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Gill Sans Bold Biology Preliminary Course Stage 6 Patterns in nature 0 20 In BIOPRE 43209 2 r e to b T S c O EN g in D M t a r EN o p r co A M P0025942 Number: 43209 Title: Patterns in nature This publication is copyright New South Wales Department of Education and Training (DET), however it may contain material from other sources which is not owned by DET. We would like to acknowledge the following people and organisations whose material has been used: Photographs courtesy of the Australian Key Centre for Microscopy and Microanalysis, University of Sydney Part 1 pp 8, 18, Part 4 pp 5, 6, 9, 11 Photographs courtesy of Jane West Part 1 pp14-16, Part 5 p 9, Part 8 pp 9, 10 Diagram of a cross-section of a leaf, Messel, H (Chair) (1963) Science for high school students. University of Sydney Part 5 p 12 COMMONWEALTH OF AUSTRALIA Copyright Regulations 1969 WARNING This material has been reproduced and communicated to you on behalf of the New South Wales Department of Education and Training (Centre for Learning Innovation) pursuant to Part VB of the Copyright Act 1968 (the Act). The material in this communication may be subject to copyright under the Act. Any further reproduction or communication of this material by you may be the subject of copyright protection under the Act. All reasonable efforts have been made to obtain copyright permissions. All claims will be settled in good faith. Published by Centre for Learning Innovation (CLI) 51 Wentworth Rd Strathfield NSW 2135 _______________________________________________________________________________________________ _ Copyright of this material is reserved to the Crown in the right of the State of New South Wales. Reproduction or transmittal in whole, or in part, other than in accordance with provisions of the Copyright Act, is prohibited without the written authority of the Centre for Learning Innovation (CLI). © State of New South Wales, Department of Education and Training 2008. Contents Module overview Outcomes ............................................................................................ iv Indicative time...................................................................................... iv Resources............................................................................................ iv Icons ................................................................................................... vii Glossary............................................................................................. viii Part 1: Chemicals in cells ...................................................1–17 Part 2: Osmosis and diffusion .............................................1–23 Part 3: Cell theory and the light microscope........................1–26 Part 4: Electron microscopes and cell organelles ...............1–25 Part 5: Obtaining and transporting materials in plants ........1–40 Part 6: Obtaining materials in animals ................................1–15 Part 7: Transporting materials in animals ...........................1–21 Part 8: Growth and repair....................................................1–18 Student evaluation of the module Introduction i ii Patterns in nature Module overview Living things use raw materials in different ways to construct new living tissues and repair existing tissues. All living organisms carry out similar processes to form the structures that make up their bodies. To carry out these processes, raw materials need to be obtained. The types of raw materials and the way in which these raw materials are obtained differ between living organisms. There are more similarities than differences in the overall processes involved, the elements used and the molecules made. Intake of the materials required by all living organisms and the removal of waste products are influenced by the surface areas of membranes through which these nutrients and waste products must pass. In large multicellular forms, complex organ systems with large surface area to volume ratios, have evolved to allow movement of material across the membranes. These organs are concerned with specialised functions in the bodies of large multicellular organisms. In this module you will be learning about the structure and function of cells in plants and animals. In order to make the most of this information the following assumed knowledge is required. Introduction • Diffusion involves random movement of particles. • Systems in multicellular organisms serve the needs of cells. • Systems in multicellular organisms supply the needs of cells. • Word equations can be used to describe a range of reactions. • The role of cell division in growth, repair and reproduction in multicellular organisms. • Information is transferred as DNA on chromosomes when cells reproduce. • Genes consist of DNA. iii Outcomes This module increases students’ understanding of the history, nature and practice of biology and current issues, research and developments in biology. Indicative time This module is designed to take forty indicative hours. The module is divided into eight parts, each approximately five hours of work. Resources The following materials will be required for each part. You may wish to read through the list and plan ahead to ensure you have what you need when you get to each activity. Alternative activities are given. For Part 1 you will need: • Tes-tape® (can be purchased at the chemist) • iodine (use antiseptic preparation such as Betadine® from the chemist) • brown paper, such as the kind used for baking or as lunch bags For Part 2 you will need: iv • a packet of jelly crystals or • potassium permanganate • two 12 cm lengths of dialysis tubing. Dialysis tubing is selectively permeable. You could substitute cellophane wrapping paper. • glucose powder, a sugar • two small glass jars of the same size and shape • 4 pieces of strong cotton or thread • some fine plastic (cling wrap) for covering jars • a piece of Tes-tape® about 5 cm long, cut into three equal lengths • a spoon or spatula for stirring or mixing Patterns in nature • waterproof pen. • calcium hydroxide (about 1/4 tsp) • phenolphthalein (about 1/4 tsp) • powdered gelatine or yellow jelly crystals. Do not use any other coloured jelly crystals. • a jug or measuring cylinder for measuring 150 mL of boiling water. • a small mixing bowl or 250 mL beaker. The bowl should have straight sides. • some vinegar. Vinegar is an acidic solution containing acetic acid. • a refrigerator to set your jelly. For Part 3 you will need: • microscope lamp (if the microscope does not have one built into the unit) • clean glass slides and coverslips • dropper • onion, moss or very soft fleshy plant stem • meat blood (obtained by collecting the liquid remaining after frozen goods are defrosted) • iodine (or an antiseptic preparation containing iodine such as Betadine®) • blade or small vegetable knife • cutting board. Alternative exercises are provided if you do not have access to a microscope. For Part 5 you will need: • 1 large beaker or saucepan • 1 small beaker or glass jar • Bunsen burner or hot plate • tripod and gauze (if using Bunsen) • 250 mL water • 50 mL methylated spirit • a few soft fleshy leaves such as a geranium • aluminium foil • a variegated leaf plant Introduction v • iodine solution • stick of celery • glass of water with food colouring (red/blue works best) • knife, small kitchen type • hand lens or microscope with lamp • glass slides and cover slips if using microscope • thin glass tubing or clear plastic tubing • Vaseline® or petroleum jelly • soft, fleshy plant stem eg. Impatiens • marker pen or sheet of graph paper • scissors • retort and clamp or similar For Part 6 you will need: • mortar and pestle or a suitable grinding tool and vessel • petri dish or small plate • Bunsen burner or hotplate • 3 test tubes or similar • sand • small quantity of liver from a butcher • hydrogen peroxide (this can be purchased at a pharmacist) For Part 8 you will need: • microscope and lamp • two slides and a cover slip • onion with fresh roots (you need to soak onion base in water at least a week in advance) • methyl green pryonin or aceto-orcein stain. Alternatively use prepared slides of a root tip (if available). If you do not have access to a microscope or prepared slide, use the photographs provided. vi Patterns in nature Preparing resources Some activities have alternative suggestions. You may wish to skim through the parts to decide which activities you will be doing. Where preparation is required, the instructions have been included in the activity outline. Icons The following icons are used within this module. The meaning of each icon is written beside it. The hand icon means there is an activity for you to do. It may be an experiment or you may make something. You need to use a computer for this activity. Discuss ideas with someone else. You could speak with family or friends or anyone else who is available. Perhaps you could telephone someone? There is a safety issue that you need to consider. There are suggested answers for the following questions at the end of the part. There is an exercise at the end of the part for you to complete. Introduction vii Glossary The following words, listed here with their meanings, are found in the learning material in this module. They appear bolded the first time they occur in the learning material. viii alimentary canal tube through which food passes between the mouth and anus amino acid nitrogen containing basic building block molecule of proteins antibodies a type of protein that reacts in with a specific antigen, part of the body defence mechanism aqueous used to describe substances that contain water biconcave concave shape on either side of a lens bond something that combines or holds things together Brownian motion describes a pattern of random movement of particles in liquids or gases cloaca the terminal part of the gut in most vertebrates except the higher mammals compound a pure substance composed of two or more elements desiccation the drying out or removal of moisture disaccharide a molecule with double units of sugar distended enlarged, stretched or swollen enzyme a highly specialised cellular protein that reduces the amount of energy required to initiate a chemical reaction, thereby increasing the speed of reaction flaccid limp guard cells pair of specialised cells in a plant epidermis forming a pore or stomate haemoglobin a protein molecule found in red blood cells that transport oxygen histologist a person who studies detailed or microscopic tissue structure hypertonic higher solute concentration than another fluid hypotonic lower solute concentration than another fluid Patterns in nature Introduction ion an atom that carries a charge due to loss or gain of electrons isotonic similar solute concentration as another fluid lenticel pore found on stems and roots in higher plants for gas exchange lignin thickening substance found in cell walls of plants lymph glands organs in the body that produce lymph or interstitial fluid which is clear and assists in the bodies defence system magnification to increase the size of something mangroves vegetation found in estuarine areas metabolism describes the chemical reactions occurring within an organism monosaccharide a molecule with single unit of sugar multicellular organisms composed of more than one cell nectar a sugars secretion of a plant that attracts birds and insects organelle any part of a cell that has a specific functional role organism any living plant or animal orifice a tube like opening oxidation reaction a chemical reaction in which the proportion of oxygen in the molecule is increased plasma membrane also called cell membrane, the outer boundary of a cell polysaccharides a molecule with multiple units of sugar precipitate a solid formed from the reaction of two liquid substances prion an infectious particle composed of protein, containing no genetic material radioisotope natural or artificial isotope exhibiting radioactivity, used as a source for medical or industrial purposes resolution the ability of optical instruments to produce separate images of close objects respiration the process by which carbohydrates and oxygen are combined to release energy, carbon dioxide and water ix x saturated maximum uptake of a substance has been achieved secrete to produce and pass through a membrane out of a cell stomata a pore through which gas exchange takes place, usually located on a leaf translucent diffuse transmission of light through a surface that is not smooth tripe lining of a ruminant stomach turgid describes the swollen or distended state of a cell unicellular describes organisms composed of only one cell vesicles a small sac like structure villi finger like growth on the inside wall or lining of the small intestine virus disease causing microscopic organism composed of nucleic acid surrounded by a protein coat, dependent on the metabolic and reproductive processes of the cell they invade viscosity the tendency of a material to resist movement through it Patterns in nature Gill Sans Bold Biology Preliminary Course Stage 6 Patterns in nature Part 1: Chemicals in cells 2 0 0 In r2 e b S o t c NT O ng DM E i t ra E N o rp A M o c Gill Sans Bold Contents Introduction ............................................................................... 2 Chemicals in cells...................................................................... 4 Organic compounds in cells.................................................................5 Inorganic compounds in cells ............................................................10 Testing for chemicals in cells.............................................................11 Suggested answers................................................................. 13 Exercises – Part 1 ................................................................... 15 Part 1: Chemicals in cells 1 Introduction In this part you are going to investigate the major groups of chemicals found in cells and carry out some simple tests for these chemicals. In this part you will be given opportunities to learn to: • identify the major groups of substances found in living cells and their uses in cell activities In this part you will be given opportunities to: • plan, choose equipment or resources and perform a first–hand investigation to gather information and use available evidence to identify the following substances in tissues: – glucose – starch – lipids – proteins – chloride ions – lignin Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. The most up-to-date version can be found on the Board's website at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html This version November 2002. 2 Patterns in nature Gill Sans Bold There are some practical experiments to do in this part of the module. Alternative exercises are given wherever possible. To do all of the practical exercises you will need the following items. • Tes–tape® • iodine • brown paper Part 1: Chemicals in cells 3 Chemicals in cells Chemical compounds are substances consisting of two or more elements chemically combined in a definite proportion. Water is a compound composed of the elements hydrogen and oxygen. Sucrose (a type of sugar) is a compound composed of the elements carbon, hydrogen and oxygen. Chemical compounds can be divided into two groups, inorganic and organic compounds. Organic compounds have a structure based on carbon atoms which are often linked to form carbon chains. Examples of organic compounds include carbohydrates, lipids, proteins and nucleic acids. Inorganic compounds may or may not contain carbon. They may be found in living and non–living things. Examples of inorganic compounds are water, carbon dioxide and salts eg. sodium chloride (common salt) and calcium phosphate (found in bone). The most abundant inorganic compound in our body is water (H2O); about 70% of our body is water. Many chemicals dissolve in water to form ions. Ions are charged particles. For example, sodium chloride, found in our blood and body fluids exists as sodium ions (Na+) and chloride ions (Cl–). 1 What is the difference between an organic and an inorganic substance? _____________________________________________________ _____________________________________________________ _____________________________________________________ 4 Patterns in nature Gill Sans Bold 2 Complete the table below by listing the organic and inorganic substances mentioned in the previous information. Organic substances Inorganic substances Check your answers. Membranes around cells provide separation from and links to the external environment. Organic compounds in cells Now you have some background information you will focus on the main organic compounds that are found in cells–carbohydrates, lipids, proteins, nucleic acids, lignin and vitamins. Carbohydrates Carbohydrates are organic compounds commonly found in food as starches and sugars. 1 Make a prediction about which elements are present in carbohydrates. _____________________________________________________ 2 You may have heard the word carbohydrate used in association with diets and training in the media. Name some common foods that contain carbohydrates. _____________________________________________________ _____________________________________________________ Check your answers. Part 1: Chemicals in cells 5 Carbohydrates are organic compounds. Therefore they contain carbon. This is indicated by the carbo part of carbohydrate. The hydr part indicates hydrogen while the ending ate indicates oxygen. Carbohydrates are important sources of energy in cells. Carbohydrates are broken down into glucose during the process of digestion. Glucose is required by all cells for the process of respiration which provides energy. If we eat more carbohydrate than the body needs, the excess is stored as fat. It may be stored under the skin or around the internal organs. There are three groups of carbohydrates: • monosaccharides • disaccharides • polysaccharides. Monosaccharides (mono–sack–ah–rides) are the simplest carbohydrates. They are single sugar units such as glucose. Glucose is found in all cells. It is the main source of energy. Other monosaccharides are fructose (fruit sugar) and ribose a sugar in nucleic acids (acids such as RNA). Disaccharides (di–sack–ah–rides) are double units of sugars. An example is sucrose or table sugar which comes from sugar cane and sugar beet. Sucrose is made when a glucose molecule and a fructose molecule are bonded together. A molecule of water is lost in this reaction. Polysaccharides are complex carbohydrates consisting of multiple sugar units which form huge molecules. Examples are starch and cellulose. cellulose starch Cellulose and starch molecules. One starch molecule consists of two to three thousand glucose molecules joined together. Cellulose is the main component of plant cell walls. It consists of more than two thousand glucose molecules joined together. The previous illustrations show small sections of a cellulose and starch molecule. Both are insoluble in water. 6 Patterns in nature Gill Sans Bold Testing for carbohydrates Sugars (reducing type that contain certain disaccharides and monosaccharides) can be identified by using Benedict’s solution. Benedict’s solution is blue–green in colour. The solution changes to an orange–red when heated in the presence of sugars such as glucose. Glucose can also be tested for by using Tes–tape®. The paper tape changes from a yellow to a green colour in the presence of glucose. Starches can be tested for using iodine solution, which turns a dark blue–black colour in the presence of starch. Cellulose can be tested for by adding iodine solution then concentrated (70%) sulfuric acid. When iodine is placed on cellulose it remains brown. After a few drops of acid are added, the iodine changes colour to purple or black if cellulose is present. Lipids Lipids include fats, oils, waxes and steroids. Lipids are found in both plant and animal cells. Excess lipids are stored in the body as fat in animals. Lipids are used to store energy. This fat store also provides protection around vital organs. Some large mammals such as whales, seals and polar bears use fat to insulate them from extreme temperatures. Lipids, like carbohydrates, contain the elements carbon, hydrogen and oxygen. However, the hydrogen and oxygen are not in a 2:1 ratio. Simple fats consist of three fatty acids combined with one glycerol molecule. Two types of lipids exist, those that have single bonds between the carbon atoms. These are most often the animal fats such as lard and butter. They are called the saturated lipids. Unsaturated lipids have some carbon atoms that have two bonds. These are the vegetable oils which are liquid at room temperature. You may have heard these terms used when referring to margarine products. Lipids can be tested for with a piece of thin brown paper such as that used as a lunch bag. If fat is present a translucent stain or smear appears on the paper. Name some examples of lipids used in the home. _________________________________________________________ Check your answers. Part 1: Chemicals in cells 7 Proteins Proteins are another important group of organic compounds. Proteins are used for growth and development and form part of many important substances in the body such as enzymes and antibodies. There are about 2000 different proteins in any human cell. Proteins contain the elements carbon, hydrogen, oxygen and nitrogen. Sometimes they contain sulfur and phosphorus. Proteins, like polysaccharides, are large molecules built from the linking of many smaller molecules. The small molecules in this case are amino acids. The bonds between the amino acids are peptide bonds. There are commonly 20 different amino acids and they can join in any order. The order determines the type of protein formed. 1 List some food which are high in protein. _____________________________________________________ _____________________________________________________ 2 Why are proteins important in our diet? ______________________________________________________ ______________________________________________________ Check your answers. Testing for proteins The Biuret test is used to test for the presence of protein. To carry out the test a few drops of sodium hydroxide are combined with dilute copper sulfate and heated in a water bath. If protein is present a purple colour is produced. Nucleic acids Nucleic acids are commonly found in the chromosomes of the nucleus of a living cell. Two nucleic acids are commonly found in the nucleus. These nucleic acids are deoxyribose nucleic acid (DNA) and ribose nucleic acid (RNA). DNA is formed from building blocks called nucleotides (new–klee–oh–tides). Each nucleotide itself is formed from three parts, sugar, phosphate unit and a base. The sugar is called deoxyribose sugar. It is ribose sugar with one less atom of oxygen. 8 Patterns in nature Gill Sans Bold The bases are adenine (add–en–een), guanine (gwar–nene), thymine (thigh–meen) and cytosine (site–oh–seen). A T C G C G sugar nitrogen base T A C G phosphate unit T A A Nucleotide unit. T C G Nucleotide units combine to form part of a DNA molecule. A T C The structure of this molecule is like a ladder. The sides are formed from the sugar and phosphate groups. The rungs are formed from the bases. The bases bond in such a way that adenine pairs with thymine (A–T), and cytosine pairs with guanine (C–G). The order of the these pairs is the genetic code for an organism. G G A C C T G DNA double helix. Testing for nucleic acids The presence of nucleic acids is indicated by using aceto–orcein. When a few drops are added to nucleic acid a blue green colour is produced. Lignin Lignin forms much of the wood in trees. It enables cells to become rigid and provide support and protection. The presence of lignin can be tested by the addition of a solution of toluidine blue on fresh plant material. Lignin will stain green–blue while unlignified parts will be pink–purple. Part 1: Chemicals in cells 9 Vitamins Vitamins are organic compounds needed in very small quantities for normal growth and health of organisms. Their main functions are in the enzyme systems in the body, without them, enzymes would not function. Most vitamins are obtained directly from food although some are formed in the body. For example, carotene (the yellow–orange pigment in carrots and other yellow or orange vegetables and fruits) is changed into vitamin A in the body. As well, a substance in our skin is changed to vitamin D when our skin is exposed to sunlight. Complete Exercise 1.1. Inorganic compounds in cells By far the most abundant substance in our bodies is water (between 60% and 70%). Expressed another way, a typical 70 kg person would have 42 L of water in the body. While people can survive several weeks without food, they can last only a few days without water. Plants also contain large amounts of water. What happens to a pot plant if it is not watered regularly? Other inorganic substances found in cells are mineral salts. These are simple chemical compounds that exist as ions when dissolved in water. For example, common table salt (sodium chloride) NaCl, becomes Na+ and Cl– ions when dissolved in water. Mineral ions are essential for many body processes, the amount of each type varying over the lifespan of the organism. Other mineral ions required by the body are listed below. 