Biology Student Textbook Grade 11 PDF

Biology Student Textbook Grade 11 Author: Steve Potter Adviser: Alemu Asfaw Evaluators: Solomon Belayneh Getachew Bogale Silas Araya Federal Democratic Republic of Ethiopia Ministry of Education Acknowledgments The development, printing and distribut...

Biology Student Textbook Grade 11 Author: Steve Potter Adviser: Alemu Asfaw Evaluators: Solomon Belayneh Getachew Bogale Silas Araya Federal Democratic Republic of Ethiopia Ministry of Education Acknowledgments The development, printing and distribution of this student textbook has been funded through the General Education Quality Improvement Project (GEQIP), which aims to improve the quality of education for Grades 1–12 students in government schools throughout Ethiopia. The Federal Democratic Republic of Ethiopia received funding for GEQIP through credit/financing from the International Development Associations (IDA), the Fast Track Initiative Catalytic Fund (FTI CF) and other development partners – Finland, Italian Development Cooperation, the Netherlands and UK aid from the Department for International Development (DFID). MOE/GEQIP/IDA/ICB/001/09 The Ministry of Education wishes to thank the many individuals, groups and other bodies involved – directly and indirectly – in publishing the textbook and accompanying teacher guide. 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We would be pleased to insert the appropriate acknowledgement in any subsequent edition of this publication. © Federal Democratic Republic of Ethiopia, Ministry of Education First edition, 2002 (E.C.) ISBN: 978-99944-2-012-4 Developed, Printed and distributed for the Federal Democratic Republic of Ethiopia, Ministry of Education by: Pearson Education Limited Edinburgh Gate Harlow Essex CM20 2JE England In collaboration with Shama Books P.O. Box 15 Addis Ababa Ethiopia Second Edition 2007 (E.C.), By Tan Prints India Pvt. Ltd. All rights reserved; no part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise without the prior written permission of the copyright owner or a licence permitting restricted copying in Ethiopia by the Federal Democratic Republic of Ethiopia, Federal Negarit Gazeta, Proclamation No. 410/2004 Copyright and Neighboring Rights Protection Proclamation, 10th year, No. 55, Addis Ababa, 19 July 2004. Disclaimer Every effort has been made to trace the copyright owners of material used in this document. We apologise in advance for any unintentional omissions. We would be pleased to insert the appropriate acknowledgement in any future edition Printed in Malaysia (CTP-PPSB) Contents Unit 1 The science of biology 1 1.1 The methods of science 2 1.2 The tools of a biologist 15 1.3 The relevance and promise of biological science 25 1.4 Biology and HIV/AIDS 30 Unit 2 Biochemical molecules 42 2.1 Inorganic and organic molecules 42 2.2 Inorganic molecules 43 2.3 Organic molecules 52 Unit 3 Enzymes 79 3.1 Nature of enzymes 80 3.2 Functions of enzymes 88 3.3 Factors affecting the functions of enzymes 93 Unit 4 Cell biology 111 4.1 Cell theory 112 4.2 Types of cells 121 4.3 Parts of the cell and their functions 125 Unit 5 Energy transformation 151 5.1 Respiration 152 5.2 How do plants harness light energy in photosynthesis? 170 Grade 11 iii The science of biology Unit 1 Contents Section Learning competencies 1.1 The methods Define science as a way of knowledge of science and explain it as a way of looking at and (page 2) thinking about natural events. Describe and explain the main steps that scientists follow when they are investigating something. Demonstrate scientific methods by narrating how Louis Pasteur and Alexander Fleming used the scientific method to solve problems. Plan and conduct an experiment to investigate a particular observation. Write a report for a scientific experiment. 1.2 The tools of Name and describe the function of a biologist the main pieces of apparatus that are (page 15) used by biologists the world over. Describe how these pieces of apparatus work. Explain how, and under what circumstances, these pieces of apparatus would be used and demonstrate the use of some of them. Classify the apparatus as laboratory tools, field tools or both. Be aware of possible health and safety implications of using these tools. 1.3 The relevance Explain how biological science is and promise relevant to food production, health and of biological disease, conservation, and control of the science population. (page 25) Explain the promise of biology in relation to genetic engineering and biotechnology. 1.4 Biology and Explain how biologists are actively HIV/AIDS involved in the fight against AIDS. (page 30) Describe how you can help community efforts to control AIDS. Describe the decisions you will need to take to help control AIDS. Grade 11 1 UNIT 1: The science of biology 1.1 The methods of science By the end of this section you should be able to: Define science as a way of knowledge and explain it as a way of looking at and thinking about natural events. Describe and explain the main steps that scientists follow when they are investigating something. Demonstrate scientific methods by narrating how Louis Pasteur and Alexander Fleming used the scientific method to solve problems. Plan and conduct an experiment to investigate a particular observation. Write a report for a scientific experiment. Scientists investigate natural events to try to find out exactly why and how they happen. To arrive at an answer, they need conclusive evidence that a certain factor causes the event. Very often, this kind of evidence can only be obtained by carrying out experiments. You will learn how to proceed from identifying the problem to planning and carrying out an investigation in such a way that the results will enable you to conclude that the factor you are investigating does (or does not) cause the event to happen. Along the way, you will see how some of the greatest biologists have used this scientific method in their investigations. You will also learn how to write a report on a scientific investigation in such a way that scientists all over the world would be able to instantly recognise the stages in your investigation and carry it out for themselves if they wanted to check your results. What is the science of biology? Biology is the science of life and living organisms. You know from earlier studies that an organism is a living being made from one cell (for example bacteria, unicellular algae) or many cells (for example, animals, plants and most fungi). The word biology is derived When we think of biologists, we often have quite a narrow view of from two Greek words: what they do. But, just as all chemists don’t wear white coats, all bios – meaning ‘life’ and biologists don’t look down microscopes in laboratories. Here are just a few of the areas of biological study. logos – meaning ‘study’ Some biologists become astrobiologists. These biologists engage in all kinds of research to try to find evidence of life on other planets in our Solar System and in galaxies elsewhere in the Universe. Other biologists take part in biomedical research. These biologists help in many areas, including the development of new drugs and vaccines. They also study the ways in which diseases develop to gain a better understanding of them so that cures can be found. 