DISTANCE EDUCATION CENTREBIOLOGY UNIT 3 2014

BIOLOGY REVISION BOOKLET

This booklet is specifically prepared for students who have not covered these topics in Biology Unit 1 or Biology Unit 2 in Year 11. It will also be useful for new students who have been out of school for a while and are returning to study; it will help to prepare you for the study of Biology Unit 3 in year 12.

There are countless millions of individual living things, or organisms, on Earth. Some kinds are familiar to us, such as the various animals and plants which surround us; others such as fungi and bacteria are less familiar and may even be invisible to the naked eye.

Biology - the scientific study of life – is concerned with the ways in which biologists investigate the living world, with the knowledge that has come from those investigations, and with the ways that knowledge can be applied to help solve human problems.

How is a city similar to a cell?

We all live in a civilised society - we either live in or have visited a large town or city. Did you know that the organisation within a city can be compared to the organisation within a single plant or animal cell?Cities have a clearly defined edge, whether it is a strong, defensive wall as in Medieval times, or a more modern ring-road. Cells, too, have an outer edge called the plasma membrane, which controls what enters and leaves the cell. Many energy-rich activities occur within the city and hence the city needs a constant supply of energy to be distributed to where it is needed. In the cell the mitochondria perform this function. During this process, however, waste is produced, and like the waste-disposal service available to a city, the cell has to recycle, break down or remove any waste that is generated.A city is organised so that different activities occur in different buildings or areas - you would not want a hospital in the same building as an abattoir! So, too, a cell, which is capable of carrying out thousands of chemical reactions at once, has different membrane-bound compartments where these reactions occur - they are the organelles. These compartments represent the 'factories" of the cell. New goods and products which are needed by the cell, such as proteins and glucose are continually being made from raw materials. This production usually takes place on a cellular production line until the final product is achieved.The sites of various activities are not randomly distributed within either a city or a cell. In a city there are industrial zones, residential zones and central business districts. These are all linked by an effective communication system. It is the same in a cell; a cell has a complex set of structures that define the centre, distinguish one end from the other and provide routes for transportation.Like cities, cells are highly organised, so at the city centre lies the city council who are in charge of the city, and at the centre of the cell lies the

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Key WordsOrganism: a living plant, animal, fungus, bacterium or virusBiology:The study of living organisms

nucleus. Inside the nucleus are the chromosomes, which carry in chemical code on the DNA all the instructions on how the cell is to develop and function. In this booklet we will investigate the structure and functioning of cells and how they are organised to achieve the amazing array of events that occur within them.

Life at the molecular level

Living things share a suite of characteristics: movement, respiration, sensitivity, growth, reproduction, excretion and nutrition.

Living organisms are amazingly diverse in appearance - from tiny insects to huge trees, from worms to elephants, from bacteria to mushrooms. But the closer you look at all of them, the more similar they become.

Just like a city has buildings (and streets and drains), a tree has leaves (and branches and a trunk); just like the buildings are made of smaller units (bricks), so the tree is made of smaller units (cells).

Like the tree, all of these organisms are composed of cells. So, what is a cell?

Cell sel (plural cells) / nounbasic unit of living thing: the smallest independently functioning unit in the structure of an organism, usually consisting of one or more nuclei surrounded by cytoplasm and enclosed by a membrane. Cells also contain organelles such as mitochondria, lysosomes, and ribosomes.(Source: Encarta http://encarta.msn.com/dictionary_/cell )

The cell is the site of life; it is the functioning unit structure from which living organisms are made. This is one of the fundamental principles of biology known as The Cell Theory. While cells share many common features, there are also differences between cells that are related to their particular roles in organisms.

If we are to understand life we need to understand how cells work. In the 17th Century, microscopes capable of viewing cells were made for the first time. The English scientist Robert Hooke (1635 – 1703) was the first person to observe cells - he viewed thin pieces of cork through a microscope. What he saw had no name then; he called them “cells” because they reminded him of little boxes, like the cells of a honeycomb. Since then, studies of cells from all types of organisms by various scientists have led to the formulation of the cell theory which states that:

• All organisms are composed of cells (and the products of cells).• All cells come from pre-existing cells.• The cell is the smallest living organisational unit.

When Robert Hooke viewed the cork cells under his microscope he was only looking at a very thin slice and so was not looking at whole cells.

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Key WordCell:

The cell is the smallest unit in a living organism that can work on its own. A cell can make its own food and reproduce without help from other cells.

Key Word:Bacteria (singular: bacterium)Microscopic living organisms that live all around you and inside you. Many are harmless and useful, but some

Cells are three-dimensional. However, like Hooke, when looking under the microscope we are only seeing a two dimensional slice through a cell or one side of a whole cell.

Go to the following website to see cells in 3-D:

http://www.ibiblio.org/virtualcell

Now try these questions:

Question 1

(a) Why were cells unknown until the 17th century?

(b) Biologists often cut several sections of a cell to find out about its structure.Give two reasons why having several sections from different areas of the same cell is important.

Please note: Answers to all of the questions in this booklet are provided at the end of the booklet, so you don’t have to do the questions - you can refer to the response sheet if you like.

Exceptions to the cell theory

Viruses present some problems to the cell theory. What are viruses? Are they living or non-living organisms?

Viruses are the smallest living things known – they can be over a million times smaller than bacteria. Viruses are so small that they can only be seen under a special type of microscope called an electron microscope. Electron microscopes are used to study fine details and very small things – they can magnify things by up to one million times. (You will learn more about microscopes later in this chapter).

Some viruses are harmless, but many cause illnesses, ranging from the common cold (Influenza virus) to AIDS (HIV).Viruses are not regarded as cells because they do not have the basic structures of cells (i.e. the nucleus, cytoplasm and cell membrane). They not only lack the complex structures found in cells but only show a few characteristics of living things. They cannot become active outside a living host cell, which means that they cannot live on their own. Instead they force their way into the cells of living creatures and use these cells to make more viruses. After a time these infected cells die and the viruses set off to find new cells to attack. They simply exist as inert virus particles called virions.