10 • Calcium essential for bone development and blood clotting. • Iron which is used for the formation of haemoglobin in red blood cells. • Chlorine required for water balance as well as acid–base balance in the blood and formation of hydrochloric acid (HCl) in the stomach. Chlorine is present as chloride ions (Cl-). The presence of chloride ions can be detected by using silver nitrate solution. A white precipitate results when chloride ions are present. • Sodium is required for water balance and is essential for the nervous system. Sodium is present as ions (Na+). Patterns in nature Gill Sans Bold • Potassium is involved in muscle contraction which is essential for movement. It is present as ions (K+). The ratio of sodium and potassium ions controls the nervous system. • Phosphorus is an important component of the chemicals involved in energy transformations around the body. Testing for chemicals in cells The substances you need to know tests for are glucose, starch, lipids, proteins, chloride ions and lignin. Read the information in this section again to identify the tests used to detect the presence of the substances listed here. Complete the table below. Chemical compound Test Indication glucose starches chloride ions protein lipids lignin Check your answers. In this activity you will be carrying out some tests on substances found in tissues. To do this experiment you will need to obtain the following materials. • Tes–tape® (this can be obtained at a pharmacy) • Iodine (this can be substituted by using a preparation such as Betadine®, from a pharmacy) • Brown paper (use a brown paper lunch bag) Part 1: Chemicals in cells 11 Testing for glucose Glucose is a chemical widely distributed in cells. Glucose is the organic compound usually involved in respiration. It is the compound from which we obtain energy. All cells need energy, so we would expect to find glucose in cells. The test for glucose is simple with Tes–tape®. All you have to do is to press the yellow paper tape, Tes–tape®, against the cells or tissue being tested. If you want to test some potato for glucose, cut a fresh section and press the Tes–tape® against it. Leave the paper for several minutes and note any colour change. If testing a liquid produced by cells, such as milk, dip the Tes–tape® in the liquid, then remove it. Wait for a few minutes to see if there is a colour change. A colour change from yellow to green indicates glucose. Test any three tissues for glucose. Any skin on plant foods needs to be removed. Record your test on a sheet of paper. Suggested tissues are potato, celery and any fruit. Complete Exercise 1.2. Testing for starch Starch is a polysaccharide carbohydrate. It is the form in which plants store excess sugar (in animals, excess sugar is usually stored as fat). To test plant cells or tissue for starch, you add a few drops of iodine to a freshly cut section. A colour change from yellow–brown to blue–black, indicates that starch is present. Remember that iodine is a chemical used to stain cells so that their organelles can be more easily seen. Test any three tissues for starch eg. seeds (such as rice), banana, potato. Complete Exercise 1.3. Testing for lipids Lipids can be found in common foodstuff such as butter or oil. To carry out the test, you will need to get a brown paper bag (lunch bag) and rub the test sample on the paper and look for the translucent smear or stain. Try rubbing butter, margarine or oil onto a brown paper bag. Complete Exercise 1.4. To finish this part visit the LMP science online site for links to view animations of food tests. www.lmpc.edu.au/science 12 Patterns in nature Gill Sans Bold Suggested answers Types of chemical compounds 1 Organic compounds all contain carbon. Many are found in living things. Inorganic compounds don’t necessarily contain carbon and are found in both living and non–living things. 2 Organic substances Inorganic substances carbohydrates water lipids carbon dioxide proteins sodium chloride nucleic acids calcium phosphate Carbohydrates 1 Carbohydrates contain the elements carbon, hydrogen and oxygen. 2 Examples of foods high in carbohydrates include cereals, bread, pasta, potato and rice. Lipids Lipids in the home include lard, dripping, oil, cream, butter and margarine products. Foods such as nuts and grains are high in lipids. Proteins 1 Food high in proteins include: peanuts, meat, fish, cheese, eggs. 2 Proteins are used for growth and repair in the body. Part 1: Chemicals in cells 13 Testing for chemicals in cells 14 Chemical compound Test Indication glucose Testape® paper tape changes from yellow to green on drying starches iodine solution yellow solution changes to purple or black chloride ions add a few drops of silver nitrate solution a grey/white precipitate results if chloride ions are present protein Biuret test. Add a few drops of sodium hydroxide solution then dilute copper sulfate a purple colour is produced lipids rub sample with brown paper a translucent stain on paper is produced lignin toluidine blue green–blue colour Patterns in nature Gill Sans Bold Exercises - Part 1 Exercises 1.1 to 1.4 Name: _________________________________ Exercise 1.1: Chemicals in cells a) Identify the major groups of substances found in living cells. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ b) Fill in the table below showing the uses in cell activity of the substances listed. Substance Uses in cell activity Carbohydrates Lipids Proteins Nucleic acids Lignin Vitamins Part 1: Chemicals in cells 15 Exercise 1.2: Testing for glucose a) Name the tissues you tested for glucose. ______________________________________________________ ______________________________________________________ b) Explain what you did and describe the results. ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ c) What are your conclusions? ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ Exercise 1.3: Testing for starch a) Record your observations of iodine on food products. ______________________________________________________ ______________________________________________________ b) Explain what you did and describe the results. ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ c) What are your conclusions? ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ 16 Patterns in nature Gill Sans Bold Exercise 1.4: Testing for lipids a) Name the foods you tested for lipids. _____________________________________________________ _____________________________________________________ b) Explain what you did and describe the results. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ c) What are your conclusions? _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 1: Chemicals in cells 17 Gill Sans Bold Biology Preliminary Course Stage 6 Patterns in nature Part 2: Osmosis and diffusion 2 0 0 In r2 e b S o t c NT O ng DM E i t ra E N o rp A M o c Gill Sans Bold Contents Introduction ............................................................................... 2 Membrane structure .................................................................. 4 Movement across a membrane................................................. 5 Investigating diffusion...........................................................................6 Investigating osmosis...........................................................................7 Active transport ..................................................................................11 Why are cells so small?........................................................... 13 Surface area to volume ratio..............................................................14 Suggested answers................................................................. 19 Exercise–Part 2 ....................................................................... 21 Part 2: Osmosis and diffusion 1 Introduction In this part you are going to investigate the role of membranes in cells and how they separate the internal chemicals of the cell and also act as a link to the outside environment. In this part you will be given opportunities to learn to: • identify that there is movement of molecules into and out of cells • describe the current model of membrane structure and explain how it accounts for the movement of some substances into and out of cells • compare the processes of diffusion and osmosis • explain how the surface area to volume ratio affects the rate of movement of substances into and out of cells. In this part you will be given opportunities to: • perform a first–hand investigation to model the selectively permeable nature of a cell membrane • perform a first–hand investigation, to demonstrate the difference between osmosis and diffusion • perform a first–hand investigation to demonstrate the effect of surface area to volume ratio on rate of diffusion. Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. The most up-to-date version can be found on the Board's website at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html This version November 2002. 2 Patterns in nature Gill Sans Bold There are some practical experiments to do in this part of the module. Alternative exercises are given wherever possible. To do all of the practical exercises you will need the following items. • a packet of jelly crystals or • potassium permanganate • two 12 cm lengths of dialysis tubing. Dialysis tubing is selectively permeable. You could substitute cellophane wrapping paper. • glucose powder, a sugar • two small glass jars of the same size and shape • 4 pieces of strong cotton or thread • some fine plastic (cling wrap) for covering jars • a piece of Tes–tape® about 5 cm long, cut into three equal lengths • a spoon or spatula for stirring or mixing • waterproof pen. Part 2: Osmosis and diffusion • calcium hydroxide (about 1/4 tsp) • phenolphthalein (about 1/4 tsp) • powdered gelatine or yellow jelly crystals. Do not use any other coloured jelly crystals. • a jug or measuring cylinder for measuring 150 mL of boiling water. • a small mixing bowl or 250 mL beaker. The bowl should have straight sides. • some vinegar. Vinegar is an acidic solution containing acetic acid. • a refrigerator to set your jelly. 3 Membrane structure Cells are bound by a plasma membrane. Although not visible even under the strongest light microscope, its existence has been verified in the last three decades. The cell membrane separates the contents of the cell from its surroundings providing a barrier to its external environment. Water, gases, ions and other small molecules are able to move through the membrane, while other substances are not. This ability to allow some substances through and not others means that the membrane is selectively permeable (also known as semipermeable or differentially permeable). The current model of plasma membrane structure was proposed by Singer and Nicholson in 1972. They described it as a ‘fluid mosaic model’ in which a double layer of lipid molecules has proteins and glycoproteins embedded within it. The layers have tiny pores or openings that allow the movement of materials in and out of the cells. protein double lipid layer glycoprotein molecule cholesterol Fluid mosaic model of the structure of a plasma membrane. 4 Patterns in nature Gill Sans Bold Movement across a membrane All matter consists of atoms, ions and molecules. In liquids and gases these molecules are not fixed in position–they are moving at random. Substances move in and out of cells in solution, this means that the substance is dissolved in a liquid (usually water). The cell membrane allows some substances to pass across it but not others depending on the size of the particles or molecules. Molecules that can move across such a selectively permeable membrane include glucose, oxygen and carbon dioxide. Starch and protein are too large. The kinetic theory of matter provided some qualitative explanations for the motion of particles in solution toward the end of the 19th century. This described particles in the various states of matter in a constant state of motion depending on the temperature of the matter. The higher the temperature, the faster the motion. solid liquid gas Particles in solids, liquids and gases are in a constant state of motion. This movement of particles results in collisions. Each collision changing the particle’s velocity by a small amount, resulting in a random motion of the particles. 1 What happens to the motion of the particles in a solid if it is heated? _____________________________________________________ Part 2: Osmosis and diffusion 5 2 If a gas is cooled, describe the effect that this would have on the motion of its particles. ______________________________________________________ 3 Can you predict the effect a temperature change might have on the diffusion of particles within a liquid in a cell? ______________________________________________________ Check your answers. Investigating diffusion Diffusion is the random movement of particles from regions where they are in a high concentration to regions of lower concentration. This produces a uniform distribution. You have experienced diffusion when a bottle of perfume is opened in one part of a room. After a while, you can smell it across the room. The perfume, as a gas, has diffused across the room. After a while the smell of the perfume is all over the room. Diffusion is important in living things as it allows organisms to take in materials that they need and lose waste material. This process is a passive process as it requires no energy from an organism. It occurs because of the random movement of particles. Materials required: • two glass jars • two crystals of potassium permanganate or one packet of coloured jelly crystals • one cup of cold water • one cup of hot water Method 6 1 Pour a cup of cold water into a glass jar. 2 Drop one crystal of either potassium permanganate or jelly into the water. 3 Observe the crystal as it sinks to the bottom of the jar and then continue to watch for two to three minutes. Answer the questions below. Then repeat the procedure, using hot water. Patterns in nature Gill Sans Bold a) What happens to the crystal as it drops to the bottom of the jar? _________________________________________________ b) Explain using your knowledge of particle movement during diffusion, what is occurring as the crystal remains in the water for 2–3 minutes. _________________________________________________ _________________________________________________ _________________________________________________ c) What was the most significant difference in your observations when the procedure was repeated using hot water? _________________________________________________ _________________________________________________ Investigating osmosis Osmosis is a special case of particle movement as it describes the movement of water across a selectively permeable membrane from an area where there is more water (less concentrated or dilute) to an area that has less water solution (more concentrated) to achieve a uniform distribution. selectively permeable membrane solute less concentrated (more water) solute more concentrated (less water) net movement of water molecules water solute Osmosis occurs when water moves across a selectively permeable membrane from a region where the solute is less concentrated to a region where the solute is more concentrated. Part 2: Osmosis and diffusion 7 same concentration Osmosis results in solutions of the same concentration either side of a selectively permeable membrane. Aim: To investigate the process of osmosis. Material needed: • glucose powder (a sugar) • two 12 cm lengths of dialysis tubing. Dialysis tubing is selectively permeable. You could substitute cellophane wrapping paper. • two small glass jars of the same size and shape • 4 pieces of strong cotton or thread • some fine plastic (cling wrap) for covering jars • a piece of Tes–tape® about 5 cm long, cut into three equal lengths • a spoon or spatula for stirring or mixing • waterproof pen. Method 1 Run water over the dialysis tubing and rub it firmly with your thumb and forefinger to open it up. Take care not to put a hole in it. 2 Use the thread to tie one end of the dialysis tubing. This must be very firm so no liquid can seep through it. If using cellophane, cut a square shape and bring the four corners together. The solution can be poured into this and tied up using string or thread. 8 3 Mix the glucose in about 50 mL of water to dissolve it. Dip a small piece Tes–tape® into the glucose solution and then remove it. Notice its colour as it dries. 4 Pour the glucose solution into the dialysis tubing until it is about half full. Patterns in nature Gill Sans Bold 5 Firmly tie another piece of thread around the other end of the dialysis tubing, making a bag. Ease out some of the air as you do this. 6 Wash the bag thoroughly to remove any glucose solution which may be on the outside. 7 Half fill one small glass jar with water. Using a waterproof pen, mark the level of the water on the outside of the jar. Note: you need to mark this level very accurately. 8 Put the same amount of water in the other jar and mark the level, as you did for the first jar. This container will be the control as you will compare what happens in this container with what happens in the container with the bag of glucose solution. 9 Put the bag of glucose solution in one of the jars of water. Immerse it as much as possible. 10 Prepare another dialysis tubing bag and this time half fill it with water only. Immerse it in the second jar of water. You have now set up the control. 11 Cover both jars with plastic (such as gladwrap) and leave overnight. Both set ups are now similar in all ways except there is glucose in the bag in one jar and water only in the bag in the other. Remember that the water levels in the two jars were the same before the bags were added. 12 Next day lift the bag of glucose solution and let the water drip off it into its jar. What do you notice about the water level in this jar now? 13 Lift the bag of water and let the water drip off it into its jar. Compare the water level in this control jar with the level in the first jar. 14 Check whether the glucose molecules moved through the dialysis tubing by dipping some Tes–tape® into the water in both jars. Remember to let the Tes–tape® dry for a while before making a decision. Results The level of water in the control beaker remained the same while the level in the experimental beaker has gone down. The dialysis tubing from the experimental beaker is more taut than at the beginning. The dialysis tubing from the control experiment has remained the same. Part 2: Osmosis and diffusion 9 Experiment Control mark water level Experiment Control mark water level glucose solution water dialysis tubing Next day remove the bagsof dialysis tubing Experiment Control water level change In Exercise 2.1 write a brief conclusion to the experiment. 10 Patterns in nature Gill Sans Bold Active transport Active transport is required when materials required by the cell are in a lower concentration surrounding the cell. This can occur, for example, when the concentration of dissolved ions in root cells is higher than in the surrounding soil water. In active transport molecules, within the membrane itself, attach to a substance and pull it across the membrane against the concentration gradient. These are called carrier molecules. In the diagram below potassium ions (K+) are being actively transported across a membrane with the aid of carrier (transporter) molecules. outside cell cell membrane inside cell transporter molecule Active transport across a selectively permeable membrane. Active transport requires energy to move materials across the membrane, usually against the diffusion gradient. Some materials still cannot move across the membrane. The reasons for this include size, solubility, or they are not able to bind with the proteins in the membranes in order to carry them through. A summary to learn • Water enters cells across selectively permeable membranes from an area that has more water (dilute or less concentrated) to an area that has less water (more concentrated solution). This process is called osmosis and is an example of passive transport as energy is not required. Part 2: Osmosis and diffusion 11 • Differences in concentration are called a concentration or diffusion gradient. • Solutes such as sodium or calcium ions enter plant cells by diffusion from a region of low concentration of solute to a high concentration. This is against the concentration gradient and so requires energy. It an example of active transport. • A selectively permeable membrane is one that allows some, but not all, substances to pass through it. Diffusion Osmosis Movement of particles from a region of high concentration to a region of low concentration. A special type of diffusion. Movement of water across a selectively permeable membrane from a region of high concentration of water to a region of low concentration of water. Complete Exercise 2.2 now. 12 Patterns in nature Gill Sans Bold Why are cells so small? Have you ever wondered why cells are so small? What is the advantage to being small? The answer lies in the relationship between volume (the amount of space occupied) and surface area. All cells need to take in substances from their surroundings and release wastes. These substances must pass through the physical boundary separating the inside of the cells from the outside. The larger the size of this boundary, compared to the size or volume of the cell, the more efficient this process is. The following two shapes are both cubes. They are different sizes. 1 cm cube 2 cm cube If these shapes represented sponges, which one would become saturated first when placed in a puddle of water? Suggest a reason for your answer. _________________________________________________________ _________________________________________________________ _________________________________________________________ Check your answer. Part 2: Osmosis and diffusion 13 Surface area to volume ratio A ratio is a proportional relationship between two quantities. In this case it is the relationship between volume and surface area. To understand how this relationship affects movement of materials across a membrane you will now use a model. In this model consider ‘cells’ of three different sized cells: • a cell with sides measuring 3 cm • a smaller cell with sides measuring 2 cm • and a model of an even smaller cell with sides measuring 1 cm. To calculate the ratio of the surface area to volume, you need to find both the surface area and volume of each ‘cell’. Surface area The surface area is the sum of the total area (length ¥ width) of all sides. There are six faces on a cube. Area is calculated by multiplying the length by width. • The area of one face of the large cell is 3 cm ¥ 3 cm (9 cm2) • The area of one face of the medium cell is 2 cm ¥ 2 cm (4 cm2). • The area of one face of the smallest cell is 1 cm ¥ 1 cm (1 cm2). The total surface area of each cell is multiplied by six since a cube has six faces. The total surface area of each cell is calculated as follows. • Total surface area of large cell is 9 cm2 x 6 = 54 cm2 • Total surface area of medium cell is 4 cm2 x 6 = 24 cm2 • Total surface area of small cell is 1 cm2 x 6 = 6 cm2 Volume Volume of a cube is calculated by multiplying the length ¥ width ¥ depth. Here is how you calculate the volume for each of the model cells. 14 • The volume of the large cell is 3 cm x 3 cm x 3 cm = 27 cm3. • The volume of the medium cell is 2 cm ¥ 2 cm x 2 cm = 8 cm3. Patterns in nature Gill Sans Bold • The volume of the smallest cell is 1 cm ¥ 1 cm x 1 cm = 1 cm3. You can express the surface area (SA) and volume (V) as a ratio (SA:V). • SA:V (large cell) = 54:27 = 2:1 • SA:V (medium cell) = 24:8 = 3:1 • SA:V (small cell) = 6:1 You can see that the smaller the cell, the higher the surface area to volume ratio. Check that this is true by doing some calculations yourself. 1 Calculate the surface area to volume ratio of a model cell of sides 4 cm x 4 cm x 4 cm. _____________________________________________________ _____________________________________________________ _____________________________________________________ 2 Calculate the surface area to volume ratio of a model cell of sides 0.1 cm x 0.1 cm x 0.1 cm. _____________________________________________________ _____________________________________________________ _____________________________________________________ 3 How does the surface area to volume ratio change as the cell becomes smaller? _____________________________________________________ Check your answers. A small cell has relatively more surface area to absorb substances. This means that small cells have an advantage over large cells when materials are moving in and out. Therefore, there is an advantage in small size. Part 2: Osmosis and diffusion 15 Advantage of small size investigation The experiment outlined on the next page will help you to verify your ideas on how size affects the movement of substances. Aim: To demonstrate the advantage of small size, or a large surface area to volume ratio in a model cell. Background information: In this experiment, you will make three model cells out of jelly. The cells will be made alkaline by using calcium hydroxide (an alkali). You will be colouring your cells pink by using phenolphthalein. Phenolphthalein turns pink in alkaline solution. During your experiment, you will put your alkaline, pink cells in some acid. When an acid reacts with an alkali, it neutralises it. As the acid diffuses into your model cells, the acid will neutralise the alkali and the pink colour will disappear leaving the model cells colourless or pale yellow. From this observation you will be able to make inferences about the movement of acid into your model cells. Then you may be able to extrapolate and draw a conclusion about the movement of materials into cells and the effect size has on this process. Note: If you cannot obtain any calcium hydroxide or phenolphthalein, it is possible to do the same exercise using potato cubes and a solution of iodine. The iodine can be purchased in the form of antiseptic preparations such as iodine tincture or iodine paint. What you need: 16 • calcium hydroxide (about 1/4 tsp) • phenolphthalein solution (about 1/4 tsp) • powdered gelatine or yellow jelly crystals. Do not use any other coloured jelly crystals. • a jug or measuring cylinder for measuring 150 mL of boiling water. • a small mixing bowl or 250 mL beaker. The bowl should have straight sides. • some vinegar. Vinegar is an acidic solution containing acetic acid. • a refrigerator to set your jelly. Patterns in nature Gill Sans Bold What to do: 1 Put 6 tsp of gelatine powder in a small mixing bowl (or 250 mL beaker). Add 150 mL of boiling water. Stir well until all the gelatine is dissolved. If you are using jelly crystals, use half the packet of crystals with 150 mL of boiling water. 2 Add about 1/4 tsp of calcium hydroxide and 2 drops of phenolphthalein. Do not handle these chemicals. Use a spoon. 