Grade 10 Life Sciences Textbook PDF

VERSION 1 CAPS VERSION 1 CAPS EVERYTHING SCIENCE GRADE 10...

VERSION 1 CAPS VERSION 1 CAPS EVERYTHING SCIENCE GRADE 10 GRADE 10 BY LIFE SCIENCES LIFE SCIENCES WRITTEN BY VOLUNTEERS WRITTEN BY VOLUNTEERS WRITTEN BY VOLUNTEERS FRONTAL LOBE: PRIMARY SENSORY CORTEX: Decides when you PRIMARY MOTOR CORTEX: Judges the texture of this book will study for your Moves your body to the to let your hands know they’re exam and makes bathroom when you take holding paper. THIS TEXTBOOK IS AVAILABLE you feel happy a break from this book. when this book ON YOUR MOBILE TEMPORAL LOBE: has helped you PARIETAL LOBE: Hears your teacher’s pass a test. Turns the letters of this voice and processes it book into words, and those so you can remember words into thoughts. what was said in class. LIFE SCIENCES | GRADE 10 OCCIPITAL LOBE: Processes the visual information of this book. Everything Science BROCA’S AREA: Allows your facial muscles to form a frown when you’re trying to solve a problem in this book. CEREBELLUM: This book is available on web, mobi and Mxit. Raises your hand Read, practice intelligently or see solutions at m.everythingscience.co.za PONS: Chooses whether at the exact time you’ll doze off you have a question or stay awake about this book. in class while being taught from this book. MEDULLA OBLONGATA: SPINAL CORD: Takes care of your body’s The highway that is busy vital functions, like breathing channelling the signals on your behalf, while you between your body study this book. and brain as we speak. Don’t break your brain over this one, it’s just a piece of paper. EVERYTHING LIFE SCIENCES ISBN 978-1-920423-91-9 9 78 1 920 4239 1 9 2436_SIYAVULA_GRADE 10_LIFE SCI_FA.indd 1 2012/11/12 5:03 PM EVERYTHING SCIENCE GRADE 10 LIFE SCIENCES VERSION 1 CAPS WRITTEN BY VOLUNTEERS  AUTHORS AND CONTRIBUTORS Siyavula Education Siyavula Education is a social enterprise launched in 2012 with capital and support from the PSG Group Limited and the Shuttleworth Foundation. The Everything Maths and Science series is one of the titles developed and openly released by Siyavula. For more information about the writing and distribution of these or other openly licensed titles: www.siyavula.com [email protected] 021 469 4771 Siyavula Authors Megan Beckett; Vinayak Bhardwaj; Melanie Hay; Ewald Zietsman Siyavula and DBE team Dr. Erica Makings; Dr. Mark Horner; Bridget Nash; Delita Otto; Marthélize Tredoux; Heather Williams; Kanthan Naidoo; Susan Wiese; Rebecca Govender; Albert Lethole Siyavula contributors Shireen Amien; Bianca Amos-Brown; Julia Baum; Marvin Patrick Bester; Jennifer de Beyer ; Vinayak Bhardwaj; Ingrid Bunge; Anine Burger; Ashley Chetty; Alec Chinhengo; Mari Clark; Hillette Coetzee; Zelmari Coetzee; Rosemary Dally; Carol Drew; Sariana Faure; Shaun Garnett; Danuelle Geldenhuys; Sanette Gildenhuys; Dr Kerry Gordon; Raedene Gouldie; Umeshree Govender; Veeraj Goyaram; Martli Greyvenstein; Suzanne Grové; Henré Hanekom; Pauline Hanekom; Melanie Hay; Pierre van Heerden; Dr Fritha Hennessy; Anna Herrington; Jess Hitchcock; Dr Ardil Jabar; Mohamed Jaffer; Reginald Jako; Miles Jarvis; Jaisubash Jayakumar; Laura Kannemeyer; Mike Kendrick; Elvis Kidzeru; Hein Kriek; Elsabe Kruger; Lounette Loubser; Thapelo Mahlangu; Dr Erica Makings; Dr Nayna Manga; Gary Mann; Peter Mann; Hassiena Marriott; Nicole Masureik; Dr Thalassa Matthews; Cailey Mills; Emang Molojwane; Christopher Muller; Corene Myburgh; Nithya Nagarajan; Eduan Naudé; Hlumani Ndlovu; Dr Natalie Nieuwenhuizen; Edison Nyamayaro; Nkululeko Nyangiwe; Lucy Olivier; Jan Oosthuizen; Ronell Palm; Koebraa Peters; Dr George S Petros; Poobalan Pillay; Bharati Ratanjee; Brice Reignier; Matthew Ridg- way; Dominique Roberts; Dr Marian Ross; Dominique le Roux; Rhoda van Schalkwyk; Prof Trevor Sewell; Hélène Smit; Lindri Steenkamp; Dr Angela Stott; Timo Tait; Rodney Titus; Katie Viljoen; Alykhan Vira; Christina Visser; Hanri Visser; Miranda Waldron; Dr Karen Wallace; Rudi van der Walt; Lesley Williams; Kate West With thanks to Pinelands High School and Parklands College Secondary Faculty for kindly hosting our authoring workshops.  SPONSOR This textbook was designed and developed with corporate social investment funding from the Vodacom Foundation  EVERYTHING MATHS & SCIENCE The Everything Mathematics and Science series covers Mathematics, Physical Sciences, Life Sciences and Mathematical Literacy. The Siyavula Everything Science textbooks The Siyavula Everything Maths textbooks  DIGITAL TEXTBOOKS READ ONLINE Watch this textbook come alive on the web. In addition to all the content in this printed copy, the online version is also full of videos, presentations and simulations to give you a more comprehensive learning experience. www.everythingmaths.co.za and www.everythingscience.co.za CHECK YOUR ANSWERS ONLINE OR ON YOUR PHONE Want the answers? View the fully worked solutions to any question in this textbook by entering its shortcode (4 digit combination of letters and numbers) into the search box on the web or mobi sites. www.everythingmaths.co.za and www.everythingscience.co.za or m.everythingmaths.co.za and m.everythingscience.co.za from your cellphone.  MOBILE & TABLET MOBI You can access this whole textbook on your mobile phone. Yes, the whole thing, anytime, anywhere. Visit the mobi sites at: m.everythingmaths.co.za and m.everythingscience.co.za MXIT Don’t stress if you haven’t got a smart phone. All Mxit users can read their Everything Series textbooks on Mxit Reach too. Add Everything Maths and Everything Science as Mxit contacts or browse to the books on Mxit Reach. mxit>tradepost>reach>education> everything maths or everything science DOWNLOAD FOR TABLETS You can download a digital copy of the Everything Series textbooks for reading on your PC, tablet, iPad and Kindle. www.everythingmaths.co.za and www.everythingscience.co.za  PRACTISE INTELLIGENTLY PRACTISE FOR TESTS & EXAMS ONLINE & ON YOUR PHONE To do well in tests and exams you need practice, but knowing where to start and getting past exams papers can be difficult. Intelligent Practice is an online Maths and Science practice service that allows you to practise questions at the right level of difficulty for you and get your answers checked instantly! Practise questions like these by registering at everythingmaths.co.za or everythingscience.co.za. Angles in quadrilaterals YOUR DASHBOARD Your individualised dashboard on Intelligent Practice helps you keep track of your work. Your can check your progress and mastery for every topic in the book and use it to help you to manage your studies and target your weaknesses. You can also use your dashboard to show your teachers, parents, universities or bursary institutions what you have done during the year. Contents 1 Introduction to Life Sciences 4 1.1 About this chapter................................. 4 1.2 What is Life Sciences?............................... 4 1.3 Why study Life Sciences?............................. 4 1.4 How science works................................ 6 1.5 Biological drawings and diagrams........................ 12 1.6 Tables....................................... 14 1.7 How to draw graphs in Science.......................... 15 1.8 Mathematical skills in Life Sciences....................... 20 1.9 Lab safety procedures............................... 21 2 The chemistry of life 24 2.1 Overview..................................... 24 2.2 Molecules for life................................. 25 2.3 Inorganic compounds............................... 25 2.4 Organic compounds............................... 30 2.5 Vitamins..................................... 48 2.6 Recommended Dietary Allowance....................... 50 2.7 Summary..................................... 52 3 The basic units of life 62 3.1 Overview..................................... 62 3.2 Molecular make up of cells............................ 62 3.3 Cell structure and function............................ 70 3.4 Cell organelles.................................. 79 3.5 Summary..................................... 91 3.6 End of chapter exercises............................. 92 4 Cell division 98 4.1 Overview..................................... 98 4.2 The cell cycle................................... 98 4.3 The role of mitosis................................ 102 4.4 Cancer....................................... 103 4.5 Summary..................................... 111 4.6 End of chapter exercises............................. 112 5 Plant and animal tissues 116 5.1 Overview..................................... 116 5.2 Tissues....................................... 116 5.3 Plant tissues.................................... 