The main parts of a typical virus are shown below. After you have read about cells, you will see how different viruses really are.

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Did you know?

All viruses can gradually change to form new versions or strains of that type of virus. That is why scientists discover a new strain of flu every year.

Figure 1: A typical Virus

Looking at CellsThere are many different types of cells. The shell of an emu egg has a single cell inside it (which is made up of the egg yolk and white). On the other hand, about a hundred thousand bacterial cells could fit on an area the size of a full stop! So, you see, cells have a large range of sizes.

Most living things start life as just one cell. In fact, you started life as only one cell. So how did you become so big? How does a single cell become millions of cells?A single cell can divide into two, these two then grow to full size and divide into four, and so on. They do this by a process known as Mitosis (you will study this process later in the course).

Not only can cells replicate, they can also differentiate (meaning: to become different) to become many different types of cells.Your body now has a variety of tissues - these are groups of the same types of cells. Examples of tissues are muscle tissue and connective tissue. Groups of tissues in turn make up organs such as your heart and lungs and groups of organs form organ systems, such as the respiratory system.

As various organisms have adapted to their environment, the degree of cellular organisation has altered. All cells need a constant input of substances like oxygen, glucose and a removal of wastes such as carbon dioxide and nitrogenous wastes.There is really no such thing as a typical cell. Cells are specialised for many different purposes and their structures reflect those purposes. However, there are some features that are shared by all cells. Examination of cells using various microscopes reveals much about their internal organisation. Each living cell is a small compartment with an outer boundary known as the plasma membrane (also referred to as the cell membrane or plasmalemma). Inside each living cell is a fluid, known as the cytosol which consists mainly of water containing many dissolved substances.Another feature of all living cells is that they contain genetic material in the form of DNA, which carries hereditary information, directs the cell’s activities, and is passed accurately from generation to generation. Living

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Did you know?

Your body is made out of about 100 million, million cells.

Did you know?

A drop of blood the size of a pinhead contains about five million red blood cells, 7,500 white blood cells and over 250,000 platelets!

things can be classified into two different kinds on the basis of their internal structure - prokaryotes and eukaryotes.

Prokaryotic cells Prokaryotic cells are relatively simple and very little internal structures can be seen, even with an electron microscope. They lack membrane-bound organelles and in particular, they lack a clearly defined structure to house their DNA - the nucleus. They contain a single circular DNA chromosome in the middle of the cell. They are small cells which range in size from 0.5 to 1.0 micrometre (or micron).Organisms that are made of prokaryotic cells are called Prokaryotes and include bacteria and cyanobacteria. They are unicellular organisms which means that they are made up of just a single cell (uni: meaning “one”) and are so small that they are invisible to the naked eye.

Figure 2: Prokaryotic Cell Structure Courtesy: http://micro.magnet.fsu.edu/cells/procaryotes/images/procaryote.jpg

Eukaryotic cellsEukaryotic cells have a much more complex structure than prokaryotic cells. They contain many different kinds of membrane-bound structures called organelles suspended in the cytosol. These organelles carry out specific functions within the cell. One of these organelles is a nucleus with a clearly defined membrane called a nuclear membrane or nuclear envelope. The DNA of a eukaryotic cell is located inside the nucleus. Eukaryotic cells are relatively large cells which range in size from 30 to 150 micrometres.Organisms that are made up of eukaryotic cells are called Eukaryotes. They are multicellular organisms (multi: made up ofmany cells) and include all animals, plants, fungi and protists. So the majority of organisms typically contain eukaryotic cells.

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FACT1 micrometre - abbreviated as 1 µm - is one millionth of a metre, i.e. 10-6m (or one thousandth of a millimeter).

Key Words

Unicellular: one-celled.

Multicellular: many-celled.

Key WordProkaryote Latin: pro, before + Greek: karyon, a nut, kernel or nucleus.

Figure 3: Anatomy of a eukaryotic cellCourtesy: http://micro.magnet.fsu.edu/cells/bacteriacell.html

Key properties of Prokaryotes and Eukaryotes

Characteristics Prokaryotes Eukaryotes

Size of cell Small cell size (0.2 – 2 µm.) Larger cell size(10 -200 µm.)

Nucleus No nuclear membrane or nucleoli

True nucleus consisting of nuclear membrane and nucleoli

Membrane enclosed organelles

Absent Present

Cell wall Usually present, chemically complex.Rigid cell walls

When present, chemically simple.Flexible cell walls

Chromosomes(DNA) Single circular chromosome Multiple linear chromosomes, enclosed in nucleus

Cell division Binary fission (cell splitting) Mitosis

Note: The pictures you see of cells here, in the textbook and other sources are only flat two-dimensional images - just like photographs of you are flat two-dimensional images. Cells, also like you, are three dimensional in reality.

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Key WordEukaryote: from the Greek - eu, well + karyon, nucleus

Eukaryote organelles

Just as a human body contains many specialised organs essential for survival, such as the heart, kidneys, liver, lungs and brain, a cell contains many organelles.Organelles are subcellular structures involved in specific functions of the cell. In other words, each organelle has a specific job to carry out within the cell to keep the cell working. Many organelles are found in most cells. Each organelle is surrounded by a membrane and they are found inside the cytosol of the cell.Organelles within a cell do not act in isolation, but interact with each other. The normal functioning of each kind of cell depends on the combined actions of its various organelles. All types of cells perform similar basic processes and many also carry out highly specialised functions. The activities of cells require considerable energy, and require the production of a variety of biological molecules that are assembled into new organelles, used for repair or exported from the cell. All these processes are catalysed by enzymes and are precisely regulated. Some biochemical processes involve hundreds of enzymes operating sequentially along a complex integrated chemical pathway; each step is tightly controlled.

