Unit 1 – Cell Structure and Organisation 1.1 – Plant and Animal Cells, 1.2 – Specialised cells, tissues and organs
SUFEATIN SURHAN BIOLOGY 5090 2012
SYLLABUS CHECKLIST
Candidates should be able to:
a) examine under the microscope an animal cell (e.g. from fresh liver) and a plant cell (e.g. from Elodea, a
moss, onion epidermis, or any suitable, locally available material), using an appropriate temporary staining technique, such as iodine or methylene blue;
b) draw diagrams to represent observations of the plant and animal cells examined above;
c) identify, from fresh preparations or on diagrams or photomicrographs, the cell membrane, nucleus and
cytoplasm in an animal cell;
d) identify, from diagrams or photomicrographs, the cell wall, cell membrane, sap vacuole, cytoplasm,
nucleus and chloroplasts in a plant cell;
e) compare the visible differences in structure of the animal and the plant cells examined;
f) state the function of the cell membrane in controlling the passage of substances into and out of the cell;
g) state, in simple terms, the relationship between cell function and cell structure for the following:
absorption – root hair cells; conduction and support – xylem vessels; transport of oxygen – red blood cells;
h) identify these cells from preserved material under the microscope, from diagrams and from
photomicrographs;
i) differentiate cell, tissue, organ and organ system as illustrated by examples covered in sections 1 to 12,
15 and 16.
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What is Biology?
Biology is the study of life. Biology allows us to answer questions such as:
Various fields of study in Biology include:
Genetics: Study of heredity. Virology: Study of viruses. Entomology: Study of insects. Anatomy: Study of the structure of organisms. Botany: Study of plants. Zoology: Study of animals. Histology: Study of tissues. Mycology: Study of fungi.
The 8 characteristics of living things
M MOVEMENT: Animals move its whole body by using limbs or their equivalent. A plant moves only by growing part of itself towards or away from influences important to it.
E EXCRETION: The process involving the removal of metabolic waste products such as carbon dioxide, water, mineral salts and nitrogenous waste products. These substances will harm organisms if not removed.
R REPRODUCTION: The process of the production of new generation of offspring necessary for the survival of species.
I IRRITABILITY: The process of sensing and responding to stimuli or any changes in the immediate environment (light, sound, touch, pressure, temperature).
G GROWTH: An increase in the cell numbers, size, dry mass or volume of an organism as a result of converting absorbed food into living protoplasm. This may make an organism more complex or even change its form e.g. germination of a seed, caterpillar changing into a butterfly.
R RESPIRATION: The release of energy from the oxidation of food; the energy is used for movement, growth, reproduction, etc.
A ADAPTABILITY: Organisms have the ability to adjust and adapt themselves to changes in their environment.
N NUTRITION: The process where organisms take in food substances and convert them into the living protoplasm of the organism.
Cell, Basic unit of life
The cell is the structural and functional basic unit of
living organisms.
It is the simplest unit of life, basic unit of life or the simplest organized unit of living matter.
There are two major types of cells: 1. Prokaryotic cells: Cells in unicellular organisms
which exists singly as independent organisms showing all the characteristics of life e.g. amoeba, bacteria, paramecium.
2. Eukaryotic cells: Cells in multicellular organisms. These cells become modified for specific functions e.g. root hair cells, red blood cells, epithelial cells.
Living cells are made of protoplasm. The protoplasm of a cell consists of a cell membrane, cytoplasm and nucleus.
Protoplasm is the mass of living matter. It is a complex jelly like substance of which 70-90% is water while the rest consists of mineral salts and organic compounds. Chemical reactions take place here.
The cytoplasm contains structures which perform functions. They are known as organelles.
Organelles include nucleus, vacuoles, mitrochondrion, ribosomes, endoplasmic reticulum, golgi body, centrioles and chloroplasts.
Cells can only be seen under high magnification. Cells have many features in common but their precise structure is closely related to the work they do.
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Cell Structure
All cells have the following structural features in common:
Structure Function
Cell membrane - made up of two layers of lipids and proteins
Selectively controls the passage of substances entering and leaving the cell (selectively permeable) General rule: Small molecules can enter easily e.g. water (osmosis), oxygen, carbon dioxide (diffusion); Large molecules cannot e.g. proteins and starch
PR
OT
OPLA
SM
( Liv
ing m
att
er
)
Cytoplasm
- a jelly-like substance within the cell - consists of 90% water with dissolved salts and sugars; fats and proteins are suspended in it
Site of chemical reactions (metabolic reactions) where organelles can be found e.g. nucleus, mitochondria Temporary food storage e.g. oil globules, starch granules (in plants only)
Nucleus (pl: nuclei)
- largest organelle (visible in the light microscope) - has DNA, enclosed by nuclear membrane - In non-dividing cells, DNA forms long chromatin threads - In dividing cells, DNA condenses (coils up) into visible chromosomes
Contains chromosomes which carry genetic information of the cell; Chromosomes possess genes for programming the cytoplasm to manufacture particular proteins Controls all chemical reactions within the cell and cell division
Mitochondrion (pl: Mitochondria)
- smaller sized organelle (visible only with electron microscope)
Site of respiration
Ribosomes
- Very tiny round organelles present in the cytoplasm
Site of synthesis of proteins from amino acids
Plant cells have the following additional structures:
Structure Function
Cellulose cell wall
- Cellulose form fibres that criss-cross over one another to form a very strong covering of the cell.