117 5.4 Animal tissues................................... 130 5.5 Applications of indigenous knowledge and biotechnology........... 143 5.6 The leaf as an organ................................ 150 5.7 Summary..................................... 154 6 Support and transport systems in plants 158  6.1 Overview..................................... 158 6.2 Anatomy of dicotyledonous plants........................ 158 6.3 Transpiration.................................... 169 6.4 Uptake of water and minerals in the roots.................... 180 6.5 Summary..................................... 185 7 Support systems in animals 190 7.1 Overview..................................... 190 7.2 Skeletons..................................... 190 7.3 Human skeleton.................................. 195 7.4 Musculoskeletal tissues.............................. 207 7.5 Human locomotion................................ 212 7.6 Muscle structure and function.......................... 212 7.7 Diseases...................................... 214 7.8 Summary..................................... 216 8 Transport systems in animals 220 8.1 Overview..................................... 220 8.2 Circulatory systems in animals.......................... 220 8.3 Lymphatic circulatory system........................... 239 8.4 Cardiovascular diseases.............................. 243 8.5 Summary..................................... 248 9 Biospheres to ecosystems 256 9.1 Overview..................................... 256 9.2 Biosphere..................................... 256 9.3 Biomes....................................... 258 9.4 Environment.................................... 268 9.5 Ecosystems.................................... 269 9.6 Energy flow.................................... 277 9.7 Nutrient cycles.................................. 281 9.8 Ecotourism..................................... 285 9.9 Summary..................................... 287 10 Biodiversity and classification 294 10.1 Overview..................................... 294 10.2 Biodiversity.................................... 294 10.3 Classification schemes.............................. 297 10.4 Five kingdom system............................... 302 10.5 Summary..................................... 310 11 History of Life on Earth 314 11.1 Overview..................................... 314 11.2 Representations of life’s history......................... 314 11.3 Life’s History................................... 323 11.4 Mass extinctions.................................. 330 11.5 Impact of humans on biodiversity and environment............... 334 11.6 Fossil tourism................................... 335 11.7 Summary..................................... 335 2 CONTENTS  CHAPTER 1 Introduction to Life Sciences 1.1 About this chapter 4 1.2 What is Life Sciences? 4 1.3 Why study Life Sciences? 4 1.4 How science works 6 1.5 Biological drawings and diagrams 12 1.6 Tables 14 1.7 How to draw graphs in Science 15 1.8 Mathematical skills in Life Sciences 20 1.9 Lab safety procedures 21  1 Introduction to Life Sciences 1.1 About this chapter DUMMY The aim of this chapter is to provide you with an overview of the skills that you develop as you learn to become a Life Scientist. Living systems exhibit levels of organisation from molecules to biomes. In addition, all life on earth is dynamic, with various processes main- taining equilibrium at every level of organisation. The life forms we observe today are a result of billions of years of change. In this chapter you will learn how we gather evidence using the scientific method in order to form theories to explain what we observe. The scientific method requires us to constantly re- examine our understanding, by testing new evidence with our current theories and making changes to those theories if the evidence does not meet the test. The scientific method therefore is the powerful tool you will use throughout the Physical and Life Sciences. 1.2 What is Life Sciences? DUMMY Life Sciences is the scientific study of living things from molecular level to the ecosystem level, and involves a study of the interactions of organic molecules to the interactions of animals and plants with their environment. The list below contains some of the various branches of Life Sciences. Anatomy (plant and animal) Biochemistry Biotechnology Botany Ecology Entomology Environmental Studies Genetics Medicine Microbiology Morphology Physiology (plant and animal) Sociobiology (animal behaviour) Taxonomy Zoology 1.3 Why study Life Sciences? DUMMY Here are some reasons to study Life Sciences: 4 1.1. About this chapter  To increase knowledge of key biological concepts, processes, systems and theories. To develop the ability to critically evaluate and debate scientific issues and processes. To develop scientific skills and ways of thinking scientifically that enables you to see the flaws in pseudo-science in popular media. To provide useful knowledge and skills that are needed in everyday living. To create a greater awareness of the ways in which biotechnology and knowledge of Life Sciences has benefited humankind. To show the ways in which humans have impacted negatively on the environment and organisms living in the environment. To develop a deep appreciation of the unique diversity of biomes In Southern Africa, both past and present, and the importance of conservation. To create an awareness of what it means to be a responsible citizen in terms of the environment and life-style choices that they make. To create an awareness of the contributions of South African scientists. To expose you to the range and scope of biological studies to stimulate interest in and create awareness of possible specialities and fields of study. To provide sufficient background for further studies and careers in one or more of the biological sub-disciplines. An A to Z of possible careers in Life Sciences DUMMY Ever wondered what you can do with Life Sciences after school? Below are some careers which you could study: Agronomist: someone who works to improve the quality and production of crops. Animal scientist: a researcher in selecting, breeding, feeding and managing of domes- tic animals, such as cows, sheep and pigs. Biochemist: someone who investigates the chemical composition and behaviour of the molecules that make up living things and uses this knowledge to try understand the causes of diseases and find cures. Botanist: someone who studies plants and their interaction with the environment. Developmental biologist: studies the development of an animal from the fertilised egg through to birth. Ecologist: a person who looks at the relationships between organisms and their envi- ronment. Food Scientist: someone who studies the biological, chemical and physical nature of food to ensure it is safely produced, preserved and stored, and they also investigate how to make food more nutritious and flavourful. Geneticist: a researcher who studies inheritance and conducts experiments to inves- tigate the causes and possible cures of inherited genetic disorders and how traits are passed on from one generation to the next. Horticulturalist: a person who works in orchards and with garden plants and they aim to improve growing and culturing methods for home owners, communities and public areas. Marine biologist: a researcher who studies the relationships between plants and ani- mals in the ocean and how they function and develop. They also investigate ways to minimise human impact on the ocean and its effects, such as over fishing and pollu- tion. Chapter 1. Introduction to Life Sciences 5  Medical doctor or nurse: someone who uses the current latest understanding of the causes and treatments for disease to treat people who are ill or improve a person’s well-being. Medical illustrator: someone who illustrates and draws parts of the human body to be used in textbooks, publications and presentations. Microbiologist: a researcher who studies microscopic organisms such as bacteria, viruses, algae and yeast and investigates how these organisms affect animals and plants. Nutritionist: someone who gives advice to individuals or groups on good nutritional practices to either maintain or improve their health and to live a healthy lifestyle. Palaeontologist: a researcher who studies fossils of plants and animals to trace and reconstruct evolution, prehistoric environments and past life. Pharmacologist: a scientist who develops new or improved drugs or medicines and conducts experiments to test the effects of drugs and any undesirable side effects. Physiologist: a researcher who studies the internal functions animals and plants during normal and abnormal conditions. Science teacher: someone who helps students in different areas of science, whether it is at primary school, high school or university. Science writer: someone who writes and reports about scientific issues, new discover- ies or researcher, or health concerns for newspapers, magazines, books, television and radio. Veterinarian: someone who looks after the health and wellbeing of pets, domestic animals, animals in game parks and zoos. Zoologist: a researcher who studies the behaviour, interactions, origins and life pro- cesses of different animal groups. 