A brief summary of the structure and functions of the different parts of cells and organelles follows (in alphabetical order):

Cell wall: Found in bacterial (prokaryotic), fungal and plant cells only, a non-living, cellulose structure outside the plasma membrane. The cell wall provides support, prevents expansion of the cell, and allows water and dissolved substances to pass freely through it. The cell wall varies in composition between plants, fungi and bacteria.

Centrioles: A pair of small cylindrical structures composed of micro tubules. They are involved in the separation of chromosomes during cell division in animal cells and protists.

Chloroplast: Found in the photosynthetic cells of green plants and algae; a green organelle (due to the abundant presence of the pigment chlorophyll) in which photosynthesis takes place. It is composed of many folded layers of membrane. Chloroplasts are often called the "sunlight trappers" because they trap the radiant energy of sunlight and transform it to chemical energy present in organic molecules such as sugars.

Cytoplasm: (From the Greek: kytos, a hollow vessel + plasma, fluid). The contents of a cell, other than the nucleus. It is jelly-like, more than 90% water and contains ions, salts, enzymes, food molecules and organelles.

Cytosol: The fluid component of cytoplasm in which organelles are located.

Endoplasmic reticulum: A network of intracellular membranes, which links with the plasma membrane and other membranous organelles. It may be rough (associated with ribosomes attached) or smooth (lacking ribosomes). Transport of substances within cells occurs through this system of channels. Present in both prokaryotes and eukaryotes.

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Key WordOrganelles: “little organs” or tiny structures inside cells, each of which has a specific function.

Golgi apparatus (also called a Golgi complex or Golgi bodies):This is the “warehouse” of the cell. The cell does not use all of the proteins that it makes, so the spare proteins are stored here until they are needed. It consists of a stack of flat membrane sacs where the final synthesis and packaging of proteins into membrane-bound vesicles occurs before they are secreted from the cell. It is linked to the endoplasmic reticulum. Only found in eukaryotes.

Lysosomes: Found in most animal cells; membrane-bound vesicles that contain powerful enzymes which break down debris and foreign material that is brought into their sacs. They also destroy old and diseased parts of the cell.

Mitochondria: Found only in eukaryotes, they are organelles composed of many folded layers of membrane. Mitochondria are involved in the energy transformations that release energy for use by the cell. Cellular respiration occurs in mitochondria, so it is known as the "energy-supplying" organelle. The more active a cell is the more mitochondria it needs. For example, liver cells work hard at changing food into energy so the liver has plenty of mitochondria to enable it to do this.

Nucleus: (From the Latin: nucleus, a kernel or nut). This is the “headquarters” or the control centre of the cells of animals, plants, algae and fungi (the eukaryotes).It is a large organelle, surrounded by a double-layered nuclear membrane containing pores that allow movement between the nucleus and the cytoplasm. It stains differently from cytoplasm and so often looks darker in prepared slides. The nucleus contains genetic material (DNA) and controls cellular activities. Some cells such as the human liver cells contain more than one nucleus.

Plasma membrane: Forms a protective layer around the cell. It encloses the cytoplasm in all cells (holding in the contents of the cell) and controls the movement of substances into and out of the cell. It is responsible for recognition, adhesion and chemical communication between cells.

Plastids: A group of organelles found only in plant cells, all of which develop from simple organelles called proplasts. Chloroplasts and amyloplasts are plastids. Amyloplasts store starch in roots or storage tissue, such as in potato tubers, and may be involved in geotropism and chromoplasts (which contain colour pigments and are found in petals and fruit).

Ribosomes: Present in both prokaryotes and eukaryotes, they are tiny organelles located in the cytosol. They are not enclosed by a membrane. Although they are free within prokaryotic cells, in eukaryotes many are attached to membranous internal channels called endoplasmic reticulum, within the cell. They are the organelle where protein production occurs and so are the “chemical factory” of the cell.

Tonoplast: Vacuole membrane in plant cells, which regulates the movement of substances into the vacuole.

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Vacuoles: Membrane-bound liquid-filled spaces found in most cells in variable numbers. Plant cells typically have large fluid-filled vacuoles, containing cell sap, that provide physical support (turgidity) and storage. In other cells, vacuoles may be involved in intracellular digestion (food vacuoles) or water balance (contractile vacuoles).

Vesicles: Membrane-bound organelles often associated with transport within the cell.

Please go to the following website to see some animations and 3-D diagrams of the different types of cells as well as the structure and functions of their organelles. Once you are in the site, select a topic and press "GO". The site contains a lot of very useful and interesting information.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/cells/cellsrev3.shtml

Try out these other websites as well:

http://www.ibiblio.org/virtualcell www.cellsalive.com

What do cells look like when viewed under the electron microscope? Refer to the following diagrams which show the composition of plant and animal cells.

Animal cells

The cells in your body are not very different from the cells of a frog or an elephant. In fact all animal cells have the parts shown below:

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Plant cells

Almost all plant cells have the parts shown below:

Courtesy: Nash B. &Wilkinson J., Biology 12,Macmillan, 199l.

Using the above diagrams of the animal and plant cells, please answer the following questions:

Question 3Scientists group cells into four main types: bacterial cells, fungal cells, animal cells and plant cells.

Look at the generalised diagrams below showing the four main types of cells.

Question 2

(a) Identify 3 features that ALL cells have in common.

(b) State 3 differences between a plant cell and an animal cell.

(c) State 3 ways in which they are similar.

(d) Name a structure which is unique to plant cells.

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What are fungi?

Fungi (singular: fungus). Types of organisms that has no leaves, roots or flowers. Moulds, mushrooms and toadstools are all fungi.

Complete the following table to show the presence () or absence (x) of the following features - distinct nucleus, mitochondria, size <10 µm, chloroplasts and cell wall in the different cell types. You may like to do some additional research.