3 Stir well to mix thoroughly. A bright pink should be produced. Add a little extra calcium hydroxide if the pink colour does not appear. 4 Put the pink jelly in the refrigerator for about an hour to set firmly. Make sure you warn family members that the jelly is for an experiment. Do not eat. Place a warning sign on the jelly. 5 When the pink jelly has set, remove it intact from the beaker or bowl. Run a knife around the sides, invert it and tap the bottom to free it. 6 Use your knife and ruler to make three different sized cubic cells: – a large one with sides 3 cm – a medium–sized one with sides 2 cm – a small one with sides 1 cm. Make the sizes of the cubes as accurate as possible. Plan your cutting areas before you start, otherwise you may find yourself short of jelly. Your mixing bowl must be a shape that allows you to cut out the three ‘cells’ with the volumes indicated. 4 Put your three model cells into the empty beaker or bowl. Cover them with vinegar. 5 Leave until the small one has just lost all its pink colour. Remove the cells from the vinegar immediately using a spoon. 6 Slice each of the larger cubes in half and quickly measure in centimetres the width of the pink centres. Make your measurements as accurate as possible. For the alternate version cut your cubes out of potato and immerse in a solution of iodine. Complete Exercise 2.3. Part 2: Osmosis and diffusion 17 18 Patterns in nature Gill Sans Bold Suggested answers Movement across the membrane 1 The particles in a solid speed up and move apart when heated. 2 Particles in a gas that has been cooled would slow down and move closer together (condense). 3 Diffusion could occur faster in cells at a higher temperature compared to those at a lower temperature. Why are cells so small? The smaller sponge would become saturated first. Surface area to volume ratio 1 Surface area = 42 x 6 = 96 cm2 Volume = 4 x 4 x 4 = 64 cm3 SA:V = 96:64 = 1.5:1 2 Surface area = 0.12 x 6 = 0.06 cm2 Volume = 0.1 x 0.1 x 0.1 = 0.001 cm3 SA:V = 0.06:0.001 = 60:1 3 The smaller the cell, the higher the surface area to volume ratio. Part 2: Osmosis and diffusion 19 20 Patterns in nature Gill Sans Bold Exercises – Part 2 Exercises 2.1 to 2.3 Name: _________________________________ Exercise 2.1: Investigating osmosis Write a brief conclusion for your experiment. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 2.2: Osmosis and diffusion Compare the differences between diffusion and osmosis. The word compare can be defined as ‘show how things are similar or different’. In this case there are both similarities and differences between diffusion and osmosis. Write your answer with the definition of compare in mind. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 2.3: Advantage of small size a) Use the results from your experiment to complete the table following. If you were unable to do the experiment use the answers supplied to answer the questions. Part 2: Osmosis and diffusion 21 22 Patterns in nature 1x1x1 2x2x2 Your results 3x3x3 Worked examples only 3x3x3 2x 2 x 2 1x1x1 Dimensions of the model cells (cm) 2.53 or 15.6 cm3 1cm3 0cm3 2.5 cm 1cm 0cm 0 (Assume it is perfectly cubic…this will be the measurement in the previous column cubed.) (A) (Use a decimal point giving as accurate a measurement as possible) 0 Volume of coloured centre. Width of the coloured centre in centimetres 1 cm3 27 cm3 8cm3 1 cm3 (Use the first column.) (B) Volume of the whole cube—the entire ‘cell’. 1 cm3 11.4 cm3 7cm3 1 cm3 This will be (B—A) Volume of the uncoloured part of the cell. 100% 11.4/27 x100= 42% 7/8 x100= 87.5% 1/1 x100= 100% (This is the measurement in the previous column divided by the total volume (B) multiplied Percentage of the cell which is uncoloured Gill Sans Bold b) The last column of the table represents the percentage of each cell which was colourless. Why was this part of the cell colourless? _____________________________________________________ _____________________________________________________ c) i) If the jelly blocks were living cells, and the acid was a normal nutritional requirement of a cell, which block would be supplied most efficiently by diffusion? _________________________________________________ _________________________________________________ _________________________________________________ ii) Why is this cell supplied most efficiently with ‘nutrients’? Refer to the surface area and volume in your answer. _________________________________________________ _________________________________________________ _________________________________________________ c) Explain the advantage to cells of small size or a large surface area to volume ratio. _____________________________________________________ _____________________________________________________ _____________________________________________________ d) Explain how the SA:V affects the rate of movement of substances into and out of cells. _____________________________________________________ _____________________________________________________ _____________________________________________________ e) Can you think of other examples where SA:V in living things has a significant effect? Hint: think about adaptations to the surrounding environment. _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 2: Osmosis and diffusion 23 Gill Sans Bold Biology Preliminary Course Stage 6 Patterns in nature Part 3: Cell theory and the light microscope 2 0 0 In r2 e b S o t c NT O ng DM E i t ra E N o rp A M o c Gill Sans Bold Contents Introduction ............................................................................... 2 What is cell theory? ................................................................... 4 The historical development of the cell theory .....................................4 Evidence to support the cell theory .....................................................6 Problems with the cell theory...............................................................6 The microscope......................................................................... 7 The light microscope ............................................................................8 Cell organelles ........................................................................ 11 Using a light microscope....................................................................11 Summary................................................................................. 17 Suggested answers................................................................. 21 Exercises–Part 3 ..................................................................... 23 Part 3: Cell theory and the light microscope 1 Introduction Organisms are made of cells which have similar structural characteristics. In this part you will be given opportunities to learn to: • outline the historical development of the cell theory, in particular, the contributions of Robert Hooke and Robert Brown • describe evidence to support the cell theory • discuss the significance of technological advances to developments in cell theory • identify cell organelles seen with current light microscopes In this part you will be given opportunities to: • use available evidence to assess the impact of technology, including the development of the microscope on the development of the cell theory • perform a first–hand investigation to gather first–hand information using a light microscope to observe cells in plants and animals and identify nucleus, cytoplasm, cell wall, chloroplast and vacuoles. Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. The most up-to-date version can be found on the Board's website at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html This version November 2002. 2 Patterns in nature Gill Sans Bold There is a practical activity in this part that requires the use of a microscope and the following equipment: • microscope lamp (if the microscope does not have one built into the unit) • clean glass slides and coverslips • dropper • onion, moss or very soft fleshy plant stem • meat blood (obtained by collecting the liquid remaining after frozen goods are defrosted) • iodine (or an antiseptic preparation containing iodine such as Betadine®) • blade or small vegetable knife • cutting board. Alternative exercises are provided if you do not have access to a microscope. Part 3: Cell theory and the light microscope 3 What is cell theory? You have previously studied cells and you know that living things are made of cells and that cells share similar structural characteristics. But did you know that the existence of cells had to wait for the historical development of the microscope for their discovery? To examine this history you need to look at the contributions of a range of scientists including, Robert Hooke and Robert Brown. The historical development of the cell theory Before looking at the historical development of the cell theory it is useful to be clear about what the cell theory means. The cell theory was proposed by Scheilden and Swann in 1839 and added to by Virchow in 1858. In summary the cell theory states that: • cells are the basic units of life and reproduction • most organisms consist of a cell or cells and cell products • all cells come from pre–existing cells. Most cells are so small that they are invisible to the naked eye. This meant that the discovery of cells had to wait until there were magnifiers to see them. The simplest magnifiers are single lenses such as those used in a magnifying glass. The development of the cell theory depended on the manufacture and use of lenses and magnifying devices such as microscopes as well as the combined investigation efforts of many scientists. This occurred over a period of 300 years. 4 Patterns in nature Gill Sans Bold Robert Hooke In 1665 Robert Hooke, an English scientist, used a compound microscope to observe the cellular nature of cork. (A compound microscope consists of two or more lenses which are positioned inside a tube.) Hooke’s microscope magnified objects about 270 times (x270) their normal size. Hooke's microscope. Hooke's drawing of cork cells. He called the structures seen in the cork, cells because they reminded him of the small rooms (cells) that monks lived in. Anton van Leewenhoek A few years later in 1676 Anton van Leeuwenhoek (lay–van–hook), a Dutchman made amazing discoveries of unicellular organisms like bacteria. Leeuwenhoek used, not compound microscopes, but single lens microscopes. These magnified about 250 times (x250). Van Leeuwenhoek was a master lens grinder. Unfortunately, he was extremely secretive about his method of grinding lenses and didn’t pass on his Van Leeuwenhoek's knowledge and skills. microscope. Part 3: Cell theory and the light microscope 5 Robert Brown Robert Brown (1773–1858) was a Scottish botanist who accompanied Matthew Flinders to Australia in 1801. As well as identifying new genera of plants in Australia, he is known for discovering Brownian movement and the cell nucleus. Evidence to support the cell theory The main evidence for the cell theory occurred when the theory of spontaneous generation was disproved. This theory stated that life arose from non–living matter such as piles of rubbish and organisms such as rats and flies were produced by rotting meat. Francesco Redi (1626–1697) showed that maggots only arose from meat that flies had visited and Louis Pasteur (1822–1888) showed that micro–organisms only come from other micro–organisms. The work of these two scientists convinced people that living things are made of cells and that all cells come from pre–existing cells. This led to important changes in hygiene and medical practices. Problems with the cell theory Since the time when the cell theory was proposed, viruses and prions have been identified. How do viruses and prions fit into the cell theory? They do not structurally resemble cells. They are much smaller than cells. They do not have a nucleus, cell membrane or cytoplasm. Viruses consist mainly of a core of deoxyribose nucleic acid (DNA) and a protein coat. Prions are an infectious protein particle that causes various nervous diseases in mammals. Mad cow disease is an example of a disease caused by a prion. Prions do not contain any genetic material. While viruses often appear to be non–living, they can reproduce when they are within a living cell. So, they pose a problem. Are they living or non–living? Many people regard viruses as living, but they differ from other living things in that they are not cellular. Complete Exercise 3.1. 6 Patterns in nature Gill Sans Bold The microscope The development of the cell theory was closely related to the technological advances that occurred with the development of improved lenses. As well as the improvement in microscopes, other technological advances have occurred. These include machines called microtomes that are capable of cutting ultra–thin sections of material. Also the ability to use different chemicals as staining agents. Some stains are taken up selectively by different materials and can be used to identify chemicals such as starch or different structures within the cell. Examples of commonly used stains are iodine, toluidine blue and eosin. When looking at microscopes there are two factors that are important, magnification and resolution. Magnification is the amount that the object is magnified or how much larger the object appears. A light microscope magnifies up to 1000 times. The new generation of microscopes are the electron microscopes, the first of which was built in 1933 by Ernst Ruska. The magnification of an electron microscope is about one million times the normal size. Resolution (resolving power) is the ability of a microscope to distinguish two or more points together, as discrete objects. If the resolution of a microscope is poor you can continue magnifying an object but it just appears to be more blurred and bigger. The magnification of an electron microscope can be up to one million times with a resolving power of up to 0.0002 µm (micrometres). The light microscope can only resolve up to 0.2 µm. This is about 500 times more than the human eye can resolve. Part 3: Cell theory and the light microscope 7 The light microscope The light microscope passes a beam of light through a specimen which is magnified by the objective lens. The light then travels up the body of the microscope and is then magnified again as it is passes through the lens in the eyepiece. Light microscope. © Australian Key Centre for Microscopy. In this activity you have to use available evidence to assess the impact of technology, including the development of the microscope on the development of the cell theory.. To do this look for information from a range of resources including popular scientific journals, CD–ROMs and the Internet. Illustrate the trends and patterns by creating a table such as the one below that shows the development of the microscope. Look for a logical progression of ideas as technological advances lead to the development of the cell theory. 8 Patterns in nature Gill Sans Bold There are some useful starting points on the LMP Science Online site, http://www.lmpc.edu.au/science. Also try the interactive activities dealing with the microscope. 1590 Father and son team, Hans and Zacharias Janssen, construct the first compound microscope. 1665 Robert Hooke using a compound microscope observed cork. 1672 Marcello Malpighi (1628–1699) discovered capillaries. 1676 Anton van Leeuwenhoek (1632–1723) described unicellular organisms. His great skill was in producing outstanding lenses that had a better resolution than any other lenses of the time. 1824 Rene Dutrochet (1776–1847) was he first to state that all animals and plants are made of cells. 1831 Robert Brown (1773–1858) named the nucleus and found it was present in both plants and animal cells. 1839 Mathias Schleiden (1804–1881) and Theodor Schwann (1810–1882) were given credit for the cell theory. 1855 Rudolf Virchow (1821–1902) added the third statement of the cell theory that all cells come from pre–existing cells. 1880 Walther Flemming (1843–1905) described cell division or mitosis from observations on living and stained cells. 1932 Ernst Ruska built the first electron microscope. Today The best light microscopes today have a magnification of 1500x. Electron microscopes can have a magnification of up to one million times and high resolving power. Part 3: Cell theory and the light microscope 9 1 List the main features of the cell theory. • ____________________________________________________ • ____________________________________________________ • ____________________________________________________ 2 Use the information in the table on the previous page to answer the following questions. a) Who observed that plant and animal cells have a nucleus? _________________________________________________ b) Who are given credit for the cell theory? _________________________________________________ c) Who stated that cells come from pre–existing cells? _________________________________________________ 3 Complete the following sentences. a) Hooke’s compound microscope magnified objects about ____ X. Van Leeuwenhoek’s microscopes magnified object about ___ X. A modern compound microscope can magnify about ______ X. b) The different microscopes were developed as a result of _____ changes. c) One important improvement in microscopes has been that they have increased the __________________________ of objects. Check your answers. Do Exercise 3.2 now. 10 Patterns in nature Gill Sans Bold Cell organelles Within a cell there are structures that are common to many cells. These are called organelles. All cells are held together as a unit by the cell membrane (also called the plasma membrane). In plant cells, the cell membrane is surrounded by a cell wall composed of cellulose. Common organelles that you may have heard of include the nucleus, mitochondria, chloroplasts and ribosomes. Some cell organelles are visible using a light microscope; more are seen with an electron microscope. You will look firstly at the organelles that are visible under a light microscope. Using a light microscope The table below shows the cell structures that can be seen when using a light microscope to examine plant and animal cells. Animal cells Plant cells nucleus nucleus cell membrane cell membrane cytoplasm cytoplasm nuclear membrane nuclear membrane cell wall chloroplasts vacuole Part 3: Cell theory and the light microscope 11 The cell wall and chloroplasts of some plant cells can be clearly seen. The chloroplasts in plant cells show up clearly because they are green. This is due to the presence of the green pigment, chlorophyll. Vacuoles can be large in mature plant cells but very small in animal cells, if it is present at all. Observing plant and animal cells The following activity will help you identify structures in some cells. You will be observing plant and animal cells using a light microscope. You can revise how to use and set up the microscope in the Science resource book or if you have access to the Internet the following web site will provide you with an address. http://www.lmpc.edu.au/science. If you do not have access to a microscope to carry out the activity, you can use the light microscope photographs on the following pages to answer the questions in this section. Materials: • microscope • microscope lamp (if the microscope does not have one built into the unit) • clean glass slides and coverslips • dropper • onion, moss or very soft fleshy plant stem • meat blood (obtained by collecting the liquid remaining after frozen goods are defrosted) • iodine (or an antiseptic preparation containing iodine such as Betadine®) • blade or small vegetable knife • cutting board. Method: 1 Prepare a very thin section of specimen. Use the blade to cut a very thin section of the plant material. Caution: Always cut away from your fingers. 2 12 Prepare a wet mount of each specimen for investigation under the microscope. Patterns in nature Gill Sans Bold To make a wet mount use the dropper to place a drop of water onto the clean glass slide. Place the thin section of plant material onto the drop of water and gently lower the cover slip. If onion is being used, a drop of iodine can be added to the slide to provide a greater contrast. (Iodine will stain any starch present.) Gently lower a cover slip using the techniques illustrated below. The blood can be placed directly onto the slide and smeared thinly. Lower the coverslip gently onto the smear. Cut a thin section, place a drop of water on the slide,. add the section and then cover with a coverslip. 3 Place the slide on the microscope stage and use the coarse focus to move the objective as close as possible to the slide while watching from the side. Then whilst looking through the eyepiece move the coarse focus away from the slide until the image is focused. If the image does not appear ecogni, then repeat the steps again (more slowly), making sure that the objective is once again lowered whilst watching from the side to ensure that the slide and objective are not accidentally damaged. For more detail rotate the objective stage so that the high power objective is being used to bring your specimen into clear view. If you have a fine focus knob it should only be used when looking through the high power objective. 4 Draw a ecogni diagram of each of the specimens observed in the spaces on the following pages. Label any of the structures you were able to identify. Remember when drawing diagrams: • use pencil for the drawing • make the diagrams at least a half page in size • use a heading and label any structures you ecognize. Part 3: Cell theory and the light microscope 13 Photograph of human blood viewed through a light microscope. The larger cell is a white blood cell showing the lobed nucleus. The rest are red blood cells with no nucleus. (Photo Jane West) Drawing showing the biconcave shape of red blood cells. Your drawing of human blood cells. 14 Patterns in nature Gill Sans Bold Human cheek cells as seen through a light microscope.(Photo Jane West) Drawing of an animal cell as seen through a light microscope. Your drawing of animal cells. Part 3: Cell theory and the light microscope 15 Photograph of a plant epidermis viewed through a light microscope under high magnification. (Photo Jane West) A drawing of a plant cell. You may notice that it is difficult to see the chloroplasts and vacuole in the photograph. Your drawing of plant cells. Do Exercise 3.3 now. 16 Patterns in nature Gill Sans Bold Summary Use this self–correcting summary to check your knowledge of the cell theory and the technology that has led to the discovery of cell organelles. 1 What are the three main generalisations in the cell theory? _____________________________________________________ _____________________________________________________ _____________________________________________________ 2 Which type/s of technology has made it possible for us to know that cells exist? _____________________________________________________ _____________________________________________________ _____________________________________________________ 3 Outline one improvement in microscopes following Hooke’s early discoveries. _____________________________________________________ _____________________________________________________ _____________________________________________________ 4 Study the photograph of the light (optical) microscope on the next page. a) Identify the parts labelled and state a function of each part. Do this by using a table with the three headings: Letter, Name of part, and Function on your own paper. You may need to refer to the Science resource book if you were unable to use a microscope. Part 3: Cell theory and the light microscope 17 Light microscope. © Australian Key Centre for Microscopy. b) Explain briefly how you would prepare a wet mount. __________________________________________________ __________________________________________________ __________________________________________________ c) Name one chemical that can be used to stain cells. __________________________________________________ d) Why are stains useful when examining cells using the microscope? __________________________________________________ __________________________________________________ __________________________________________________ 18 Patterns in nature Gill Sans Bold e) Briefly outline the steps involved in observing a specimen using the low power of a light (optical) microscope. _________________________________________________ _________________________________________________ f) What is the term used to describe the ability to see fine details clearly? _________________________________________________ Check your answers. Part 3: Cell theory and the light microscope 19 20 Patterns in nature Gill Sans Bold Suggested answers The microscope 1 Life and reproduction is not possible without cells. Living things are made up of cells. Cells are produced from other cells. 2 a) Robert Brown b) Schleiden and Schwann c) Rudolf Virchow 3 a) Hooke’s compound microscope magnified objects about 270 X. Van Leeuwenhoek’s microscopes magnified object about 250 X. A modern compound microscope can magnify about 1000 X. b) The different microscopes were developed as a result of technological changes. c) One important improvement in microscopes has been that they have increased the magnification of objects. Summary 1 Cells are the basic units of life and reproduction. Most organisms consist of a cell or the products of cells. All cells come from pre–existing cells. 2 Magnifiers and microscopes make it possible for us to know that cells exist. 