2 Grade 11  UNIT 1: The science of biology Others still become microbiologists. These biologists study how micro-organisms of all kinds function. Some micro-organisms cause disease, and understanding how they work makes a treatment more likely. Many microbiologists are studying the human immuno-deficiency virus (HIV) to get a better understanding of how AIDS develops and how it can be treated. Paleobiology is a fascinating area of study to many people. Paleobiologists try to find out more about the way in which life began on Earth and how it has evolved from simple life forms into more complex ones. They use evidence from fossils and from studies of the chemistry of ancient rocks to make estimates of when and how new life forms appeared on the planet. Many different biologists are involved in the Human Genome Project. This enormous project has produced the first ever map of the 46 chromosomes found in human cells. It has located the tens of thousands of genes and has determined the exact structure of each chromosome. Although the ‘map’ is finished, there is still much to be found out. Analysis will continue for many years to come. Besides these biologists, there are others who are, perhaps, more recognisable. These include: doctors, dentists, veterinary surgeons, nurses, physiotherapists, botanists, zoologists, physiologists, biochemists, agricultural biologists, ecologists, ethologists, entomologists, geneticists, oncologists, neurobiologists, parasitologists...... and many, many others besides. What is science? The word science comes from the Latin word scientia, which means Genetics, paleobiology, biomedics... ‘knowledge’. But science isn’t just about having knowledge: science Even trying to find signs of life on is a unique system of acquiring knowledge based on the scientific other planets: it's all Biology! method. This science is sometimes called experimental science, because it depends very heavily on experimentation to obtain the information. This is different from applied science, in which scientific research is used to meet certain human needs. However, it is often difficult to separate the two. Activity 1.1: What do you think science is? Gregor Mendel was a monk and so not obviously ‘a scientist’. He was puzzled by the patterns of certain features in the offspring of mice and pea plants. He carried out many carefully KEY WORDS controlled breeding experiments with pea plants and, by scientific method the process analysing his results thoroughly, he was able to form the basic by which scientists approach laws of how genes are inherited. their work Isaac Newton is famous the world over because an apple falling experimental science the on his head gave him an idea. Why did the apple fall towards use of experiments to obtain the earth and not travel away from the earth into space? After information some considerable thought and work, Newton worked out the basic laws of gravitation that apply to all particles and bodies applied science the use of anywhere in the Universe. Naturally, he couldn’t test this easily scientific research to meet by experiment! certain human needs Grade 11 3  UNIT 1: The science of biology ‘Recipe’ for bees: Kill a young Both of these men are ranked as great scientists, yet the work bull and bury it in an upright they did seems to be very different. So what is it that allows position so that its horns us to call them scientists? What is science? protrude from the ground. Write a short paragraph to explain why we would consider After a month, a swarm of Mendel and Newton to be scientists. bees will fly out of the corpse. ‘Recipe’ for mice: Place a dirty shirt or some rags in an open Science is an ongoing effort to find new information and principles pot or barrel containing a which can increase human knowledge and understanding. In their few grains of wheat or some research, scientists collect evidence that supports or disproves a wheat bran. In 21 days, mice particular suggested explanation of a natural phenomenon. One will appear. There will be adult important idea in science is that any suggested explanation of a males and females present and phenomenon should be capable of being proved wrong. If there is they will be capable of mating no way of proving it wrong, how can other people accept that it is and reproducing more mice. correct? This is what distinguishes science from religious beliefs. People had seen swarms of bees flying from a bull’s What is the scientific method? carcass and mice emerging This is the process by which biologists and all other scientists from containers containing approach their work. For centuries, people based their explanations dirty shirts and cereal. They of what they saw going on in the world around them on assumed that, because the two observations, without testing their ideas to see if they were true. events were linked, that one One ancient belief was that simple living organisms could come into caused the other. How could being by spontaneous generation. This idea suggests that non- you repeat the ‘mice from living objects can give rise to living organisms. shirts’ investigation to show As an example: conclusively that the mice did (or did not) come from Observation: Every year in the spring, the river Nile flooded the shirts? areas of Egypt leaving behind mud containing many nutrients that enabled the people to grow that year’s crop. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times. Conclusion: Muddy soil gives rise to frogs! Ask question Also, before the invention of the refrigerator, animal carcasses were hung by the heels in butcher’s shops and people would ask the Do background research butcher to cut off the part they wanted. The shop was always full of flies. So people believed that the meat had turned into flies! Construct Think! Because of these and other observations, many people, including quite eminent ‘scientists’ of the day, produced recipes for ‘creating’ hypothesis Try again life from non-living objects. It took the work of Louis Pasteur using Test with an experiment the proper scientific method to finally disprove this myth. Read the information and question in the box on the left and think Analyse results draw conclusion about how you would test whether an explanation is true or false. Hypothesis is true Hypothesis is false or partially true What are the main steps of the scientific method? The scientific method consists of a number of stages. These are Report results summarised in the flowchart. So what is happening at each of these stages? What is the biologist Figure 1.1 The scientific method doing and what do we mean by hypothesis? 4 Grade 11  UNIT 1: The science of biology To help you understand what is happening at each stage of the KEY WORDS scientific method, an example using the growth of a tomato seed is detailed below. spontaneous generation the appearance of living organisms from non-living matter Table 1.1 How a biologist would follow the scientific method hypothesis an educated guess Step of the method What happens at this step about what a biologist thinks the Ask a question Something catches our imagination. explanation of an observation We know that tomato seeds germinate will be. But it has to be stated in when they are planted. But, why don’t such a way that it can be tested tomato seeds grow inside tomatoes? by an experiment Do background Before we start trying to do the whole prediction an educated guess as research investigation ourselves, we will first to how the biologist thinks his/ check scientific magazines and the her experiment will turn out internet to see if anyone else has looked into the problem, or into a similar problem. We find out that there are substances in plants that control growth, called growth regulators. Construct hypothesis ‘There are chemicals in tomatoes that stop the seeds from growing whilst they are still in the tomatoes themselves.’ This hypothesis is testable by an Figure 1.2:Tomato seeds don’t experiment. We think that it is a germinate inside tomatoes. What’s chemical that is responsible. So stopping them? how do we prove that? We could try covering some seeds with tomato juice A hypothesis that said ‘There is and others with water and see if any something in tomatoes that stops germinate. Based on our hypothesis, seeds germinating’ would be too we can make a prediction: ‘Seeds vague and we couldn’t test it by covered in tomato juice will not experiment. germinate as well as seeds covered in water’. Design and carry out 1. Put several tomatoes in a blender. an experiment to 2. Filter (strain) the blended material test the hypothesis through some muslin. 