Phagocytes These are white blood cells that engulf pathogens (Figure 5.16).

Figure 5.16: Phagocyte

Macrophages These are large, longer living phagocytes. Some move around the body and act as scavengers while others remain in a fixed place. There are many that are present in our lymph system.

Complement defence proteins

These are substances produced by other protein or in response to the presence of foreign material in the body and that trigger or participate in a ccomplement reaction. This is a reaction to the presence of a foreign microorganism in which a series of enzymatic reactions, triggered by molecular features of the microorganism, resulting in the bbursting or engulfing of the pathogen.

Interferons These are defence proteins that are produced by the body cells that are infected by a virus. They travel to the nearby cells and prevent the spread of the virus.

Inflammation Cells that have been infected produce a chemical called histamine. This chemical causes the blood capillaries to dilate and become more porous. As a result, the area swells, gets red, becomes warm, and is painful. This results in more white blood cells coming to the area to fight the infection. If the inflammation happens over the whole body, we get a ffever. The fever is the bodyÊs way to combat bacteria and viruses. The higher temperature inhibits the pathogen from reproducing.


5.5.3 Specific Defence System

If all the defences fail, then we have a sspecific defence system. This system target specific invaders. This can happen with the production of aantibodies or wwhite blood cells engulfing a particular pathogen. Let us look at Table 5.5, which shows specific defence system.

Table 5.5: Specific Defence System

Specific Defence System Description

White blood cells LLymphocytes and monocytes are produced in the bone marrow. Then, they are transported by the blood to lymph vessels, lymph nodes, the spleen or the thymus gland.

(a) MMonocytes These are white blood cells that become mmacrophages. These are

large white blood cells. They engulf invaders. Once engulfed, part of the invader remains on the surface of the microphage. This is called an aantigen. AAntibodies are produced to fight off these future invaders.

(b) LLymphocytes Some attack body cells that have antigens (parts of the invader)

on their surface. Other lymphocytes produce antibodies.

Antibodies LLymphocytes produce antibodies as a result of antigens (Figure 5.17). These are proteins in the group called iimmunoglobulins. Each antigen will only stimulate the production of one specific antibody that will fit into its receptor area. This is called nnatural aactive iinduced immunity. It is protection gained against a particular pathogen by the production of specific antibodies after the antigen on the pathogen has been detected.

Figure 5.17: Antibodies by lymphocyctes Source: http://www.learner.org


Let us learn more about antibodies. These antibodies act in numerous ways as illustrated in Figure 5.18:

�Figure 5.18: Different actions by antibodies

Source: http://www.learner.org As can be seen in Figure 5.18, the three ways are:

(a) Some bind to the antigens on the surface of the pathogens. This pprevents the pathogen from entering the host cell.

(b) Others cause the pathogens to clump together. Phagocytes then engulf the clumped pathogens.

(c) Some antibodies activate the ccomplement system, which then acts to burst the pathogen.


This antibody protection remains in our body. When the same pathogen invades, the antibodies are quickly produced because some of the lymphocytes from the previous invasion are still present.

�

TRANSPORT SYSTEM IN PLANTS

Water and nutrients are usually absorbed by the roots of the plants and food is synthesised in leaves. So how aare water and food distributed to other parts of the plants? There is no heart to pump and no blood circulatory system like in animalss, but plants do need a transport system to move food, water and minerals around. They use two different systems as shown in Figure 5.19:

(a) Xylem moves water and minerals from the roots to the leaves; and

(b) Phloem moves food substances from leaves to the rest of the plant.

Figure 5.19: Vascular system in stem

Both of these vascular systems (xylem and phloem) are rows of cells that make continuous tubes running the full length of the plant.

5.6

ACTIVITY 5.3

Draw a flow-chart to show how our body defends itself when bacteriatry to invade us.


5.6.1 Transport of Water and Minerals

Water enters through the rroot hair cells and then moves across into the xylem tissue in the centre of the root. Water moves in this direction because the soil water has higher wwater potential than the solution inside the root hair cells. Minerals are also absorbed, but their absorption requires energy in the form of ATP because they are absorbed by aactive transport. They have to be pumped against the concentration gradient. Remember, you have learnt about the different types of substances movement in Topic 2. Then, how do water and minerals get transported upwards in the plants? They do so with the help of transpiration, root pressure and sometimes guttation. Let us learn more about that. (a) TTranspiration Transpiration explains how wwater moves up the plant aagainst gravity in

tubes made of dead xylem cells without the use of a pump. Transpiration is the process of water loss from the stomata in plant leaves. However, it also occurs in flowers, stems and roots.

Water on the surface of spongy and palisade cells (inside the leaf) evaporates and then ddiffuses out of the leaf. More water is drawn out of the xylem cells inside the leaf to replace what is lost. Note that water flows from an area of higher water (hydrostatic) pressure to an area of lower pressure. Through transpiration, the upper parts of the plants have a lower amount of water and a lower hydrostatic pressure. Therefore, water is able to flow from the roots to the upper parts of the plant, through the xylem tubes.

Factors that speed up transpiration will also increase the rate of water uptake from the soil. When water is scarce, or the roots are damaged, it increases a plantÊs chance of survival if the transpiration rate can be sslowed down. Plants can do this themselves by wwilting, or it can be done artificially, like removing some of the leaves from cuttings before they have a chance to grow new roots. Table 5.6 describes factors that affect the transpiration rate.


Table 5.6: Factors that Affect Transpiration Rate

Factor Description Explanation

Light In bright light transpiration increases.

The stomata (openings in the leaf) open wider to allow more carbon dioxide into the leaf for photosynthesis.

Temperature Transpiration is faster in higher temperatures.

Evaporation and diffusion are faster at higher temperatures.

Wind Transpiration is faster in windy conditions.

Water vapour is removed quickly by air movement, speeding up diffusion of more water vapour out of the leaf.

Humidity Transpiration is slower in humid conditions.

Diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air.

However, there are times when transpiration is not necessary or not

possible. For instance, during the night, transpiration stops. Furthermore, the plant detects when too much water is lost. To prevent further water loss, the stomata close, effectively shutting down transpiration.

(b) RRoot Pressure Root pressure is an osmotic pressure within the cells of a root system that

causes the sap to rise through a plant stem to the leaves. Root pressure occurs in the xylem of some vascular plants when the soil moisture level is high either at night or when transpiration is low during the day. When transpiration is high, the xylem sap is usually under tension, rather than under pressure, due to transpirational pull. At night in some plants, root pressure causes guttation or exudation of drops of xylem sap from the tips or edges of leaves. Root pressure is studied by removing the shoot of a plant near the soil level. Xylem sap will exude from the cut stem for hours or days due to root pressure. If a pressure gauge is attached to the cut stem, the root pressure can be measured.

Root pressure is caused by the active distribution of mineral nutrient ions

into the root xylem. Without transpiration to carry the ions up the stem, they accumulate in the root xylem and lower the water potential. Water then diffuses from the soil into the root xylem due to osmosis. Root pressure is caused by this accumulation of water in the xylem pushing on


the rigid cells. Root pressure provides a force, which pushes water up the stem, but it is not enough to account for the movement of water to leaves at the top of the tallest trees. The maximum root pressure measured in some plants can raise water only to about seven metres, and the tallest trees are over 100 metres tall.

(c) GGuttation When transpiration cannot take place, plants secrete water through a

process called guttation. Guttation is the elimination process of excess water in the form of water drops from the injured margin of leaf or through the hydathodes. Hydathodes (Figure 5.20) consist of water pores which remain permanently open.

Figure 5.20: Hydathodes Guttation usually takes place early in the morning when the rate of water absorption and the root pressure are higher and the rate of transpiration is low. Sometimes, it takes place at a low temperature, higher pH, or under certain conditions like high relative humidity in the atmosphere and plants of water in the soil. These guttation „tears‰ appear at the leaf tips or margins and contain various salts, sugars and other organic substances.


5.6.2 Transport of Food

The phloem is another transport system in plants that carries food or sucrose, a type of sugar, from the leaves to other plant parts. Sucrose is actually an end-product of photosynthesis. Up to 30% of the phloem sap is made up of sucrose. Phloem transport is bidirectional, which means that transport occurs in two directions. In flower-bearing plants or „angiosperms‰, the special cells in phloem are called sieve-tube members. Phloem is always alive, which is why it does not form rings like those of xylem. What is translocation? Basically, the phloem sap moves from a sugar source (leaves) to a sugar sink (like roots). The phloem loading and unloading process is called ttranslocation. During translocation, the sugar molecules are moved from their source to the sink through the tube system. Phloem vessels still have cross walls called sieve plates that contain pores. Companion cells actively load the sugars into the phloem. Water follows the high solute in the phloem by osmosis. A positive pressure potential develops, moving the mass of the phloem sap forward. The sap must then cross the sieve plate. Then, companion cells actively unload the sugars into the sink. Energy in the form of ATP is used during this process. Sugars are stored as starch at the sink. Water is released and recycled in xylem. Figure 5.21 shows diagrammatically the process of translocation.