Animal Plant Fungi BacteriaDistinct nucleusMitochondriaSize < 10 µmChloroplastsCell wall

Question 4

The following diagram shows a cross section of an ovary cell.

Examine the above diagram and complete the following table:

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animal cell (>10 µm) plant cell (>10 µm)

fungal cell (>10 µm) bacterial cell (<10 µm)

Structure Function

A Endoplasmic Reticulum

B Ribosome

C Packages and distributes material for

transport out of cell

D Nucleus

E Major site of ATP production

F Contains fluid mixture of digestive

enzymes.

(Answers are provided at the end of the booklet)

The composition of living organisms

The similarities between different organisms become even greater when you look more closely at cells and the atoms and molecules they are composed of. All life is composed of the same few elements. There are 92 naturally occurring elements. Only 11 of these are found in organisms in more than trace amounts, and four of these - carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) - make up 99% of organisms by weight. The similarities of all organisms at the molecular level points to their common origin. Understanding the structure and properties of these molecules and the ways they interact is fundamental to developing an understanding of biological processes and the functions of organisms.

THE CELL MEMBRANE

What is the cell membrane?The boundary of all living cells is a plasma membrane which controls entry of dissolved substances into and out of the cell.Most organelles, including the nucleus, endoplasmic reticulum, mitochondria, plastids (chloroplasts), lysosomes, and vacuoles are also surrounded by membranes. These membranes form discrete compartments and control the intracellular movement of substances.

The composition of the plasma membrane

The plasma membrane is an ultra thin and pliable layer with an average thickness of less than 0.000 01mm. and can be seen using an electron microscope.

The outer cell membrane is thicker than the membranes of the intracellular organelles. Otherwise, the basic structure of all cell membranes is the same.

What are the components of the membranes?

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Key WordThe cell membrane forms a protective layer around the cell. It also holds the contents of the cell together.

They have a basically similar phospholipid bilayer structure. The central region of the membrane consists of two layers of phospholipid molecules in the fluid state and the molecules are arranged with their hydrophobic (water repelling) tails aligned towards each other, and their water attracting or hydrophilic (polar) heads towards the outside. Associated with the membrane are other molecules including proteins, carbohydrates, and cholesterol as represented by the fluid mosaic model shown above The lipid molecules and some proteins are free to move about within the layers.

Proteins Proteins are composed of the elements carbon, nitrogen, oxygen and hydrogen (and some also contain sulphur).These are located somewhat randomly throughout the membrane. Some are present only on the surface, others are wholly or partially embedded in the lipid layers; some of these may penetrate all the way through the membrane. Proteins provide pores or channels which allow polar (having negative and positive charges) molecules and ions below certain sizes to go through. They also form channels or gates which permit or enhance the passage of specific ions and molecules. Sometimes the passage of these specific molecules requires the expenditure of energy (this is known as "active transport").

Membrane proteins may also be enzymes that carry out membrane-associated reactions e.g. final digestion of some food molecules as they pass through the membrane of the gut.

Other proteins are receptors for hormones or other specific compounds.

Carbohydrates Those associated with the plasma membranes are usually found on the outer surface of the membrane, linked to protruding proteins. They are thought to play a role in the adhesion of cells to one another, in the 'recognition' of molecules that interact with cells such as hormones antibodies and viruses. Carbohydrates are composed of carbon, oxygen and hydrogen.

Cholesterol Cholesterol is so much in the news these days in terms of heart attack risk.Membranes in higher organisms contain large numbers of cholesterol molecules, located in between the phospholipid molecules. They make the membrane less fluid and more stable. Without these cholesterol molecules, the cell membrane rapidly breaks down, and releases its contents. Cholesterol also decreases the permeability of the membrane to small water-soluble molecules, making it an important component of cell membranes.So health conscious people, beware of restricting cholesterol too much in your diet!

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Movement in and out of cells

All cells must be able to take in and expel various substances across their membranes in order to survive, grow and reproduce. Generally, these substances are in solution, but in some cases, may be tiny solid particles.Because a plasma membrane allows only some dissolved materials to cross it, the membrane is said to be a partially-permeable (partially-permeable may also be called semi or selectively or differentially-permeable) boundary.

What structures can pass through the membrane?

Not all dissolved substances can cross the membrane equally well. Factors affecting the passage of substances are:

• molecular size• electrical charge• number of attached water molecules• solubility in fats.

Generally, substances which dissolve in alcohol or oil penetrate particularly rapidly through the membrane, so the membrane is said to be permeable to these substances - it allows them to pass through easily.

Due to its phospholipid bilayer, the membrane is impermeable to water-soluble molecules - this means that it does not allow them to pass through.

The special functions of membranes

Cell membranes play an important role in cells and some of the functions are listed below:

• prevent dilution of cell cytoplasm.

• permit selective control of molecules that enter and leave cells.

• establish intracellular compartments (separating hereditary material, lysosome enzymes, secretory products of cells, cytoplasm).

• restrict movement of substances between one part of a cell and another.

• prevent uniform mixing of cellular contents.

• permit the regulation of many enzymatic processes that take place within the cell.

• produce electrical activity of excitable cells, and

• have receptors involved in intercellular communication (directly between cells and by hormones and nerves).

Because life is 'watery', one of the most important properties of membranes is that they are impermeable to most water-soluble molecules. Small-uncharged molecules such as water, oxygen and carbon dioxide, can go through but large molecules are prevented from passing in and out.

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KEY WORDSPermeable: allows substances to pass through.Impermeable: does not allow substances to pass through.Semipermeable: allows only some substances to pass through.

Having studied the structure and properties of the membrane, answer the following questions:

Question 5

(a) List two functions of membranes in cells.(b) What is meant by the label partially permeable in reference to the

plasma membrane?(c) Why do volatile anaesthetics such as chloroform and ether work

quickly? In other words what properties could they have which would enable them to easily cross over cell membranes?