3. Collect the tomato seeds and wash Filtering removes all the cells. them in distilled water. Washing in distilled water means 4. Place 20 in a Petri dish on filter that there are no chemicals on the paper and cover them with the seeds at the start of the experiment. tomato juice obtained from filtering A Petri dish is a convenient the tomatoes. container. Filter paper inside can 5. Place 20 in a Petri dish on filter hold water for the seeds. Placing paper and cover them with the same equal numbers of seeds in each volume of distilled water. and keeping them in the same conditions makes it a ‘fair test’. The 6. Place them in a growth cabinet only difference between them is that will keep the temperature and the chemicals in the tomato juice. lighting conditions constant. Continued Grade 11 5 UNIT 1: The science of biology Any difference in the results 7. Leave them for four days. must be due to this difference 8. Check the number that have in the two conditions. The germinated in each condition. seeds that were covered only in distilled water form the control 9. Repeat the experiment 50 times to group. This is a standard against confirm your results. which we can compare. If we Analyse results and Out of 1000 seeds sown in each had just used the experimental draw conclusions condition, 668 germinated in the group (the ones covered in distilled water (13.36 per dish) and tomato juice), we would have 265 germinated in the tomato juice had nothing to compare them (5.3 per dish). It seems like something with. We wouldn’t have known in the tomato juice is affecting the whether or not germination germination of the seeds. It can’t be was the same, better or worse the cells themselves, because they than normal. were filtered off. It must be a chemical in the juice. Control group and Accept or reject the It seems as though the hypothesis experimental group hypothesis is along the right lines; the tomato A control group acts as a juice will only contain chemicals, not ‘standard’ for comparison. It is cells, and it does reduce the amount used to ‘isolate’ the factor we of germination. So we accept the are investigating and show that hypothesis. But inside the tomatoes changes are due to this factor. themselves, none of the seeds For example, in drug trials, germinate. There is a bit more work to one group of people with the do yet! condition the drug is used to treat is given a tablet containing Report results We must now decide whether or not to the drug (the experimental report the results to other biologists. group). Another group is given Someone else might decide to take a placebo – a tablet containing the work further and try to isolate no drug (the control group). a particular chemical from the many If both groups get better, in the juice to find exactly what is then it seems that the drug is stopping them from growing inside the having little effect. If only the tomato itself. experimental group get better, this must be due to the drug. Without the control group we The next section of this unit gives some case studies taken from the wouldn’t have been sure. experiences of some scientists. KEY WORDS How did the scientific method disprove the idea of spontaneous generation? control group the standard group in an experiment in What about the belief that rotting meat produces flies? How could which the experimental groups you disprove that by using the scientific method? Well, in 1668 are compared with an Italian biologist, Francesco Redi, did just that. Many scientists consider this to be the first true ‘experiment’. He used wide-mouth experimental group the jars containing meat. Some jars were left open to the air. Others group in an experiment which were covered with a piece of gauze. is being experimented on in order to compare with the After several days, maggots and then flies could be seen in the open control group jars, but none appeared in the closed jars. 6 Grade 11  UNIT 1: The science of biology Figure 1.3 Francesco Redi’s 1668 experiment Redi hypothesised that only flies could produce more flies and predicted that, in his experiment, flies would be found in the open jars, but not in the covered jars. He maintained all the jars under the same conditions and so he controlled many variables. By choosing to cover some jars with gauze rather than an impermeable seal, he allowed air to enter all the jars – again he controlled a variable that could have affected the outcome of the experiment. His results matched his prediction and when other people tried the experiment, they too got the same results. Redi was able to conclude that flies cannot be produced from rotting meat. He also went on to say that it was unlikely that any form of spontaneous generation was possible. neck of flask Most people accepted this for larger organisms, but, at round about this time, the microscope had been invented and the whole world of microbiology was opened up. Many people still believed that micro-organisms could arise by spontaneous generation. It took the work of Louis Pasteur to disprove this. In 1859, Pasteur carried out experiments to show that the micro-organisms that caused wine lowest point and broth to go cloudy came from the air and were not made from of neck the broth itself. He used special ‘swan-necked flasks’ like that shown in Figure 1.4. Figure 1.4 A swan-necked flask Pasteur boiled broths in swan-necked flasks to kill any micro- like the ones used by Louis organisms that might be in them. The boiling forced steam and air Pasteur out of the flasks. When the boiling stopped and the broth cooled, air was sucked back into the flasks. Some contained a filter to prevent all solid particles from getting into the growth medium from the air. Others had no filter but, in these, the dust (and the micro- organisms) in the air settled in the lowest part of the neck of the flask. All the flasks were kept under the same conditions in Pasteur’s laboratory. Pasteur found that the broths stayed clear for months. At the end of this time, he treated the flasks in one of three ways: He left some of them as they were. He broke the necks on some. He tilted others to allow the dust in the low part of the neck to mix with the broths. Grade 11 7 UNIT 1: The science of biology trapped air escapes bacteria and dust from open end of flask settle in the bend hours/days 1. Broth 2. Broth 3. Broth stays 4. Flask tilted so that 5. Bacteria grow Figure 1.5 A summary of sterilised allowed to cool slowly sterile indefinitely sterile broth interacts with bacteria and and multiply in broth Pasteur’s procedure dust from the air The broths in the second two groups of flasks turned cloudy (due to the presence of micro-organisms) within days. The broths in the KEY WORDS first group remained clear. After this, people were forced to admit independent variable the that spontaneous generation, even of micro-organisms, could not variable that the experimenter happen. changes to see if this affects the performance of the Activity 1.2 Pasteur's work dependent variable. Does Pasteur’s work is another good example of the scientific the presence or absence of a method at work. See if you can identify the various stages. drug in a tablet (independent variable) affect the recovery 1. What do you think might have been Pasteur’s hypothesis? of the patient? 