3 The grinding of lenses for single lens microscopes. Part 3: Cell theory and the light microscope 21 4 4 a) Letter Name Function e eyepiece magnification lens o objective magnification lens c condenser focuses light from mirror onto specimen s stage support for specimen l light light source f focus knob moves the stage to focus image b) A wet mount is made by placing a thin section of a specimen into a drop of water on a clean slide. This is covered with a coverslip. A stain may be added to the specimen if required. c) Examples of stains are iodine, toluidine blue and eosin d) Stains are useful because they make the image easier to see by increasing the contrast between structures. They are also useful because they can indicate the presence of different types of compounds for example iodine turns blue–black in the presence of starch. e) Direct lamp or light source into microscope using the mirror. Place slide on the stage. Lower low power objective whilst looking from the side. Look down eyepiece and slowly wind the coarse focus knob up, until the image comes into focus. f) 22 Resolution Patterns in nature Gill Sans Bold Exercises – Part 3 Exercises 3.1 to 3.3 Name: _________________________________ Exercise 3.1: What is cell theory? a) What are the three main generalisations of the cell theory? _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ b) What was the contribution of the following two scientists to the cell theory. Robert Hooke _____________________________________________________ _____________________________________________________ _____________________________________________________ Robert Brown _____________________________________________________ _____________________________________________________ _____________________________________________________ c) Outline the theory of spontaneous generation. Name two scientists whose work disproved the theory of spontaneous generation and gave support to the cell theory. _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 3: Cell theory and the light microscope 23 Exercise 3.2: The microscope a) Complete the sequence scaffold below highlighting the historical developments in the establishment of technology in developing the cell theory. The first one has been done for you. 24 Date Event 1590 Father and son team, Hans and Zacharias Janssen, construct the first compound microscope . Patterns in nature Gill Sans Bold 1665 1676 circa 1900 circa 1933 b) The diagram above shows the development of the microscope. These technological advances were important in the development of the cell theory. Discuss the significance of technological advances to developments in cell theory. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Exercise 3.3: Cell organelles a) Compare and contrast plant and animal cells. This means that you must look at the similarities and differences between the two types of cells. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 3: Cell theory and the light microscope 25 b) Draw a diagram in the space below of a generalised plant and animal cell as seen through a light microscope, labeling the structures identified. 26 Patterns in nature Gill Sans Bold Biology Preliminary Course Stage 6 Patterns in nature Part 4: Electron microscope and cell organelles 2 0 0 In r2 e b S o t c NT O ng DM E i t ra E N o rp A M o c Gill Sans Bold Contents Introduction ............................................................................... 2 The electron microscope ........................................................... 3 Using an electron microscope .............................................................4 Structure and function..........................................................................5 Tissues, organs and organ systems........................................ 14 Summary................................................................................. 15 Suggested answers................................................................. 17 Exercises–Part 4 ..................................................................... 21 Part 4: Electron microscope and cell organelles 1 Introduction Plants and animals have specialised structures to obtain nutrients from their environment. You may recall that plants and animals obtain nutrients differently. Plants rely on the Sun to manufacture food by a process called photosynthesis. Plants are autotrophic organisms. Animals cannot manufacture their own food; they consume or eat other organisms in order to gain the nutrients they require for life processes. Animals are heterotrophic organisms. Plants and animals have specialised cells, tissues and organs to obtain the nutrition they require and carry out their body processes. Some of these will be investigated in this part. In this part you will be given opportunities to learn to: • identify cell organelles seen with an electron microscope • describe the relationship between the structure of cell organelles and their function • identify some examples that demonstrate the structural and functional relationships between cells, tissues, organs and organ systems in multicellular organinsms In this part you will be given opportunities to: • process information from secondary sources to analyse electron micrographs of cells and identify mitochondria, chloroplasts, Golgi bodies, lysosomes, endoplasmic reticulum and cell membranes. Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. The most up-to-date version can be found on the Board’s website at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html. This version November 2002. 2 Patterns in nature Gill Sans Bold The electron microscopes There are two main types of electron microscopes: • the transmission electron microscope and • the scanning electron microscope. Unlike light microscopes that use a beam of light passing through the specimen electron microscopes use a beam of electrons. The transmission electron microscope uses the electrons that pass through very thin specimens, to show detailed images of internal structures. The scanning electron microscope produces images of the surface features of objects, often coated with a very thin layer of metal atoms to enhance the image. One disadvantage of using electron microscopes is that the preparation of specimens is very expensive. For example, the specimen must be kept in a vacuum to avoid scattering the electron beam or it must be fixed in heavy metal compounds eg. gold. This means that it is not possible to view live specimens, also a disadvantage. It is unclear whether such harsh treatment of specimens might actually distort the true nature of the structure of the cells. An electron microscope Part 4: Electron microscope and cell organelles 3 The advantage of the electron microscope is that the magnification (x 1 million) and the resolution (0.0002 micrometre) are very high. Do Exercise 4.1 now. Using an electron microscope Under a light microscope there is a limit to the organelles that are visible even with the latest technology. The story is different however, under an electron microscope where there are many more organelles visible. The table below lists the cell structures that are visible with an electron microscope. 4 Cell structure Animal cells Plant cells nucleus present present nucleolus present present cell membrane present present cytoplasm present present nuclear membrane present present mitochondria present present Golgi bodies present present ribosomes present present endoplasmic reticulum present present lysosomes present absent cell wall absent present chloroplasts absent present vacuole absent present Patterns in nature Gill Sans Bold Structure and function The nucleus The nucleus is usually large and spherical. The nucleus is enclosed by a double membrane. This membrane has pores that allow fairly large molecules to move in and out of the nucleus. The nucleus often contains a nucleolus which is involved in the manufacture of proteins in the cell. (Refer to the electron micrograph below showing the nucleus and other organelles.) Nucleus in a rat intestinal wall. (g—Golgi bodies, m—mitochondrion, nu—nucleolus, n—nucleus, rer—rough endoplasmic reticulum) © Australian Key Centre for Microscopy. The nucleus controls the activities of the cell. It does this largely by controlling the formation of proteins in the cell. The nucleus contains the chromosomes, which carry the genes. Genes are units of inheritance and determine which types of proteins are formed. Part 4: Electron microscope and cell organelles 5 What sort of structural feature/s does the nucleus have that makes it suited for its function? _________________________________________________________ _________________________________________________________ _________________________________________________________ Check your answer. Plastids and chloroplasts Plastids are oval–shaped organelles. Some store substances such as food made by plants eg. starch. Other plastids contain pigments such as the green pigment, chlorophyll. Plastids that contain chlorophyll are called chloroplasts. Chloroplast in soybean leaf. (g — granum, r — ribosomes, s — starch grains) © Australian Key Centre for Microscopy. 6 Patterns in nature Gill Sans Bold Look at the three dimensional drawing of a chloroplast below. Note that it has, like a nucleus, a double membrane. Within a chloroplast is a membrane known as the lamella. In some areas, the lamella is densely packed into grana (singular granum). These resemble stacks of coins and increase the surface area. The grana are embedded in a colourless substance called the stroma. ring of DNA double membrane starch grain stroma or lamella ribosome stack of grana (thylakoids) Photosynthesis occurs in chloroplasts. So, essentially, the chloroplasts are the food–making organelles of plants. The chlorophyll is contained in the grana. It is the chlorophyll that absorbs light energy which makes the process of photosynthesis possible. Describe how the structure of a plastid such as a chloroplast assists the process of photosynthesis in plant cells. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Check your answer. The cell membrane The cell membrane, also known as the plasma membrane, surrounds all cells. It is a physical barrier but it is thin and contains pores that allow selected materials to pass through. In plant cells the cell membrane is surrounded and protected by the cell wall. The function of the cell membrane, apart from keeping the cell together, is to regulate the flow of substances into and out of the cell. The membrane is described as selectively permeable. This means it allows some substances to pass through while stopping other substances. Part 4: Electron microscope and cell organelles 7 Describe how the structure of the cell membrane enables it to carry out the function described here. _________________________________________________________ _________________________________________________________ _________________________________________________________ Check your answer. A summary Following is a summary of important points so far. Fill in the missing words as you read this summary. 1 The _____________ is a large spherical organelle that controls the activities of the cell. This organelle is surrounded by a _____________ membrane that has _____________ in it. 2 Chloroplasts are one type of _____________. They are green coloured because they contain the green pigment, _____________. Like the nucleus, the chloroplast is surrounded by a _____________ membrane. Chloroplasts absorb _____________ energy, which drives the food–making process called _____________. 3 The cell or plasma membrane keeps the cell intact. It allows some substances to enter and leave while preventing others from entering or leaving. It is therefore described as _____________ permeable. Check your answers. Mitochondria Cells may contain several or hundreds of mitochondria. The more active a cell is, the more mitochondria there are. 1 Make a prediction to explain why there are more mitochondria in an active cell than one not involved in activity. _____________________________________________________ _____________________________________________________ . A mitochondrion is surrounded by a double membrane. Look at the photomicrograph on the next page, which shows some mitochondria. You can see that the inner membrane is highly folded. Folded membranes like this provide a very large surface within a small space. 8 Patterns in nature Gill Sans Bold Mitochondria in unicellular algae. © Australian Key Centre for Microscopy. Mitochondria are the organelles in which the final stages of cellular respiration occur. They are the organelles in which the energy produced is released by cellular respiration. The wastes from this process, carbon dioxide and water, are also formed in these structures. Mitochondria are often referred to as the powerhouses of the cell because they are the organelles which provide energy for the cell. 2 How does the structure of a mitochondrion support its function? _____________________________________________________ _____________________________________________________ Check your answers. Golgi bodies A Golgi body was first observed and identified as an organelle by Camillo Golgi (1844–1926), an Italian histologist. Hence, Golgi is always spelt with a capital letter. We are inclined to get the impression that these not so well known organelles were discovered when the electron microscope came into use. This is not so. Part 4: Electron microscope and cell organelles 9 The Golgi body was actually discovered when Golgi used an optical microscope and a dye containing a silver compound. There was originally much argument as to whether or not it was a new organelle or simply a product of the staining technique he used. The matter was not resolved for about 60 years when electron microscopes verified Golgi’s claims. Find the Golgi body in the electron micrograph below. Note that the Golgi body consists of stacks of membranes which bulge out in places to travel through the cell. Small Golgi body in a grass leaf cell. (g — Golgi body, rer — rough endoplasmic reticulum, cw — cell wall) © Australian Key Centre for Microscopy. The Golgi body has been found in nearly all types of cells, but is particularly abundant in cells that secrete substances eg. the salivary glands. The Golgi apparatus can absorb amino acids and sugars and use them to synthesise more complex proteins and carbohydrates. These chemicals are contained in the vesicles, which become detached from the Golgi apparatus. These vesicles appear to move away from the Golgi apparatus across the cytoplasm to the cell membrane. Finally, the small vesicles fuse with the cell membrane and the protein–carbohydrate substances are discharged (secreted) from the cell. 10 Patterns in nature Gill Sans Bold So, the Golgi body prepares and secretes various chemicals for use either within or outside the cell. How is the function of a Golgi body supported by its structure? _________________________________________________________ _________________________________________________________ Check your answer. Ribosomes Compared to the nucleus, mitochondria, chloroplasts and Golgi body, ribosomes are very small indeed. They are tiny, spherical organelles which are found throughout the cell. Ribosomes are found within other organelles such as the nucleus and chloroplasts. They are also found attached to a membrane system known as the endoplasmic reticulum. Rough endoplasmic reticulum in rat intestine. (Arrowheads indicate ribosomes attached to the surface of the rough endoplasmic reticulum). © Australian Key Centre for Microscopy. Part 4: Electron microscope and cell organelles 11 Ribosomes are the organelles where proteins are made. They are most numerous in cells that produce proteins. The small size of ribosomes gives a high surface area to volume ratio. How does the structure of a ribosome enable it to produce proteins? _________________________________________________________ _________________________________________________________ Check your answer. Endoplasmic reticulum The endoplasmic reticulum is a network of membranes that run through the cytoplasm. The rough endoplasmic reticulum looks rough because there are ribosomes attached to it. Smooth endoplasmic reticulum has no ribosomes on it. The endoplasmic reticulum is an intricate combination of canals. Rough endoplasmic reticulum in mouse intestine. Parallel sheets of rough endoplasmic reticulum can be seen surrounding the nucleus. (n — nucleus, nu — nucleolus, m — mitochondria, rer — rough endoplasmic reticulum) © Australian Key Centre for Microscopy. The endoplasmic reticulum forms a complex system of canals or channels along which substances are transported throughout the cell. Smooth endoplasmic reticulum is involved in the formation of lipids (fats). It also helps inactivate some drugs. 12 Patterns in nature Gill Sans Bold How does the structure of endoplasmic reticulum relate to its function? _________________________________________________________ _________________________________________________________ Check your answer. Lysosomes Lysosomes were first described in the 1950s. They are smaller than mitochondria and are enclosed by single membranes. The membrane does not permit the movement of enzymes from within and is capable of resisting their digestive action. Lysosomes are more commonly found in animal cells. The lysosome is thought to contain enzymes that take in and break down older cell organelles. If a lysosome should rupture (break) the enzymes would break down and destroy the cell. How is the structure of a lysosome relevant for the function it performs? _________________________________________________________ _________________________________________________________ _________________________________________________________ Check your answers. You will need to look carefully at the micrographs throughout the module and familiarise yourself with them, as you may be required to identify such pictures/diagrams at a later stage. Use other secondary sources of electron micrographs to identify mitochondria, chloroplasts, Golgi body, lysosomes, endoplasmic reticulum and cell membranes. Use the electron micrographs on the previous pages and the LMP Science webpage for more sources of pictures. Make sure you can identify the above cell organelles. Complete Exercise 4.2. Part 4: Electron microscope and cell organelles 13 Tissues, organs and organ systems Cells are not a disorganised mass of matter. Instead cells are grouped together to form tissues, tissues make up organs and organs make up organ systems. The table below summarises this information. Definition Animal example Plant example tissue a group of cells of the same type with the same function blood phloem organ part of an animal or plant forming a structural and functional unit which is made up of one or more tissues heart leaf organ system a group of organs that function together as a unit blood system vascular system Explain the difference between tissues, organs and organ systems. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Check your answer. Do Exercise 4.3 to complete this part. In the next part you will go on to investigate how specialised structures are used by organisms to obtain nutrients from their surroundings. 14 Patterns in nature Gill Sans Bold Summary Self–correcting summary. 1 a) What are two advantages of using electron microscopes over light microscopes? _________________________________________________ _________________________________________________ b) In what way is the use of the electron microscope limited? _________________________________________________ c) Which organelles would you be able to see using an electron microscope that were not visible using a compound or light microscope? _________________________________________________ 2 Complete the summary of cell organelle structure and function following by filling in the missing words. a) Mitochondria (singular ________________ ) are organelles with a double ________________. The inner membrane is highly ________________ producing a large surface area. Mitochondria are described as the powerhouses of cells because they provide cells with ________________ to do work. The final stages of the energy–releasing change called ________________ occur in these organelles. b) A Golgi body consists of ________________. These membranes bulge out to form ________________. These vesicles contain various chemicals which are used whether within the cell or ________________ by the cell for use elsewhere. c) ________________ are small, spherical structures which are the site of protein synthesis. Part 4: Electron microscope and cell organelles 15 d) The endoplasmic reticulum is a network of ________________ which form canals or passageways. The canals ________________ a variety of substances throughout the cell. Endoplasmic reticulum with ribosomes attached is called ________________ endoplasmic reticulum. 16 Patterns in nature Gill Sans Bold Suggested answers The nucleus The nucleolus is involved in the formation of proteins which controls the activities of the cell. Substances are able to move in and out of the cell through the pores in the nuclear membrane. Plastids and chloroplasts The stack of grana in chloroplasts increases the surface area available within the chloroplast for photosynthesis. Chloroplasts contain chlorophyll which absorbs light energy and makes photosynthesis possible. The cell membrane The cell membrane is a physical barrier, it is thin and contains tiny pores to enable the diffusion of matter across it. A summary 1 The nucleus is a large spherical organelle which controls the activities of the cell. This organelle is surrounded by a double membrane that has pores in it. 2 Chloroplasts are one type of plastid. They are green coloured because they contain the green pigment, chlorophyll. Like the nucleus, the chloroplast is surrounded by a double membrane. Chloroplasts absorb light energy, which drives the food–making process called photosynthesis. 3 The cell or plasma membrane keeps the cell intact. It allows some substances to enter and leave while preventing others from entering Part 4: Electron microscope and cell organelles 17 or leaving. It is therefore described as selectively (or semi) permeable. Mitochondria 1 Active cells require large amounts of energy. Energy in cells is provided by the process of respiration. Mitochondria might be the site where respiration occurs, therefore providing the energy needed. 2 The highly folded inner membrane increases the surface area for respiration. The large surface area provided by a folded membrane provides more places for respiration to occur. So, respiration can occur on a large–scale. Golgi body The Golgi consist of stacks of membranes which increase the surface area for diffusion and synthesis of complex molecules. The vesicles function is transporting these molecules to the cell membrane. Ribosomes The large surface area to volume ratio enables efficient movement of materials across the ribosome’s membrane. Endoplasmic reticulum The large surface area enables the endoplasmic reticulum to efficiently transport materials around the cell. Lysosome The semipermeable nature of the membrane prevents the enzymes escaping into the cell and destroying it. Tissues, organs and organ systems Cells are fundamental units that make up a living thing. Similar cells work together to form tissues and different tissues work together in an organ. 18 Patterns in nature Gill Sans Bold Summary 1 a) Greater magnification and resolution b) Specimens are killed in the process of preparation for viewing with an electron microscope. No guarantee that the resulting images are true representations of the original living tissue. The cost of electron microscope technology is very high. c) Nucleolus, Golgi, endoplasmic reticulum (rough and smooth), lysosome, mitochondria, ribosomes. 2 a) Mitochondria (singular mitochondrion) are organelles with a double membrane. The inner membrane is highly folded producing a large surface area. Mitochondria are described as the powerhouses of cells because they provide cells with energy to do work. The final stages of the energy–releasing change called respiration occur in these organelles. b) A Golgi body consists of membranes. These membranes bulge out to form vesicles. These vesicles contain various chemicals which are used whether within the cell or secreted by the cell for use elsewhere. c) Ribosomes are small, spherical structures which are the site of protein synthesis. d) The endoplasmic reticulum is a network of membranes, which form canals or passageways. The canals transport a variety of substances throughout the cell. Endoplasmic reticulum with ribosomes attached is called rough endoplasmic reticulum. Part 4: Electron microscope and cell organelles 19 20 Patterns in nature Gill Sans Bold Exercises – Part 4 Exercises 4.1 to 4.3 Name: _________________________________ Exercise 4.1: The electron microscope a) Identify two types of electron microscopes. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ b) Describe two disadvantages of using an electron microscope. _____________________________________________________ ____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ c) What magnification and resolution are available with an electron microscope? _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 4: Electron microscope and cell organelles 21 Exercise 4.2: Observing plant and animal cells The following diagrams show the structure of a generalised plant and animal cell, as viewed with an electron microscope. cytoplasm Golgi apparatus plasma membrane cell wall ribosomes chloroplast vacuole nucleus nucleolus mitochondrion endoplasmic reticulum Plant cell (as seen with an electron microscope). mitochondrion nucleus Golgi apparatus nucleolus smooth endoplasmic reticulum plasma membrane lysosome rough endoplasmic reticulum Animal cell (as seen with an electron microscope). 22 Patterns in nature Gill Sans Bold a) Which structures are you able to see with an electron microscope that are not possible to see with a light microscope? _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ b) Identify differences between plant and animal cells. _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ _________________________________________________ c) You are a biologist working in a research laboratory comparing plant and animal cells. Prepare a comparison of the two types of cells, their structure and function. You may find it more convenient to put this information into a table. A suggested table with headings is provided here for you. You may select headings of your own. For each organelle state how the structure enables it to carry out its specific function. Part 4: Electron microscope and cell organelles 23 Organelle structure 24 Function Found in animal cells Found in plant cells Patterns in nature Gill Sans Bold Exercise 4.3: Tissues, organs and organ systems a) Define the following terms tissues _______________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ organs _______________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ organ systems _________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ b) Organ systems in multicellular organisms supply the needs of cells. For example, the circulatory system transports oxygen from the lungs to the cells. Outline how one other organ system supplies the needs of cells. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ Part 4: Electron microscope and cell organelles 25 Gill Sans Bold Biology Preliminary Course Stage 6 Patterns in nature Part 5: Obtaining and transporting materials in plants 2 0 0 In r2 e b S o t c NT O ng DM E i t ra E N o rp A M o c Gill Sans Bold Contents Introduction ............................................................................... 2 Autotrophic and heterotrophic cells ........................................... 4 Obtaining nutrients in plants...................................................... 5 Photosynthesis .....................................................................................5 Function of leaves ..............................................................................11 The stem.............................................................................................13 Roots...................................................................................................16 Transport systems in plants .................................................... 18 Xylem ..................................................................................................19 Phloem................................................................................................28 Gas exchange in plants........................................................... 30 Suggested answers................................................................. 37 Exercises–Part 5 ..................................................................... 39 Part 5: Obtaining and transporting materials in plants 1 Introduction Plants have specialised structures to obtain nutrients from their environment. You may recall that plants and animals obtain nutrients differently. Plants rely on the Sun to manufacture food by a process called photosynthesis. Plants are autotrophic organisms. Animals cannot manufacture their own food; they consume or eat other organisms in order to gain the nutrients they require for life processes. Animals are heterotrophic organisms. Plants and animals have specialised cells, tissues and organs to obtain the nutrition they require and carry out their body processes. Some of these will be investigated in this part. In this part you will be given opportunities to learn to: 2 • distinguish between autotrophs and heterotrophs in terms of nutrient requirements • identify the materials required for photosynthesis and its role in ecosystems • identify the general word equation for photosynthesis and outline this as a summary of a chain of biochemical reactions • explain the relationship between the organisation of the structures used to obtain water and minerals in a range of plants and the need to increase the surface area available for absorption • explain the relationship between the shape of leaves, the distribution of tissues in them and their role • outline the transport system in plants including: – root hair cells – xylem – phloem – stomates and lenticels Patterns in nature Gill Sans Bold In this part you will be given opportunities to: • plan, choose equipment or resources and perform first–hand investigations to gather information and use available evidence to demonstrate the need for chlorophyll and light in photosynthesis • perform a first–hand investigation and gather first–hand data to identify and describe factors that affect the rate of transpiration • perform a first–hand investigation of the movement of materials in xylem or phloem. Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. The most up-to-date version can be found on the Board’s website at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html. This version November 2002. To complete the practical activities in this part you will require the following equipment. Alternative exercises have been included. • • • • • • • • • • 1 large beaker or saucepan 1 small beaker or glass jar Bunsen burner or hot plate tripod and gauze (if using Bunsen) 250 mL water 50 mL methylated spirit a few soft fleshy leaves such as a geranium aluminium foil a variegated leaf plant iodine solution Part 5: Obtaining and transporting materials in plants • stick of celery • glass of water with food colouring (red/blue works best) • knife, small kitchen type • hand lens or microscope with lamp • glass slides and cover slips if using microscope • thin glass tubing or clear plastic tubing • Vaseline® or petroleum jelly • soft, fleshy plant stem eg. Impatiens • marker pen or sheet of graph paper • scissors • retort and clamp or similar. 3 Autotrophic and heterotrophic cells Cells can be classified as either autotrophic or heterotrophic depending on how nutrition is obtained. Autotrophic cells are those which can make their own food (auto = self; trophic = feeding). Plant cells with chloroplasts are autotrophic. The Sun’s energy is used to combine simple substances like carbon dioxide and water. These two raw materials are used to make glucose. Glucose can be changed into starch and other more complex substances like cellulose. Heterotrophic cells are those which cannot make their own food (hetero = other). Heterotrophs depend on food made by others. Heterotrophic cells include animal cells, fungal cells and some bacterial cells. Examples of autotrophic cells are: _________________________________________________________ Examples of heterotrophic cells are: _________________________________________________________ Check your answers. Complete Exercise 5.1. 4 Patterns in nature Gill Sans Bold Obtaining nutrients in plants Photosynthesis Plants carry out the food–making process called photosynthesis. In this process plants convert the Sun’s energy into chemical energy stored in sugars such as glucose. To do this, plants must have access to materials such as carbon dioxide and water. Oxygen and water are also produced in the process. Inputs carbon dioxide water light Outputs oxygen water sugars What do you remember about photosynthesis? 1 Where does photosynthesis take place in a plant? _____________________________________________________ 2 Name the cell organelle where photosynthesis takes place. _____________________________________________________ Part 5: Obtaining and transporting materials in plants 5 3 Describe the conditions necessary for photosynthesis to take place. ______________________________________________________ ______________________________________________________ Check your answers. Plants are producers as they make their own food. Plants are the first step in a food chain. They use light energy to produce carbohydrates like glucose. These carbohydrates are eaten by animals (herbivores and omnivores). In turn, herbivores are eaten by carnivores and so on through the food chain. So, in an ecosystem photosynthesis is an important step in the flow of energy. The phases of photosynthesis There are two main stages or phases in the photosynthetic process. These are called the light and dark phases. The light phase During this phase, light is absorbed by chlorophyll and the splitting of water molecules occurs. Water molecules are split to form oxygen and hydrogen ions. Light acts on the chlorophyll. The energy is converted from light to chemical energy. These reactions take place in the grana of the chloroplast. Many enzymes are used to carry out the process. light chlorophyll a ENERGY oxygen released splits H2O H+ to the second phase Simplified light phase of photosynthesis. 6 Patterns in nature Gill Sans Bold The dark phase The dark phase is often called the fixation of carbon phase. Carbon dioxide is fixed into glucose molecules using hydrogen ions and energy obtained during the light phase. energy from light phase hydrogen from light phase H+ + 5C sugar CO2 many steps Simplified dark phase of photosynthesis. This phase also involves a number of steps in the reaction where specific enzymes are required. This series of reactions occur in the colourless fluid of the chloroplast called the stroma that surround the grana. Light is not required for these reactions. Glucose is synthesised during the dark phase. 1 Outline what happens in the light phase of photosynthesis. _____________________________________________________ _____________________________________________________ 2 Outline what happens in the dark phase of photosynthesis. _____________________________________________________ _____________________________________________________ Check your answers. Word equations are used to describe reactions. They can also be used as a summary for complex pathways. The general word equation for photosynthesis is shown below. light energy carbon dioxide + water sugar + oxygen chlorophyll You can see from the previous diagrams that photosynthesis is a complex process. So, this equation is a summary of the biochemical reactions that make up the process of photosynthesis. You do not need to learn these biochemical reactions. Part 5: Obtaining and transporting materials in plants 7 A general equation for photosynthesis is: 6CO2 +6 H2O C6H12O6 + 6O2 Radioactive tracing has shown that a more correct equation for photosynthesis is: 6CO2 +12 H2O C6H12O6 +6O2 + 6H2O Complete Exercise 5.2. Why do most plants appear green? Photosynthetic pigment is a mixture of a number of different pigments, including chlorophyll. Chlorophyll absorbs mostly blue–violet and red light and reflects green. This characteristic of reflecting green light is why most leaves appear green in colour. Engelmann’s experiment Thomas Englemann was a German biologist who investigated the wavelength of light used by plants during photosynthesis. He used bacteria to detect the presence of oxygen by observing the change in bacteria numbers in different light environments. The environments were created by projecting the whole spectrum onto a filament of algae. The results indicated that red and violet wavelengths are absorbed by chlorophyll pigments, resulting in the increased production of oxygen and increased numbers of bacteria in the corresponding regions. The need for chlorophyll and light in photosynthesis In this activity you will be investigating the need for chlorophyll and light in photosynthesis. The first experiment examines the production of starch as an indicator that photosynthesis has occurred in parts of a leaf. The second experiment focuses on the production of starch in areas of leaves that do not contain chlorophyll. 8 Patterns in nature Gill Sans Bold Variegated leaves have areas that do not contain chlorophyll (Photo J West). Aim The aim of this experiment is to demonstrate the need for chlorophyll and light in photosynthesis. Materials required: • 1 large beaker or saucepan • 1 small beaker or glass jar • Bunsen burner or hot plate • tripod and gauze (if using Bunsen) • 250 mL water • 50 mL methylated spirit • a few soft fleshy leaves such as a geranium • aluminium foil • a variegated leaf plant (leaves with a mixture of colours – choose one that is a mixture of yellow and green) • iodine solution. Method: 1 Place aluminium foil over one half of your leaf on the plant, secure with paperclips and leave overnight. Part 5: Obtaining and transporting materials in plants 9 2 Place in direct sunlight for several hours. 3 Place your variegated plant in sunlight for several hours. 4 Pick the leaves from both plants and place the leaves in a beaker with the water. Remove the foil from the soft leaf. Heat the water and leaves gently, until they go very limp. 5 Turn off the heat source. 6 Remove the leaves from the water and place into the small beaker or jar with the methylated spirit. Care should be taken using methylated spirit, as it is a flammable substance. Avoid contact with a naked flame. Even methylated spirits vapours are flammable. 10 7 Place the small beaker or jar into the hot water and allow to stand for approximately five minutes. The green pigment should be extracted from the leaves after this time. If the methylated spirit has not become very dark green, stir the leaves and leave for a few extra minutes. 8 After there has been sufficient chlorophyll extracted, remove the leaves and wash them in water. 9 Now place your two leaves onto a white surface and flood them with iodine. Remember that iodine turns blue–black in the presence of starch and starch is produced in areas that are actively photosynthesising. Patterns in nature Gill Sans Bold Results In the areas that produce starch and are carrying out photosynthesis the iodine will turn blue–black or purple. In the yellow areas of variegated plants there is no chlorophyll so these areas should not be coloured. In the leaf that was covered with aluminium foil the light would not have got under the foil and photosynthesis would not have occurred. Conclusion The experiment demonstrated that photosynthesis does not occur unless there is both light and chlorophyll present. Do Exercise 5.3 now. Function of leaves Go outside into the garden or take a walk to a park. Look at the leaves on the plants and sketch three different ones on your own paper. Note, on your drawings, three similarities and three differences in the leaves you selected. You will have noticed that most leaves are thin and flat. There are a large range of leaf shapes. Being thin and flat means that leaves have a large surface area to volume ratio which is important for the absorption of light, oxygen and carbon dioxide. Part 5: Obtaining and transporting materials in plants 11 epidermis cuticle cells containing chloroplasts palisade mesophyll layer spongy mesophyll stomate air space xylem phloem cell wall vascular bundle Cross–section of a leaf. Source: Messel, H (chair). (1963.) Science for high school students. The Foundation for Nuclear Energy. University of Sydney. The chloroplasts are located in the mesophyll (middle leaf) region of the leaf. Gases enter and leave the leaf through the stomates. Therefore, the structure of the leaf ensures that the photosynthetic cells that contain chlorophyll are close enough to the top of the leaf to receive light and close enough to the stomates to gain the gases they require. 1 Outline the features of leaves. _____________________________________________________ _____________________________________________________ 2 Identify the major role of leaves. ______________________________________________________ ______________________________________________________ 12 Patterns in nature Gill Sans Bold 3 a) Identify the tissue where photosynthesis occurs in leaves. How does the location of this tissue assist in photosynthesis? _________________________________________________ _________________________________________________ b) Xylem carries water up through the plant. How does the location of this tissue help in photosynthesis? _________________________________________________ _________________________________________________ c) Xylem is associated with phloem in plants. Predict a role related to photosynthesis for phloem in plants.? _________________________________________________ _________________________________________________ 4 Can you suggest a reason why leaves are thin and flat? (Hint: Think about the effects of the SA:V.) _____________________________________________________ _____________________________________________________ Check your answers. The stem You have looked at the structure of leaves. This is where photosynthesis occurs. But how does the products of photosynthesis get to the other parts of the plants. To answer that question you need to look at the structure of the stem. Sketch a plant from your garden and label the stem, leaves, flowers and buds. Use your own paper. Stems can be recognised because they have leaves and buds. Most stems are above ground, forming part of the shoot system of plants. Some plants have underground stems and their leaves may be reduced to scales. Although the arrangement varies with different types of plants, stems usually form a complex branching pattern. The leaves are spaced along them to gain maximum exposure to sunlight. Part 5: Obtaining and transporting materials in plants 13 Tissues in stems Stems are usually green when young and can carry out photosynthesis. They may become woody when older. At the tip of each stem is a terminal bud, a growing point for the plant. Stems also support the flowers and fruit of the plant. One of the main functions of stems is transport. Internally, stems contain tubes of conducting tissue, the xylem and phloem. This vascular tissue carries materials between the shoot and root systems. The conducting tissue is arranged in a ring or scattered throughout the stem tissue. The outer covering of stems, the epidermis, forms an impermeable layer protecting the inner cells and preventing water loss. There are stomates for the exchange of gases on young green stems and lenticels which serve the same purpose on woody stems. Cells in the cortex and pith usually store food but may also contain chloroplasts and photosynthesise. There are air spaces between cells for the circulation of gases. Some stems are hollow with little or no pith. Cross–section of a stem showing vascular bundles. (Photo Jane West) 14 Patterns in nature Gill Sans Bold Close–up of a vascular bundle showing xylem, cambium and phloem (Photo Jane West) Vascular bundles Vascular bundles are groups of conducting tissue in a stem. Each bundle contains three types of tissue: xylem, phloem and cambium. Xylem forms long tubes up to 1 m in length. They are dead cells (they have no nucleus). These long tubes are known as xylem vessels. Xylem vessels are thickened with woody material, with cross walls that have broken down. Xylem gives support, strength and rigidity to the stem, and transports water and mineral ions upwards from the roots to the leaves. Note; Water and mineral ions travel only in one direction in the xylem–upwards. Phloem consists of living sieve–tube cells forming long columns. There are perforations in the cell walls so that the cytoplasm of the cells connects along the tubes. Associated with the sieve–tube cells, are companion cells and other supporting tissue. Organic materials including sugars, amino acids and hormones are transported by the living Part 5: Obtaining and transporting materials in plants 15 sieve–tube cells of phloem tissue. This movement is called translocation. Materials move both up and down through the plant in the phloem. The movement is too fast to be caused only by diffusion. There are several theories suggesting possible forces involved but the exact mechanism remains unknown. Cambium cells are capable of cell division. They divide to form cells which become new xylem and phloem tissue. In older stems division of the cambium cells results in a continuous ring of vascular tissue. Roots You have now read about how and why plants transport water. Have you asked yourself where they get the water? Roots do not photosynthesise but grow through the soil anchoring the plant and supplying the plant with water and mineral ions. To do this roots have to have an extensive surface area to be able to absorb water. The drawing below shows a young root covered in root hairs. The root hairs greatly increase the surface area of the root so that water can pass from the soil into the plant. As well as root hairs plants have different types of roots. The two main types of roots are fibrous roots and tap roots. 16 Patterns in nature Gill Sans Bold fibrous taproot 1 Outline the differences between taproots and fibrous root systems. _____________________________________________________ _____________________________________________________ _____________________________________________________ 2 What structures of root systems increase surface area to improve water uptake? _____________________________________________________ 3 Explain how the large surface area of roots assists in the survival of plants in dry weather. _____________________________________________________ _____________________________________________________ _____________________________________________________ Check your answers. Complete Exercise 5.4. Part 5: Obtaining and transporting materials in plants 17 Transport systems in plants You have already looked at some of the structures involved in the transport system of plants. Answer these questions below for revision. 1 What is the role of the root, stem and leaf in flowering plants? _____________________________________________________ _____________________________________________________ 2 Plants have a system of vascular bundles to transport sugars, gases and water within the plant. The term vascular bundle is used to describe the conducting tissue in a stem. What type of tissue is found in a vascular bundle? ______________________________________________________ ______________________________________________________ Check your answers. xylem tubes move water up the plant from the roots phloem tubes move sugars dissolved in water throughout the plant 18 Patterns in nature Gill Sans Bold Like all multicellular organisms, plants need to transport materials from one place to another. Sugars are produced by the process of photosynthesis in the leaves. Every cell in a plant requires sugars for respiration. So, sugars are transferred from where they are produced to where they are needed. The same is true for water and minerals. These are taken into the plant through the root hairs and are needed by every cell in the plant. This transport function is carried out by xylem tissues (for water and minerals) and phloem (for sugars). Cambium cells are capable of cell division. They divide to form cells, which become new xylem and phloem tissue. In older stems, division of the cambium cells results in a continuous ring of vascular tissue. Xylem Xylem forms long tubes up to one metre in length. They are made up of dead cells, thickened with woody material (lignin), the cross walls have broken down. They are known as xylem vessels. Xylem gives support, strength and rigidity to the stem, and transports water and mineral ions upwards from the roots to the leaves. Note: water and mineral ions travel only in one direction in the xylem–upwards. Movement of water and dissolved chemicals takes place in xylem vessels which form part of the vascular bundles within roots, stems and leaves. Detailed information on the processes involved in the movement of substances through the xylem can be found in the Additional resources section of this part. Stems can be recognised because they have leaves and buds. Most stems are above ground, forming part of the erect shoot system of plants. Some plants have underground stems and their leaves may be reduced to scales. Stems are usually green when young and can carry out photosynthesis. They may become woody when older. At the tip of each stem is a terminal bud, a growing point for the plant. Stems also support the flowers and fruit of the plant. Part 5: Obtaining and transporting materials in plants 19 In this activity you will be investigating the movement of water through the plant. Materials required: • stick of celery • glass of water with food colouring (red/blue works best) • knife, small kitchen type • hand lens or microscope with lamp • glass slides and cover slips if using microscope. What you will do: 1 Place a stick of celery into the glass of coloured water for a few hours. Place the celery into the glass. (Photo: J West) 2 20 Remove celery from water and cut in half, carefully, cutting away from fingers. Using the hand lens, examine the stem and the location of the coloured water. Patterns in nature Gill Sans Bold Cut across the stem. (Photo: J West) The coloured liquid is seen in the xylem. (Photo: J West) 4 Where in the stem is the coloured water located? _____________________________________________________ 5 Name the tissue in which the water is located. _____________________________________________________ Part 5: Obtaining and transporting materials in plants 21 6 Draw a sketch of your observations. If you have access to a microscope, prepare a slide of a cross–section of the celery stem. Observe this specimen under the microscope and look at it. (A cross–section is produced by cutting across, not lengthways.). Water enters the plant through the roots. The roots are covered by fine root hairs which increase the surface area for absorption of water. The root hairs are single celled extensions of the root epidermis (surface or outer layer of the root). Water enters the root hair by diffusion. The concentration of solutes in the soil water is lower than inside the root hair cells. Water will move from an area of high water concentration (in the soil) to an area of low water concentration (within the root hair cells). root hair soil particles water Water moves into the plant from the soil through the root hairs. 