1.4 How science works DUMMY Science investigation and research requires many skills and processes to come together in order to be successful and worthwhile. To be accepted as a science, certain methods for broadening existing knowledge, or discovering new things, are generally used. These methods must be repeatable and follow a logical approach. The methods include formulating hypotheses and carrying out investigations and ex- periments to test the hypothesis. Crucial skills are making objective observations, taking measurements, collecting in- formation and presenting the results in the form of drawings, written explanations, tables and graphs. A scientist must learn to identify patterns and relationships in data. It is very important to then communicate these findings to the public in the form of scientific publications, at conferences, in articles or TV or radio programmes. Scientific method DUMMY The scientific method is the basic skill process in the world of science. Since the beginning of time humans have been curious as to why and how things happen in the world around us. The scientific method provides scientists with a well structured scientific platform to help find the answers to their questions. Using the scientific method there are very few things we 6 1.4. How science works can’t investigate. Recording and writing up an investigation is an integral part of the scientific method. A step-by-step guide to the scientific method 1. The question Scientists are curious people, and most investigations arise from a scientist noticing some- thing that they don’t understand. Therefore the first step to any scientific investigation is: Ask a question to which you want to find an answer. – What is happening? – How is it happening? – When is it occurring? – Why is it happening? Example: A farmer notices that his tomato plants that are shaded have smaller tomatoes than his plants that are in a sunny spot, which makes him wonder: ’Does the amount of sunlight a tomato plant receives affect the size of tomatoes?’ Chapter 1. Introduction to Life Sciences 7  Figure 1.1: Overview of scientific method. 2. Introduction Once you have a general question, background research needs to be undertaken. Your background research will ensure that you are not investigating something that has already been researched and answered. It will also tell you about interesting connections, theories, explanations and methods that people have used in the past to answer questions related to yours. Science always builds on the work of others, and it ensures that our theories are constantly improved and refined. It is important to acknowledge the work of the people upon whose work your theory relies in the form of referencing. It is also vital to communicate your findings so that future scientists can use use your work as a basis for future research. 3. Identify variables Your background research will help you identify the factors that influence your question. Factors that might change during the experiment are called variables. 8 1.4. How science works  Firstly think of all the relevant variables you can change. Secondly think of all the variables you can measure or observe. Different types of variables are given special names. Below is a list of some important variable types: The dependent variable is the thing that you want to measure or investigate. The independent variable is a factor (or factors) that changes which will have an effect on the dependent variable. In every experiment you need to know which independent variable you are testing, and keep all the other possible variables constant. We call the the variables we keep constant fixed variables, or controlled variables Example: In this investigation, variables might include: the amount of sunshine, the types of soil in which the tomatoes are growing, the water available to each of the plants, etc. To which variable type does each factor belong? Dependent variable is the one you measure to get the results, e.g. the mass of tomatoes Independent variable is the ONE thing you vary to see how it affects the dependent variable, e.g. how much light the tomatoes are exposed to (dark / dim light or shade / bright light) Fixed/ Controlled variables are kept the same in all trials under investigation, because they may interfere with the results. All tomato plants will: – Be the same species of tomato – Get the same fertiliser (type and amount) – Grow in the same type of soil – Grow in the same type of container – Get the same amount of water – Can you think of more? 4. Hypothesis Write down a statement or prediction as to what you think will be the outcome or result of your investigation. This is your hypothesis. The hypothesis should: be specific relate directly to the question you are asking be expressed as a statement that includes the variables involved (the ‘cause’ and ‘ef- fect’) be testable not expressed as a question but rather as a prediction be written in the future tense Example: During your background research you would have learnt that tomatoes need sun- shine to make food through photosynthesis. You may predict that plants that get more sun will make more food and grow bigger. In this case your hypothesis would be: I think that the more sunlight a tomato plant receives, the larger the tomatoes will grow’. Chapter 1. Introduction to Life Sciences 9  NOTE: A scientific investigation does not aim to prove a particular event occurs or a particular rela- tionship exists. Rather, an investigation shows that it cannot disprove a particular suggestion or prediction. Therefore, it is important to note that an incorrect prediction does not mean that you have failed. It means that the experiment has brought some new facts to light that you might not have thought of before. Therefore even if your hypothesis (prediction) turns out to be wrong, DO NOT go back and change the hypothesis! To test the hypothesis in life Sciences, you can follow the step-by-step guide which is outlined below. 5. Aim In the aim you need to state what you going to be investigating. Key words you can use are: – To determine... – To show that... – To investigate... – To find out... – To observe... – To measure... Example: In this case, your aim would be: to investigate the effect of different amounts of sunlight on tomatoes. NOTE: In science we never ‘prove’ a hypothesis through a single experiment because there is a chance that you made an error somewhere along the way, or there may be an alternate explanation for the results that you observe. What you can say is that your results SUPPORT the original hypothesis. 6. Apparatus All the apparatus that you will need for the investigation needs to be listed. Sizes of beakers, test tubes and measuring cylinders Specialised equipment that you may need must also be included (make sure that this equipment is available for your research). Include all chemicals and quantities that are required for your investigation. 7. Method The next step is to test your hypothesis. An experiment is a tool that you design to find out if your ideas about your question are right or wrong. You must design an experiment that accurately tests your hypothesis. The experiment is the most important part of the scientific method. We will discuss independent and dependent variables as well as controls later. These are all important concepts to know when designing an experiment. In science, another researcher may want to repeat your method, to verify your results, improve it or do a variation of your experiment. Listing the apparatus helps others to verify that you used a suitable method, and enables them to replicate the experiment. Write down the scientific method in bullet format for your investigation. 