(d) Why is alcohol absorbed more quickly from the gut than food?

(Answers are provided at the end of the booklet)

How do substances pass in and out of membranes?

Dissolved substances that are able to cross a plasma membrane - from outside a cell to the inside or from the inside to the outside - mainly do so by the following processes:

• diffusion• osmosis• active transport• endocytosis

DiffusionWhat happens if you put some coloured solution at one end of a water filled container with some water in it? In this case, the coloured solution id added to the left-hand side of the container (see diagram below).After a few hours, the colour has spread evenly throughout the solution. How does this happen? There is a movement of particles from the region of high concentration of colour molecules (on the left-hand side) to a region of low concentration of colour molecules (the water). Such a process is known as diffusion.

Diffusion is the result of the constant motion of particles

• it can occur through the pores of cell membranes

• no energy is expended by a cell when diffusion occurs – so this is a passive process, and is called “passive diffusion”

• gas particles diffuse more quickly than other molecules across membranes

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Key WordDiffusion:The movement of particles from a region of high concentration to a region of lower concentration, resulting in an even distribution.

• diffusion occurs in both directions across a membrane

• the net or overall direction of flow is from the area of the higher concentration of a substance to an area of lower concentration of a substance.

Once diffusion is complete, the end result is a uniform or even concentration on each side of the membrane.

For an animation of simple diffusion, go to:

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/cells/cells3.shtml

Why is diffusion important to the cell?

Diffusion is one way cells take in materials from the environment; it is also one way they lose unwanted materials (wastes) when they are produced in the cell.

Water, oxygen, carbon dioxide and small ions and molecules can diffuse freely through the cell membrane, in both directions, because the membrane is permeable to them. Do you think all substances can pass through the cell membrane? The answer is no. Remember that the membrane acts as a barrier to some substances while allowing others to pass through - such a membrane is said to be selectively permeable or partially-permeable because it only allows certain substances to pass through it, but not others.

OsmosisOsmosis is a special type of diffusion. It is the movement of water molecules through a semi-permeable membrane and down a concentration gradient.

The water diffuses from a region of high water concentration to a region of lower water concentration.

Another way of saying this is that the water diffuses from a region of low solute concentration to a region of high solute concentration (the solute is the substance that is dissolved in the water eg. salt or sugar).

To see an animation of osmosis go to:

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa_pre_2011/cells/cells4.shtml

Now answer the following questions :

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Key WordsSolution:A mixture of one substance (the solute) dissolved in another (the solvent).

Question 6

It is possible to dissolve the outer hard shell of a hen's egg. This leaves just the cell membrane undamaged and the cell contents intact. Shells were removed in this way from several eggs and each egg was placed in one of the three different solutions below:

Solution l Distilled water

Solution 2 0.5M sucrose (M = molar concentration)

Solution 3 l .5M sucrose

The weight of the eggs was recorded at regular time intervals over an hour. Using your knowledge of diffusion:

a. What difference would you expect between the weights of the eggs placed in distilled water and that placed in the 0.5M sucrose? Explain.

b. Under what conditions would an egg show neither an increase nor a decrease in weight?

1) Distilled Water 2) 0.5M sucrose solution 3) 1.5M sucrose solution

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Question 7

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(Answers are provided at the end of the booklet)

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Facilitated Diffusion

The movement of some substances across the plasma membrane is assisted or facilitated by carrier protein molecules. This form of diffusion, involving a specific carrier molecule, is known as facilitated diffusion (meaning “assisted” diffusion). The net direction of movement is from a region of higher concentration of a substance to a region of lower concentration, and so the process does not require energy. Movement of substances by facilitated diffusion mainly involves substances that cannot diffuse across the plasma membrane by dissolving in the lipid layer of themembrane. For example, the movement of glucose molecules across the plasma membrane of red blood cells involves a specific carrier molecule.

See the following websites for animations of facilitated diffusion:

http://highered.mheducation.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

http://www.d.umn.edu/~sdowning/Membranes/diffusionanimation.html

Active transportThis involves the movement of dissolved substances into or out of cells against the concentration gradient.

Because the net or overall movement is against a concentration gradient, active transport uses energy to pump materials or carry them across the membrane. It is an energy requiring process. They otherwise might have been blocked by the diffusion gradient or their own mineral salts entering the cells in this way.

Active transport plays an important role in some animals that live in fresh water, for example frogs. Frogs tend to lose salts by diffusion across their skin-cell plasma membranes into the surrounding fresh water. So to balance the loss of salt that occurs, energy is used to drive active transport of salts from a region of low concentration in the surrounding water, across plasma membranes, into the frog skin cells that have a high concentration of salts.

See the website below for an animation of active transport.

http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_pre_2011/homeostasis/importancerev6.shtml

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Endocytosis An entirely different type of active uptake is endocytosis. This is a process used when solid or large particles, which cannot pass across the plasma membrane passively, need to be taken into a cell. In this process the cell membrane folds around the particles and 'pulls' them into the cytosol of the cell as shown in the diagram below.

The particles enclosed in a vesicle are then acted upon and broken down by enzymes. (If enzyme action does not occur, the vesicle is disintegrated by lysosomes).

When the material to be transported is a solid food particle, the type of endocytosis is called phagocytosis. This type of food transport is used by the single-celled organisms called Amoeba.Although some cells are capable of phagocytosis, most cells are not.

Most eukaryotic cells rely on pinocytosis, a form of endocytosis that involves material that is in solution being transported into cells.

When large molecules and particles need to be taken out of the cell, a small membrane-bound vesicle moves through the cytoplasm to the plasma membrane, where it joins with it and then releases its contents out of the cell - this is called exocytosis (as in exit). Note the summary below.