2. Outline the plan of his experiment. Did he have any dependent variable the controls? factor in an experiment 3. What do you think he might have predicted? that the scientist measures to see if it changes when 4. Did his results support his prediction? the independent variable is 5. What conclusion was he able to draw? changed One stage in the scientific method is to ‘do background research’. Pasteur certainly did that. He knew that other scientists had tried to disprove spontaneous generation before him and he was able to draw on the results of their experiments and improve their technique. What do we mean by cause and effect? Scientific experiments try to establish cause and effect. This means that they try to prove that a change in one factor brings about a Activity 1.3 Library search change in another factor. The factor that the scientist changes, or manipulates, is called the independent variable (or IV for short). Do a library search to find The factor that the scientist measures to see if it changes when the out about the work of Lazzaro IV is changed is called the dependent variable (or DV for short). Spallanzani. How do you The scientist will want to find out if changes in the independent think his work influenced variable produce changes in the dependent variable. In the example Pasteur? on pages 5 and 6, the independent variable was the presence or absence of tomato juice. The dependent variable was the number of tomato seeds germinating. To prove cause and effect – to prove that it is changes in the IV (and nothing else) that are causing changes in the DV – we must 8 Grade 11  UNIT 1: The science of biology take all the steps we can to ensure that the experiment is a fair KEY WORDS test. We must make sure that any other factors which could affect the results are the same for the different conditions we set up. fair test an experiment in In the tomato seed example, if one group of seeds had been at a which the only difference higher temperature than the other group, this could have made between different repeats of them germinate faster. We wouldn’t have known whether it was the experiment is the different the tomato juice affecting the results or the temperature. Our values of the independent experiment would not be valid. So we must keep constant anything variable, all other factors that other than the IV that might influence the results. These are could affect the outcome have controlled variables. In the tomato seed experiment, the controlled been kept constant (they have variables were: been controlled) temperature controlled variables factors other than the independent lighting conditions variable that are kept constant number of seeds per dish, and in order to avoid influencing volume of liquid added (water or tomato juice). results confounding variable a factor Occasionally, there is a variable that might influence the results that that can’t be controlled which you can’t control. Such a variable is a confounding variable. This is may influence the result of the because it ‘confounds’ the interpretation of the results. You couldn’t experiment be certain that it was the IV producing the changes in the DV because of the presence of the confounding variable. accuracy how precisely something has been measured For example, if you measure the carbon dioxide uptake by wheat or counted plants as the light intensity changes over the day, you cannot control the effect of change in temperature. It could be a confounding variable. Accuracy, reliability and validity in scientific experiments People often confuse these ideas, but they are really quite separate notions and all are important to how well an experiment is received by other scientists. Accuracy Accuracy refers to how precisely you measure or count something. For example, you could measure time with a clock, a wristwatch or a stop-clock accurate to 0.01 seconds. The level of accuracy you choose must reflect the magnitude of what you are measuring. You don’t always need the most accurate measuring instrument. For example, if you were timing a reaction that was likely to last a few minutes at most, the stop-clock would be the best choice. But if you were timing something that lasts several hours, you just don’t need that level of precision and it might even be a hindrance – by measuring the seconds accurately, you might lose track of the hours! To measure volume, you could use: a syringe a measuring cylinder a pipette a burette Grade 11 9 UNIT 1: The science of biology All of these come in various sizes. Look at the ones shown in the diagrams. 4 29 70 10 3 20 30 30 2 40 60 31 50 60 1 50 32 a pipette reading a a measuring reading a a burette reading a a syringe pipette cylinder measuring burette cylinder Figure 1.6 Different measuring apparatus To measure 3.5 cm3 accurately, the pipette would be best. To measure 200 cm3 you would use the measuring cylinder. This one holds 100 cm3 and so you would have to fill it twice. The burette KEY WORDS would be more precise, but less convenient and would you need the reliability a measure of how extra precision on quite a large volume? dependable and consistent the results of an experiment are Reliability anomalous results are really Reliability is a measure of how dependable our results are. If we odd results that do not fit the were to repeat the investigation, would we get more or less the same general pattern results? There are several things we can do to increase the reliability of our experiments. colorimeter measures how much light passes through a We can standardise all our procedures, so that we always do liquid exactly the same thing. This makes it much more likely that we will be able to repeat our results. We can repeat it many times ourselves. This allows us to see, Activity 1.4 hopefully, a general pattern. It also allows us to: Which apparatus would you – spot any anomalous results and, if it is justified, to exclude use to measure out 36 cm3 these of water? – calculate an average result, which is likely to be more representative than any individual result We can try not to use personal judgement. For example, if in a given experiment we have to wait until a solution turns a certain shade of red, one person’s judgement will almost certainly differ from the next person’s. There are ways around this: – We can have a ‘standard’ to compare our experiment to. In other words, something containing the chemical that is the exact colour we need it to be. This helps, but we must still make a judgement. – We can use a special apparatus called a colorimeter. This measures how much light passes through a liquid. It is nearly always better to measure than to judge. 10 Grade 11  UNIT 1: The science of biology Validity Example This is about whether or not our experiment measures what it says it is measuring. In the tomato seed experiment, we said that our results were due to the presence or absence of tomato juice. For our experiment to be valid, we must be certain that our results were only due to the changes in the independent variable and spot 1 spot 2 spot 3 nothing else. So had we not controlled all the other variables, our experiment would not have been valid. Figure 1.7 Using a standard to Activity 1.5: Planning investigations compare colour changes Now it’s your turn! Plan experiments to investigate the In the investigation following observations: demonstrated above we are 1. When a winemaker used lactose (milk sugar) instead of waiting for the chemical to sucrose (ordinary table sugar) the wine he made tasted like change colour from being blue fruit juice. (Hint: you need to know how well the yeast is (as in the first spot) to the fermenting the two sugars.) same yellow as that in spot 3. Clearly, spot 2 hasn’t quite got 2. In the area near an old copper mine, no plants grow. Go there. The experiment isn’t further away and more and more plants are growing. An quite over yet. But without the analysis of the soil near the mine found that there was an ‘standard’ to compare against, unusually high concentration of copper dissolved in the we might have thought that water in the soil. (Hint: remember plants grow from seeds!) it was. However, it would 3. The leaves of plants wilt more quickly on a hot day than on be even more reliable if we a cooler day. (Hint: think what you lose more of on a hot measured it in a colorimeter. day than a cool day.) Don’t forget, you will need to have: Activity 1.6 Spotting a hypothesis (from which you can make a prediction) anomalous results a plan, containing: Which is most likely to be – a clear method of changing the independent variable an anomalous result in the following table? Explain – a clear method of measuring the dependent variable your reasoning. – methods of controlling other potentially confounding Temperature Enzyme variables (°C) activity (%) – methods of ensuring appropriate levels of accuracy, 5 3 reliability and validity 10 17 15 36 How do we write reports on scientific experiments? 