Figure 5.21: Translocation through the phloem tube

Source: http://click4biology.info


Now, let us look at Figure 5.22, which shows how translocation and transpiration happen in the plants.

Figure 5.22: Translocation and transpiration

Source: http://click4biology.info/c4b/9/plant9.2.htm As shown in Figure 5.22, photosynthesis occurs in the leaves of plants producing glucose as the end product. Glucose is then converted into sucrose for transport. The companion cell then actively loads the sucrose into the phloem tube. Water flows in from the xylem by osmosis. The sap volume and pressure increase to give the mass flow of food. The sucrose is then unloaded into the „sink‰ by the companion cell. Sucrose is then stored as the insoluble and unreactive starch. Water that is released is picked up by xylem to be recycled as part of transpiration or to resupply the sucrose loading.


�

ACTIVITY 5.4

Contrast between xylem and phloem cells. Use a graphic organiser to present the information.

SELF-CHECK 5.5

Figure 5.23 (a) and (b) show parts of the same plant at different times of the day.

(a)� (b)Figure 5.23: Parts of the same plant at different times of the day

1. Explain the cause of the differences in appearance. 2. Explain how this condition affects the rate of photosynthesis.


� Blood is made up of a liquid component (plasma) and a cellular component

(red blood cells, white blood cells and platelets). � The function of red blood cells is to transport oxygen and carbon dioxide. � The function of white blood cells is to protect the body against diseases. � Platelets are important for the clotting of blood. � There are two types of leukocytes: granulocytes and agranulocytes. � The functions of blood include: medium of transport for dissolved gases,

hormones, nutrients and waste products, regulation of body temperature; maintaining balanced conditions within body; body defence system.

� Human blood can be categorised into four groups, which are A, B, AB and O. � During a blood transfusion, the recipientÊs blood must be compatible with the

donorÊs blood. � The human blood circulatory system consists of three main parts: the heart,

blood vessels and blood which flows inside blood vessels. � The heart comprises of four chambers, which are the right atrium, left atrium,

right ventricle and left ventricle. � Between the atria and the ventricles are the atrioventricular valves (bicuspid

and tricuspid), which prevent the backflow of blood from the ventricles to the atria.


� There are two semilunar valves: the pulmonary valve at the base of the pulmonary artery and the aortic valve at the base of the aorta which prevents the backflow of blood into the ventricles.

� The atrium and the ventricle on the right are separated from the left atrium

and ventricle by a thick wall of muscle called the septum. � The left atrium receives oxygenated blood rich in oxygen from the lungs

while the right atrium receives deoxygenated blood rich in carbon dioxide from the tissues.

� The right ventricle pumps deoxygenated blood in the lungs whereas the left

ventricle pumps oxygenated blood to all parts of the body. � There are three types of blood vessels in the body: the arteries, veins and

capillaries. � The human circulatory system consists of two parts: the pulmonary

circulation and systemic circulation. � The pulmonary circulation involves the flow of blood from the heart to the

lungs and back to the heart. � The systemic circulation involves the flow of the blood from the heart to all

parts of the body, and back to the heart. � The human circulatory system is also known as a double circulatory system

as the blood passes through the heart twice on one circuit of the body. � People use pulse rate in order to measure the heart beat. � The coronary circulation refers to the flow of blood through the heart. � Tissue fluid, which is also known as interstitial fluid or intracellular fluid, is

the medium surrounding body cells. � The lymphatic system consists of lymphatic vessels, lymph nodes, lymph and

lymphatic organs (spleen and thymus).


� The functions of the lymphatic system include: removal of excess tissue fluid, transport of fatty acids and glycerol; production and storage of white blood cells; body defence.

� Control systems that help to maintain our internal environment is called

homeostasis. � A negative feedback control system responds when conditions change from

the ideal or set point and returns the conditions to this set point. � Osmoregulation is the active regulation of the osmotic pressure of bodily

fluids to maintain the homeostasis of the bodyÊs water content. � The hormones, anti-diuretic hormone (ADH) and Aldosterone, play a major

role in this. � The first parts of the defence system are really the physical barriers that stop

the pathogens from entering the body. � The major components of the general defence system are: phagocytes,

macrophages that complement defence proteins, interferons, and inflammation.

� There is also a specific defence system such as the production of antibodies

by white blood cells. � A vascular system is a transport system for plants. It consists of xylem, which

transports water and minerals, and phloem, which transports food produced in the leaves to other parts of the plants.

� Transpiration, root pressure, and guttation are processes that help to

transport water upwards from the root to the upper parts of the plants. � Translocation is the process that transports the sugar molecules from their

source to the sink through the phloem tube system.


Agranulocytes

Aldosteron

Anti-diuretic hormone

Aortic valve

Arteriole

Artery

Atrioventricular valves

Atrium

Basophil

Bicuspid (mitral) valve

Blood

Capillary

Coronary circulation

Double circulatory system

Eosinophil

Erythrocytes

Granulocytes

Hemoglobin

Homeostasis

Leukocytes

Lymph

Lymph nodes

Lymphatic vessels

Lymphocytes

Monocytes

Negative feedback

Neutrophil

Osmoregulation

Phloem

Plasma

Pulmonary circulation

Pulmonary valve

Pulse

Semilunar valves

Septum

Spleen

Systemic circulation

Thymus

Tissue fluid

Translocation

Transpiration

Tricuspid valve

Vascular tissue

Vein

Ventricle

Venule

Xylem


BBC. (2012). Biology: Homeostatic control. Retrieved March 20, 2012 from http://www.bbc.co.uk/scotland/learning/bitesize/higher/biology/contr

ol_regulation/negative_feedback_rev2.shtml BBC. (2012). Physical education: The circulatory system. Retrieved March 20,

2012 from http://www.bbc.co.uk/schools/gcsebitesize/pe/appliedanatomy/

0_anatomy_circulatorysys_rev1.shtml BBC. (2012). Science: Transport in plants Retrieved March 20, 2012 from http://www.bbc.co.uk/schools/gcsebitesize/science/add_gateway_pre_2

011/greenworld/planttransportrev2.shtml CHW. (2012). Overview of blood and blood components. Retrieved March 20,

2012 from http://www.chw.org/display/PPF/DocID/21846/router.asp FI. (2012). Home: Where the heart is. Retrieved March 20, 2012 from http://www.fi.edu/learn/heart/index.html Hudec, K. (2011). Map of the human heart. Retrieved March 20, 2012 from http://www.pbs.org/wgbh/nova/body/map-human-heart.html Irvine, J. (2010). Osmoregulation. Retrieved March 20, 2012 from http://www.jirvine.co.uk/Biology_GCSE/B1A/b1al3.htm Leavingbio. (2009). Blood. Retrieved March 20, 2012 from http://leavingbio.net/Blood.htm. Leavingbio. (2009). The circulatory system. Retrieved March 20, 2012 from

http://leavingbio.net/CIRCULATORY%20SYSTEM/CIRCULATORY%20SYSTEM.htm

LymphNotes. (2010). Understanding the lymphatic system. Retrieved March 20,

2011 from http://www.lymphnotes.com/article.php/id/151/ Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., &

Jackson, R. B. (2010). Campbell biology (9th ed.). San Francisco: Pearson - Benjamin Cummings Pub.


Roberts, M. B. V. (1986). Biology: A functional approach. Surrey: Thomas Neson & Sons Ltd.

The Annenberg Foundation. (2012). Immune system overview. Retrieved March

20, 2012 from http://www.learner.org/courses/biology/archive/

animations/hires/a_hiv1_h.html The Franklin Institute. (2012). Blood. Retrieved March 20, 2012 from http://www.fi.edu/learn/heart/blood/blood.html ��

� INTRODUCTION

Do you know that you can survive for several days without water and for a month without food? But, do you know that you cannot survive for more than five minutes without oxygen? Oxygen is part of the air that we bbreathe in. Oxygen is used in the process of respiration to produce energy. Living things need energy for the activities of life. The energy produced during rrespiration is used for biochemical reactions, growth and repair of cells, making your muscles work, maintaining body temperature and for making larger molecules in your body. Respiration is the process by which energy is produced through the oxidation of food. Respiration involves two stages � eexternal respiration (bbreathing) and internal or ccell respiration. Breathing is a physical process that involves the exchange of gases (oxygen and carbon dioxide) between the organism and the external environment. Cell respiration is a biochemical process which occurs within cells and oxidises food to obtain energy. Every living cell in every living organism uses respiration to make energy all the time.