22 Patterns in nature Gill Sans Bold One of the main functions of stems is transport of substances around the plant. Stems contain tubes of conducting tissue or vascular bundles, which consist of the xylem and phloem, that carry materials between the shoot and root systems. The conducting tissue is arranged in a ring or scattered throughout the stem tissue. Transpiration When stomates are open gases including carbon dioxide can diffuse into a plant. At the same time, however, water molecules can diffuse into the air because of the higher water concentration inside the plant. Water evaporates from the cell surfaces, diffuses through the intercellular spaces and out through the stomates. This diffusion of water from a plant is called transpiration. Water loss by transpiration is unavoidable by a plant with the stomates open. The water lost needs to be replaced by uptake through the roots. There is a constant upward flow of water through a plant. This is known as the transpiration stream. If water loss exceeds water intake, the stomates close and cells lose their turgidity. The stems and leaves wilt and the plant may die. Transpiration is an important part of the mechanism by which water and mineral ions are transported from the roots to the stems and leaves. The evaporation of water has a cooling effect on the plant, particularly the leaves. Factors affecting transpiration The structure of the plant has an effect on the transpiration rate. Stomates may be open or closed. When they are closed the transpiration rate drops and diffusion occurs at a much slower rate through the cuticle. Normally, stomates are open during the day for the exchange of gases in photosynthesis and closed at night. Some plants have special features (adaptations) to reduce the transpiration rate. Structural features may include a very thick cuticle, sunken stomates, hairs on the leaf or a reduction in leaf surface area. Physiological features may include the closure of the stomates or rolling up of the leaf to reduce surface area, during the day when the temperature is high. There are a number of external (environmental) factors that affect transpiration in a plant. These are temperature, humidity, wind, light and soil. Part 5: Obtaining and transporting materials in plants 23 • In high temperatures, diffusion is more rapid (warm air holds more water than cold air). • If the atmosphere is saturated with water vapour (conditions of high humidity) transpiration is decreased. • Moving air increases the transpiration rate. Water vapour is carried away from the leaf and a high diffusion gradient maintained. • Light intensity affects stomate opening and this in turn affects the transpiration rate. • The water content of the soil and the solute concentration affect the rate at which water can be taken up by a plant. Measuring transpiration A potometer is an instrument which can be used to measure the rate of transpiration. There are several varieties of potometers. In a potometer, water is run into the apparatus through a glass funnel. A soft, fleshy twig or branch is pushed into the tubing which must be completely filled with water (it may assist to colour the water so that the movement can be easily seen). This must be a tight fit, otherwise water will run out of the capillary tube and the instrument will not function correctly. The area around the neck of the tubing where the plant has been inserted needs to be sealed, using Vaseline® or petroleum jelly. soft fleshy plant funnel or well water base very thin gradated glass tubing Experimental set up to measure the rate of transpiration. 24 Patterns in nature Gill Sans Bold As time passes, the thin thread of water moving along the capillary tube towards the plant will be visible. A scale fitted behind the capillary tube helps in the measurement of the rate of transpiration. It is possible to accelerate the process by changing the environmental conditions of the plant. For example, by using a fan it is possible to simulate windy conditions. Other variables (factors) such as temperature can be investigated for their effect on the rate of transpiration. The effect of the environment on transpiration Optional activity If you have access to the equipment below then carry out the experiment. If not, answer the questions at the end of the experiment in the results section. The aim of this experiment is to compare the rate at which a leaf loses water, that is, transpires, under different conditions. Materials required: • thin glass tubing or clear plastic tubing (look at the diagram to see what it could look like) • Vaseline® or petroleum jelly • soft fleshy plant stem eg. Impatiens • marker pen or sheet of graph paper • scissors • retort and clamp or similar. What you will do: 1 Fill the funnel with water. 2 Insert the soft, fleshy branch into the tubing 3 Smear Vaseline®, paraffin or fat around the join between the stalk and the tubing. This join must be airtight when removed from the water. 4 Check that there is no water leaking from your potometer at any point. Water is most likely to escape in the area where the stalk is placed into the tubing. 5 Set up a second potometer in the same way, but this time omit the leafy branch. The second potometer is used as the control. What is the function of a control? _____________________________________________________ Part 5: Obtaining and transporting materials in plants 25 6 7 26 Expose the potometer and the control to the following conditions and measure the time taken for the water to move 2 cm along the glass tube. Conditions to which the experiment and control and to be exposed are: • cool and shady (in a room away from a window or draught) • cool and windy (use a fan for creating ‘wind’) • hot and shady (use a radiator) • hot and windy (use a radiator plus a fan). Draw up a table of results on your own paper and enter your measurements. Patterns in nature Gill Sans Bold Results: 1 Outline the conditions where you would expect the transpiration rate to be greatest. _____________________________________________________ _____________________________________________________ 2 Which type of conditions causes plants to wilt? _____________________________________________________ _____________________________________________________ 3 Why do people need to top up the water in vases with cut flowers? _____________________________________________________ _____________________________________________________ 4 Not all the water lost from vases of flowers is taken up by the plants. Explain. _____________________________________________________ _____________________________________________________ Conclusion Transpiration rate is affected by different external conditions. For each of the conditions below describe the rate of transpiration (fast, medium, slow). • cool and shady ________________________________________ • cool and windy ________________________________________ • hot and shady _________________________________________ • hot and windy ________________________________________ Explain briefly how nutrients are obtained and transported around plants. Your answer should include the names of the main structures and processes involved. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Check your answer. Part 5: Obtaining and transporting materials in plants 27 Summary of processes of water transport Several processes appear to be involved in the upward movement of water in plants. • Adhesion: forces of attraction between different particles are called forces of adhesion. The cellulose cell walls in plants soak up water by this process, in much the some way as a blotter soaks up water. • Capillarity: capillarity is the rise of water in thin tubes by forces of adhesion and cohesion. The water rises up thin tubes because of attraction between the particles of the plant and water particles (adhesion) and because of the attraction between the water particles themselves (cohesion). • Root pressure: this refers to the upward movement of water caused by the pressure from water moving into the root as a result of osmosis. • Transpiration–cohesion: the transpiration cohesion theory proposes that the loss of water molecules from the leaves, that is, transpiration, results in the upward movement of more water molecules since these molecules are attracted to each other by forces of cohesion. • Guttation: is the loss of water in the form of a liquid from openings on the leaves. Phloem Phloem tissue like xylem tissue, consists of tube–like cells. In phloem these cells are called sieve cells and they form long columns. When these cells mature they lose their nuclei. There are perforations in the cell walls at the end so that the cytoplasm of the cells can connect along the tubes. These are called sieve plates. Associated with the sieve tube cells are companion cells (which retain their nuclei and cytoplasm) and other supporting tissue. 28 Patterns in nature Gill Sans Bold Phloem tube. Translocation Organic materials including sugars, amino acids and hormones are transported by the living sieve tube cells of the phloem tissue. This movement is called translocation. The material that flows through phloem is called sap. The approximate composition is 30% plant sugars and 70% water. Materials move both upwards and downwards through the plant. The movement is too fast to be caused only by diffusion. There are several theories suggesting possible forces involved however the exact mechanism remains unknown. Probably the most widely accepted explanation for the mechanism of phloem translocation is the pressure flow hypothesis of Ernst Much, which was proposed in 1930. Leaves and roots can be sources of nutrients; nutrients are unloaded into stem apexes, flowers, fruits and roots. Movement of sap through the phloem results in pressure within the cells. When aphids stick a feeding tube into the phloem, the sap is forced through the aphid’s body. Complete Exercise 5.4. Part 5: Obtaining and transporting materials in plants 29 Gas exchange in plants Like multicellular animals, multicellular plants usually have specialised tissues for gas exchange. You will look mainly at angiosperms (flowering plants) and algae (seaweeds and their relatives) in this section. Respiration is the process by which energy is released for use by the cell. All plant cells respire. Plant cells respire aerobically (most of the time). This means that they use oxygen gas in the process and release carbon dioxide gas as a waste product. Some plant cells produce glucose by the process of photosynthesis. During photosynthesis carbon dioxide is used and oxygen is released. During daylight a plant respires as well as carrying out photosynthesis. In sunlight, plants: • release more oxygen from photosynthesis than their cells use in respiration • use all the carbon dioxide released by their cells in respiration in photosynthesis • take in additional carbon dioxide from the atmosphere to satisfy the needs of photosynthesis. At night, plants: • do not photosynthesise • take in oxygen gas from the atmosphere for respiration. • release carbon dioxide gas as a product of respiration. Overall plant metabolism results in the release of more oxygen than carbon dioxide. If a plant was placed in a sealed container for several days and nights the composition of air in the container would change. Even though plants do not photosynthesise at night, they still release more oxygen during photosynthesis than they absorb by respiration. 30 Patterns in nature Gill Sans Bold So, what is the evolutionary significance of plants releasing more oxygen than carbon dioxide? Prior to the evolution of photosynthesising organisms, the Earth’s atmosphere was significantly different as it contained no free oxygen gas. It probably contained gases like methane as well as higher levels of carbon dioxide than today. As free oxygen, produced by photosynthesis, became available it could react with the methane to produce carbon dioxide. That carbon dioxide was then available for photosynthesis. Since photosynthesis produces a net amount of oxygen, the atmospheric oxygen levels were able to gradually increase. Photosynthesis has changed the composition of the atmosphere of the planet. This must surely be one of the most significant change made by living things on the planet. 1 Imagine that you have placed a plant into an airtight container. There is air in the container, but it cannot escape from the container. The container is placed outside and left in sunlight for eight hours. What would you expect to happen to the composition of the air in the container? _____________________________________________________ _____________________________________________________ 2 Return to the plant in the sealed container. What would happen to the composition of the air in the container at night? _____________________________________________________ _____________________________________________________ Check your answers. Gas exchange in leaves Green plants require gas exchange for two purposes: • provision of carbon dioxide gas for photosynthesis • provision of oxygen gas for respiration. When these gases are not available within the cells of a plant then the gases need to be brought in from the surrounding atmosphere. The leaf is one of the most important gas exchange sites. Cells in leaves respire and are also some of the most important cells involved in the process of photosynthesis. Part 5: Obtaining and transporting materials in plants 31 You will already know that the outer surface of a leaf has a waxy covering (cuticle). The cuticle is a most unsatisfactory surface for gas exchange. However, it does prevent excessive water loss. Gases enter the leaf through tiny holes called stomates. Cells in the interior of a leaf do not have a waxy covering. In most plants, there are more stomates on the underside of the leaf than on the upper surface. This reduces the amount of water that can be lost through the stomatal openings. Look at the diagram of a cross–section of a leaf following. cuticle epidermal cell palisade mesophyll many chloroplasts in cytoplasm of cell xylem and phloem cells in leaf vein spongy mesophyllwith fewer chloroplasts in cytoplasm air space epidermis cuticle The stomate is shown on the lower surface of the leaf. The two guard cells of a stomate surround a pore. When the guard cells are turgid (full of fluid) they are curved like a banana. The curve of the two turgid guard cells creates the opening that allows gases into and out of the leaf. When the guard cells are flaccid they collapse, sealing the stomate. When stomates are closed, water vapour and gases cannot pass into or out of the leaf. 32 Patterns in nature Gill Sans Bold Leaf epidermis. Note the stomates are all open. Many consider stomate closure to be an adaptation to prevent desiccation or drying out. Explain. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Check your answer. Where does gas exchange occur? Gas exchange in plants occurs on the surface of each cell in the leaf. Moisture on the outside of the cells allows gases to dissolve into fluid. Once dissolved, gases can diffuse into the cell. Wastes are removed by a similar method. The waste gases diffuse to the moisture on the outside of each cell and from there to the gases in the cavities within the leaf. For cells that are not immediately adjacent to a leaf cavity, gases are passed by diffusion from cell to cell to deliver gases to cells deeper in the leaf. Stomates open into cavities and there are considerable air spaces within the leaf. Because the cells within the leaf are so tiny, the surface area to volume ratio is high for each cell adjacent to a leaf cavity. Just as in lungs, gills and insect tracheoles a high surface area to volume ratio is important for gas exchange in plants. Part 5: Obtaining and transporting materials in plants 33 Gas exchange is required for all plant cells, even the ones that are not photosynthesising. Gas exchange in stems As stems are often thick, a different structure is required to allow gases to pass through outer coverings such as bark. This structure is the lenticel. Lenticels are a loose association of cells with many intercellular spaces between them. These spaces allow oxygen to pass from the atmosphere to the respiring cells within the stem. Lenticels also allow waste carbon dioxide to leave the plant. lenticels Lenticels can be found on a woody stem. lenticel Lenticels allow gas exchange to occur. Root hairs are sufficiently moist, small and thin to allow adequate gas exchange between the gases in the soil air and the roots. 34 Patterns in nature Gill Sans Bold 1 With the aid of examples, explain why gas exchange surfaces have a high surface area to volume ratio. _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ _____________________________________________________ 2 Outline the role of stomates in: a) gas exchange _________________________________________________ b) prevention of desiccation. _________________________________________________ 3 A number of plants growing in arid parts of Australia close their stomates during the heat of the day. Their stomates are only opened during the evening, early morning and late afternoon. Make a hypothesis to explain these observations. _____________________________________________________ _____________________________________________________ Check your answers. Complete Exercise 5.5. Part 5: Obtaining and transporting materials in plants 35 36 Patterns in nature Gill Sans Bold Suggested answers Autotrophic cells and heterotrophic cells Autotrophic cells include plant cells and some bacterial cells. Heterotrophic cells include animal cells, fungal cells and some bacterial cells. Photosynthesis 1 Photosynthesis takes place in the green parts of plants, especially the leaves. 2 Photosynthesis occurs in the chloroplasts. 3 Light provides the energy that drives the process, photosynthesis. Chlorophyll (in the chloroplasts), carbon dioxide and water are necessary materials. The phases of photosynthesis 1 Light is absorbed by chlorophyll and water molecules are split into hydrogen and oxygen. 2 Carbon fixation and glucose is synthesised in the dark phase of photosynthesis. Function of leaves 1 Leaves are mostly green, thin and flat. They have a network of veins. 2 The major role of leaves is to provide the plant with food. Photosynthesis occurs mainly in the leaves. 3 a) Photosynthesis occurs in mesophyll (spongy and palisade). The mesophyll is located between the layers of epidermis. Mesophyll has access to carbon dioxide that enters through the stomata. Part 5: Obtaining and transporting materials in plants 37 b) Xylem provides water for photosynthesis. c) Phloem transports the products of photosynthesis to the rest of the plant. 4 The flat shape increases the SA:V ratio. This means there is a large surface area available for light absorption for photosynthesis. Because leaves are thin, the mesophyll is close to the epidermis. So, carbon dioxide can easily absorb to the mesophyll for the process. Roots 1 Tap roots have a main central root from which the root hairs grow. Fibrous roots do not have a central root, but simply a collection of fine roots spreading out. 2 Roots have root hairs on their surface that increase the surface area. 3 The increased surface area enables the plants to spread out within the soil to gather available moisture and dissolved nutrients. This aids in the survival of the plants, particularly in times/areas when there may be a water shortage. Transport systems in plants 1 Roots absorb water and dissolved nutrients from the soil. The stem supports the plant and the leaf is the site of photosynthesis. 2 Each vascular bundle contains three types of tissue: xylem, phloem and cambium. (Note: cambium is not a conducting tissue.) The effect of the environment on transpiration Nutrients are absorbed through the root hairs on the root system of a plant. They are transported via the xylem by adhesive and cohesive forces, to the leaves. The movement of water upward through the plant is called transpiration. From the leaves, the products of photosynthesis are transported via the phloem to the rest of the plant. The movement of sugars around the plant is called translocation. 38 Patterns in nature Gill Sans Bold Exercises – Part 5 Exercises 5.1 to 5.5 Name: _________________________________ Exercise 5.1 Outline the main difference between autotrophs and heterotrophs. _________________________________________________________ _________________________________________________________ Exercise 5.2: The phases of photosynthesis a) Write down the general word equation for photosynthesis. b) Explain why this equation can be thought of as a summary of a chain of biochemical reactions. _____________________________________________________ _____________________________________________________ _____________________________________________________ Exercise 5.3: Photosynthesis a) List the materials required for photosynthesis. _____________________________________________________ _____________________________________________________ b) What is the role of photosynthesis in the ecosystem? _____________________________________________________ _____________________________________________________ Part 5: Obtaining and transporting materials in plants 39 Exercise 5.4: Absorption of water and minerals in plants Plants obtain water and minerals through their root systems. Roots are generally long and thin. Root hairs are found along the tips of growing roots. How does the structure of the root system affect a plant’s ability to obtain water and minerals? _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 5.5: Transport systems in plants a) Multicellular plants and animals have transport systems. Why is this necessary? ______________________________________________________ ______________________________________________________ b) Describe the movement of water through a plant starting with root hairs and finishing with the water leaving the plant. ______________________________________________________ ______________________________________________________ ______________________________________________________ c) You have learned that materials move upwards in xylem. Substances move upward and downward in the phloem. How do we know this? Briefly describe the evidence for movement of substances in the xylem or the phloem. You may need to consult a biology textbook and another source such as the Internet. ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ 40 Patterns in nature Gill Sans Bold Biology Preliminary Course Stage 6 Patterns in nature Part 6: Obtaining materials in animals 2 0 0 In r2 e b S o t c NT O ng DM E i t ra E N o rp A M o c Gill Sans Bold Contents Introduction ............................................................................... 2 Obtaining nutrients in animals ................................................... 4 Increased surface area in animals ......................................................4 Digestion in grazing herbivores ...........................................................6 Digestion in carnivores.........................................................................8 Nectar feeders ....................................................................................10 Suggested answers................................................................. 13 Exercises–Part 6 ..................................................................... 15 Part 6: Obtaining materials in animals 1 Introduction Animals have specialised cells, tissues and organs to obtain the nutrition they require and carry out their body processes. Some of these will be investigated in this part. In this part you will be given opportunities to learn to: • describe the role of teeth in increasing the surface area of complex foods for exposure to digestive chemicals • explain the relationship between the length and overall complexity of digestive systems of a vertebrate herbivore and a vertebrate carnivore with respect to: – the chemical composition of their diet – the functions of the structures involved. In this part you will be given opportunities to: • perform a first–hand investigation to demonstrate the relationship between surface area and rate of reaction • identify data sources, gather, process, analyse and present information from secondary sources and use available evidence to compare the digestive systems of mammals, including a grazing herbivore, carnivore and a predominantly nectar feeder. Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. The most up-to-date version can be found on the Board’s website at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html. This version November 2002. 2 Patterns in nature Gill Sans Bold To complete the practical activities in this part you will require the following equipment. Alternative exercises have been included. • • • • • • mortar and pestle or a suitable grinding tool and vessel petri dish or small plate Bunsen burner or hotplate 3 test tubes or similar sand small quantity of liver from a butcher • hydrogen peroxide (this can be purchased at a pharmacist) Part 6: Obtaining materials in animals 3 Obtaining nutrients in animals You have seen that plants have structures such as root hairs that increase surface area for absorption. Animals have increased surface area for the absorption of nutrients, as well. Food and water are taken in through the mouth and pass through the alimentary canal. The nutrients are digested and absorbed along the way. The physical breakdown in the mouth by the teeth increases the surface area for chemical digestion in the stomach and the small intestine. The lining of the intestines is made of folded membranes called villi that increase the surface area for the absorption of nutrients. Increased surface area in animals The following activity will help you demonstrate how increased surface area assists the digestive process in the body. If you grind up a substance you produce a much larger surface area for any reaction to occur. This is what happens in your mouth when you chew on your food. You increase the surface area for enzymes to work on the food. In this experiment you will compare the rate of reaction of a whole piece of liver and one that has been ground up. The whole piece of liver will have a smaller SA:V than the equal size piece of ground liver. Hydrogen peroxide is broken down by an enzyme found in the liver. This produces oxygen which can be seen as bubbles in the container. Materials required: 4 • mortar and pestle or a suitable grinding tool and vessel • petri dish or small plate • 3 test tubes or similar • Bunsen burner or hotplate • sand Patterns in nature Gill Sans Bold • small quantity of liver from a butcher • hydrogen peroxide (this can be purchased at a chemist) Procedure 1 Divide the liver into two equal quantities. 2 Place a small quantity of clean sand into a test tube or onto a dish or plate. 3 Take one piece of liver and grind it together with the sand and place into test tube or onto dish. 4 Place one piece (whole) into a test tube or onto dish. 5 Add an equal volume of hydrogen peroxide to each of the four test tubes and observe carefully. Observations 1 Describe what is seen in each of the test tubes by completing the table below. 