Fully permeable membrane i.e. allows any substance to pass through it Supports non-woody plant organs (by turgor pressure) Supports and protects the cell (prevents from bursting) and give shape to cell
A large, central vacuole / Sap Vacuole
- contains a solution called cell sap consisting of 90% water and dissolved salts and sugars - separated from the cytoplasm by the vacuolar membrane = tonoplast - Dividing cells do not have a vacuole
Important for osmoregulation (regulation of water content by osmosis) For food storage Helps to maintain the shape of the cell
Chloroplasts
- small organelles in the cytoplasm
Contains green pigments, chlorophyll, for absorption of sunlight required for photosynthesis
Summary
ANIMAL CELL PLANT CELL
SIMILARITIES
Cell membrane present
Cytoplasm present
Nucleus present
Mitochondria present
Ribosome present
DIFFERENCES
Cell wall absent Cell wall present
Sap vacuole absent
* Have many temporary vesicles
Sap vacuole present
Chloroplasts absent
Chloroplasts present
Starch granules absent; glycogen granules usually
present
Starch granules present
Tonoplast is absent
Tonoplast, a thin membrane that
surrounds the sap vacuole is present
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Specialised cells, tissues and organs
In unicellular organisms, one cell must be able to carry out all functions of a living organism.
In multicellular organisms, cells are usually modified to carry out one main function. The appearance of the cell will vary depending on what that main function is.
There is a relationship between the structure of a cell and its function. This specialisation of cells to carry out particular functions in an organism is referred to as ‘division of labour’.
The Root Hair Cell
Functions:
Absorption of water from the water film surrounding the soil particle by osmosis.
Allows simple diffusion of dissolved mineral salts in the soil solution to pass into the root hair.
Absorb minerals that are present in low concentration in the soil by active transport.
Adaptations:
1. It has a long, tubular shape.
- Able to form very close contact with the water film surrounding many soil particles (able to penetrate between the soil particles).
- Greatly increases the surface area of the cell available for uptake of water and mineral salts (due to its shape and large number of root hairs).
2. Has a very concentrated cell sap in its vacuole - Increases the water potential gradient between
the soil water and the root hair cell so that water will tend to move into the cell by osmosis.
The Xylem vessel
Functions: To conduct or transport water and mineral salts
from roots to stems, leaves, flowers and fruits.
To provide mechanical support for the parts of the plant above the ground.
Adaptations:
1. Conduction:
- Xylem vessels are stacked end-to-end and the end walls are digested away to form long, continuous, narrow tubes, stretching from the roots, through the stem to the leaves.
- They have hollow lumen i.e. no cytoplasm, allowing water and its dissolved mineral salts to pass through unimpeded (no obstruction). This is why xylem vessels are dead cells.
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2. Support: - The cell walls of xylem vessels are strengthened
by the strong, rigid and waterproof substance called lignin. As the lignin in the walls build up, it eventually kills the xylem vessels. Hence, the hollow lumen.
- Xylem vessels are part of the vascular bundles which run through the stem of plants like steel reinforcements in concrete pillars. They help to resist bending strains caused by the wind.
The Red Blood Cells or Erythrocyte
FUNCTION: To carry oxygen around the body in the form of
oxyhaemoglobin. ADAPTATIONS: 1. The cytoplasm in red blood cells contains the
pigment haemoglobin. Haemoglobin combines with oxygen in the lungs to become oxyhaemoglobin. This is a reversible process.
2. The absence of nucleus (enucleated) means space for more haemoglobin enabling more oxygen to be transported increasing their efficiency.
3. The cells are small and there are many of them, so they have a very large surface area for oxygen absorption.
4. They have a flat, biconcave shape making their surface area for absorption (by diffusion) even larger.
5. They are flexible, allowing them to be pushed easily through the small blood vessels i.e. capillaries whereby they become bell-shaped.
Muscle cells
FUNCTION: To cause movement when they
contract.
(Contraction brings about a decrease in length of the cell. Muscles can only do work when they contract, never when they relax)
ADAPTATIONS: 1. They are long and thin, allowing many to work side-
by-side for greater force, or to form a contractile network.