20 55 When biologists write a report on an investigation they have just 25 42 done, they write it with a view to having it published in a scientific 30 85 journal, such as Nature or Science. These journals are read by 35 97 many other biologists who will want to understand their work and, perhaps, repeat it to check on the results. It is important, then, that the layout of the report is recognisable to everyone and understandable by everyone. So, there is a set way to lay out such a report. It is not always identical in every case, but there are certain ‘rules’ to follow. Grade 11 11 UNIT 1: The science of biology Experiments can be reliable There must be: without being necessarily a title, which states clearly what is being investigated valid. If you consistently omit a hypothesis, stated clearly in terms of how the independent the same important step (for variable is expected to influence the dependent variable, often example, consistently forget extended to a prediction for the particular experiment to control the same variable), you may well keep getting the a clear description of the experimental procedure; this must be in same results. But they will be such detail that anyone of the same level of understanding could the wrong results and your easily replicate the procedure and it must include: experiment will not be valid. – the apparatus used (a diagram of the assembled apparatus is useful) You can measure the rate of – details of any chemicals used; what volumes or concentrations fermentation of yeast using or masses were used simple equipment as shown – details of any organisms used (for example, yeast, mice) – what in the diagram below. You can strain and how many count the number of bubbles of carbon dioxide produced in – details of any control experiments five minutes and work out a a full account of the results obtained; it is often helpful to rate per minute. summarise these (where appropriate) in graphs, charts and tables the conclusions that have been drawn from the results an evaluation of the procedure; this is an honest assessment of the limitations of the procedure that has been used, pointing out oil layer any unavoidable limitations and inaccuracies that arose an acknowledgement of the use of any other person’s work; this yeast in sugar solution is usually done by identifying by a number the place in the report water where other work has been used, and then listing the sources at bubbles of the end of the work carbon dioxide So, for the tomato seed experiment, the report could look something like this: Section How it would be written Title An investigation into the effect of tomato juice on the germination of tomato seeds. Hypothesis A chemical in tomato juice inhibits the germination of seeds. Prediction Seeds covered in tomato juice will germinate less well than seeds covered in distilled water. Procedure 30 tomatoes were blended for five minutes. The blended material was then filtered through some muslin and the liquid (juice) was collected. The seeds were extracted from the cellular material, which was then discarded. The juice was diluted with distilled water to give a total volume of 550 cm3. The tomato seeds were washed in distilled water for 30 seconds, to remove any chemicals from their surface. They were dried briefly on filter paper. 100 Petri dishes were prepared by placing a piece of filter paper in each. Each piece of filter paper had a 0.5 cm grid drawn on it. 12 Grade 11  UNIT 1: The science of biology 20 seeds were placed in each Petri dish on the intersections of the lines of the grid (to ensure even spacing in all dishes). 10 cm3 tomato juice was added to half of the Petri dishes and 10 cm3 distilled water was added to the other half. All the dishes were placed in an incubator at a temperature of 20 °C for four days. At the end of this time the number of successful germinations in each dish was recorded and means for each condition were calculated. If a radicle (root) of 0.5 cm or more was present, the seed was said to have germinated. Results Out of 1000 seeds sown in each condition, 668 germinated in the distilled water (13.36 per dish) and 265 germinated in the tomato juice (5.3 per dish). Conclusion The hypothesis is accepted. The germination of the seeds in the tomato juice is much less successful than in distilled water. Some chemical in the tomato juice must therefore be inhibiting the germination. In tomato fruits, no seeds germinate, but it must be remembered that in our investigation, the juice had been diluted to give sufficient volume for 50 replicates of the investigation. Evaluation There were no anomalous results. The germination of seeds in all of the dishes in the experimental condition (the tomato juice) was less successful than in the dishes in the control condition (distilled water). The experiment was not without limitations. It was only carried out for four days (to limit the development of fungal growth that might have interfered with germination). Had it been carried out for longer, the pattern may have been different. It was only carried out at one temperature; this may have influenced the experimental and control conditions differently. Repeating the investigation at a range of temperatures would help to clarify this. The judgement of germination (a radicle of 0.5 cm length) was somewhat arbitrary, but it did overcome the problem of including in the count seeds that had merely swollen with water but not produced any growth. We are of the opinion that these limitations had only a minor effect on the validity and reliability of this experiment. Acknowledgements Biology – Martin Rowlands – information on plant growth regulators. The above report has been tabulated for your ease of understanding. An actual report in a scientific journal would not be tabulated, although it would have many of the headings shown here. Activity 1.7: Writing a report on an experiment Write a report in this format as though you were Louis Pasteur and had just carried out the investigation that was to finally disprove the idea of spontaneous generation. Try to incorporate as much detail as possible so that anyone could follow your description of the procedure and repeat the investigation. Think of a way of presenting the results so that it is immediately obvious what happened. Don’t forget to explain your conclusions and to write an evaluation. Grade 11 13 UNIT 1: The science of biology Activity 1.8 Review questions A scientist observes that Choose the correct answer from A to D. crocodiles often fight and 1. Which of these best describes what science is? bite each other. Their teeth A a body of knowledge are covered in bacteria yet crocodiles rarely get infected B a way of doing experiments bites. Brainstorm how a C a way of looking at and thinking about the natural world scientist would develop and test a hypothesis to explain D a series of ideas this observation. Turn your 2. The scientific method involves: observations into a flowchart A putting forward hypotheses in a form that can be tested of the process. B carrying out experiments C analysing results and drawing conclusions D all of these 3. Which of the following is NOT a type of biologist? A geneticist B entomologist C astrophysicist D doctor 4. Scientists often use statistics when drawing conclusions because: A statistics are more accurate than human opinion B statistics are more reliable than human opinion C statistics are infallible D none of these 5. The independent variable in an experiment is the variable that: A is measured by the experimenter B is controlled by the experimenter C is changed (manipulated) by the experimenter D upsets the reliability of