10 1.4. How science works  The method should be written so that a complete stranger will be able to carry out the same procedure in the exact same way and get almost identical results. The method should be written in the past tense using the passive voice. The method must be clear and precise instructions including – the apparatus – exact measurements or quantities of chemicals or substances Ensure that your method is written out in the correct sequence, with each step of the experiment numbered. State the criteria you will look for or measure to get results. Give clear instructions how the results should be recorded (table, graph etc.) Include safety precautions where possible. 8. Results Record your observations from doing the investigation. It is important that you do not write out an explanation for the results. Present your results in a suitable format such as tables and graphs. It is also important to note that not getting the result you expected is still a result. Even if there is no change at all, this is still a result that needs to be recorded. 9. Analysis of results or Discussion The analysis of the results is stating in words what the results are often saying in ta- bles/graphs. Discuss if there are there any relationships between your independent and dependent variables. It is important to look for patterns/trends in your graphs or tables and describe these clearly in words. 10. Evaluation of results This is where you answer the question “What do the results mean?” You need to carefully consider the results : – Were there any unusual results? If so then these should be discussed and possible reasons for them can be given. – Discuss how you ensured the validity and reliability of the investigation. ∗ Vailidity: Was it a fair test and did it test what it set out to test? ∗ Reliability: If the experiment were to be repeated would the results obtained be similar? – The best way to ensure reliability is to repeat the experiment several times and obtain an average. – Discuss any experimental errors that may have occurred during the experiment. These can include errors in the methods and apparatus used and what make suggestions what could be done differently next time. 11. Conclusion The conclusion needs to link the results to the aim and hypothesis. In a short paragraph, write down if what was observed is supported or rejected by the hypothesis by restating the Chapter 1. Introduction to Life Sciences 11  variables that were tested. If your original hypothesis does not match up with the final results of your experiment, do not change the hypothesis. Instead, try and explain what might have been wrong with your original hypothesis. What information did you not have originally that cause you to be wrong in your prediction. Example: after conducting your experiment you may have found that tomato plants that received more sunlight grew larger than tomato plants grown in the shade or without light. Therefore you might conclude your investigation with the following: – It was clear that tomato plants form bigger tomatoes when they are exposed to bright sunlight. The original hypothesis was supported. Important principles and relationships in Life Sciences DUMMY Surface area and volume Depending on the system it is advantageous to either have a large surface to volume ratio or a small surface to volume ratio This is highlighted in the following examples: Flatworms and leeches have more surface area to volume to increase the area for diffusion for nutrients and respiratory gases across their whole bodies. In animals the shapes of organs are defined by surface area to volume requirements. For example, in the lungs there are many branches to increase the surface area through which gases can be exchanged. Cells with a greater volume compared to surface area are able to metabolise more and ingest and excrete more through the membrane. Structure and function In living organisms, the structure of a particular biological feature is related to what function it performs. Thus for all the structures you will study in Life Sciences, the important questions to ask are the following: 1. What makes this structure suited to its function? 2. How has the structure adapted to its function? 3. Why is this structure so efficient for its function? 1.5 Biological drawings and diagrams DUMMY Drawings and diagrams are an essential part of communication in science, and especially Life Sciences. Remember it is not an artwork or sketch! But rather it is a clear representation of what you observe which can be used to interpret what you saw. Some rules to follow Drawings and diagrams must: 12 1.5. Biological drawings and diagrams  Be drawn in a sharp pencil for clear, smooth lines. Be large so that all structures can be clearly seen (at least 10 lines of paper). Be drawn in the middle of the page. Be two dimensional (no shading)! Have a heading or caption. Specify the section in which the specimen was sliced, i.e. transverse section (T/S), cross section (C/S), or longitudinal section (L/S). State the source of the drawing or diagram, i.e. From a biological specimen, a micro- graph or a slide. Indicate the magnification or scale of the drawing, either in the caption or in the corner of the drawing. Label lines should be drawn and they must: – be parallel to the top of the page and drawn with a ruler. – not cross each other or have an arrow at the end. – clearly indicate the structure which is being named. – be aligned neatly, one below the other and preferably on one side of the page, unless there are many labels in which both sides can be used. Activity: Identifying the key aspects of producing biological drawings Instructions: Make a list of what makes the above drawings good and bad. Figure 1.2: Identify the features of the images that make each one good or bad. Chapter 1. Introduction to Life Sciences 13  Two-dimensional (2-D) and three-dimensional (3-D) diagrams DUMMY Objects in Life Science can be drawn in three dimensions because they have depth. Diagrams of apparatus are generally drawn in two-dimensions so that the shape of each item of apparatus is simplified and looks similar to a section through the apparatus. 1.6 Tables DUMMY What is a table? A table is a summary of data, using as few words as possible. It is a grid divided up into rows and columns. The heading is placed above the table. The heading should include both variables under investigation- the dependent and independent variables. Independent variable is placed in the first column. The column headings should mention the units that were used, eg. grams, hours, km/hr, cm. When to use a table? To summarise information. To compare related things or aspects. To record the results of an experiment. To illustrate patterns and trends. To record the data which will be used to construct a graph. 14 1.6. Tables 1.7 How to draw graphs in Science DUMMY Presenting data graphically Line Graphs Line graphs are used when: The relationship between the dependent and independent variables is continuous. Both dependent and independent variables are measured in numbers. Features of line graphs: An appropriate scale is used for each axis so that the plotted points use most of the axis/space (work out the range of the data and the highest and lowest points). The scale must remain the SAME along the entire axis and use easy intervals such as 10’s, 20’s, 50’s, and not intervals such as 7’s, 14’s, etc, which make it difficult to read information off the graph. Each axis must be labelled with what is shown on the axis and must include the appropriate units in brackets, e.g. Temperature (◦ C), Time (days), Height (cm). Each point has an x and y co-ordinate and is plotted with a symbol which is big enough to see, e.g. a cross or circle. The points are then joined. With a ruler if the points lie in a straight line (see Figure 3) or you can draw a line of best fit where the number of points are distributed fairly evenly on each side of the line. Freehand when the points appear to be following a curve (see Figure 4). DO NOT start the line at the origin unless there is a data point for 0. If there is no reading for 0, then start the line at the first plotted point. The graph must have a clear, descriptive title which outlines the relationship between the dependent and independent variable. If there is more than one set of data drawn on a graph, a different symbol must be used for each set and a key or legend must define the symbols. Chapter 1. Introduction to Life Sciences 15 FACT Table headings are always written ABOVE the table. Graph headings are always written BELOW the graph. Figure 1.3: Graph showing change in plant height over 10 days Bar Graphs Bar graphs are used when: The independent variable is discontinuous (i.e. The variables on the x-axis are each associated with something different) Independent variables are not numerical. For example, when examining the protein content of various food types, the order of the food types along the horizontal