2 A control is used in an experiment to ensure that a fair test is being carried out. Which test tube is the control in this experiment? _____________________________________________________ Results Sample Description of reaction Amount of gas produced sand only fresh liver ground with sand whole piece of liver Conclusion What can you say about surface area and rate of reaction from this experiment? _________________________________________________________ _________________________________________________________ Part 6: Obtaining materials in animals 5 Digestion in grazing herbivores Digestion begins in the mouth. The shape of the teeth give a clue to the type of food eaten by an animal. Herbivores have large grinding molars that crush the food to increase the surface area for digestion. incisors molars Herbivore teeth. Herbivores have diets high in complex carbohydrates. These complex carbohydrates such as cellulose and lignin require a complex digestive system. The ruminant digestive system. Can you identify the components? 6 Patterns in nature Gill Sans Bold Grazing herbivores use micro–organisms contained within their digestive systems to break down complex carbohydrates such as cellulose. The process of cellulose digestion is called fermentation. This may occur before or after the stomach. Many farm animals like sheep, cattle, goats and camels are foregut fermenters. The have complex digestive systems with three or four stomach compartments to deal with their diet. The largest of these stomach compartments is called the rumen, so they are called ruminant animals. Cattle, for example, have a stomach that is made of four compartments called the rumen, reticulum, omasum and abomasum. It is the special ruminant bacteria that are located in the rumen that carry out the majority of the fibre digestion. oesophagus reticulum omasum rumen abomasum duodenum small intestine caecum large intestine Organs of the ruminant digestive system. Ruminant animals require water, carbohydrates, proteins, fats, vitamins and minerals in their diet. Part 6: Obtaining materials in animals 7 Animals use carbohydrates to provide energy. All animals can make use of sugars and starches in food, but only ruminants such as sheep and cattle can make full use of the complex carbohydrate, cellulose. The great benefit of the ruminant digestive system is that it can decompose cellulose through the activity of micro–organisms in the rumen. Proteins are the basic structural material of many parts of an animal and its products. In the rumen the protein that an animal eats is altered. The protein requirements of grazing animals are mostly supplied from the pasture they graze. However, ruminants are able to make their own proteins through the action of micro–organisms. Cell contents also contain minerals. These are chemical substances needed by all animals for proper growth and development. Most ruminant animals live in sunlight and have access to green feed, so they usually do not suffer from a shortage of vitamins. Ruminant animals have an inbuilt supply of the B group vitamins, which are synthesised by micro–organisms in the rumen. The other main group of grazing herbivores are the hindgut fermenters. Examples of this group are horses, rabbits and possums. They carry out cellulose digestion in an organ after the stomach called the caecum. In rabbits the caecum has the capacity ten times the stomach and it fills most of the abdomen. Digestion in carnivores Carnivore teeth are adapted to catching and holding prey and then ripping it to pieces. They have large canines. Examples of carnivores are dogs, cats and the Tasmanian devil. incisors canines molars Carnivore teeth. 8 Patterns in nature Gill Sans Bold The digestive systems of carnivores are the simplest among mammals. The large intestine of carnivores is relatively shorter than herbivores. The food source for carnivores is animal cells eg. muscle cells. These do not have a cell wall and so they can be digested rapidly. Muscle cells in meat are high in protein so carnivores do not need to eat large amounts of food to gain the same amount of nutrients that a herbivore requires. Muscle cells are also higher in energy content and take less energy to digest than the food of herbivores. The differences in food eaten are reflected in the different structures in the digestive systems of herbivores and carnivores. Herbivores have to take in a large amount of food that requires complex digestion. They have large specialised digestive systems. Carnivores take in a smaller amount of high energy food and have smaller and less complex digestive systems. stomach small intestine dog (Canis familiaris) 10 cm (for a 80 cm length dog) rectum colon Digestive system of a dog. 1 What type of teeth is used for eating meat? Can you suggest a reason for their special shape? _____________________________________________________ _____________________________________________________ 2 What type of teeth is used by animals that eat only plants? Can you suggest why they have a different shape to that of the meat eaters? _____________________________________________________ _____________________________________________________ 3 What type of teeth do humans have? How does this reflect the type of food eaten? _____________________________________________________ _____________________________________________________ Part 6: Obtaining materials in animals 9 4 Carnivores do not possess a four chambered stomach. They do not have a use for fibre digestion, as they consume only meat. Carnivorous animals have only one stomach chamber. How many stomach chambers do humans have? Can you suggest a reason for this? ______________________________________________________ ______________________________________________________ ______________________________________________________ Check your answers. Nectar feeders The length and structure of the intestines will vary according to the diet of the organism. The more complex the substances that enter the intestines the longer they are. Organisms such as nectar feeders that eat simple carbohydrates will have a shorter digestive tract overall compared to that of the animals that eat complex carbohydrates such as the herbivores and carnivores. This is due to the fact that their primary food source is simple sugars which are easily digested or broken down. stomach honey possum (Tarsipes rostratus) small intestine 1 cm rectum colon The honey possum – an example of a nectar feeder. Comparison of different digestive systems You have seen from the previous information that the digestive systems of different species have different structures that reflect their food source. Each has structural differences that allow the animal to obtain the appropriate nutrients. The table on the next page summarises this information. 10 Patterns in nature Gill Sans Bold Feature Herbivore Carnivore Nectar feeder major chemical composition of diet complex carbohydrates including cellulose proteins, fats simple sugars, protein teeth large grinding molars to crush food sharp canines and molars for catching and holding prey few teeth time in mouth chewed for a long period of time rapidly swallowed rapidly swallowed time spent eating most of the day short feeding period Honey possums can drink up to 20% of their body mass in minutes stomach foregut fermenters (ruminants eg. cattle) have a four chambered stomach for break down of cellulose small, one chambered stomach two chambered stomach, one may be for nectar storage intestines hindgut fermenters have an enlarged caecum for break down of cellulose short and unspecialised large and small intestines indistinguishable, no caecum You will need to gather, process and analyse information from secondary sources to carry out the following task. Suggested places to look for information include Internet, journal articles, and text–books. There is also some information above. Make sure your source is reliable by checking it against other sources. A table such as the one above is a good way of presenting information. You need to identify your data source and present information to compare the digestive systems of mammals, including a grazing herbivore, carnivore and a nectar feeder There are some good starting points on the LMP website. http://www.lmpc.edu.au/science Complete Exercise 6.1. Part 6: Obtaining materials in animals 11 12 Patterns in nature Gill Sans Bold Suggested answers Digestion in grazing herbivores 1 Canines and incisors for cutting and tearing the meat, molars for chewing. 2 Incisors for cutting and molars for chewing or grinding. 3 Humans have an omnivorous diet and so have incisors for cutting, canines for tearing and molars for chewing. 4 Humans have one stomach. They do not eat significantly high proportions of fibre compared to herbivores and do not have the ruminant bacteria for this purpose. Part 6: Obtaining materials in animals 13 14 Patterns in nature Gill Sans Bold Exercises – Part 6 Exercise 6.1 Name: _________________________________ Exercise 6.1: Obtaining nutrients in animals a) Describe the role of teeth in increasing the surface area of food for the exposure to digestive enzymes. _____________________________________________________ _____________________________________________________ _____________________________________________________ b) Prepare a table to summarise the differences between the digestive tract of vertebrate herbivores, carnivores and nectar feeders. Organise your answers into the columns shown in the table below. Type of vertebrate Chemical composition of diet Structures of the digestive system Function of structure herbivore carnivore nectar feeder Part 6: Obtaining materials in animals 15 Gill Sans Bold Biology Preliminary Course Stage 6 Patterns in nature Part 7: Transporting materials in animals 2 0 0 In r2 e b S o t c NT O ng DM E i t ra E N o rp A M o c Gill Sans Bold Contents Introduction ............................................................................... 2 Transport systems in animals.................................................... 3 Respiratory system ..............................................................................3 Circulatory system................................................................................3 Excretory system..................................................................................4 Circulatory systems ................................................................... 5 Gas exchange in animals .......................................................... 8 Insects...................................................................................................8 Fish .....................................................................................................10 Frogs...................................................................................................11 Mammals ............................................................................................12 Investigative technology .......................................................... 16 Exercises–Part 7 ..................................................................... 19 Part 7: Transporting materials in animals 1 Introduction In plants and animals transport systems and gaseous exchange move chemicals through the internal environment as well as the external environment. In the previous parts you have identified the nutrients required by living things and how they are obtained form the surroundings. In this part you will be looking at how these nutrients are transported around animals. In this part you will be given opportunities to learn to: • compare the roles of the respiratory, circulatory and excretory systems • identify and compare the gas exchange surfaces in an insect, a frog, a fish and a mammal • explain the relationship between the requirements of cells and transport system in multicellular organisms • compare open and closed circulatory systems using one vertebrate and one invertebrate as examples In this part you will be given opportunities to: • use available evidence to discuss, using examples, the role of technologies, such as the use of radioisotopes in tracing the path of elements through living plants and animals. Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. The most up-to-date version can be found on the Board's website at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html This version November 2002. 2 Patterns in nature Gill Sans Bold Transport systems in animals In animals there are three systems that move materials around the body and between the body and the surrounding environment. These systems are: • respiratory system • circulatory system • excretory system. Respiratory system The respiratory system is responsible for the movement of gases throughout the body. Oxygen is required for every cell in the body and carbon dioxide must be removed from every cell in the body. The respiratory system performs this function. Organs that are part of the respiratory system of animals are lungs, gills and spiracles in insects. Circulatory system The circulatory system transports food, oxygen and wastes throughout the body. Every cell has requirements for nutrients and must get rid of poisonous waste materials. This is the role of the circulatory system. Organs of circulatory systems are heart, veins, arteries, capillaries and the haemocoel in insects. Circulatory systems may be open or closed. Part 7: Transporting materials in animals 3 Excretory system All animals need to excrete wastes produced from metabolic processes in their cells. A build–up of wastes can produce unwanted effects and many substances such as urea can become toxic in excess qualities. Wastes substances that have to be remove include water, carbon dioxide and nitrogenous compounds. Organs of excretion include kidneys, lungs, skin and malpighian tubules in insects. Comparison of the systems All three systems have different tasks but they share common features and common roles. The circulatory system has a role in the other two systems because the blood vessels move materials to the organs of respiration and excretion. Organs of the respiratory system such as the lungs have a function in excretion of carbon dioxide. All three systems work together to transport nutrients and waste products from where they enter the body to where they leave the body. The table below summarises this information. Respiratory system Circulatory system Excretory system Organs Lungs, gills, skin, spiracles Heart, blood vessels, lymph, haemocoel Kidneys, lungs, skin, malpighian tubules Function Movement of gases through the body Transport nutrients and waste products around the body Rid the body of waste materials, water balance Complete Exercise 7.1. 4 Patterns in nature Gill Sans Bold Circulatory systems All multicellular plants and animals require a transport mechanism to move nutrients, gases and wastes to and from cells. These materials need to be moved around an organism’s body efficiently. This to ensure that all cells obtain the appropriate materials to maintain function and any products and wastes are removed. Both plants and animals have methods of transporting materials within the body. However, the transport of materials occurs in different ways. In this section you will focus on transport in animals. The circulatory system transports oxygen, food material and wastes to and from cells. The movement of the blood through an organism depends on the action of a heart. All vertebrates and some invertebrates such as earthworms have a closed circulatory system. This means that blood is transported around an organism within muscular tubes or blood vessels. The diagram following shows the movement of blood through the human circulatory system. Invertebrates such as arthropods have an open circulatory system. A pool of blood is circulated by the action of a heart, there are no specialised vessels for transporting blood. An insect’s blood is in direct contact with its body cells–blood is not contained in blood vessels as such. The internal space of an insect’s body can be considered as a single blood vessel called the haemocoel. This name comes from Greek words: haima (blood) and koilia (hollow). An insect’s circulation system is in fact not entirely ‘open’ as they have pumping vessels to promote the flow of blood. Part 7: Transporting materials in animals 5 anterior vena cava capillaries in arms and head capillaries in lungs capillaries in lungs posterior vena cava pulmonary artery right atrium pulmonary vein left atrium right ventricle left ventricle hepatic portal vein hepatic artery capillaries in liver mesenteric vein capillaries in stomach and small intestine renal vein mesenteric artery capillaries in kidneys renal artery capillaries in legs and abdominal organs oxygenated blood de-oxygenated blood Human circulatory system – a closed system. accesory pump haemocoel pumping vessel brain gut Insect circulatory system – partially open system. 6 Patterns in nature Gill Sans Bold A closed circulatory system ensures that there is one pathway ensuring tissues are supplied with blood. It relies on a central heart to pump the blood around within the specialised blood vessels. These require large amounts of energy. All vertebrates have a closed circulatory system. Open circulatory systems do not require the large amounts of energy required by closed circulatory systems. They suit smaller animals that do not make rapid movements. Complete Exercise 7.2. Part 7: Transporting materials in animals 7 Gas exchange in animals All animal cells respire. Animal cells respire aerobically (most of the time). They use oxygen gas in the process and release carbon dioxide gas as a waste product. Animal cells do not photosynthesise. In this section you will investigate and compare gas exchange surfaces of an insect, a fish, a frog and a mammal. The gas exchange tissues and organs of major groups of multicellular animals are often different. In this section you will examine those differences. Insects Insects do not have lungs or gills. Insects exchange gases with the atmosphere using trachea, tracheoles and spiracles. longitudinal trachea spiracle tracheoles Structures used in gas exchange in an insect. 8 Patterns in nature Gill Sans Bold Insects carry out gas exchange through a series of internal tubes (trachea) that connect to the outside through holes (spiracles) located at various points on the insect body. The trachea branch into smaller and smaller tubes (tracheoles). Tracheoles are very tiny (about one micron in diameter). The branching into many tiny tubes has two advantages for the insect. • Because the tracheoles are extensively branched throughout the insect, most cells are close to specialist gas exchange surfaces. • The branching and the small size of the tracheoles greatly increases the surface area to volume ratio of the gas exchange surfaces. Fluid collects in the ends of the tracheoles and it is into this fluid that gases dissolve before diffusing into the surrounding cells. The tracheoles are close to body cells. When waste gases eg. carbon dioxide concentrations are higher in the cell than the neighbouring trachea, then the waste gases diffuse out of the cell. When oxygen levels are higher in the trachea than the surrounding cells oxygen will diffuse into the cells. The spiracles connect the trachea to the atmosphere surrounding the insect. When the insect uses its muscles the trachea are compressed and this causes gases to be pushed out of the spiracles. When the muscles relax the trachea are not compressed and gases flow back into the trachea. Spiracles are able to close to help reduce water loss. Because the internal parts of the body are very humid it is possible for water be removed as a vapour from the body. Spiracles also have fine hair–like structures to prevent dust entering the system. If dust were to enter, the tracheoles could become blocked and this would reduce the efficiency of the gas exchange surfaces. Part 7: Transporting materials in animals 9 Fish Most fish use gills for gas exchange. Gills are external structures–they hang outside the main body cavity and often have a protective cover over them. Gills have a large surface area because they are thin and highly folded. water from mouth gill raker gill arch cartilage water flows out behind operculum lamella water primary filaments operculum Gas exchange in fish Water enters a fish’s mouth and passes over the gills. When most fish are stationary they gulp water to maintain the flow over the gills. This also explains why so many fish (sharks included) swim with their mouth open–this allows the water to pass into the mouth and over the gills without the need to gulp water. Gases are exchanged between the surrounding water and the fish on the gill surface. The gases enter the circulatory system where they are transported to cells throughout the body. The main blood vessels entering the gills branch into tiny tubes called capillaries. The capillaries are very close to the gill surface. It is the colour of the blood in the capillaries that makes gills appear red. Capillaries being tiny and numerous make the surface area to volume ratio for diffusion of gases very high in the gills. 10 Patterns in nature Gill Sans Bold Frogs Frogs have two methods of gas exchange: gas exchange via the lungs and gas exchange via the skin. The diagram below shows the structures involved. lungs diffusion in moist skin Frogs exchange gases through their lungs and moist skin. Gas exchange via the lungs Lungs are internal organs involved in gas exchange. The gas exchange surfaces of terrestrial organisms are usually internal to prevent desiccation (drying out). You will have noticed that the gas exchange surfaces of insects (also terrestrial) are internal too. Frogs ventilate their lungs by positive pressure breathing. This means that they force air into the lungs. This method of breathing is very different to the negative pressure breathing seen in mammals. You will look at negative pressure breathing later. Unlike human nostrils, which stay open all the time, frogs are able to open and close their nares (nostrils). To breathe, a frog • closes its mouth and opens its nares • lowers the floor of the mouth causing air to be ‘sucked’ into the mouth cavity • closes the nares (nostrils) • raises the floor of the mouth. This forces the air in the mouth into the lungs. Part 7: Transporting materials in animals 11 Lung structure of a frog The internal structure of a frog lung is not too dissimilar to a human lung. Air enters the lungs and then moves through a series of branching tubes. The tubes become smaller and smaller as they branch (this is becoming a familiar theme for gas exchange). The finest tubes are in close association with capillaries (small blood vessels). Gases diffuse into and out of the blood at these sites. Like the fish, the circulatory system delivers gases to the cells. The circulatory system also receives the waste gases from cells and delivers them to the lungs. You will take a much closer look at the structure of lungs in the next section. Gas exchange via the skin The skin of a frog is thin and kept moist by the habitats in which the frog lives. The skin is permeable to water (unlike human skin). Frogs dehydrate rapidly if they are not kept in a moist environment. This is why you find frogs in moist locations. Gases from the atmosphere dissolve into the moisture on the skin. From there the gases can diffuse into the capillaries beneath the skin. The skin does not exchange sufficient gases for all of a frog’s needs. However, the gas exchange is important and allows the frog to remain submerged for longer than if it had to depend on lungs alone. While submerged, gaseous exchange occurs on the frog’s skin. Mammals Mammalian lungs are internal. This helps to reduce the loss of water and heat through these structures that have a high surface area to volume ratio. To get air into the lungs the mammal lowers the air pressure in the lungs. When the air pressure in the lungs is lower than the surrounding atmosphere, air enters via the nose. To remove air from the lungs, mammals increase the pressure of the air in the lungs. When air pressure in the lungs is higher than the surrounding atmosphere air moves out of the lungs. The structure of the human respiratory system is shown on the diagram on the following page. 12 Patterns in nature Gill Sans Bold nose nasal cavity trachea wall magnified epiglottis cilia to the stomach trachea bronchus bronchiole rib right lung showing lobes left lung dissected to show internal diaphragm from pulmonary artery air to pulmonary vein cluster of alveoli capillaries Structures involved in the exchange of gases in humans. Air enters the body through the nostrils. The nasal cavity warms the air, filters it and removes dust. The air then moves into the throat region or pharynx (pronounced farrinks). It enters the largest air tube–the trachea (pronounced track–ee–ah) through the opening called the glottis. The epiglottis is a flap of tissue that closes over the glottis and stops food going down the wrong way when we swallow. The trachea branches into two bronchi (pronounced bron–key). Each bronchus (singular) branches into smaller air passages called bronchioles (bron–key–oles) and these end in very thin–walled alveoli (pronounced al–vee–oh–lie), singular alveolus. Blood capillaries are wrapped closely around the alveoli. It has been estimated that the total surface area of the alveoli of an adult male is about one third the area of a tennis court. A large surface area obviously allows for a greater quantity of gases to be exchanged. The thinness of the walls of the alveoli allows for rapid diffusion of oxygen into the blood and carbon dioxide out of the blood. The moisture in the alveoli walls allows gases to dissolve. Part 7: Transporting materials in animals 13 blood from body (low in oxygen, high in carbon dioxide) blood capillary wall of alveolus air inhaled air exhaled carbon dioxide oxygen blood cell blood to rest of body (high in oxygen, low in carbon dioxide) Movement of material in an alveolus. Composition of inhaled and exhaled air is shown in the table below. Gases Percentage in inhaled air (%) Percentage in exhaled air (%) oxygen 21 16 0.04 4 about 80 about 80 varies according to the humidity of the air more than in inhaled air carbon dioxide nitrogen water vapour Air passages Rings of cartilage keep the trachea and bronchi open and prevent them closing when the air pressure inside the body falls. The lining cells of the air passages have numerous cilia (sill–ee–ah). These are minute hair–like projections that sweep to and fro. Mucus is secreted by special gland cells, also present in the lining or epithelial (ep–e–theel–e–al) cells. Dust particles and bacteria in the air are trapped by the mucus film. The movements of the cilia sweep them 14 Patterns in nature Gill Sans Bold away in the mucus to the larynx and the mucus is swallowed or coughed up. The nose hairs and mucus also trap dust and foreign particles. Around the lungs is a membrane, the pleural (ploo–ral) membrane, which covers the outside of the lungs and the inside of the chest cavity. It contains a fluid that lubricates the surface so that there is no friction between the tissues during breathing movements. The mechanism of breathing In mammals, breathing refers to the movements of the chest that result in air entering and leaving the lungs. The movement of air in and out of our chest is bought about by changes in the pressure of the air in the chest cavity. This pressure varies because the volume of the chest cavity varies. The chest cavity is airtight and enclosed by ribs with intercostal (inter–cos–tal) muscle between them. At the base of the chest cavity is the diaphragm (die–ah–fram). The diaphragm is the muscular sheet separating the chest (also called thorax) and abdomen. At rest, the diaphragm is curved upwards. The intercostal muscles relax at the same time and the ribs move downwards and inwards. These collapsing movements reduce the size of the chest cavity, increase the pressure of the air in the lungs and thus force it out. During inhalation, the diaphragm contracts and flattens, being more taunt or tight in this state. At the same time, the intercostal muscles contract and move the rib cage up and outwards. This increases the volume of the chest cavity and reduces the pressure of the air in it. Air thus moves into the lungs. You can check these movements by placing your fingers over your rib cage as you inhale and exhale. Complete Exercise 7.3. Part 7: Transporting materials in animals 15 Investigative technology Much of what is known about the structure and function of living things has been directly associated with the improvements in technology available. New technology is increasing the range of investigative methods in research laboratories, industry, environmental management and in the medical profession. The use of radioisotopes have improved productivity and gained information that cannot be obtained in any other way. Radioisotopes produce radioactive emissions that can be easily detected. This property makes radioisotopes very useful as tracers. Radioactive materials can be tracked through a process, system or organism. Examples of use include mapping pathways of nutrients and toxins through ecosystems, absorption of nutrients by plants and tracing metabolic pathways. Increasingly medical diagnosis is making use of tracers for organ and tissue function. Many chemical elements have isotopes. (Isotopes have the same number of protons but a different number of neutrons in the nucleus of an atom.) Some isotopes are unstable and emit alpha or beta particles and sometimes gamma radiation. Tracers can be used to follow movement of substances in large amounts or at molecular or even atomic levels. The observations are made by measuring the radioactivity or by measuring the relative abundance of the stable isotopes. The instruments used for detecting the tracers pathway include electroscopes, scintillation counters, the Geiger–Müller counter and the mass spectrometer. 