the results 6. The dependent variable in an experiment is the variable that: A is measured by the experimenter B is controlled by the experimenter C is changed (manipulated) by the experimenter D upsets the reliability of the results 7. Having a control condition in an investigation: A gives a ‘standard’ to compare against B increases the validity of the experiment C increases the reliability of the experiment D both A and B 14 Grade 11  UNIT 1: The science of biology 8. Publishing reports of biological investigations in scientific journals is important because: A it allows biologists all over the world to understand your reports B it allows biologists all over the world to repeat your investigations C it allows biologists all over the world to challenge your results D all of the above 9. The scientific method is more reliable than opinion based on personal observation because: A scientists are more reliable than other people B the scientific method involves gathering information from controlled experiments to prove or disprove a hypothesis C observation is not a valid scientific technique D scientific method always gives the correct answer 10. The reliability of an experiment is increased by: A carrying out repeat experiments B minimising personal judgement C working as quickly as possible D using the most appropriate apparatus 1.2 The tools of a biologist By the end of this section you should be able to: Name and describe the function of the main pieces of apparatus that are used by biologists the world over. Describe how these pieces of apparatus work. Explain how, and under what circumstances, these pieces of apparatus would be used and demonstrate the use of some of them. Classify the apparatus as laboratory tools, field tools or both. Be aware of possible health and safety implications of using these tools. In this section you will be reviewing the nature and function of some basic ‘tools’ or pieces of apparatus of a biologist. Some of these you will have met before, others may be new to you. You will learn about the sort of tools that are needed in the laboratory and those that are needed when working in the field. Some pieces of apparatus are used in both situations. Grade 11 15 UNIT 1: The science of biology Activity 1.9 What apparatus do biologists use? Look at the list of basic How much time do you have? You only need consult the catalogue tools which biologists use of a supplier of biological apparatus to see that the list is a pretty in the laboratory. Copy the long one! However, we shall not be considering all the various sizes list and write down what you of test tubes or the different kinds of Bunsen burner or the different would expect each piece of kinds of electronic equipment now available for biologists. We equipment to be used for. shall confine ourselves to the main items of field and laboratory equipment that biologists everywhere would recognise and be able to use. What do biologists use in the laboratory? This is still a large list. But there are some basic tools. These include: microscopes dissecting equipment Petri dishes pipettes and syringes centrifuges measuring cylinders balances We have already considered measuring cylinders, pipettes and syringes when looking at the idea of ‘accuracy’ in scientific experiments. All these are used for measuring volumes, usually of liquids, but in some investigations they can be used to measure the volume of a gas. In this example, an upturned measuring cylinder is being used to collect oxygen gas produced when yeast converts hydrogen peroxide into water and oxygen. oxygen gas ‘20 volume’ hydrogen peroxide rubber bung 100 cm3 measuring cylinder water yeast suspension plus hydrogen peroxide Figure 1.8 Using a measuring cylinder to measure the volume of KEY WORDS oxygen produced when yeast decomposes hydrogen peroxide balances apparatus used for Some syringes are designed specifically as ‘gas syringes’ and could measuring mass be used as an alternative way of collecting the oxygen in the above dissect to cut apart or experiment. separate tissue for anatomical Balances are used for measuring mass. They come in a range of study sizes and properties. Some can measure the mass of very heavy 16 Grade 11  UNIT 1: The science of biology objects, but not with any great degree of precision. Others measure smaller masses to the nearest 0.0001 g (one ten-thousandth of a gram). gas syringe Sometimes biologists need to dissect specimens to find out what they are like inside. This need not always mean dissecting a whole organism. Quite often, students dissect organs, such as the heart or the conical flask kidney, to find out about their structure. Biologists may dissect owl pellets – these are pellets containing yeast suspension plus hydrogen the parts of food that the owl has eaten and that peroxide cannot be digested and have been regurgitated. Figure 1.9 Using a gas syringe to measure Dissecting these can give information about what the the volume of oxygen produced when yeast bird has been eating. decomposes hydrogen peroxide DID yOU kNOW? AW 1.2.6 – photo of a biologist dissecting under a microscope Sometimes small specimens are dissected under a microscope. This biologist A B is dissecting insects using a Figure 1.10A This balance is accurate to 0.01 g dissecting microscope. The B This balance is accurate to 0.0001 g. magnification is not as great as other microscopes, but Figure 1.11 shows a standard dissecting kit containing a magnifying the image is very clear and glass, scalpels, scissors, forceps (tweezers) and mounted needles. allows delicate dissection to Figure 1.12 shows a student dissecting a frog. The student is using a be carried out. Such work is scalpel to cut away the skin and reveal the abdominal organs. These necessary to help to classify can then be removed and studied individually. new species of insects. Figure 1.11 A standard dissecting kit Figure 1.12 Dissecting a frog Grade 11 17 UNIT 1: The science of biology Petri dishes are round dishes made from glass or from plastic. They are used in many different ways, but usually to culture some organisms. They are often filled with a ‘jelly’ called agar and used to culture bacteria. There are many different agars containing different balances of nutrients. Each type of agar can encourage the growth of different bacteria. By marking a grid on the surface of the Petri dish, biologists can estimate how much of the dish is covered by bacteria and then use this to estimate how fast the bacteria are growing. Petri dishes are also used to propagate or culture plants. The Figure 1.13 Bacteria growing small ‘plantlets’ or ‘explants’ in figure 1.14 have been grown on a on agar in a Petri dish. The grid special agar from just a few plant cells. They will grow roots and allows biologists to work out then shoots and leaves. When they are big enough, they will be what proportion of the Petri transplanted into pots of soil or compost and grown into mature dish is covered with each type of plants. bacterium. Petri dishes can also be used to: KEY WORDS show how effective different antibiotics are against certain types of bacteria agar jelly-like substance obtained from seaweed, used show how well different concentrations of enzymes digest a for culturing micro-organisms substance in a Petri dish This Petri dish has one type to culture organisms means of bacterium growing all over to grow them under special it – except in some of the conditions that are likely to areas near the white discs. help their growth These discs contain different antibiotics. The clear zones around the discs are areas where no bacteria are growing. Clearly some antibiotics are Figure 1.15 Bacteria being more effective against this cultured on agar in a Petri dish bacterium than others. with several different antibiotic This Petri dish contains agar discs mixed with starch. There are several ‘wells’ in the agar which Figure 1.14 Plantlets or ‘explants’ contain a starch-digesting