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Figure 6: A summary of Endocytosis

Go to the following website for a visual representation of phagocytosis:

http://www.stolaf.edu/people/giannini/flashanimat/cellstructures/phagocitosis.swf

To sum up:

In general, substances pass in and out of cells by four main processes:

Diffusion- simple and facilitated Passive processes ( (no energy is required)

Osmosis- diffusion of water Active transport

Energy requiring processes Bulk transport

EndocytosisBulk transport of material into a

cell

If material to be transported is solid

If material to be transported is liquid

The process is called: Pinocytosis

From the Greek: pinus=drinkand cyto=cell

The process is called:Phagocytosis

From the Greek:phagos=eatingand cyto=cell

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Now, try the question below:Question 8Substances may move across the cell membrane by a variety of mechanisms. Some of these require respiratory energy while others do not. Draw and complete the table below, which details how various substances MOST TYPICALLY move across the cell membrane.An example has been completed.Substance Mechanism of

Movement

Main part of

membrane involved

Is respiratory

energy

required?

Carbon

dioxide

Diffusion Phospholipid bilayer No

Water

Glucose

Alcohol

(Answers are provided at the end of the booklet)

Surface Area and Volume

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When an object (e.g. a cell) is small it has a large surface area in comparison to its volume. In this case diffusion will be an effective way to transport materials (e.g. gases) into the cell. 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 a cell, with the effectiveness of diffusion being the controlling factor.

Volume: = 8 cm3 Volume: = 8cm3 for 8 cubes

Surface area: = 24 cm2 Surface area: = 6 cm2 for 1 cube

= 48 cm2 for 8 cubes

The eight small cells and the single large cells have the same total volume, but their surface areas are different. The small cells together have twice the total surface area of the large cell, because there are more exposed (inner) surfaces. Real organisms have complex shapes, but the same principles apply. The surface-area volume relationship has important implications for processes involving transport into and out of cells across membranes. For activities such as gas exchange, the surface area available for diffusion is a major factor limiting the rate at which oxygen can be supplied to tissues.

The diagrams below shows four imaginary cells of different sizes (cells do not actually grow to this size, their large size is for the sake of the exercise). They range from a small 2 cm cube to a large 5 cm cube. This exercise investigates the effect of cell size on the efficiency of diffusion.

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Now try the next question:

Question 9

Calculate the volume, surface area and the ratio of surface area to volume for each of the four cubes above (the first has been done for you). When completing the table below show your calculations.

Cube size Surface area Volume Surface area to volume ratio

2 cm cube2 x 2 x 6 = 24

cm2

(2 cm x 2 cm x 6 sides)

2 x 2 x 2 = 8 cm3

(height x width x depth) 24 to 8 = 3:1

3 cm cube

4 cm cube

5 cm cube

Courtesy Year 12 Biology Student Resource and Activity Manual 2003, Biozone

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Microscopes and Microscopy

Types of Microscopes

Since cells are so tiny, a microscope must be used to study them. There are two main types of microscopes – optical and electron. Optical microscopes are the kind usually found in homes or schools. Electron microscopes are very complex and expensive machines and are mainly used in medicine and industry.

Optical microscopes

The light or optical microscope is one of the most important instruments used in biology practicals, and its correct use is a basic and essential skill of biology. Most optical microscopes can magnify objects from about 50 up to 1000 times their real size. The most powerful ones can magnify objects up to 2000 times. You will find that optical microscopes are easy to use, especially once you know a little about them.High power light microscopes use a combination of lenses to magnify objects up to several hundred times. They are called compound microscopes because there are two or more separate lenses involved. Some microscopes have only one piece and are called monocular microscopes; some have two eyepieces and are therefore called binocular microscopes.

Some microscopes such as the one in Figure 7 below have a mirror rather than a built-in internal light source. The specimens viewed under these types of microscopes must be thin and mostly transparent. They are usually mounted onto a microscope slide and may be stained for easier observation of internal structure.

Bacteria and red blood cells can be seen in this way as they can be magnified up to 1500 times ( this can be written as:1500 x ). Light is focused up through the condenser and if the specimen is thick or opaque, little or no detail will be visible.

Did you know?

Mono: refers to one or single.Bi: refers to two (for example bicycle)Ocular: (Latin: oculus) Of or relating to the eye

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Courtesy: http://www.eduplace.com/kids/sla/6/microscope.html

What about focusing? How do you do that?

a. Turn to the lowest magnification-the lenses must click firmly into place.

b. Point a bench lamp at the mirror, direct as much as light as possible up to the eyepiece.

Did you know?

Most bacteria are so small that

you could fit 1,000 middle-sized ones on this full stop.

That is why they can only be seen

with a

FACTScientists use microscopes to test samples of river and lake water for pollution. The number and type of plants they can see, especially blue-green algae, help them to measure how polluted the water is.

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c. Put a slide on the stage. The part you wish to see must be right in the middle of the hole in the stage.

d. Looking from the side, turn the focusing knob until the stage is almost touching the objective. Make sure that it does not touch the slide.

e. Look through the eyepiece. Turn the focusing knob slowly to separate stage and objective until you have a sharp, clear picture. It is now in focus.

f. Move the slide around until you have the appropriate part of the specimen in the centre of your field of view.

g. Change to a higher magnification for a closer look.

FIELD OF VIEW

The area of the slide that you see when you look through a microscope is called the field of view. If you know how wide your field of view is, you can estimate the size of things you see in the field of view.

By carefully placing a thin metric ruler on the stage and focusing under low power, we can measure the field of view in millimetres. But when we use a microscope we should measure in micrometers or microns (µm).

A micron is one millionth of a meter.1 000 000 µm = 1000 mm = 100 cm = 1 mIt is handy to remember that 1000 µm = 1 mm

MICROSCOPIC MEASUREMENTS

Let’s look at these examples:

Example 1:

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If the diameter of the low power field is 1.6 mm = 1600 µmFor example, if it takes four cells to stretch across a field of view 1600 µm long then each cell will be approximately 400 µm long.

eyepiece X10 How can you calculate the magnification?

objective lens:X40

The magnification can be calculated by multiplying the magnification written on the eye piece (in this case x 10) by the magnification of the objective lens you are using (here it is x 40).For this microscope this is:

10 x 40 = 400 x (the x means 'times' ). So, the object you are looking at appears 400 times larger than it is in real life.