TTooppiicc

66

� Respiration and Gaseous Exchange

LEARNING OUTCOMES


1. Compare between aerobic and anaerobic respiration;

2. Identify the parts of our respiratory system;

3. Describe the breathing mechanism in humans;

4. Discuss how gas exchange occurs in animals; and

5. Explain gas exchange in plants.

� TOPIC 6 RESPIRATION AND GASEOUS EXCHANGE 146

In this topic, you will learn about aerobic and anaerobic respiration, the breathing mechanism and respiration in humans. You will also explore gaseous exchange in animals and plants. �

�

AEROBIC AND ANAEROBIC RESPIRATION

There are two types of respiration: aerobic and anaerobic respiration. What are they exactly? Let us read further.

6.1.1 Aerobic Respiration

Aerobic means „with air‰. So, aerobic respiration refers to respiration that needs oxygen. When oxygen is present, glucose can be completely broken down. Aerobic respiration can be represented by this equation:

The waste products of aerobic respiration are carbon dioxide and water. Energy is produced in the form of high energy molecules called AATP (aadenosine triposphate). During aerobic respiration, 38 molecules of ATP are produced for every molecule of glucose that is oxidised. Aerobic respiration occurs in the cell mitochondria. All plants and animals need oxygen and respire aerobically.

6.1.2 Anaerobic Respiration

Anaerobic respiration refers to respiration that occurs in the absence of oxygen. Fungi, such as yeasts, respire anaerobically when there is a lack of oxygen. This process is called aalcoholic fermentation, as the waste products are ethanol and carbon dioxide. Overall, two molecules of ATP are produced. The equation is shown here:

6.1

Glucose + Oxygen � Carbon Dioxide + Water + ENERGY

ACTIVITY 6.1

Most people often use the term „respiration‰ to mean „breathing‰.Biologists use these terms in a different way. Can you tell the differencebetween respiration and breathing?

TOPIC 6 RESPIRATION AND GASEOUS EXCHANGE � 147

Vertebrate skeletal muscle respires anaerobically when the tissue is temporarily short of oxygen. The sole waste product is lactic acid. This process is called lactate fermentation. An excessive amount of lactic acid in muscles causes fatigue and muscle pain. After doing strenuous exercises, you have to breathe deeply for a period of time to take in extra oxygen. The extra oxygen is used to break down the lactic acid to carbon dioxide and water. As with anaerobic respiration in yeast, only two molecules of ATP are produced per glucose molecule. Anaerobic respiration occurs in the cell cytoplasm. The equation for anaerobic respiration is shown here:

Glucose � Lactic Acid + ENERGY

Glucose � Ethanol + Carbon Dioxide + ENERGY

SELF-CHECK 6.1

1. Explain the following terms:

(a) Breathing

(b) Cell respiration 2. Compare and contrast aerobic and anaerobic respiration using

Table 6.1:

Table 6.1: Comparison between Aerobic and Anaerobic Respiration

Aerobic Respiration Anaerobic Respiration

Organism

Location

Number of ATP from 1 molecule of glucose

Respiratory Products

Oxygen


ACTIVITY 6.2

Do the following experiment to show anaerobic respiration in yeast. Take a test tube and add about 10 ml of 10% glucose solution in it. Add a pinch of dry bakerÊs yeast into the glucose solution and cover the surface of the liquid carefully with a layer of oil to prevent contact with air. Fix a holed cork into the mouth of the test tube and pass a delivery tube through it. The other end of the delivery tube is dipped in lime water. The whole apparatus is made air tight. The test tube with glucose is kept in warm water (37oC�40oC) in a beaker. All these can be seen in Figure 6.1.

Figure 6.1: Experiment to show anaerobic respiration in yeast

1. What changes do you see in the lime water? What is your

conclusion? Open the cork and observe the smell. What do you think is produced?

3. What are the products of anaerobic respiration in yeast?�


RESPIRATION IN HUMANS

At rest, a human adult breathes 5 to 7 dm3 of air per minute. How does this volume of air get into and out of the lungs? Gaseous exchange in humans occurs in the lungs. The lungs are a part of the human respiratory system. This respiratory system is shown in Figure 6.2.

Figure 6.2: The human respiratory system Source: http://www.doctortee.com�

The lungs are large organs that fill your chest cavity or tthoracic cavity. The thoracic cavity is bounded on its sides by the ribs and on the bottom by a thick layer of muscle called the ddiaphragm. The diaphragm separates the thoracic cavity from the abdominal cavity. Let us now look at how air reaches our lungs.

6.2


We breathe air through the nnostrils, which are the openings of the nose. The lining of the nose secretes a slimy fluid called mmucus. The mucus and the tiny hairs in your nose help catch dust and bacteria. The lining of the nose also has tiny capillaries that heat the air. Once the air travels through the nnasal cavity, it becomes cleaner and warmer. This air then moves to the back of the throat, the pharynx and into a tube called the ttrachea. At the top of the trachea is the voice box or llarynx. At its lower end, the trachea branches into two bbronchi (singular: bronchus) which go into the lungs. �In the lungs, the two bronchi branch into smaller tubes called bbronchioles. The bronchioles end in the aalveoli (singular: alveolus). The alveoli look like a bunch of grapes and are surrounded by a network of blood capillaries as shown in Figure 6.3. The alveoli are well designed for gas exchange. �

�Figure 6.3: Alveolus

Source: http://www.beltina.org��Do you know that the walls of both the alveolus and blood capillary are only one cell thick? This allows gas exchange to take place easily. Oxygen diffuses from the alveoli into the blood, and carbon dioxide diffuses from the blood into the alveoli. The lining of the alveolus is covered by a thin layer of fluid and the oxygen dissolves in it before it passes through into the blood. The lungs contain about 300 million alveoli. If you combine their surface areas, the alveoli would cover 70 square meters or 750 square feet. That is roughly the size of two tennis courts! The process of gas exchange is really important for the body to provide a very big surface area just for that purpose. Without gas exchange, life would not be possible!


THE BREATHING MECHANISM

What makes the air come in and out of your lungs? Put your hand on your chest and breathe in and out. What do you feel? Breathing takes place by the movements of your chest. We can divide breathing into two parts:

(a) IInhalation, which is the movement of air into the lungs; and

(b) EExhalation, which is the forcing of air out of the lungs.

6.3

1. Label the human respiratory system in Figure 6.4.

�Figure 6.4: Unlabelled human respiratory system

2. Discuss the adaptations of alveolus that allows efficient gas

exchange.

SELF-CHECK 6.2


Study Figure 6.5 and Table 6.2 which show what happens during inhalation and exhalation. The diaphragm, rrib cage and iintercostal muscles play an important role during inhalation and exhalation.

Figure 6.5: What happens during inhalation and exhalation Source: http://blm1128.blogspot.com

Table 6.2: What Happens during Inhalation and Exhalation

Inhalation EExhalation

� Rib muscles (intercostal muscles) contract.

� Rib cage moves up and out. � Diaphragm contracts and flattens. � Thorax volume increases. � Pressure decreases. � Air is drawn into lungs.

� Rib muscles (intercostal muscles) relax. � Rib cage moves down and in. � Diaphragm relaxes and moves up. � Thorax volume decreases. � Pressure increases. � Air is forced out of lungs.


GAS EXCHANGE IN ANIMALS

All animals breathe in oxygen and give out carbon dioxide, just like us humans. However, not all animals breathe the way humans do. Respiratory systems of animals depend on the:

(a) Size of the organism;

(b) Amount of exposed body surface; and

(c) Type of habitat (aquatic or terrestrial). Now, look at Table 6.3, which shows the different respiratory systems of animals.

Table 6.3: The Different Systems for Gas Exchange in Animals

Gas Exchange Systems Types of Animals

Body surface Used by small organisms. For example, Amoeba, earth worms and frogs.

Gills Used by animals living in water. For example, fish.

Tracheal system Used by insects. For example, housefly and grasshopper.

Lungs Used by terrestrial vertebrates. For example, humans and birds.

6.4

SELF-CHECK 6.3

1. Explain what happens to the ribs when you breathe out. 2. Explain what happens to the diaphragm when you breathe in.


6.4.1 Gas Exchange Through the Body Surface

In small organisms, the respiratory surface is the general body surface. Gases diffuse in and out of the organism over the surface. For an example, in simple aquatic unicellular organisms like Amoeba, gaseous exchange occurs through diffusion as the cells are in contact with the environment. This can be seen in Figure 6.6.

Figure 6.6: Gas exchange in Amoeba

Source: http://chaos28.wordpress.com In earthworms, gaseous exchange occurs through the skin. The earthworm lives in damp soil and comes out only at night to feed and reproduce. Why is this so? It is to prevent the skin from drying or desiccation. Respiratory gases dissolve and diffuse through the skin. The earthwormÊs skin is also kept very moist by the secretion of mucus as can be seen in Figure 6.7. The blood capillaries are so close to the skin that the gases can diffuse into and out of the blood through the skin.