axis is irrelevant. Bar graphs have the following features: The data are plotted as columns or bars that do not touch each other as each deals with a different characteristic. The bars must be the same width and be the same distance apart from each other. A bar graph can be displayed vertically or horizontally. A bar graph must have a clear, descriptive title, which is written beneath the graph. Figure 1.4: Bar graph showing how many learners use each type of transport Histograms 16 1.7. How to draw graphs in Science Histograms are used when the independent variable (x-axis) represents information which is continuous, such as numerical ranges, i.e. 0-9, 10-19, 20-29, etc. Histograms have the following features: Unlike a bar graph, in a histogram the data are plotted as columns or bars that touch each other as they are related to each other in some way. The numerical categories must not overlap, for example, 0-10, 10-20, 20-30, etc. The ranges must be exclusive so that there is no doubt as to where to put a reading, for example, 0-9, 10-19, 20-29, etc. The bars can be vertically or horizontally drawn. A histogram must have a descriptive heading with is written below the graph and the axes must be labelled. Figure 1.5: A histogram showing the number of learners in a Grade 10 Life sciences class with a particular percentage test score Pie charts DUMMY You want to give a visual representation of percentages as a relative proportion of the total of a circle. They are a type of graph even though they do not have any axes. A pie chart is a circle divided into sectors (think of them as the slices of a cake). 100% represents the whole complete circle, 50% represents a half circle, 25% is a quarter circle, and so on. Example: 1. Count the number of each species and record it in a table. 2. Work out the total number of species in the ecosystem. 3. Calculate the percentage of each species. 4. Use the following formula to work out the angle of each slice: v × 360◦ a= t Chapter 1. Introduction to Life Sciences 17  Species No of % Slice angle types Insects 17 17 × 100 34 × 360 = 34% = 122,4◦ 50 100 Plants 16 16 × 100 16 × 360 = 32% = 115,2◦ 50 100 Birds 9 9 × 100 18 × 360 = 18% = 65◦ 50 100 Amphibians 8 8 × 100 16 × 360 = 16% = 57,6◦ 50 100 Table 1.1: Table showing recordings and calculations for construction of a pie chart 1. Use a compass to draw the circle and a protractor to measure accurate angles for each slice. 2. Start with the largest angle/percentage starting at 12 o’ clock and measure in a clock- wise direction. 3. Shade each slice and write the percentage on the slice and provide a key. Figure 1.6: Pie chart showing the relative proportions of different categories of organisms in an ecosystem Activity: Converting tables to graphs Reason: 18 1.7. How to draw graphs in Science It is very important to be able to convert tables to graphs, and vice versa. Below are some exercises to practice this. Questions: 1. Convert the data in the graphs below into Tables. Remember to identify which is the independent variable in the graphs and to place this in the first column of the Table. Figure 1.7: The average height in boys and girls between the ages of 10 and 18 years. Figure 1.8: Proportion of each blood group in a small population. 2. Convert the data in the following tables into graphs. Look back at the features of each type of graph to decide which one you will use. Favourite take away restaurant in a class of learners Take aways restaurant Learners (%) Kauai 40 Anat Falafel 15 Nandos 25 Burger King 20 Chapter 1. Introduction to Life Sciences 19  1.8 Mathematical skills in Life Sciences DUMMY Mathematical skills are important in Life Sciences. Below are explanations of some of the skills you will encounter. NB. You must state the UNITS at the end of each calculation, e.g. cm, degrees, kg, etc. Scales A scale is given in a diagram, drawing or electron micrograph so that the actual size of the object that is being shown can be determined. The object could be bigger or smaller in real life. Example: To measure the diameter of a chloroplast with a scale line of 1 µm. 1) Measure the length of the scale line on the micrograph in mm, e.g. 1 µm = 17mm 2) Measure the diameter of the organelle in millimetres, e.g. = 60mm 3) True diameter of chloroplast: measured size × true length of scale line = measured length of scale line 60 mm × 1 µm = 17 mm = 3,53 µm Averages To find an average of a set of numbers, you add all the items and divide the total by the number of items. Example: Find the average height in a class of 10 learners with the following heights in cm: 173, 135, 142, 167, 189, 140, 139, 164, 172, 181 cm. Total = 1602 (add all 10 heights together) Average 1602 Average = 10 = 160,2 cm Percentages To calculate a percentage, multiply the fraction by 100. Formula for calculating percentage (%): Number with feature (A) Percentage = times100 Total number (B) Example: Calculate the percentage of learners in your class that are left-handed. 20 1.8. Mathematical skills in Life Sciences 1) Count how many learners are left handed (A). 2) Count the total number of learners in the class (B). There are 48 learners and 4 of them are left handed. Therefore, % of left-handed: A = × 100 B 4 = × 100 48 = 8,3% 8,3% of the learners in your class are left-handed. The percentage of right-handed learners: = 100 − 8,3 = 91,7% 91,7% of the learners in your class are right-handed. Some conversions From unit: To unit (number of these units per “From unit”): m mm µm nm m 1 1000 1 000 000 1 000 000 000 mm 10−3 or 1/1000 1 1000 1 000 000 −6 −3 µm 10 or 10 or 1/1000 1 1000 (micrometres) 1/1 000 000 nm 10−9 or 10−6 or 10−3 or 1/1000 1 (nanometres) 1/1 000 000 000 1/1 000 000 1.9 Lab safety procedures DUMMY The Life Science Laboratory has rules that are enforced as a safety precaution. These rules are: Take care when pouring liquids or powders from one container to another. When spillages occur you need to call the teacher immediately to assist in cleaning up the spillage. Take care when using acids. A good safety precaution is to have a solution of sodium bicarbonate in the vicinity to neutralise any spills as quickly as possible. Safety goggles and/ or gloves may need to be worn when doing experimental work, working with various chemicals, or heating substances, as spitting may occur. When lighting a Bunsen burner the correct procedure needs to be followed. Remember that when heating a substance in a test tube, the mouth of the test tube must face away from you and members in your group. Chapter 1. Introduction to Life Sciences 21  Do not to overheat the solution when heating substances in a test tube. Ensure that you are dressed appropriately: hair should be tied back and loose clothing that could potentially knock over the equipment or catch alight if too near a flame should be avoided. Before doing any scientific experiment make sure that you know where the fire extin- guishers are in your laboratory and there should also be a bucket of sand to extinguish fires. If scalpel blades, pins and knives are used, take care not to cut yourself. If you do cut yourself and draw blood call the teacher immediately. When working with chemicals and gases that are hazardous a fume cupboard should be used. 22 1.9. Lab safety procedures  CHAPTER 2 The chemistry of life 2.1 Overview 24 2.2 Molecules for life 25 2.3 Inorganic compounds 25 2.4 Organic compounds 30 2.5 Vitamins 48 2.6 Recommended Dietary Allowance 50 2.7 Summary 52  2 The chemistry of life 2.1 Overview DUMMY Introduction DUMMY In this chapter we will study the molecular structure and biological functions of key molecules important to life. We will study the chemistry of proteins, carbohydrates, lipids, vitamins and nucleic acids and will learn the role of each nutrient class in plant and animal life. We will also learn how our diet allows us to obtain sufficient quantities of each of these nutrients. Key concepts Organic molecules always contain carbon (C), and usually also contain hydrogen (H) and oxygen (O). Some important organic molecules also contain nitrogen (N), phos- phorous (P), sulfur (S), iron (Fe) and other elements. Water (H2 O) is an inorganic compound made up of two H and one O. Water helps with temperature regulation, form and support, transport and lubrication and is a medium for chemical reactions. Minerals are required as part of a healthy diet. A deficit in essential minerals results in deficiency diseases in plants and animals. Fertilizers are a way that essential nutrients can be added to the soil to improve plant growth. Carbohydrates are made up of C, H and O. They can be in the form of monosaccha- rides (single sugars), disaccharides (double sugars) or polysaccharides (many sugars), and are an important energy source for plants and animals. Lipids are made up of C, H and O. Triglycerides are a type of lipid that contains glycerol and three fatty acid chains. Cholesterol, another type of lipid, can increase the risk of heart disease. Proteins are made up of C, H, O, N, and some have P, S and Fe. Proteins consist of a long chain of amino acids that fold into a very specific three-dimensional structure. Proteins are an important building block in plants and animals and play a role in the immune system and in cell communication. Enzymes are a type of protein that act as a biological catalyst to speed up reactions. They work by a ”lock and key” mechanism and are affected by temperature and pH. Nucleic acids such as DNA and RNA are made of C, H, O, N and P. DNA contains the genetic information for heredity, and RNA has the instructions on how to make protein. Vitamins are important organic molecules that must be obtained in the diet. They often help enzymes to work properly, or act in growth or differentiation. In order to understand the chemistry of living systems, it is important to understand how all living systems are arranged from the smallest unit (atomic scale) to the largest unit (ecosys- tems). A simple way to describe the levels of organisation of livings things can be given as follows: 24 2.1. Overview atom →molecule→cell→tissue→organ→organism→ecosystem FACT Because all compounds contain more than one 2.2 Molecules for life DUMMY atom, all compounds are molecules. Although life at the macro level is diverse, the chemistry making up that life is remarkably However, not all molecules are similar. All living things are made up of basic building blocks called elements. An element is compounds. a substance that cannot be broken down into simpler substances using chemical means. Car- bon, oxygen, hydrogen, nitrogen, sulfur, calcium, sodium and iron are examples of elements FACT you will come across in Life Sciences. WATCH: simulation on building a Each element is distinguished by the composition of its atom. An atom is the basic unit of molecule See video: matter. Molecules are formed when one or more atoms are covalently bonded together. The SHORTCODE at atoms of a molecule can be identical, such as 02 or H2 or differ such as H2 O. A compound www.everythingscience. is formed when atoms of different elements join together. Compounds are divided into organic and inorganic compounds. Organic compounds al- ways contain carbon, but not all compounds that contain carbon are organic. A general rule of thumb is that organic compounds contain carbon, with at least one of these car- bons bonded to hydrogen atoms. Carbon dioxide is therefore an inorganic compound even though it contains carbon. The major organic compounds found in living organisms include: carbohydrates, fats, proteins and nucleic acids. These will be discussed in detail later in this chapter. Substance Percentage Inorganic Water 65% Mineral salts 1% Organic Protein 18% Carbohydrate 5% Other organic macromolecules 1% Table 2.1: The composition of macromolecules in humans by percentage. 2.3 Inorganic compounds DUMMY The role of water in the maintenance of life DUMMY As mentioned in Table 2.1, up to 65% of our bodies are made up of water. Water is an inorganic compound made up of two hydrogen atoms and one oxygen atom. Its molecular formula is H2 O. Water plays an important role in the maintenance of biological systems. Temperature regulation: in humans, the sweat glands produce sweat which cools the body as it evaporates from the body surface in a process called perspiration. In a similar way, plants are cooled by the loss of water vapour from their leaves, in a process called transpiration. Form and support: water is an important constituent of the body and plays an important role in providing form and support in animals and plants. Animals, such as worms and jellyfish, Chapter 2. The chemistry of life 25  use water in special chambers in their body to give their bodies support. This use of water pressure to provide body form, and enable movement is called a hydrostatic skeleton. Plants grow upright and keep their shape due to the pressure of water ( turgor pressure) inside the cells. Transport medium: water transports substances around the body. For example, water is the main constituent of blood and enables blood cells, hormones and dissolved gases, elec- trolytes and nutrients to be transported around the body. Lubricating agent: water is the main constituent of saliva which helps chewing and swallow- ing and also allows food to pass easily along the alimentary canal. Water is also the main constituent of tears which help keep the eyes lubricated. Solvent for biological chemicals: the liquid in which substances dissolve is called a solvent. Water is known as the universal solvent as more substances dissolve in water than in any other liquid. Medium in which chemical reactions occur: all chemical reactions in living organisms take place in water. Reactant: water takes place in several classes of chemical reactions. During hydrolysis reac- tions, water is added to the reaction to break down large molecules into smaller molecules. Water can also be split into hydrogen and oxygen atoms to provide energy for complex chemical reactions such as photosynthesis. Temperature Structure and support Lubrication Figure 2.1: (Attribution: ??) Sweating helps Jellyfish and worms use a Water helps Water is an important human bodies hydrostatic (water maintain the lubricant in the eye. cool down. pressure) skeleton to upright structure keep their body shape. of plants. Minerals DUMMY Dietary minerals are the chemical elements that living organisms require to maintain health. In humans, essential minerals include calcium, phosphorous, potassium, sulfur, sodium, chlorine and magnesium. Macro-elements (macro-nutrients) are nutrients that are required in large quantities by living organisms (e.g carbon, hydrogen, oxygen, nitrogen, potassium, sodium, calcium, chloride, magnesium, phosphorus and sulfur). 26 2.3. Inorganic compounds Micro-elements (micro-nutrients) are nutrients that are required in very small quantities for development and growth and include iron, cobalt, chromium, copper, iodine, manganese, selenium, zinc and molybdenum. Table 2.2 below summarises some important minerals required for proper functioning of the human body. Proper nutrition involves a diet in which the daily requirements of the listed mineral nutrients are met. Mineral Food Source Main Functions Deficiency Disease Macro-nutrients Calcium (Ca) most fruit and strong bones and teeth; rickets, vegetables, meat, muscle contraction; blood osteoporosis dairy products clotting; nerve function Magnesium (Mg) nuts, meat, dairy strong bones and teeth; osteoporosis, products nerve and muscle function; muscle cramps energy production Phosphorus (P) nuts, meat, dairy strong bones and teeth; rickets, products nerve function; part of osteoporosis nucleic acids and cell membranes Potassium (K) bananas, meat, dairy growth and maintenance, muscle cramps; products water balance, heart function heart, kidney and lung failure Sodium (Na) table salt, fruit and regulates blood pressure and muscle cramps vegetables volume; muscle and nerve function Sulfur (S) meat, dairy products, part of proteins; detoxifies disorder unlikely eggs, legumes the body; good skin; hair and nails Micro-nutrients Iron (Fe) meat, legumes part of haemoglobin (the anaemia oxygen transport protein); part of some enzymes Iodine (I) seafood, iodated salt production of hormones by goitre, stunted the thyroid gland; strong growth, mental bones and teeth; good hair; problems skin and nails Zinc (Zn) seafood, meat immune function; male stunted growth, reproductive system prostate problems Table 2.2: Minerals required by humans. Nutrients required for plant growth The previous section examined the key nutrients important for animal growth. In Table ?? we will now look at the key nutrients required for plant growth. Chapter 2. The chemistry of life 27  Mineral Source Main Functions Deficiency Disease Macro-nutrients Calcium (Ca) inorganic fertilisers; part of the plant cell wall; chlorosis Ca ions in the soil transport and rention of other elements Magnesium (Mg) inorganic fertilisers; component of chlorosis (the low Mg ions in the soil chlorophyll (pigment for production or loss of photosynthesis); activates chlorophyll in plant many enzymes required leaves) for growth Nitrogen (N) inorganic fertilisers in component of stunted growth; the form of nitrates; chlorophyll; nucleic