Example 2:

x 100 field of view The diagram shows the edge of a millimetre ruler viewed under the microscope with the lenses listed below. The field shown is the low power field of view.Magnification of the eye piece = 10 xLow power objective = 10 xHigh power objective = 40 x

a. What is the highest magnification you could get using this microscope? 10 x 40 = 400 x

b. What is the approximate width of the field of view in micrometers? Each white space is 1mm.We can see approximately 3 ½ white spaces. That is equivalent to 3.5mm. So, the answer is 3500 µm.

c. What would be the width of the field of view under high power?The ratio of low to high power for this microscope is 10/40 or ¼. So, under high power we will see ¼ of the low power field of view.Therefore, the width of the field of view under high power is ¼ x 3500 = 875 µm.

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d. If 5 cells fit across the high power field of view, what is the approximate size of each cell?The high power field of view = 875 µm, so the size of one cell = 875 /5 = 175 µm.

Although this looks confusing right now, don’t worry!

It will all make sense once you actually get to use a microscope in the laboratory.

Electron microscopesElectron microscopes (EMs) use a beam of electrons, instead of light, to produce an image. The higher resolution of EMs is due to the shorter wavelengths of electrons. There are two basic types of electron microscopes: scanning electron microscopes (SEM) and transmission electron microscopes (TEM).

In SEMs, the electrons are bounced off the surface of an object to produce detailed images of the external appearance or the outside surface of the specimen only. A microscope of this power can easily obtain clear pictures of organisms as small as bacteria and viruses. It can magnify specimens 100 000 times (100 000 X).

TEMs produce very clear images of specially prepared very thin sections of material. They can magnify objects several hundred thousand times (up to a million times or 1 000 000 X). Therefore, the internal structure or organelles of cells can clearly be seen using a TEM.

Figure 11 below shows an electron microscope image of a black ant. Note the 3-D image which reveals details that would be impossible to see with visible light.

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All electron microscope images are black and white, but scientists can add colour to them using a computer. This makes it easier to see the details in the picture. These pictures are called “false-colour images”.

Figure 11: Electron microscope image of a black ant. Courtesy: http://www.pbrc.hawaii.edu/bemf/microangela/qant.htm

For more interesting images go to the following websites

http://education.denniskunkel.com/ZoomIn.php

http://www.microscopy-uk.org.uk/full_menu.html then click onto: “Micro-organisms in Ponds”

Now try the next question:

Question 10

The following table shows the units of length used in Science:

Units of Length (international system)

UnitsMeters

Equivalent

1 meter (m) 1m =1000 millimeters1 millimeter (mm) 10-3m =1000 micrometers

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1 micrometer (µm) 10-6m =1000 nanometers1 nanometer (nm) 10-9m =1000picometeres

Using the information provided above, calculate the equivalent length in millimeters (mm) of the following measurements:

1. 0.25 µm: ______________

2. 450 µm: ________________

3. 200 nm: ________________

(Remember to check all of your answers at the end of the booklet).

Levels of organisation

Unicellular organisms such as bacteria are made up of only one cell ("uni" meaning one as in unicycle - a bicycle with one wheel); they must carry out all the metabolic processes necessary for life. They are complex cells capable of independent existence. In contrast, multicellular ("multi" meaning many) organisms have millions of cells that depend on each other for survival. During development of a multicellular organism, groups of cells become specialised to perform particular functions that serve the whole organism. Specialised cells have fewer functions than those found in unicellular organisms but the functions they have are very highly developed. In addition, each group of specialised cells must coordinate with other specialised cells. Let us look at the different levels of organisation that interact to ensure proper functioning of the whole organism.Tissues

When cells that are specialised in the same way aggregate to perform a common function, they are called a tissue. Different kinds of tissue serve different functions in an organism. For example, cardiac muscle is a special tissue found only in the heart. Epidermal tissue is any tissue that forms a thin layer around a structure - it may be a layer of plant cells forming the outermost layer of leaves or it may be the outer layer of human skin, the epidermis.

OrgansIn multicellular organisms, groups of different tissues often work together to ensure a particular function is successfully performed. A collection of such tissues is called an

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organ. Your heart, lungs, kidneys, brain and stomach are all different organs. Tissues of the stomach include epithelium, smooth muscle and blood. In plants, organs are the root, stem, flower and leaf. Tissues of a leaf include the epithelium and vascular tissue.

Organ systems

Your digestive system comprises various organs that work together to ensure that the food you eat is digested and that the nutrients it contains are absorbed and transported to all cells of your body. This organisation is called an organ system. Your digestive system commences with your mouth and includes organs such as your teeth, oesophagus, stomach, intestines and liver. Once digested food has been absorbed by cells lining the intestine, it is transported by the blood circulatory system throughout your body. This system links with the respiratory system where it picks up oxygen, also for delivery. As blood delivers nutrients and oxygen to all tissues, it collects wastes for delivery to the excretory systems of the body.Because plants do not move from place to place, their energy needs are far less than mobile animals. Hence, plants do not have the equivalent of complex organ systems that animals have. Green plants produce their own food through the process known as photosynthesis and this process also delivers oxygen directly to some cells. Other cells rely on diffusion to get their oxygen. The extensive root system of a plant ensures that it absorbs sufficient water for survival. An extensive vascular system then delivers that water to all parts of the plant.REVISION BOOKLET - ANSWER SHEET

Question 1

(a) Why were cells unknown until the 17th century?The microscope was not invented until the 17 th century, enabling people to see cells for the first time.

(b) Biologists often cut several sections of a cell to find out about its structure.Give two reasons why having several sections from different areas of the same cell is important.