Figure 6.7: Gas exchange in earthworm Source: http://www.tutorvista.com


In more complex organisms, diffusion is not an efficient way to deliver oxygen and remove carbon dioxide. Specialised structures (for example, gills and lungs) are developed for gaseous exchange. Why do you think frogs can live on both land and water? Amphibians such as frogs can live on land and in water because gaseous exchange in frogs can occur through three different ways: the skin, the lining of the mouth cavity and by the lungs. Oxygen and carbon dioxide diffuse across these three surfaces as shown in Figure 6.8.

�Figure 6.8: Gas exchange in frogs Source: http://greenanswers.com�

6.4.2 Gas Exchange through Gills

Have you ever watched a fish swimming in the water? A fish swimming in the water continuously opens and closes its mouth just as if it was trying to eat the water. Actually this is how gas exchange occurs in fish. Each time water enters its mouth, the water is pushed into the mouth cavity through specialised respiratory structures called ggills and out through a slit at the back of the mouth cavity as can be seen in Figure 6.9. This slit is covered by a flap called the ooperculum.

Figure 6.9: Gills of fish (with operculum removed)

Source: http://www.sci.sdsu.edu


Fish obtains oxygen from water by means of gills. Gill surfaces are large, especially in active fish. There is a high rate of water flowing over the gills, which have a fine structure with a rich network of blood capillaries. This allows water and blood to be in close contact. Efficient gaseous exchange is achieved by the continuous stream of water flowing over the gills and the blood flowing through the gills being in opposite directions (a ccounter current flow). It is so efficient that 80�90% of the oxygen may enter the blood.

6.4.3 Gas Exchange in the Tracheal System

In humans, oxygen is carried from the lungs to the tissues by the blood. Insects have a very different system. They have hundreds of breathing tubes through which oxygen passes to all parts of the body. This is called the ttracheal system as can be seen in Figure 6.10.

Figure 6.10: The insect tracheal system

Source: http://www.doctortee.com Air enters the tracheal system through the spiracles, which are tiny openings in the cuticle. The sspiracles open into tubes called ttracheae (singular: trachea). The trachea branches like a tree. The ends of the branches are fine tubes called tracheoles. These have thin walls and penetrate all the organs and tissues bringing oxygen to them.


GAS EXCHANGE IN PLANTS

Have you ever wondered how plants get their supply of oxygen and release carbon dioxide during respiration? At the same time, how do plants get rid of oxygen produced during photosynthesis? Plants exchange carbon dioxide and oxygen through their sstomata and llenticels. Let us now look in detail at these organs.

6.5.1 Stoma

What is a stoma? Before we go further, study Figure 6.11, which shows the cross section of a leaf.

�Figure 6.11: Cross section of leaf

Source: http://www.enchantedlearning.com

6.5

SELF-CHECK 6.4

Explain how gaseous exchange is carried out in earthworms, insectsand fish.


As can be seen in Figure 6.11, the upper and lower surfaces of a leaf are covered by a thin layer of cells that lack chlorophyll. This layer of cells is called the epidermis. Stomata are scattered throughout the epidermis (singular: stoma). Stomata are tiny openings found in leaves and young stems. Stoma allows oxygen, carbon dioxide and water to enter and leave the plant. Can you name the cells on either side of the stoma? The two cells on either side of the stoma are called gguard cells. Guard cells control the opening and closing of the stoma. Now, look at Figure 6.12 which shows an open and closed stoma. Study the guard cells. Do you notice that the inner wall of the guard cells is thicker than the outer walls? This is the special feature of guard cells that allows the opening and closing of the stoma.

�Figure 6.12: Open and closed stoma

Source: http://aunibazilahbiologynotes.blogspot.com The stomata open and close because of changes in the water pressure or turgor pressure of their guard cells. When the guard cells contain a high level of solutes, water enters them and they become tturgid (plump and swollen with water). The guard cells then bend outwards. This opens the stoma. When guard cells contain a low level of solutes, water leaves the guard cells, causing them to become shrunken or fflaccid. This flaccidity closes the stoma. Stomata usually open during the day and close at night. Can you think of a reason for this? Yes, it is because photosynthesis occurs during the day. When sugars are produced, the solute level increases in the guard cells. At night, there are no sugars produced and the guard cells contain a low level of solutes.


6.5.2 Lenticels

The bark of stems is impermeable to water and gases. However, scattered around the bark are openings called llenticels, which allow for the movement of oxygen into and carbon dioxide and water out of them. Lenticels are shown in Figure 6.13.

�Figure 6.13: Lenticels

Source: http://www.tutorvista.com

�

SELF-CHECK 6.5

ACTIVITY 6.3

Take a leaf and immerse it in warm water. Discuss all these with yourcoursemates:

(a) What do you observe?

(b) What inference can you make?

(c) Why do you think this is a necessary adaptation in plants?

1. Compare stoma and lenticels in plants.

2. Discuss the opening and closing of the stoma.


� Respiration involves two stages � external respiration (breathing) and

internal or cell respiration.

� Breathing is a physical process that involves the exchange of gases between the organism and the external environment.

� Cell respiration is a biochemical process which occurs within cells and oxidises food to obtain energy.

� Aerobic respiration refers to respiration that needs oxygen.

� Anaerobic respiration refers to respiration that occurs in the absence of oxygen.

� The human respiratory organ is the lungs.

� Gaseous exchange occurs in the alveolus.

� Breathing can be divided into inhalation, which is the movement of air into the lungs, and exhalation, which is the forcing of air out of the lungs.

� The diaphragm, rib cage and intercostal muscles play an important role during inhalation and exhalation.

� Respiratory systems of animals depend on the size of the organism, amount of exposed body surface and type of habitat (aquatic or terrestrial).

� In small organisms like the Amoeba, gases diffuse in and out of the organism through the body surface.

� In the earthworm, gaseous exchange occurs through the moist skin.

� Gaseous exchange in frogs occurs through three different ways: the skin, the lining of the mouth cavity and by the lungs.


� Gaseous exchange in fish occurs through gills.

� Gaseous exchange in insects occurs through the tracheal system, which is a network of breathing tubes.

� Plants exchange carbon dioxide and oxygen through their stomata and lenticels.

� Stomata are tiny openings found in leaves and young stems.

� The two cells on either side of the stoma are called guard cells and are responsible for the opening and closing of the stoma.

� Openings in the bark of stems are called lenticels, which allow for the movement of oxygen into and carbon dioxide and water out of the stem.

Adenosine triphosphate

Aerobic respiration.

Alcoholic fermentation

Alveolus

Anaerobic respiration.

Bronchiole

Bronchus

Counter current flow

Diaphragm

External respiration

Gills

Intercostal muscles

Internal/cell respiration

Lactate fermentation

Larynx

Lenticels

Lungs

Mucus

Pharynx

Rib cage

Spiracles

Stoma

Trachea

Tracheae

Tracheal system

Tracheoles


Clegg C. J., & Mackean, D. G. (2000). Advanced biology: Principles and

applications (2nd ed.). London: Hodder Murray. Gupta, M. (2009). Respiration in plants. Retrieved March 20, 2012 from

http://www.nios.ac.in/srsec314newE/PDFBIO.EL12.pdf Ramel, G. (2009). Gills: Gaseous Respiration in fish. Retrieved March 20, 2012

from http://www.earthlife.net/fish/gills.html Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., &

Jackson, R. B. (2010). Campbell biology (9th ed.). San Francisco: Pearson � Benjamin Cummings Pub


& Sons Ltd. The McGraw-Hill. (2006). Animation: Gas exchange during respiration. Retrieved

March 20, 2012 from http://highered.mcgraw-hill.com/sites/0072495855/student_view0/

chapter25/animation__gas_exchange_during_respiration.html White, I. (2005). Breathing: The respiratory system. Retrieved March 20, 2012

from http://www.biologymad.com/resources/Ch%205%20-%20 Breathing.pdf

p

� INTRODUCTION

Both plants and animals move. The whole body of the animals move to transport them from one place to another. However, movement in plants is only restricted to certain parts: shoot, root, leaves and flowers. Why do they move? Both plants and animals move for specific purposes. Plants move in order to respond to external stimuli. Meanwhile, animals move in order to find food, shelter and mates.

In this topic, we will be looking at how animals and plants move to accomplish these objectives. You will be looking at various types of animal skeletal system which support the animalÊs body. The skeletal and nervous system work hand-in-hand in order to move the body parts or the whole animals. You will also study how the nervous system and the endocrine system of animals coordinates the response as a result of external or internal stimuli. Lastly, you will also study how plants coordinates its response towards external stimuli.