enzyme. The whole area has been stained with iodine, which turns blue-black when it reacts This technique of growing with starch. The clear areas plants from just a few cells on around the wells show that the special agars in Petri dishes enzyme has diffused out of the is called micropropagation. wells and digested the starch. It allows thousands of plants to be produced from just one As you know already from your ‘parent’ plant. All the plants study in grade 9, microscopes Figure 1.16 ‘Starch-agar’ with produced are genetically are one of the most vital tools four ‘wells’ cut in the agar; each identical. in a biology laboratory. There well contains a different strength are two main types: of enzyme solution 18 Grade 11  UNIT 1: The science of biology A B Figure 1.17 A A light microscope; optical microscopes that use beams of light to produce B An electron microscope magnified images electron microscopes that use beams of electrons to produce Activity 1.10 magnified images In the photograph in figure You are unlikely ever to use an electron microscope, simply because 1.16, which well do you of cost. Light microscopes vary from basic microscopes that can be think contains the most used in the laboratory and even taken out and used in the field to concentrated enzyme? very sophisticated microscopes that are linked to image-enhancing computer programs to produce all kinds of images that help to make the image clearer. DID yOU kNOW? Of course, biologists also use electron microscopes that give much Resolution is the ability higher magnifications and, importantly, much higher resolution, so to distinguish between that more detail can be seen. two points that are close A B together. If resolution is Antenna poor, they will merge into Eye one point and the detail of the image will be limited. Electron microscopes have a much higher resolution than optical microscopes. vacuole KEY WORDS nucleus optical microscope uses cytoplasm beams of light to produce chloroplast magnified images electron microscope uses Figure 1.18A SEM of the head of a monarch butterfly; beams of electrons to produce B TEM of a cell from the leaf of a tobacco plant magnified images Grade 11 19 UNIT 1: The science of biology armoured casing Transmission electron microscopes allow researchers to view the structure of cells in great detail. The transmission electron micrograph (TEM) of the cell from the leaf of a tobacco plant in before after figure 1.18B shows six large chloroplasts, the vacuole of the cell and the nucleus and cytoplasm. Scanning electron microscopes do not see ‘into’ cells in the same way, but create images of the surface of a specimen by scanning it with a high-energy beam of electrons. Computer programming allows the different parts to be ‘false rapidly pellets rotating coloured’ for clearer interpretation. This is shown in the scanning rotor supernatant electron micrograph (SEM) of the head of a monarch butterfly, Figure 1.19 A centrifuge figure 1.18A. Centrifuges are used to separate solids from liquids where simple filtration is not adequate for the task. Some solid particles are very KEY WORDS tiny and float around in a liquid, although they are not properly centrifuge machine that spins dissolved in the liquid. to separate solids from liquids Centrifugation can separate these solid particles from the liquid quadrat a small frame used without the need to filter. The mixture is placed in a ‘centrifuge tube’ for ecological or population and placed in the centrifuge. The centrifuge then spins the tubes at studies high speed. As the tubes spin, the gravitational forces on the solid particles force them to the bottom of the tube. Some centrifuges, called ‘ultracentrifuges’, can spin really fast and cause extremely light particles to fall to the bottom of the tube. These ultracentrifuges are used to separate the various components of animal and plant cells. Centrifugation is commonly used in hospitals for stool tests where the ability to separate particles quickly and clearly is very useful. What do biologists use in the field? Biologists do a lot of work outside the laboratory. They study different areas to find out how the animals, plants and micro- organisms interact with each other and with the environment. They find out how an area changes over time and how it is influenced by human activity. All this involves: taking measurements of the abundance of organisms in the field taking samples of the environment (for example, soil, rocks, water) for analysis in the laboratory collecting specimens for identification and analysis in the Figure 1.20 Students recording laboratory the contents of a quadrat To gain an estimate of the abundance of organisms in an area, biologists often use quadrats. There are many different types, but the simplest is just a metal square. It is placed randomly on the ground and the organisms found inside it are counted and the numbers and types recorded. This data can be used to make an estimate of the abundance of the organisms in the area. Figure 1.20 shows students recording the contents of a quadrat. The use of quadrats is not confined to sites on land. They can be used underwater also! Figure 1.21 Using a quadrat Biologists also use quadrats to show how the numbers of a underwater particular species changes across an area. To do this, they lay down 20 Grade 11  UNIT 1: The science of biology a tape measure (or a long rope marked off every metre) across the Using a quadrat area. This is called a transect line. They then place the quadrat by the side of the transect line and record the abundance of the If your quadrat measures organisms in the quadrat. They repeat this every metre, or every 5 1 m × 1 m, it has an area of or 10 metres, depending on the length of the transect. This gives a 1 m2. Suppose you place the picture of how the abundance of each species changes across the quadrat 20 times, and find that area. species A occurs, on average, 3.5 times per quadrat. You can To collect specimens for identification in the laboratory, biologists now make an estimate of how use a range of equipment. Collecting plants is relatively easy, if they many individuals of species.A are not too large. Small parts (for example, leaves and flowers) can are in the location you are be collected and kept in reasonable condition for a short period investigating. Suppose the area in plastic jars or plastic bags. Parts of plants can also be preserved of this location is 500 m2. using a plant press. This preserves the shape and form of the plant Your records say there are parts for some time and specimens can be analysed later. Whole 3.5 per m2 so the total plants can be dug up and replanted for study in the laboratory. number must be 500 × 3.5 = 1750 in the location you are Activity 1.11: Making a plant press investigating. The quadrats A plant press does not need to be an expensive item of should be laid at random so equipment. you can make a plant press using corrugated there is no bias. This means cardboard, newspaper and you not choosing where you friction some thin rope or string. band will place them, but using The newspaper separates some other method to place individual specimens and them. Biologists usually use the cardboard provides a system of random numbers support and allows the press from a calculator to specify to be tied tight to keep the cardboard at which points to place the specimens flat. bottom and newspaper quadrats within an area. top boards However, animals pose a different problem. Because they move, they must be caught. Biologists do this in many different ways. Some insects can be caught using nets like the ones shown in frrigure 1.22. Others are caught using pitfall traps – see page 22. KEY WORDS transect line a straight line through an area random having no specific pattern, purpose or objective bias tending towards a specific result Figure 1.22 Students using nets to collect and study insects Grade 11 21 UNIT 1: The science of biology Pitfall traps Many