Observing several sections of a cell ensures that all structures within a cell are seen and it enables one to find out about the three-dimensional structure of a cell. Looking at only one section only enables us to look at a single thin layer through the cell.

Question 2

(a) Identify 3 features that ALL cells have in common.All cells contain DNA, all cells have a plasma membrane and all cells have a cytoplasm.

(b) State 3 differences between a plant cell and an animal cell.An animal cell has centrioles and small vacuoles. Plant cells have chloroplasts, a cellulose cell wall and large vacuoles.

(c) State 3 ways in which they are similar.

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Both plant and animal cells have a cell membrane, nucleus and cytoplasm.(d) Name a structure which is unique to plant cells.

Chloroplasts are unique to plant cells.

Question 3

Animal Plant Fungi BacteriaDistinct nucleus X

Mitochondria XSize <10m X X X Chloroplast X X X

Cell wall X

Eukaryotic cells must possess: a distinct nucleus, membrane bound organelles (such as chloroplast or Golgi bodies) and mitochondria and have a size > 10 m. This is not the case for prokaryotes. Bacteria are prokaryotes, while plants, animals and fungi are eukaryotes.

Question 4

Structure Function

A Endoplasmic reticulum Processes and transports proteins. Contains enzymes important for metabolism.

B Ribosomes Site of protein production

C Golgi Apparatus Packages and distributes material for transport out of the cell

D Nucleus Contains the DNA, genetic material of the cell.

E Mitochondria Major site of ATP production

F Lysosome Contains fluid mixture of digestive enzymes

Question 5

(a) List two functions of membranes in cells.

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Any of the following: To compartmentalise regions of different function within the cell. For controlling the entry and exit of substances. Fulfilling a role in recognition and communication between cells.

(b) What is meant by the label partially permeable in reference to the plasma membrane?

A partially permeable membrane only allows some dissolved substances to pass through in either direction, into or out of the cell, but not others. It is therefore selective.

(c) Why do volatile anesthetics such as chloroform and ether work quickly? In order words what properties could they have which would enable them to easily cross over cell membranes?

Chloroform and ether are lipid soluble organic substances and therefore easily dissolve into the phospholipid bilayer of a cell membrane.

(d) Why is alcohol absorbed more quickly from the gut than food?Alcohol is organic substance, which is soluble in oil and therefore penetrates

rapidly through the membrane as oils also move through the phospholipid bilayer with ease.

Question 6

(a) What difference would you expect between the weights of the eggs placed in distilled water and that placed in the 0.5 M sucrose? Explain.

The egg placed in distilled water gained more weight than that place in the 0.5 sucrose solutions. This is because when the egg is placed in distilled water, the water concentration on the outside is much higher than in the inside, causing the water to diffuse into the cell, resulting in a gain in weight.

The concentration of the water in the 0.5M sucrose is not as concentrated as the distilled water. Therefore the amount of diffusion is not as great, resulting in less weight gain.

(b) Under what conditions would an egg show neither an increase nor a decrease in weight?

The egg will have water in it but will also have some ions in it. So the water is less concentrated (fewer water molecules) than in the distilled water. When the external water concentration is the same as that of the egg, there is no net movement of water. So an egg would show neither an increase nor a decrease in weight.

Question 7

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Question 8

Substance Mechanism of Movement

Main part of membrane involved

Is Respiratory Energy required?

Carbon dioxide Diffusion Phospholipid bilayer

No

Water Osmosis Phospholipid bilayer

No

Glucose Facilitateddiffusion

Protein No

alcohol Diffusion Phospholipid bilayer

No

Question 9

Cube size Surface area Volume Surface area to

volume ratio

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2 cm cube

2 x 2 x 6 = 24 cm2

(2 cm x 2 cm x 6 sides)2 x 2 x 2 = 8 cm3

(height x width x depth)24 to 8 = 3:1

3 cm cube 3 x 3 x 6 = 54 cm² 3 x 3 x 3 = 27 cm³ 54 to 27 = 2:1

4 cm cube 4 x 4 x 6 = 96 cm² 4 x 4 x 4 = 64 cm³ 96 to 64 = 3:2

5 cm cube 5 x 5 x 6 = 150 cm² 5 x 5 x 5 = 125 cm³ 150 to 125 = 6:5

Question 10

Units of Length (international system)

UnitsMeters

Equivalent

1 meter (m) 1m =1000 millimeters1 millimeter (mm) 10-3m =1000 micrometers1 micrometer (µm) 10-6m =1000 nanometers1 nanometer (nm) 10-9m =1000picometeres

Using the information provided above, calculate the equivalent length in millimeters (mm) of the following measurements:

1. 0.25 µm = 0.00025 mm ( to convert µm to mm, you have to divide by 1,000

because there are 1,000 µm in one mm.)

2. 450 µm = 0.450 mm ( again, divide by 1,000)

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3. 200 nm = 0.000200 mm (to convert nm to mm, you have to divide by

1, 000, 000, because there are 1, 000, 000 µm in one mm.)

We hope that this revision booklet has been useful and will help to prepare you for VCE Biology. We are looking forward to teaching you Unit 3 Biology at DECV.

BIBLIOGRAPHY

Allan, R., Year 11 Biozone Student Resource and Activity Manual, Biozone International Ltd., 2002.

Allan, R., Year 11 Biozone Student Resource and Activity Manual, Biozone International Ltd., 2005.

Cells, the Units of Life, ASEP, Victoria, 1974

Heinemann Biology Two, 4th edition, Harcourt Education, 2005 Kinnear, J and Martin, M, Nature of Biology Book 1, Jacaranda Publishing, 2005

Rogers, Kirsteen. The Usborne Internet-Linked Complete Book of the Microscope. London : Usborne Publishing Ltd., 2001.

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Semple, A et al, Nelson Biology 2nd edition, 2005