TTooppiicc

77

� Support and Locomotion

LEARNING OUTCOMES


1. Identify the animals with hydrostatic, exoskeleton and endoskeletonsupport system;

2. Describe animal locomotion;

3. Describe the two divisions in human nervous system;

4. Analyse animal responses and coordinates towards stimulus;

5. Explain the chemical coordination in human beings; and

6. Analyse plant responses and coordinates towards stimulus.

� TOPIC 7 SUPPORT AND LOCOMOTION 164

SUPPORT SYSTEM

In biology and anatomy, the skeleton is defined as that part of the body which forms the supporting framework of the body and gives a proper shape to the body. A skeleton can be anything from microscopic fibres such as the skeleton of the cell (cytoskeleton), to a well-developed system of bones, joints and cartilages, as occurs in human beings. No matter what physical shape it exists in, the skeleton will perform the supporting function. The term skeleton refers to the framework of the animal body around which the whole body is built. Skeleton is the collective name for all the hard and rigid structures in the body forming the framework of the body. In animals, there are three major types of skeletal system. These are: (a) HHydrostatic Skeleton It is found in soft-bodied and cold-blooded animals. This skeleton has a

coelom, which is a fluid-filled cavity. This coelom is surrounded by muscles and the rigidity caused by the fluid and the muscles serve as a supporting structure for the organisms. The fluid pressure along with the motion of the supporting muscles helps the organisms to change shape and move. Invertebrates, the majority of the earthÊs living organisms are found in a diverse number of habitats. They could be found in the deepest part of the oceans to the thickest jungles. Echinoderms, cnidarians, annelids, nematodes and some other organisms are examples of animals that have hydrostatic skeleton. The Earthworm (Figure 7.1(a)) which is an annelid is boneless. With the help of hydrostatic skeleton, it burrows through the ground. Examples of echinoderms are the star fish and the sea urchin (Figure 7.1(b)).

�

�� (a)��(b)�

Figure 7.1: Earthworm (a) and sea urchin (b) Source: http://www.craftster.org

7.1

TOPIC 7 SUPPORT AND LOCOMOTION � 165

(b) EExoskeleton The exoskeleton is that type of skeleton which lies outside the soft parts of

the body providing a covering to them. It is in the form of hard and rigid plates composed of dead substance secreted by cells. Familiar examples of this type of skeleton are found in the insect, the horny scales, feathers and hairs. In many cases, the exoskeleton is very rigid and heavy. It restricts the movements of the animal to the extent that the animal is passive and slow or even sessile.

One group of animals, however, has attained a very successful solution of

the difficulty posed by the rigidity and weight of the exoskeleton. These animals are arthropods. The exoskeleton consists of cuticle, a multi-layered substance secreted by the epidermis. Cuticle consists of chitin, proteins and lipids. In many aquatic crustaceans, the exoskeleton is mineralised with calcium carbonate that is acquired from the surrounding water. This produces a tougher, more rigid structure. In addition, the exoskeleton instead of being formed of just one piece or even two pieces is divided into several distinct sections. Thus, the arthropods have ease of motion with a protective outer covering. This is a factor in their biological success. It presents one great disadvantage, if the animal is to grow at all, it must remove its exoskeleton. Arthropods do this by molting or ecdysis.

Many other invertebrate animals (such as shelled mollusks) also have exoskeletons as can be seen in Figure 7.2. Lobsters, for example, have tough outer shell systems which provide rigidity and shape to their bodies.

Figure 7.2: Examples of animals that have exoskeleton Source: http://www.oum.ox.ac.uk


(c) EEndoskeleton The simplest definition for endoskeleton is that it is the skeleton found inside the body.The endoskeleton supports and gives shape to the body. The tissues and muscles are formed around the skeletal system and the muscular forces are transmitted to this skeleton. This forms the basis for animal locomotion.The vertebrate skeleton is basically an endoskeleton made up of two types of tissues:

(i) BBone

Bone tissue contains concentric rings of tissue in which bone cells called oosteoblasts produce the inorganic materials (fibres and matrix) of the bone. Much of this material is calcium phosphate, formed from calcium and phosphorus delivered by the blood. Living, mature bone cells called oosteocytes are also located in the bone. Bone-destroying cells called oosteoclasts break down the bone, thus providing a turnover of bone material needed in other areas. The combination of bone cells and bone tissue comprises a unit called a HHaversian system. Blood vessels and nerves also exist within the Haversian system. Figure 7.3 shows a transverse view of an oosteon (Haversian system) � the basic unit of ccompact bone.

Figure 7.3: A transverse view of an osteon (Haversian system)

Bones come together to form a joint, which may be immovable, such as in the ssutures of the skull, or movable, such as in the joints of the elbow and shoulder. In a movable joint, a capsule of synovial fluid provides lubrication. In a joint, tough, fibrous tissue, known as ligaments, link bones to one another. Connective tissues, called tendons, attach muscles to bones.


(ii) CCartilage Cartilage is a type of connective tissue in the body that has a tough, flexible matrix made of collagen, protein, and sugar. Cartilage is found in the nose and ears, as well as joints such as the knees, hips, shoulders, and fingers. Cartilage serves to provide structure and support to the bodyÊs other tissues without being as hard or rigid as the bone. It can also provide a cushioning effect in joints. Figure 7.4 shows the skeletal system of human, an example of endoskeleton. Do you know that there are about 206 bones in our body?

�

Figure 7.4: An example of endoskeleton�


��

ANIMAL LOCOMOTION

Movement or locomotion in animals is brought about by the contraction of muscles against skeleton. Thus, you will notice that the musculoskeletal system is the basis of locomotion. In this subtopic, we are going to look at how animals that have hydrostatic skeleton, exoskeleton and endoskeleton move.

7.2.1 Earthworm

The earthworm is an animal that has hydrostatic skeleton. The earthworm has about 100�150 segments. The segmented body parts provide important structural functions. Segmentation helps the earthworm move. Each segment or section has muscles and bristles called ssetae. The bristles or setae help anchor and control the worm when moving through soil. The bristles hold a section of the worm firmly

SELF-CHECK 7.1

State whether the following statements are true or false.

1 ÂExoÊ means outside, ÂhydroÊ means liquid and ÂendoÊ means inside.

2 Tendons link one bone to another bone while connective tissues, called ligament, attach muscles to bones.

3 Cartilage is softer compared to a bone.

4 Hydrostatic skeleton has a coelom, which is a fluid-filled cavity surrounded by muscles.

5 The exoskeleton consists of cuticle which comprises chitin, proteins and lipids.

6 Bone tissue contains concentric rings of tissue in which bone cells are called osteoclasts.

ACTIVITY 7.1

Find out the names of bones of a bird. Are the names of bones in a birdthe same with our bones? How do the bones of bird differ from ourbones? Discuss with your coursesmates.

7.2


into the ground while the other part of the body protrudes forward. The earthworm uses segments to either contract or relax independently to cause the body to lengthen in one area or contract in other areas. Segmentation helps the worm to be flexible and strong in its movement. The earthworm has two kinds of muscles that it uses to move. This can be seen in Figure 7.5. �

�Figure 7.5: How earthworm moves

Source:http://tanet-sound.com� The circular muscles which surround the wormÊs body can make the body shrink or spread out. The longitudinal muscles run along the length of the body can shorten or lengthen the worm. The circular muscles contract and expand in co-ordination with the longitudinal muscle in series such as that if the posterior muscle are expanded, and the anterior circular muscles are contracted, the worm pushes and stretches its front end forward. The anterior muscles then expand to anchor its front end by the use of the setae and the rear end is pulled forward. All this happens in a smooth and rhythmic motion. At the very front end of earthworms in place of a nose is the prostomium. When earthworms are underground, it uses in conjunction with its co-ordinated hydraulic like muscle system to wedge its way between soil particles to dislodge them and consume them-if they are small enough-and form the worm burrow.


7.2.2 Grasshopper

The grasshopper can move in three ways � it can walk, jump and fly. It has exoskeleton. The skeleton provides an attachment site for muscles, allowing rapid movement. In walking, both the two pairs of walking legs and the one pair of jumping (hind) legs may be used to propel the grasshopper along the surface of the ground or up a plant stem. In jumping, the powerful muscles in the hind legs are used to project the grasshopper into the air. The two main muscles are the eextensor tibiae muscle which causes the leg to extend, and the fflexor tibiae muscle which causes the leg to flex. These muscles pull on tendons which are attached to the tibia on either side of the jjoint pivot. Figure 7.6 shows how the muscles work so that it can jump. �

Figure 7.6: How insect jump Source: biomania.weebly.com

Meanwhile, Figure 7.7 shows the muscles that are used to raise and lower the wings. It has a pair of muscles for the up-stroke (top of diagram) and one for the down-stroke (bottom of diagram). When the inner muscles contract, the wings rotate about their hinges and flap upward. When the outer muscles contract, the wings are pulled downward again.