16 Patterns in nature Gill Sans Bold Radioactive tracers Radiation is used in nuclear medicine to diagnose the functioning of organs such as the liver and kidneys. Radioactive tracers are used which emit gamma rays for very short periods of time. Radioactive materials are introduced into the body orally, by injected or they are inhaled. An image of the organ showing the location of the radioisotope is used in diagnosis. An unusual pattern indicates a malfunction in the organ. Bone and other tissue can be seen much more clearly using these imaging techniques than by x–rays. Blood flow to the brain, liver and kidney function and bone growth can be diagnosed using radioisotopes as tracers. The amount of radioisotope given to patient is a very small dose, only enough to obtain an image for diagnosis. Technetium–99 is a very common isotope used in medicine. It has a half–life of six hours. Technetium–99 emits low energy gamma rays so the patient receives only a very low radiation dose. Geiger counters A Geiger counter is a machine that measures radioactivity. In the experiment on the following page radioactive carbon was taken in by the leaves through the process of photosynthesis. The Geiger counter was used to measure the amount of radioactive carbon in the leaves and in the fruit. The next day the readings showed that the radioactive carbon had moved from the leaf to the fruit. Part 7: Transporting materials in animals 17 Day 1 sugar with radioactive carbon on scraped leaf Geiger counter HIGH tomato fruit Geiger counter LOW Day 2 sugar with radioactive carbon on scraped leaf Geiger counter LOW tomato fruit Geiger counter HIGH Gather information from secondary sources on the use of radioisotopes in tracing the path of elements through living plants and animals. You will need to carry out a search of secondary information sources such as contacting research institutions such as ANSTO, CSIRO or the Internet. Conventional sources such as libraries will have many references you can use and may be a good place to start. Process the information by answering the questions in Exercise 7.4. 18 Patterns in nature Gill Sans Bold Exercises - Part 7 Exercises 7.1 to 7.4 Name: _________________________________ Exercise 7.1: Transport systems in animals Compare the roles of the excretory, respiratory and circulatory systems in the body. systems _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 7.2: Circulatory systems a) What is the role of the circulatory system in humans? _____________________________________________________ _____________________________________________________ Part 7: Transporting materials in animals 19 b) What is the difference between open and closed circulatory systems? Give examples. ______________________________________________________ ______________________________________________________ ______________________________________________________ c) Which system is more efficient – open or closed circulatory system? Give reasons. ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ ______________________________________________________ Exercise 7.3: Comparison of gas exchange Identify and compare the gas exchange surfaces in an insect, a frog a fish and a mammal by filling in the table below. Organism Name of gas exchange structures insect frog Surface Area/Volume ratio Gas exchange structures internal/external high skin low lungs high external fish mammal 20 internal Patterns in nature Gill Sans Bold Exercise 7.4: Radioactive tracers Discuss the role of radioisotopes as tracers in medicine. What are the issues? Provide points for and against the use of radioactive materials in medicine. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Part 7: Transporting materials in animals 21 Gill Sans Bold Biology Preliminary Course Stage 6 Patterns in nature Part 8: Growth and repair 2 0 0 In r2 e b S o t c NT O ng DM E i t ra E N o rp A M o c Gill Sans Bold Contents Introduction ............................................................................... 2 Cell division ............................................................................... 3 Sites of mitosis .....................................................................................4 What happens during mitosis? ............................................................6 Mitosis in plant cells .............................................................................7 Cytokinesis .........................................................................................11 Additional resources................................................................ 12 Suggested answers................................................................. 15 Exercises–Part 8 ..................................................................... 17 Student evaluation of module Part 8: Growth and repair 1 Introduction Maintenance of organisms requires growth and repair. In this part you will be given opportunities to learn to: • identify mitosis as a process of nuclear division and explain its role • identify the sites of mitosis in plants, insects and mammals • explain the need for cytokinesis in cell division • identify that nuclei, mitochondria and chloroplasts contain DNA. In this part you will be given opportunities to: • perform a first–hand investigation using a microscope to gather information from prepared slides to describe the sequence of changes in the nucleus of plant or animal cells undergoing mitosis Extract from Biology Stage 6 Syllabus © Board of Studies NSW, originally issued 1999. The most up-to-date version can be found on the Board's website at http://www.boardofstudies.nsw.edu.au/syllabus_hsc/syllabus2000_lista.html This version November 2002. Materials required: • microscope and lamp • two slides and a cover slip • onion with fresh roots (you need to soak onion base in water at least a week in advance) • methyl green pryonin or aceto–orcein stain. Alternatively use prepared slides of a root tip (if available). If you do not have access to a microscope or prepared slide, use the photographs provided. 2 Patterns in nature Gill Sans Bold Cell division A multicellular organism such as a human, begins life as a single cell formed from the union of two sex cells. From this microscopic beginning the organism grows to become an adult. This is achieved by the process of cell division. One cell divides forming two cells and then each of these cells divide forming more cells to continue the process of cell division. Mitosis is a type of cell division that results in the replication of identical cells. Meiosis is another type of cell division which produces gametes or sex cells. Meiosis produces cells that have half the number of chromosomes of the parent cell. Mitosis results in growth of an organism, is involved in the healing of wounds and the replacement of cells eg. red blood cells and skin cells. With the exception of gametes (ova and sperm), all the body cells or somatic cells come from pre–existing cells by mitosis. 1 Write a definition, in your own words, for mitosis. _____________________________________________________ _____________________________________________________ 2 How is mitosis different from meiosis? _____________________________________________________ _____________________________________________________ 3 What is the role of cell division in multicellular organisms? _____________________________________________________ _____________________________________________________ Check your answers. Part 8: Growth and repair 3 Sites of mitosis Mitosis occurs in areas of rapid growth in organisms. These sites are in different places in different types of organisms. This is usually due to the need for rapid replication such as growth points or sites where repair to damaged tissue is required. Multicellular organisms may also have stages in their life cycle during which mitosis may occur at a greater rate such as within a developing foetus. Plants Mitosis in plants occurs in special cells called meristematic cells and in the layer of cells in the stem called cambium. These cells are responsible for the growth in length and width. In the root there is a protective area called the root cap. Behind this area is the apical meristem where active cell division is occurring. This is followed by an area of elongation where the newly formed cells increase in size. cortex growth zone xylem cell division phloem cell elongation root hair root cap Diagram of a root tip showing the growth zone. In the stems, secondary growth occurs in the cambium. The vascular cambium forms phloem and xylem cells. At the tip of the shoots there is the apical meristem where mitosis is occurring rapidly forming new cells. Buds are another structure that contain meristematic tissue which is capable of rapid growth. 4 Patterns in nature Gill Sans Bold Insects Insects have a multiple staged life cycle. During a larval stage the organism increases in size. This is due to cell enlargement and not cell division. Increased rates of mitosis occur in the epidermal cells before a moult during the pupal stage. Metamorphosis results in the breakdown of the larval tissue and the development of the adult insect. Mammals In mammals mitosis is occurring in many parts of the body. Skin, hair and nails are continually growing. Blood cells are made daily to replace those that have died. Any injury results in rapid mitosis to repair the damage. Young mammals are growing rapidly and at this stage of life mitosis rates are high. 1 Complete the following table by matching the sites of mitosis in either plant or mammal. Site of mitosis Plant/animal root tip skin digestive tract shoot tip bone marrow hair and nails stems 2 Explain why mitosis is important to insects during metamorphosis. _____________________________________________________ _____________________________________________________ Check your answers. Complete Exercise 8.1. Part 8: Growth and repair 5 What happens during mitosis? When a cell divides, a series of changes occur in the nucleus of cells. The most important parts of the nucleus involved in the process are the chromosomes. Chromosomes determine the characteristics of an organism. Genes are found along chromosomes and consist of sections of DNA (deoxyribose nucleic acid). Most of the DNA in a cell is found in the nucleus. 1 What is DNA? Why is it important? _____________________________________________________ _____________________________________________________ 2 The DNA part of chromosomes carries the genetic code as genes. Each time a cell divides by mitosis, new daughter cells end up with chromosomes, and hence DNA, which is identical to those of the original parent cell. The discovery of the structure of DNA and the way it is replicated during cell division, has been one of the most exciting and important events in 20th century biology. Mitosis is essentially the replication of chromosomes and their separation into daughter cells. What major developments in technology do you think assisted in the identification of DNA? ______________________________________________________ ______________________________________________________ Check your answers. Self replicating organelles Plastids and mitochondria are self–replicating organelles. This means that when mitosis is occurring these organelles reproduce independently of the nuclear division. Chloroplasts (a type of plastid) and mitochondria both posses genetic material (DNA) that enables them to replicate. It is thought that they may be descendants of ancient procaryotic cells that have since become part of other cells. 1 List the cell organelles that contain DNA. _____________________________________________________ _____________________________________________________ 6 Patterns in nature Gill Sans Bold 2 Most of the cell’s DNA is present in the nucleus. What parts of the nucleus are made of DNA? _____________________________________________________ 3 What is the role of DNA in the cell? _____________________________________________________ _____________________________________________________ Check your answers. Complete Exercise 8.2. Mitosis in plant cells The process of mitosis in plants is similar to that in animals. However, there are two differences: • there are no centrioles in most plants • the cell does not become constricted in the last stage of the process. In plant cells, the partition usually starts in the centre of the cell and grows outwards to meet the existing right cell wall. 1 Why do cells undergo mitosis? _____________________________________________________ _____________________________________________________ 2 What are the differences between the parent cells undergoing mitosis and the resulting daughter cells? _____________________________________________________ 3 _____________________________________________________ What is the significance of division after replication for a cell? _____________________________________________________ _____________________________________________________ Check your answers. Part 8: Growth and repair 7 Microscopic examination of mitosis in plant cells As you have already read the root tip is a site of rapid mitosis in plants. In this experiment you will examine a root tip for the stage of mitosis. Materials required: • microscope and lamp • two slides and a cover slip • onion with fresh roots (you need to soak onion base in water at least a week in advance) • methyl green pryonin or aceto–orcein stain. Alternatively use prepared slides of a root tip (if available). If you do not have access to a microscope or prepared slide, use the photographs provided following. Procedure: 1 Remove a new root from the base of the onion and place it in the centre of a clean slide (only the top portion is required if it is very long). 2 Place another slide on top and gently squash the two slides together. This should grind the root tip. 3 Remove the top slide, ensuring the squashed material remains on the lower slide. 4 Add one drop of stain to the material and cover with the cover slip. 5 Allow to stand for about 20 minutes and then examine under the microscope. Observe the cells in the slide of the root tip. You are looking for the different stages of mitosis. 8 6 Identify cells that have undergone mitosis. 7 Draw diagrams showing the stages in mitosis. Patterns in nature Gill Sans Bold Slide of root tip showing various stages of mitosis. How many stages can you pick out? (Photo Jane West) Interphase (animal cell) Interphase plant cell Your drawing of a plant cell nucleus Part 8: Growth and repair 9 10 Prophase (animal cell) Prophase plant cell Your drawing of a plant cell Metaphase (animal cell) Metaphase plant cell Your drawing of a plant cell Anaphase (animal cell) Anaphase plant cell Your drawing of a plant cell Telophase (animal cell) Telophase plant cell Your drawing of a plant cell Patterns in nature Gill Sans Bold Cytokinesis Mitosis refers to the changes involving the chromosomes during cell division. Cell division, however, usually includes the division of the cytoplasm and certain organelles within the cytoplasm. The division of the cytoplasm is called cytokinesis. In animal cells cytokinesis is usually achieved by the formation of a cleavage furrow which deepens to constrict the two parts. In plant cells, a cell wall forms across the middle, separating the two parts. 1 At what point in mitosis does cytokinesis occur? _____________________________________________________ 2 Why is cytokinesis important in cell division? _____________________________________________________ _____________________________________________________ Check your answers. Complete Exercise 8.3. You have come to the end of the module Patterns in nature. You will have come to recognise that there are patterns in living things as they adopt similar methods of solving the problems of surviving. Part 8: Growth and repair 11 Additional resources Phases in mitosis You do not need to learn the names of the stages of mitosis. 1 Interphase This stage is sometimes misleadingly called the ‘resting’ stage. In fact, the cell is very active. It is during this stage that each chromosome becomes replicated. A cell with four chromosomes would end up with eight at this stage. Cells with 46 chromosomes (a human cell) would end up with 92 and so on. Organelles, such as mitochondria, ribosomes (and chloroplasts in plants) are also replicated although how they are replicated is not clearly understood. As well, the centrioles, which are outside the nucleus, begin to separate. In most of the more complex plants there are no centrioles. 2 Prophase During this stage, the chromosomes are visible, first as long, thin strands. As the process continues, the chromosomes become shorter and thicker. Each chromosome and its replica are held together by a structure called the centromere. The identical chromosomes at this stage are called chromatids. The centrioles move to opposite ‘poles’ of the cell and spindle fibres start to form. This stage ends with the breakdown of the nuclear membrane. 3 Metaphase The spindle consists of long molecules of protein lying across the cell from pole to pole. The chromosomes move through the cytoplasm to the spindle and become fastened to it by their centromere. The centromere becomes attached along a plane about halfway between the poles. 12 Patterns in nature Gill Sans Bold This plane is called the equator. At this middle stage the chromosomes are in the middle of the cell. 4 Anaphase The centromeres divide so that each chromatid has its own centromere. Each chromatid now is a daughter chromosome. The daughter chromosomes move apart, each member of a pair moving to opposite poles of the cell. Each group of daughter chromosomes forms a densely packed group at each pole. Remember: at anaphase the chromosomes are moving apart. Notice that four chromosomes move to opposite parts (poles) of the cell. Notice also that the cells start to become constricted in the centre. 5 Telophase Nuclear membranes form around each group of daughter chromosomes. The chromosomes uncoil to become slender threads. A new cell membrane forms at the equator. The cytoplasm divides and two new daughter cells now exist, where there was originally only one parent cell. Part 8: Growth and repair 13 2 early prophase 1 interphase 3 late prophase nucleus chromatid centromere 4 metaphase spindle 6 telophase 5 anaphase Mitosis in an animal cell with two chromosomes. 14 Patterns in nature Gill Sans Bold Suggested answers Cell division 1 Mitosis is a type of cell division resulting in the replication of identical cells. 2 Meiosis produces cells that have half the number of chromosomes compared to the parent cell. This process produces the gametes or sex cells. 3 Cell division is responsible for growth, repair and reproduction of multicellular organisms. Sites of mitosis 1 2 Site of mitosis Plant/animal root tip plant skin animal digestive tract animal shoot tip plant bone marrow animal hair and nails animal stems plant Cells need to be produced rapidly when undergoing metamorphosis compared to other stages in which no mitosis occurs. Part 8: Growth and repair 15 What happens during mitosis? 1 DNA makes up the material of inheritance or the genetic material in a cell. Every cell needs to have its own DNA code for its specific structure and function. 2 The development of the electron microscope and staining techniques. Self replicating organelles 1 The nucleus, chloroplasts and mitochondria all contain DNA. 2 The chromosomes in the nucleus are made of DNA. A section of DNA with specific information is called a gene. Genes are part of chromosomes. 3 DNA contains information that is transferred when cells replicate. Mitosis in plants 1 Cells undergo mitosis for growth and repair of body tissue. 2 The parent cells are usually larger than daughter cells initially. 3 Cells must divide after replication otherwise they would end up with double the amount of genetic material. Cytokinesis 16 1 After the chromosomes have separated into two nuclei the cytoplasm divides so that the cells are able to enter interphase. 2 Cytokinesis is important because after mitosis the nucleus has divided and separate nuclear membranes of the daughter cells have formed. Then the cytoplasm must divide (cytokinesis) to produce two new cells. Patterns in nature Gill Sans Bold Exercises - Part 8 Exercises 8.1 to 8.3 Name: ________________________ Exercise 8.1: Mitosis Mitosis is a very significant process in any living thing. Write a short report to explain the significance of the process of mitosis for plants and animals. Your report should include reference to: • the role of cell division in multicellular organisms • the activities of chromosomes during mitosis (describe the sequence of change) • where mitosis occurs in plants, mammals and insects. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Part 8: Growth and repair 17 _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 8.2: What happens during mitosis? Identify the parts of a cell that contain DNA. _________________________________________________________ _________________________________________________________ _________________________________________________________ Exercise 8.3: Cytokinesis Explain the importance of cytokinesis. _________________________________________________________ _________________________________________________________ _________________________________________________________ _________________________________________________________ 18 Patterns in nature Student evaluation of the module Name: ________________________ Location: ______________________ We need your input! Can you please complete this short evaluation to provide us with information about this module. This information will help us to improve the design of these materials for future publications. 1 Did you find the information in the module clear and easy to understand? _____________________________________________________ 2 What did you most like learning about? Why? _____________________________________________________ _____________________________________________________ 3 Which sort of learning activity did you enjoy the most? Why? _____________________________________________________ _____________________________________________________ 4 Did you complete the module within 35 hours? 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