2. Their cytoplasm contains many mitochondria which are responsible for releasing energy within a cell and necessary here to bring about contraction.
Cells, Tissues, Organ System and Organism
One cell working on its own would achieve very
little in an individual plant or animal, so it is common to find many similar cells lying side-by-side and working together, performing the same function to increase efficiency.
Tissues
Many similar cells working together and performing
the same function is known as a tissue.
ANIMAL TISSUES (based on humans) Types of
tissue Contents Main Function
Epithelial tissue
Layers of cells placed end to end
To cover the external surface. To serve as a protective lining. To line tubes and spaces and form the skin.
Skeletal tissue
Hard material To support the body and permit movement.
When longitudinal
muscles contract, they
become short
When circular muscles
contract, they become
smaller
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Blood tissue Runny fluid To carry oxygen and food round the body.
Nervous tissue
Brain and nerve cells
To conduct nerve impulses and coordinate messages.
Muscular tissue
Bundles of muscles in arms, heart, etc.
To bring about movement for locomotion, breathing peristalsis.
Connective tissue
Bone, cartilage, blood
Joins body structure together. Provides protection and support. Has ability to store and transport materials.
PLANT TISSUES (based on flowering plants) Types of
tissue Contents Main Function
Epithelial tissue
Layers of cells
To cover surface of plants. To protect from physical damage and infection. To reduce water loss.
Photosynthetic tissue
Cells with chloroplasts
To provide cells with chlorophyll. To absorb sunlight. To perform photosynthesis.
Packing tissue Round balloon-like cells
To fill in spaces inside the plant for mechanical support.
Vascular tissue
Xylem
Cambium
Phloem
Xylem vessels Cambium cells Sieve tubes, sieve cells and companion cells
To transport water and mineral salts from roots to all parts of the plant. To provide mechanical support to plant. New tissue growth in the cambium. To transport food substances.
Organ
Several different tissues working together to
perform a particular function.
Organism Type of organs Function
ANIMAL
Alimentary canal To digest food
Nose, trachea, lungs Gaseous exchange
Heart and blood
vessels
Transport oxygen and
dissolved food
substances
PLANT Leaf
Photosynthesis
Transpiration
Flower Reproduction
Organ system
An organ system is a collection of different organs
working together to perform a particular function.
ORGAN SYSTEM IN ANIMALS
System Main organs of
system Main Function
Digestive system
Oesophagus, stomach, duodenum, ileum, colon, liver, pancreas
To digest the ingested food To absorb digested food To expel undigested food
Respiratory system
Trachea and lungs
To take in oxygen To get rid of carbon dioxide
Circulatory system
Heart, veins, arteries, capillaries
To carry oxygen and food around the body To regulate body temperature
Excretory system
Kidneys, urinary bladder, liver, lungs, skin
To get rid of toxic metabolic products
Sensory system
Eyes, ears, nose To detect stimuli
Nervous system
Brain, spinal cord
To control and coordinate body movements To conduct impulses from one part of the body to another
Muscular system
Muscles, skeleton
To move parts of the body
Skeletal system
skeleton To support the body To protect internal organs
Reproductive system
Testes, ovaries, uterus
To produce gametes To protect and nourish the embryo during development in the uterus
ORGAN SYSTEM IN PLANTS
The sepals, stamens, petals and carpels in a flower
make up the reproductive system of a plant.
Organism
A collection of organ system working together.
Example in human: Digestive system, circulatory system, respiratory system, urinary system, nervous system, reproductive system all combine together to form an organism.
The increasing order of cell organisation found within any living
organism is:
Cell → Tissues → Organs → Organ systems → Organisms
SURFACE AREA TO VOLUME RATIO
All animals need to take in oxygen and food substances from the environment and to eliminate carbon dioxide and other waste products from their bodies.
Small animals such as protozoa, jellyfish and flatworms carry out their exchanges by simple diffusion through their body surfaces. It is therefore important to study the relationship between surface area and volume in the living organism. This factor affects the rates of gaseous exchange, heat loss and loss of excretory products.
Notice that as the cube becomes bigger, the surface area does not increase in the same proportion as the volume.
The largest cube has the smallest surface area : volume ratio. Therefore, as the smaller the size of the cell or organism, the greater the surface area : volume ratio, the faster and more efficient the rate of diffusion of food and gases into the organism. It also means diffusion of waster products also diffuse out of the organism or cell at a faster rate.
As an object becomes larger, its surface area compared to its volume is smaller. Diffusion is no longer an effective way to transport materials to the inside. For this reason, there is a physical limit for the size of the cell, with the effectiveness of diffusion being the controlling factor. This explains why small organisms such as amoeba and bacteria undergo cell division when they grow too big.
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