Figure 7.7: Muscles to move wing Source: http://park.org

7.2.3 Bird

Most birds can fly because they have certain characteristics. They have lightweight skeleton, strong muscles to control their flight, air sacs, light beaks, small lungs and wings designed for flying. Figure 7.8 shows different modes of flying.

�Figure 7.8: Different modes of flying


Basically, birdsÊ wings are not flat but are shaped like an aerofoil � concave (Figure 7.9).

�Figure 7.9: Shape of birdÊs wing

Source: http://www.earthlife.net/birds/flight.html Air passes over or under the wing as the bird moves forward, or as the wind blows. The air that moves over the top of the wing has further to travel to get across the wing, thus it speeds up. This causes the pressure to drop because the same amount of air is exerting its pressure over a greater area. Therefore, at any given point less pressure will be experienced. This effectively sucks the wing up. Meanwhile, the air going below the wing experiences the opposite effect. It slows down, generates more pressure and effectively pushes the wing up. Hence a bird with air moving over its wings is pulled up from above and pushed up from below. The more curved the aerofoil the greater the lift providing the degree of curve does not impede the flow of air. Birds need large muscles to move their wings up and down. These muscles are attached to the wings at one end and to a special bone, called the keel bone, at the other end. The muscles work in antagonistic pairs. When one muscle contracts the wings is moved up. When the other muscle contracts it pulls the wing down. The keel is really a part of the breastbone or sternum. The two muscles are the pectoralis and the supracoracoideusas can be seen in Figure 7.10. The pectoralis provides the powerful down stroke of the wing and therefore bear most of the burden of supporting a bird in flight. The supracoracoideus � the muscle that raises the wing � acts as the antagonist to the pectorals. This muscle is located below the pectoral muscles ventrally (on the front side). �


�Figure 7.10: Muscles of bird

Source: http://www.paulnoll.com

7.2.4 Fish

The body of a fish is particularly adapted to aquatic life. A swimming fish relies on its skeleton for framework, its muscles for power and its fins for thrust and direction. Scales and mucus protect the body and keep it streamlined. The skeletal and muscular systems of fish work together to maximise its swimming power. The fish is able to swim by contracting and relaxing a succession of muscle blocks, called mmyomeres, alternately on each side of the body(Figure 7.11)starting at the head and progressing down toward the tail. The alternate shortening and relaxing of successive muscle blocks, which bends part of the body first toward one side and then toward the other, results in a series of waves travelling down the fishs body. �

�Figure 7.11: FishÊs muscles

Source: http://www.earthlife.net/fish/muscles.html


The rear part of each wave thrusts against the water and propels the fish forward as shown in Figure 7.12.

Figure 7.12: Forces experienced by fishes during swimming Source: http://www.marinebiology.org

�Movement of the head going back and forth causes drag. Drag is minimised by the streamlined shape of the fish and a special slime that fish excretes from its skin that minimises frictional drag and maintains laminar (smooth) flow of water past the fish. When thrust is greater than drag, the fish is able to move forward! The fish face problems such as rolling, pitching, and yawing as can be seen in Figure 7.13. ��

Figure 7.13: Problems faced by fishes during swimming

Source: http://www.marinebiology.org The fins (Figure 7.14) help to overcome these problems and to maintain the stability of the fish while swimming. The dorsal and ventral fins reduce the tendency to roll and yaw. They also assist in turning movements. The pectoral and pelvic fins act as hydroplanes and control the pitch. The tail fin contributes to the forward thrust.


�Figure 7.14: Fins of fishes

Source: http://www.marinebiology.org�

7.2.5 Human

Bones act as levers during movement and provide solid structures to which muscles are attached. The joints allow movement between bones and these movements are directly related to the type of joints and the range of motion. There are three types of joints: (a) IImmovable Immovable joints, like those connecting the cranial bones, have edges that

tightly interlock. (b) PPartly Movable Partly movable joints allow some degree of flexibility and usually have

cartilage between the bones; example: vertebrae. (c) SSynovial Synovial joints permit the greatest degree of flexibility and have the ends of

bones covered with a connective tissue filled with synovial fluid; example: hip.

The outer surface of the synovial joints contains ligaments that strengthen joints and hold bones in position. The inner surface (the synovial membrane) has cells producing synovial fluid that lubricates the joint and prevents the two cartilage caps on the bones from rubbing together. Some joints also have tendons which connect muscles to bones. Bursae are small sacs filled with synovial fluid that reduce friction in the joint. Muscles generally work in pairs to produce movement: when one muscle flexes (or contracts) the other relaxes, a process known as antagonism.


7.2.6 Leg Muscles

The main leg muscles are the gluteal muscles, the iliopsoas or hip flexors, the quadriceps, the hamstrings and the adductors. The lower leg muscles are the tibialis anterior or shin muscle, the gastrocnemius and soleus muscles. The muscles that allow movement of the thigh are attached to the pelvic girdle and connect to the femur (the thigh bone). The quadriceps are found at the front of the thigh and allow the straightening of the leg and flexing of the knee. The hamstrings are found at the back of the thigh and work as the antagonists to the quadriceps to flex the leg. The adductors are muscles of the inner thigh attached to the pelvis and the femur that enable you to pull your legs together. In the lower leg, the tibialis anterior or shin muscle allows the movement that points the foot upwards. The gastrocnemius and soleusmuscles found in the calves allow the foot to point downwards. All these can be seen in Figure 7.15.

Figure 7.15: The front view (a) and the back view (b) of muscles of the leg

Source: http://www.baileybio.com


�

�

NERVOUS SYSTEM

The nervous system is a very complex, sophisticated system that regulates and coordinates body activities. It is an organ system containing a network of specialised cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. It is made up of two major divisions:

(a) CCentral Nervous System (CNS) � consisting of the brain and spinal cord; and

(b) PPeripheral Nervous System (PNS) � consisting of all other neural elements.

7.3

SELF-CHECK 7.2

1. Do the term movement and locomotion mean the same?

2. Match the name of fin with its correct function.

Name of Fin Function

Dorsal and ventral fins Contributes to the forward thrust.

Pectoral and pelvic fins Assist in turning movements.

Tail fin Reduce the tendency to roll and yaw.

Control the pitch.

ACTIVITY 7.2

1. Besides the supracoracoideus, there are numerous other small muscles of the wing that allow a bird to control flight. Find outthe other muscles that assist a bird in its flight manoeuvres and control its entire range of movement.

2. You have just seen that one set of muscles will contract while theother relaxes when you want to move your leg. Find out if thesame principles apply when you want to bend and straightenyour arm.


7.3.1 Central Nervous System (CNS) – Brain and Spinal Cord

The Central Nervous System (CNS) is effectively the centre of the nervous system. It consists of the brain and spinal cord. It is responsible for receiving and interpreting signals from the peripheral nervous system and also sends out signals to it, either consciously or unconsciously. Our brain consists of cerebrum, cerebellum, medulla oblongata, pituitary, gland, hypothalamus and thalamus, as shown in Figure 7.16.

Figure 7.16: The brain

Source: http://www.neurosurgery.pitt.edu

Table 7.1 shows the specific functions for each part of human brain.

Table 7.1: Functions for Each Part of Human Brain

Part of the Brain Function

Cerebrum Responsible for conscious action such as walking, running, sitting.

Thalamus Awareness of impulses such as hot and pain.

Hypothalamus Control sleep, sleep function, hunger and emotional activity.

Cerebellum Responsible for body balance and movement.

Pituitary gland Controlling secretion of hormones for various body functions.

Medulla oblongata Responsible for unconscious actions such as digestion and respiration.

�Spinal cord connects the brain with the PNS. It means that impulses from the sensory organ are sent to the brain through the spinal cord. Conversely, impulses from the brain are transferred to the effector organs through the spinal cord.


7.3.2 Peripheral Nervous Systems (PNS)

Let us recall the human nervous system. If the CNS referred to the brain and spinal cord, then, what is the PNS? Peripheral nervous system (PPNS) is composed of nerves and ganglia that are connected to the brain but are technically outside of the brain itself and the spinal cord. The main function of this system is to connect with the central nervous system.The PNS allows the central nervous system to connect with the limbs and organs of the body. Figure 7.17 shows peripheral nervous system. �

�Figure 7.17: Peripheral nervous system

Source: http://iahealth.net


The PNS is divided into two categories: (a) SSomatic Nervous System A somatic nervous system has a function of body movement control and

receiving stimulation from an external source. It regulates activities that are under conscious control.

(b) AAutonomic Nervous System Autonomic nervous system is divided into three divisions:

(i) SSympathetic Division This is responsible for stimulation when in danger and/or stress is

present, causing an increase in blood pressure, heart rate, excitement, and other physiological changes. This is an increase in adrenaline.