smaller leaves symbiotic acids and proteins; seed nitrogen-fixing and fruit production bacteria in roots Phosphorus (P) inorganic fertilisers in photosynthetic process; stunted growth, the form of part of nucleic acids and blue/green leaves phosphates; low cell membranes; root amounts in the soil growth Potassium inorganic fertilisers; K needed for protein chlorosis; curling leaf ions in the soil synthesis, tips; brown photosynthesis, enzyme scorching, poor fruit activation, opening and quality closing of stomata; Sulfur (S) inorganic fertilisers protein synthesis; root chlorosis growth; chlorophyll formation; promotes activity of enzymes Micro-nutrients Iron (Fe) inorganic fertilisers; component of the chlorosis Fe ions in the soil enzyme that makes chlorophyll Zinc (Zn) inorganic fertilisers; part of growth-regulating poor leaf growth Zn ions in the soil enzyme systems Sodium (Na) inorganic fertilisers; maintains salt and water reduced growth Na ions in the soil balance Iodine (I) inorganic fertilisers; I needed for energy poor growth ions in the soil release during respiration Table 2.3: Nutrients required for plant growth. Use of fertilisers When crops are regularly grown and harvested on the same piece of land, the soil becomes depleted of one or more nutrients. Fertilisers are natural or non-natural mixtures of chemical substances that are used to return depleted nutrients to the soil, improve the nutrient content of the soil and promote plant growth. Inorganic nutrients (such as nitrates and phosphates) are added to the soil in the form of inorganic fertilisers. Effect of fertilisers on the environment Using large amounts of fertilisers can be harmful to the environment. Fertilisers wash off into rivers where they are poisonous to plant and animal life. The accumulation of fertilisers in rivers can lead to a process known as eutrophication. This process occurs when excessive nutrients (nitrates and phosphates) from the land (typically from fertilisers) run off into rivers 28 2.3. Inorganic compounds and lakes. This leads to high growth of water plants. Plants grow and produce food by photosynthesis which requires high quantities of oxygen. The high oxygen demand of the rapidly growing water plants removes oxygen available to other organisms in the rivers and lakes. These organisms then suffocate and die due to lack of oxygen. The biodegradation of the dead organisms results in a massive increase in bacteria, fungi and algae degrading the dead organic matter, which also require oxygen. This further depletes the available oxygen, and further contributes to the death of fish and other aquatic species. Figure 2.2: Schematic diagram showing the processes that lead to eutrophication. Figure 2.3: Algae and dead fish in a lake that has undergone eutrophication. Figure 2.4: Algal bloom in a river following eutrophication. Natural fertilisers: an application of indigenous knowledge systems The fertilisers discussed above are non-natural inorganic compounds such as nitrates, phos- phates etc. However, as a means of reducing the negative impact of the inorganic fertilisers discussed earlier, organic fertilisers that occur naturally can be used. Natural fertilisers con- sist of organic compounds derived from manure, slurry, worm castings, peat, seaweed etc. Natural fertilisers supply nutrients to the soil through natural processes such as composting. This means that the nutrients are released back to the soil slowly, and excessive nutrients do not wash off into rivers causing over-fertilisation and eutrophication. However, the use of organic fertilisers is more labour-intensive and the nutrient composition tends to be more Chapter 2. The chemistry of life 29  variable than the inorganic fertilisers. As a result it is difficult to know for sure whether the particular nutrient required by the plant is actually being supplied by the natural fertiliser. Figure 2.6: A homemade compost tumbler. Figure 2.5: Sample of compost created through processes involving degradation of dead organic matter by bacteria and fungi. 2.4 Organic compounds DUMMY An organic compound is a compound whose molecules contain C, and usually at least one C-C or C-H bond. Very small carbon-containing molecules that do not follow the above rules, such as CO2 and simple carbonates, are considered inorganic. Life on earth would not be possible without carbon. Other than water, most molecules of living cells are carbon- based, and hence are referred to as organic compounds. The main classes of organic com- pounds we will investigate in this section include carbohydrates, lipids, proteins and nucleic acids. Each of these classes of compounds consists of large molecules built from small subunits. The smallest of these subunits is called a monomer. Several monomers bond together to form polymers. Each of these polymers is characterised by a specific structure owing to the chemical bonds formed. These structures are related to the function of the compound in living organisms. We will therefore study each class of compounds under the following headings: molecular make-up: the main elements that make up the class of compounds structural composition: how the monomers join up together to form polymers biological role: importance of these molecules to animals and plants chemical test: how to detect the presence of each class of compounds Carbohydrates DUMMY Molecular make-up Carbohydrates consist of carbon (C), hydrogen (H) and oxygen (O). 30 2.4. Organic compounds  Figure 2.7: A glucose molecule is made up of carbon, hydrogen and oxygen. Structural composition Carbohydrates are made up of monomers known as monosaccharides. The monosaccharide that makes up most carbohydrates is glucose. Other monosaccharides include fructose, galactose and deoxyribose (discussed later). These monomers can be joined together by glycosidic bonds. When two monosaccharides are chemically bonded together, they form disaccharides. An example of a disaccharide is sucrose (table sugar), which is made up of glucose and fructose. Other dissacharides include lactose, made up of glucose and galactose, and maltose, made up of two glucose molecules. Monosaccharides and dissachardies are often referred to as sugars, or simple carbohydrates. Several monosaccharides join together to form polysaccharides. Examples of polysaccharides you will encounter include glycogen, starch and cellulose. Polysaccharides are usually referred to as complex carbohydrates as they take longer to break down. Figure 2.8: Examples of food sources of various monosaccharides, disaccharides and polysaccharides. Role in animals and plants The main function of carbohydrates is as energy storage molecules and as substrates (starting material) for energy production. Carbohydrates are broken down by living organisms to re- lease energy. Each gram of carbohydrate supplies about 17 kilojoules (kJ) of energy. Starch and glycogen are both storage polysaccharides (polymers made up of glucose monomers) and thus act as a store for energy in living organisms. Starch is a storage polysaccharide in plants and glycogen is the storage polysaccharide for animals. Cellulose is found in plant cell walls and helps gives plants strength. All polysaccharides are made up of glucose monomers, Chapter 2. The chemistry of life 31  but the difference in the properties of these substances can be attributed to the way in which the glucose molecules join together to form different structures. Below are images of glyco- gen and starch. Figure 2.9: A comparison between starch and glycogen. Glycogen is more extensively branched than starch. Chemical tests to identify presence of carbohydrates Substances containing starch turn a blue-black colour in the presence of iodine. An observ- able colour change is therefore the basis of a chemical test for the compound. Figure 2.10: Granules of wheat starch, stained with iodine and photographed through a light micro- scope. Investigation: Test for the presence of starch (Essential investigation-CAPS) Aim: To test for the presence of starch. Apparatus: piece of potato or bread lettuce leaf petri dish iodine solution 32 2.4. Organic compounds  FACT dropper WATCH: Watch a video demonstration of Method: the test for glucose. See video: SHORTCODE at 1. Place a piece of potato or bread and the lettuce leaf in the petri dish. www.everythingscience. 