night-flying insects are attracted to light. A strong light bulb hung in front of a vertical white sheet will attract a great range Pitfall traps come in a range of of insects which can be picked directly from the sheet when they shapes and sizes. This simple settle. An ultraviolet light bulb will increase the catch markedly. one is just a plastic carton sunk into the soil. It would be Some other instruments that biologists use in the field are covered with wood to keep it illustrated below. dark and dry and also keep any animals that fall into it out of sight of predators. Figure 1.23 Figure 1.24 Figure 1.25 A data logger – this A pH kit – this is A flow meter – this is wooden cover is used to record used to measure the used to measure the stone information pH of soil or water rate of flow of water bait Figure 1.26 A field microscope Figure 1.27 A theodolite – this – this is used to investigate the is used to measure the height of structure of specimens in the field, trees or of slopes in the area whilst still fresh One recent addition to the tool list of field biologists is the GPS (Global Positioning System) receiver. This equipment makes it possible to record positions quickly and extremely accurately. By taking several readings at different points on the perimeter of the area, an accurate map of the area can be drawn. Figure 1.28 A GPS (Global Positioning System) receiver 22 Grade 11  UNIT 1: The science of biology Activity 1.12: Types of apparatus Make a table that contains three columns. Put a heading for each column as below: Apparatus mainly used in the laboratory Apparatus mainly used in the field Apparatus that can be used in both field and laboratory Try to list at least five pieces of apparatus in each column Review questions Choose the correct answer from A to D. 1. It is not true that: A electron microscopes can only be used in the laboratory B some light microscopes can be used in the field C light microscopes give better magnification than electron microscopes D light microscopes were invented before electron microscopes 2. A theodolite is: A an item of laboratory equipment that measures height B an item of field equipment that measures height C an item of field equipment that measures slope D an item of laboratory equipment that measures slope 3. When a biologist centrifuges a suspension, the solids are separated from the liquid in the following way: A The solids float to the top because they are lighter. B The solids are pulled to the bottom because they are heavier. C The solids are pulled to the bottom because they spin faster than the liquids. D The solids float to the top because they spin slower than the liquids. 4. Fieldwork is important in biology because biologists can gather information about: A individual organisms in their natural surroundings B how organisms are distributed in a particular area C how the organisms in an area change over time D all of the above Grade 11 23 UNIT 1: The science of biology 5. Bacteria are usually cultured in: Activity 1.13 A test tubes It is important to use equipment properly to make B beakers sure that your results are C Petri dishes reliable and valid. Here are D none of these two very useful and very different pieces of equipment 6. Pitfall traps are used to catch: for studying biology: a A flying insects microscope and a quadrat. For each one produce a set of B small ground-dwelling animals instructions that would help a C damaged plants student using the equipment D all of these for the first time to use it correctly. Let a friend look 7. When estimating the numbers of a species in an area, biologists at what you have done – can use quadrats that are: they follow your instructions A placed at regular intervals along a transect correctly? B placed deliberately all over the area C placed at random D placed one after the other along a transect 8. When choosing an item of equipment to measure volume you should mainly consider: A only the total volume to be measured B only the precision to which the instrument can measure C the ease with which you can use it D both A and B 9. The ‘white sheet and bright bulb’ technique used to trap flying insects at night gives: A a good indication of numbers but a poor indication of types found in the area B a good indication of the types found in the area but a poor indication of numbers C a good indication of both types and numbers D a poor indication of both types and numbers 10. Which of the following statements is not true about transect studies of an area? A they give a good indication of how the abundance of different organisms changes across an area B they give a good indication of the overall numbers of an organism in an area C they show the strength of the current flow in a stream D they involve laying out a tape to take direct observations or lay quadrats on 24 Grade 11  UNIT 1: The science of biology 1.3 The relevance and promise of biological science By the end of this section you should be able to: Explain how biological science is relevant to food production, health and disease, conservation, and control of the population. Explain the promise of biology in relation to genetic engineering and biotechnology. At the start of this unit we defined biology as ‘the science of life’. This makes it a pretty big subject! Biology seeks to understand how all life functions – including life on other planets, should it exist. Biology attempts to give scientific answers to many questions that most people think are important. Some of these are listed below: Where did humans come from? Where did I come from? How do I work? How did all life begin? How is disease caused? How is AIDS caused? How can vaccines be developed against diseases like malaria and AIDS? What makes cancer cells different from ordinary cells? Will it ever be possible to grow a new kidney just for me? Will people one day live forever? What causes global warming? How can we solve problems of food shortage? Activity 1.14: Library search Select five questions that biology attempts to answer. you may choose from the above list, but there are many others. Do some research in a library and, for each, write a few lines (no more) about what biologists say about the topic and whether you accept the biological ‘answer’ or not. Explain why you agree or disagree. Grade 11 25 UNIT 1: The science of biology Because biology is the science of life, biologists undertake all kinds of research. Some try to find possible biological explanations for other, non-scientific, aspects of life. Some try to find biological explanations for why some people: have a strong religious belief whilst others don’t are record-breaking athletes, like Haile Gebrselassie and Meseret Defar, and others aren’t have amazing musical talent, whilst others don’t, or can write poetry, whilst others can’t. Biologists also try to find out why organisms behave in the way that they do. When this is applied to humans, it is often called ‘behavioural psychology’, but many consider it to be a branch of biology. Some of these biologists believe that it will one day be possible to understand how all the nerve cells that make up the brain interact with each other to store memories, carry out problem-solving activities and learn as well as modify behaviour patterns. The study of biology has relevance in almost every aspect of life. It would take far too long to analyse all aspects of the relevance of biology. However, there are some which are undoubtedly of great importance. 12 Biology and agriculture The world’s population is growing at an alarming rate and this poses 10 challenges to governments all over the world. The extra people all need homes, food and all the other services that are provided. estimated population of the world (billions) Many biologists are addressing the problem of how to produce the 8 extra food. However, they have another problem to consider, which is that global warming may alter the way in which crops grow. Many crops that now pr