(ii) PParasympathetic Division This is responsible for stimulation when no danger or stress is present

but rather simplistic or relaxation is occurring. This causes a slowing heart rate, digestion, and other physiological changes. This is when no adrenaline is required.

(iii) EEnteric Division

This is responsible for the management of the digestion system from the oral cavity to the small intestines.

�


1. Are you a left brain learner or a right brain learner? A current learning theory suggests that each hemisphere of brain affects how people learn. There are two hemispheres in the brain: the left and right brain. Some people tend to use the left brain to learn something whereas some use the right brain. Thus, there are different learning styles to suit each of those two groups. Table 7.2 shows the difference between the left and the right brain learner.

Table 7.2: Difference between Left and Right Brain Learner

Left Brain Learner Right Brain Learner

Processes input in a sequential and analytical manner (inconsistent font size compared to the text in other column).

Processes input more holistically and abstractly.

Specialises in recognising words and numbers (as words).

Specialises in recognising faces, places, objects and music.

See explanations for why events occur.

Puts events in spatial patterns.

Better at arousing attention to deal with outside stimuli.

Better at internal processing.

Sources: Carter (1998); Gazzaniga (1998) Which are you, right or left brain learners?

2. Our nervous system ensures that we experience high quality of daily life activities. Nevertheless, there are diseases related to the nervous system. Collect more information about those diseases. Produce a brochure about the diseases related to nervous system. Distribute the brochure to your coursemates.

ACTIVITY 7.3


RESPONSE AND COORDINATION IN ANIMALS

As mentioned in the previous subtopic, we have already learned that the nervous system coordinates its response to the external stimuli. In this subtopic, you will study the basic unit of the nervous system and how response can occur as a result of receiving stimulus.

7.4.1 Introduction – Neurone, Synapse, Reflex

A nerve cell is called a neuron. There are three types of neurons, namely, afferent(sensory), efferent (motor) and interneuron. Neuron consists of dendrites, dendrons, axon, synaptic knob and myelin sheath. Look at Table 7.3, which shows the function for each structure of a neuron.

Table 7.3: Functions of Each Structure of Neuron

Structure Function

Axon Transmits impulses from the cell body to the terminal dendrites.

Dendrites and dendrons

Receives nerve impulses and transmits those impulses to the cell body.

Myelin sheath Increases the speed of transmitting the impulses.

Synaptic knob Transmits impulses to the other neuron.

7.4


Figure 7.18 shows a diagram of motor neuron.

Figure 7.18: Motor or efferent neuron

Source: www.biologymad.com Figure 7.19 shows a diagram of interneuron.

Figure 7.19: Interneuron

Source: www.biologymad.com


Do you know that two neurons are not directly connected together? That is true, but how is impulse transmitted from one neuron to another if both neurons are not directly joined together? The transmission of the impulse can occur when there is a synapse. A synapse is a place where a neuron transmits its impulse to the next neuron. Thus, synapse permits impulse to be transmitted by a terminal dendrite of one neuron to a dendrite of the next neuron. The main types of synapse and the structure of a typical chemical synapse simplified from electron micrographs is shown in Figure 7.20.

Figure 7.20: Synapse

Source: www.biologymad.com


7.4.2 Voluntary and Involuntary Actions

The nervous system functions in a coordinated manner. It receives a stimulus through a receptor. The stimulus through sensory nerves reaches the brain and spinal cord, which integrates it and gives it action. The motor nerves pass on the action to the required organ (muscle or gland), thus a response is generated. There are two types of actions that our body carries out: (a) VVoluntary Action If you pick up a mug, clap your hands or lift weights in the gym, you are

performing voluntary actions. You are conscious of what you are doing. Your brain receives nerve impulses and analyses them before you decide what to do next.

(b) IInvoluntary Action In contrast, your heart beats and your intestines digest without your

conscious control. Involuntary actions such as these are regulated by your autonomic nervous system. The autonomic part of your peripheral nervous system ensures that all your internal organs and glands function smoothly.

Both actions involve stimuli, an impulse, neurons and effectors. However, they are quite different. Table 7.4 lists the differences between the two actions.

Table 7.4: Differences Between the Two Actions

Voluntary Actions Involuntary Actions

Initiated in the cerebral cortex of brain � due to thought.

Initiated by stimulation of receptor.

Impulse passes from the motor area in the cerebral cortex down the spinal cord.

Impulse passes through the sensory neurons and relay neurone in the grey matter of spinal cord.

Motor neurone carries impulse to effector (muscle), which contracts and produces action

Motor neurone carries impulse to effector (muscle) which contracts and produces action

Impulse passes over to the opposite side of the body

Stimulus, neurones, actions all on the same side of the body

Many cells and synapses, and longer pathway � therefore slow.

Only 3 cells, 2 synapses � therefore quicker. Secondary information passes up spinal cord to brain, so subject is aware after event.

Source: http://thumbiology.blogspot.com


Imagine a situation when someone accidentally touches a hot flame. He or she will automatically and immediately move his or her hand away from the hot flame. What causes that action to happen? The answer is a reflex. A reflex is an automatic action. It happens very fast without having a conscious thought about it. A reflex arc is a route of transmission of nerves which causes a reflex action. The flowchart shown in Figure 7.21 shows an example of a reflex action.

Figure 7.21: An example of a reflex action


The hot sensation(stimulus) is detected by pain receptors in the skin. This initiates an impulse in a sensory neuron which then travels to the spinal cord where it passes, by means of a synapse, to a connecting neuron called the relay neuron situated in the spinal cord. The relay neuron in turn makes a synapse with one or more motor neurons that transmit the impulse to the muscles of the limb causing them to contract and remove the finger from the hot object. Reflexes do not require involvement of the brain although you are aware of what is happening and can, in some instances, prevent them happening. �

�

SELF-CHECK 7.3

Fill in the blanks.

1. The central nervous system consists of _________ and ___________.

2. Pathway meant for transmission of the message from the receptors to modulators is called _____________ pathway.

3. ___________________ nerves carry impulse from brain or spinal cord to the effectors.

4. The stimulus from the receptor organ is received by the __________, conducted to the cell body of neuron and finally to the __________ organ.

5. A synapse is the point of contact between the terminal branches of the _________ of one neuron with the _________ of another neuron.


CHEMICAL COORDINATION

Previously, you have studied about how the nervous system coordinates the response to stimulus. Next, you are going to study how our body responds to stimulus through the endocrine system.

7.5

1. How does a transmission of impulse occur across a synapse?

In order to answer this question, you need to get used to several terminologies such as

(a) Synaptic knob;

(b) Synaptic cleft;

(c) Synaptic dendrite;

(d) Terminal dendrite;

(e) Dendrite; and

(f) Neurotransmitter. Find more information about the terminology to understand how the transmission of impulse occurs across a synapse.

2. Enlist your daily life activities which are related with voluntary

and involuntary action.

Voluntary Action Involuntary Action

ACTIVITY 7.4


7.5.1 Endocrine System-Introduction

The endocrine system executes various physiological processes through chemical messengers called hormones. This system is a collection of glands that secrete those hormones, which are necessary for normal bodily functions. The endocrine system, as shown in Figure 7.22, comprises the pancreas, thyroid, parathyroid, adrenals, pineal, pituitary and testes or ovaries.

Figure 7.22: The endocrine system

Source: http://www.kidshealth.org In general, the endocrine system is in-charge of the body processes that happen slowly, such as cell growth. Faster processes like breathing and body movement are controlled by the nervous system. Although the nervous system and endocrine system are separate systems, they complement each other to help the body function properly.

7.5.2 Endocrine Glands, Hormones and Functions

An endocrine gland is a group of specialised cells that produces and secretes hormones into the blood stream. Although hormones will reach the entire parts of the body through blood circulation, each hormone has its own target organ. Due to the reason, each hormone has its own specific function.


7.5.3 Hormones and Us

Previously, we have learned about the hormones and their functions. Now, let us study more about several hormones which play a significant role in our body. Those hormones are thyroxine, growth hormone and insulin. The imbalance of those hormones will be elaborated in this section. Thyroxine and growth hormones ccontrol the growth of human body. However, the imbalance of the thyroxine and growth hormones in the human body causes the improper functioning of the thyroid gland. The under-secretion of thyroxine and growth hormones during childhood will result in ddwarfism (physically retarded growth). The excessive secretion of thyroxine and growth hormones during childhood will result in ggigantism (overgrowth). Eating food may raise the blood glucose level. This condition will activate the pancreas to secrete insulin. Insulin maintains blood glucose level by lowering the blood glucose level until it reaches around 90 mg/100 mg of blood. Insulin reduces the blood glucose level by stimulating the liver to convert excess glucose into glycogen.

Excess glucose glycogen

However, the non-existence or deficiency of insulin will lead to excessive glucose in blood. This causes a person to have a disease called diabetes mellitus.