2. Using the dropper add a few drops of iodine solution onto the potato or bread. Figure 2.11: Experimental set-up: test for the presence of starch using iodine. Observations: Record your observations. Questions: Can this method be used to determine how much starch is present? Explain your answer. Certain monosaccharides, such as glucose, are known as reducing sugars. These are defined as sugars that can easily undergo oxidation reactions (i.e. lose an electron or gain an oxygen atom) and act as a reducing agent. In order to test for carbohydrates we typically test for the presence of reducing sugars using either the Benedict’s or Fehling’s test. Both solutions (Benedict’s and Fehling’s) contain copper sulphate which reacts with reducing sugars to produce a colour change. Investigation: Testing for the presence of reducing sugars (Essential investigation-CAPS) Aim: To test for presence of sugars using Benedict’s or Fehling’s test. Apparatus: 4 heat resistant test tubes 1 beaker bunsen burner or water bath with hot water (+50 ◦ C) test tube rack (if using a water bath) glucose solution Chapter 2. The chemistry of life 33  albumen solution or egg white starch solution water Benedict’s solution Fehling’s solution marking pen to mark the test tubes thermometer 10 ml syringe or measuring cylinder Safety precautions: Follow the safety procedures (listed in Chapter 1) when lighting your Bunsen burner. Do not light it in a shelf or near any lights and remove all notebooks, papers and excess chemicals from the area. Tie back any long hair, dangling jewelry and loose clothing and never leave an open flame unattended while it is burning. When heating your test tubes in the boiling water in the beakers ensure that the mouth of the test tubes point away from you and fellow learners. When handling the test tubes, especially when they are hot, use a test tube holder and wear goggles. Method: Prepare a water bath by filling a beaker to the halfway mark with water. Place the beaker on a tripod stand over a bunsen flame as shown in Figure 2.12. This will serve as your water bath. Whilst waiting for the water to boil or the water to reach temperature in the water bath, carry out the following instructions: 1. Label the test-tubes 1–4. 2. Using the syringe or measuring cylinder, add the following to the test tubes. Test tube 1: 5 ml of 1% starch solution Test tube 2: 5 ml of 10% glucose solution Test tube 3: 5 ml 1% albumen solution Test tube 4: 5 ml water. 3. Add 5 ml Benedict’s solution to each tube. 4. Place the test-tubes in the beaker of hot water on the tripod. 5. Use a thermometer to monitor the water temperature and adjust the flame to maintain the water temperature at approximately 50◦ C. 6. If using the water bath, place the test tubes into the test tube rack and place into the water bath with temperature set to 50◦ C. 7. After about 5 minutes, when a colour change has occurred in some of the test tubes, extinguish the flame, or remove the test tubes from the water bath. 8. Place the four tubes in a test-tube rack and compare the colours. 34 2.4. Organic compounds  Figure 2.12: Test for reducing sugars using Benedict’s test Results: Construct a table to record the results of this experiment. It is important to observe and record any changes that have taken place. Tube number Observations in each tube Questions: 1. What colour changes (if any) did you observe after heating the samples with Benedict’s solution? 2. The three solutions tested are examples of the chemical substances found in cells: glucose, starch, protein (albumen). Which of the samples tested positive when the Benedict’s solution was added and the test tube was heated? 3. Other than the colour, what change took place in the consistency of the Benedict’s solution? 4. What can you conclude from the investigation? 5. Why was water included in test tube 4? Lipids DUMMY Molecular make-up Chapter 2. The chemistry of life 35 FACT Lipids contain carbon (C), hydrogen (H) and oxygen (O) but have less oxygen than carbohy- When drawing drates. Examples of lipids in diet include cooking oils such as sunflower and olive oil, butter, organic molecules, margarine and lard. Many nuts and seeds also contain a high proportion of lipids. it can easily get confusing writing out all of the ’C’s Structural composition and ’H’s for carbon and hydrogen Triglycerides are one of the most common types of lipids. Triglyceride molecules are made respectively. Scientists overcome up of glycerol and three fatty acids (Figure 2.14). The fatty acid tails are made up of many this by drawing the carbons joined together. The number of carbons in the fatty acid chains can differ. carbon backbone, and leaving out the hydrogens. Carbon will always make 4 bonds with other atoms, so it is easy to figure out how many hydrogens there must be. The carbon is indicated by a point, and the bonds between carbon molecules are indicated by lines joining the points. FACT Figure 2.13: A triglyceride molecule. You will learn about the important role that lipids play in cell membranes in the following Role in animals and plants chapter on the basic units of life. Lipids are an important energy reserve and contain 37.8 kilojoules (kJ) of energy per gram. Triglyceride lipids are broken down to release glycerol and fatty acids. Glycerol can be con- verted to glucose and used as a source of energy, however the majority of energy provided by lipids comes from the breakdown of the fatty acid chains. Some fatty acids are essential nutrients that cannot be produced by the body and need to be consumed in small amounts. Non-essential fatty acids can be produced in the body from other compounds. Lipids are important for the digestion and transport of essential vitamins, help insulate body organs against shock and help to maintain body temperature. Lipids also play an important role in cell membranes. Saturated and unsaturated fats Carbon can form four bonds with other atoms. Most carbons in a fatty acid chain are bonded to two adjacent carbons, and to two hydrogen atoms. Fatty acids which form four single bonds, and have the maximum number of hydrogen atoms are called saturated fatty acids because they are ”saturated” with hydrogen atoms. However, sometimes two adjacent car- bons will from a double bond. In this case the carbons taking part in the double bond are each joined to only one hydrogen. Fatty acids that have carbon-carbon double bonds are known as unsaturated, because the double bond can be ’broken’ and an additional bond with hydrogen can be made. Double bonds are stronger than single bonds and they give the fatty acid chain a ’kink’. These kinks mean that the molecules can not pack together tightly, and the lipids are more fluid. This is why unsaturated fats tend to be liquid at room temperature, while saturated fats tend to be solid. Fatty acid chains with many double bonds are called poly-unsaturated fatty acids. 36 2.4. Organic compounds  FACT You will learn more about how cholesterol can clog arteries and lead to heart disease in the chapter on transport systems in animals Figure 2.14: Fatty acids can be saturated, mono-unsaturated or polyunsaturated depending on the number of double bonds present. Double bonds result in ”kinks” in the fatty acid chain. Cholesterol Cholesterol is an organic chemical substance known as a sterol. You are not required to understand its molecular makeup or its structural composition. It is an important component in cell membranes. The major dietary sources of cholesterol include cheese, egg, pork, poultry, fish and shrimp. Cholesterol is carried through the body by proteins in the blood known as lipoproteins. A lipoprotein is any combination of lipid and protein. Cholesterol is carried in the blood through the body by high density lipoprotein, low density lipoprotein and through triglycerides. 1. Low density lipoprotein (LDL): Low density lipoprotein transports cholesterol around the body. It has a higher proportion of cholesterol relative to protein. It is often known as ”bad” cholesterol because higher levels of LDL are associated with heart disease. 2. High density lipoprotein (HDL): High density lipoprotein is the smallest of the lipopro- teins. It has a high proportion of protein relative to cholesterol and is therefore often known as the ”good” cholesterol. HDL transports cholesterol away from cells and to the liver where it is broken down or removed from the body as waste. High levels of LDL can cause heart disease. Cholesterol builds up in blood vessels that carry blood from the heart to the tissues and organs of the body, called arteries. This leads to a hardening and narrowing of these vessels, which interferes with the transport of blood, and can potentially lead to a heart attack. The biggest contributor to the amount of cholesterol in your blood is the type of fats you eat. Saturated fats are less healthy than unsaturated fats as they increase the amount of LDL cholest