SELF-CHECK 7.4

Fill in the blanks.

1. A hormone is carried by _________ or ________ to the targetorgan.

2. Thyroid stimulating hormone is secreted by ___________.

3. ________ hormone regulates the conversion of glucose toglycogen.

4. ___________________ hormone controls the reabsorption of waterinto the kidney tubules.

5. Hypoactivity of thyroid gland leads to__________.

Insulin


1. In groups, get more information by borrowing books in the library or surfing the Internet, to group these keywords. These keywords represent endocrine glands, hormones and functions of those hormones. Good luck!

Endocrine Gland Hormone Function

2. The nervous system detects changes in the external environment while the endocrine system detects changes in the internal environment. Elaborate in the form of an essay, and discuss with your coursemates.

3. Imagine this situation: You suddenly come face to face with a tiger in a jungle. What would you do? Would you fight off the tiger? Or, maybe you should run away as fast as you can? Do you „fight or fly‰? Whatever your decision is, it has something to do with the interaction between your endocrine system and nervous system. Explain the role of our hormone, nervous system and muscles when we „fight or fly‰.

ACTIVITY 7.5


RESPONSE AND COORDINATION IN PLANTS

Animals have a nervous system for controlling and coordinating the activities of their body. But plants have neither a nervous system nor muscles. So, how do they respond to stimuli?

Plants show two types of responses: one dependent on growth and the other independent of growth.

7.6.1 Tropic Response

A growth movement of a plant part in response to an external stimulus in which the direction of a stimulus determines the direction of responses is called tropism. Thus, tropism is a directional movement of the part of a plant caused due to its growth. The direction of the responses can be either towards the stimulus or away from it. For example, the shoot of a growing plant bends towards light while the roots of a plant move away from light. So, the response of the shoot is said to be positively phototropic and the root is negatively phototropic.

7.6


Let us look at Table 7.5, which shows a few types of tropism.

Table 7.5: Types of Tropism

Types of Tropism Description

Phototropism � The movement of a plant part in response to light. � The stem of a growing plant bends towards the light (positive

phototropism), while roots of a plant move away from light (negative phototropism).

Geotropism � The movement of a plant part in response to gravity. � The roots of a plant move downwards in the direction of gravity.

On the other hand, the stem of a plant grows upwards and away from the earth (Figure 7.23).

Figure 7.23: Geotropism

Chemotropism � The movement of a plant part in response to chemicals. � The growth of pollen tubes towards ovules during the process of

fertilisation (Figure 7.24).

Figure 7.24: Chemotropism

Hydrotropism � The movement of a plant part in response to water. � The roots always grow towards water.


Thigmotropism � The directional growth movement of a plant in response to the touch of an object.

� There are some plants called climbing plants which have weak stems, cannot stand erect on their own. They have climbing organs called tendrils (Figure 7.25). Tendrils are thin, thread like structures on the stem or leaves of climbing plants. Tendrils are sensitive to touch. When they come in contact with an object, they wind around the object and cling to it. This is due to the growth of a tendril towards the object.

Figure 7.25: Thigmotropism

7.6.2 Nastic Response

In nastic movements, the movement of the plant part is neither towards the stimulus nor away from the stimulus. This movement is not a directional movement of the plant part with respect to the stimulus. In nastic movements, growth may or may not take place. The rate of these responses increases as intensity of the stimulus increases. The folding up of the leaves of a sensitive plant or touch me not plant (Mimosa pudica) on touching is an example of nastic movement. The stimulus is touch and the movement is called thigmonasty or seismonasty (Figure 7.26).


�Figure7.26: Seismonasti in Mimosa pudica

Source: https:// desktopclass.com Other types of nasticmovements are as follows:

(a) Epinasty � downward-bending from growth at the top. For example, the bending down of a heavy flower.

(b) Photonasty � response to light.

(c) Nyctinasty � movements at night or in the dark.

(d) Chemonasty � response to chemicals or nutrients.

(e) Hydronasty � response to water.

(f) Thermonasty � response to temperature.

(g) Geonasty/gravinasty � response to gravity.

SELF-CHECK 7.5

Explain the two types of responses in plants.


� Skeleton refers to the framework of the animal body around which the whole

body is built. � There are three types of skeletal system: hydrostatic, exoskeleton and

endoskeleton. � Animals with hydrostatic skeleton have a coelom, which is a fluid-filled

cavity. � The exoskeleton is the skeleton which lies outside the soft parts of the body,

providing a covering to them. The skeleton is made up of cuticle. � Endoskeleton is the skeleton found inside the body. � The tissues and muscles are formed around the skeletal system and the

muscular forces are transmitted to this skeleton. This forms the basis for animal locomotion.

� The vertebrate skeleton is basically an endoskeleton made up of two types of

tissues: bone and cartilage. � Segmentation, setae on the body and a pair of muscles found around the

body help in the earthwormÊs movement. � Two pairs of walking legs, a powerful hind leg and a pair of wings help the

grasshopper to walk, jump or fly. A pair of muscles that work in an antagonistic manner help to move the legs and another pair of muscles found under the wings help to raise and lower them.

� Birds have a lightweight skeleton, strong muscles to control their flight, air

sacs, light beaks, small lungs, and wings designed for flying. � Fishes rely on their skeletons for framework, muscles for power and fins for

thrust and direction. Scales and mucus protect the body and keep it streamlined.


� In humans, the nervous system has two divisions: the central nervous system and the peripheral nervous system.

� The central nervous system comprises brain and the spinal cord, while the

peripheral nervous system includes the nerves, which connect the central nervous system with sense organs, muscles and the glands in the body.

� Nerves are thread-like structures that emerge from the brain and spinal cord

and branch out to almost all parts of the body. � A neuron is the basic unit of nervous system. � There are three types of neurons � sensory neurons, motor neurons and

connecting relay or inter relay neurons. � A synapse is the junction of the terminal branches of the axon of one neuron

with the dendrites or cell body of another neuron. It is the site of transfer of nerve impulse from one neuron to another.

� The brain has three parts � cerebrum, cerebellum and medulla oblongata. � A reflex action is a spontaneous, autonomic and mechanical response to a

stimulus controlled by the spinal cord without the involvement of the brain. � The pathway followed by sensory or motor nerves in a reflex action is called

the reflex arc. � Endocrine system is a collection of glands that secretes hormones, which are

necessary for normal bodily functions. These hormones coordinate the response to internal stimulus.

� There are two types of plant responses: tropic and nastic responses. � Tropic responses are growth movement and directional towards or away

from the stimulus. � Nastic responses are not growth movement and non directional.


Antagonistic

Brain

Central nervous system

Endocrine gland

Endoskeleton

Exoskeleton

Extensor muscles

Flexor muscles

Hormones

Hydrostatic skeleton

Inter relay neuron

Involuntary action

Motor neuron

Nastic responses

Peripheral nervous system

Reflex arc

Sensory neuron

Sensory organ

Spinal cord

Synapse

Tropic responses

Voluntary action

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http://www.biologymad.com/master.html?http://www.biologymad.com/nervoussystem/nervoussystem.htm

Biology-Online.org. (2012). The human nervous system. Retrieved March 20,

2012 from http://www.biology-online.org/8/1_nervous_system.htm Buchheim, J. (2012). A quick course in ichthyology. Retrieved March 20, 2012

from http://www.marinebiology.org/fish.htm#how%20fish%20swim Cambridge.org. (2010). Coordination and response. Retrieved March 20, 2012

from http://assets.cambridge.org/97805211/46531/excerpt/ 9780521146531_excerpt.pdf


Discovery Communications, INC. (2010). Muscles group. Retrieved March 20, 2012 from

http://www.yourdiscovery.com/homeandhealth/article.jsp? section_id=4& theme_id=4&subtheme_id=9&article_id=328&site=uk

Hamdan Mohd Nor, et al. (2005). SPM fokus biologi. Kuala Lumpur: Penerbitan

Pelangi Sdn Bhd. Kids Health. (2012). Endoctrine system. Retrieved March 20, 2012 from http://www.kidshealth.org/parent/general/body_basics/endocrine.html. KidsHealth. (2012). Your ears. Retrieved March 20, 2012 from http://www.kidshealth.org/kid/htbw/ears.html. Nios. (2009). Coordination and control: The nervous and endocrine systems.

Retrieved March 20, 2012 from http://www.nios.ac.in/ srsec314newE/PDFBIO.EL16.pdf Pming. (2011).Voluntary and involuntary actions. Retrieved March 20, 2012 from

http://thumbiology.blogspot.com/2011/03/voluntary-and-involuntary-actions.html


& Sons Ltd. Sousa, D. A. (2001). How the brain learns: A classroom teacherÊs guide. Thousand

Oaks, California: Corwin Press.

HBSC1203 BIOLOGY I

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