Biology Grade 9 Textbook PDF

Biology Student Textbook Grade 9 Author: Ann Fullick 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 tex...

Biology Student Textbook Grade 9 Author: Ann Fullick 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). 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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ISBN: 978-99944-2-008-7 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 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 Contents Unit 1 Biology and technology 1 1.1 Renowned Ethiopian biologists 1 1.2 Biological research in Ethiopia 7 Unit 2 Cell biology 13 2.1 The microscope 13 2.2 The cell 22 2.3 The cell and its environment 33 Unit 3 Human biology and health 50 3.1 Food and nutrition 51 3.2 The digestive system 69 3.3 The respiratory system 82 3.4 Cellular respiration 99 3.5 The circulatory system 104 Unit 4 Micro-organisms and disease 123 4.1 Micro-organisms 124 4.2 Diseases 137 4.3 HIV and AIDS 158 Unit 5 Classification 171 5.1 Principles of classification 171 5.2 The five kingdoms 178 Unit 6 Environment 200 6.1 Ecosystems 200 6.2 Food relationships 204 6.3 Recycling in nature 212 6.4 Adaptations 218 6.5 Tree-growing project 223 Index 226 Grade 9 iii  Biology and technology Unit 1 Contents Section Learning competencies 1.1 Renowned Ethiopian Name at least one renowned Ethiopian biologist. biologists (page 1) Explain the contributions of these Ethiopian biologists to international biological knowledge. 1.2 Biological research Explain how scientific institutions contribute to scientific research. in Ethiopia Name some Ethiopian institutions involved in biological research. (page 7) Explain the activities and contributions of some of these Ethiopian research institutions. 1.1 Renowned Ethiopian biologists By the end of this section you should be able to: Name at least one renowned Ethiopian biologist. Explain the contributions of these Ethopian biologists to international biological knowledge. Welcome to the study of biology! Biology is the study of life and living organisms. All around you there are many different types of plants, animals and other living organisms. They depend on each other and on the environment where they live. Biologists study both the outer appearance and the internal workings of living things. They study how living organisms interact and where human beings fit into the living world. All of our biological knowledge comes to us by the work of biologists, scientists who study living organisms. Biology, like all the sciences, moves forward most of the time in small, steady steps. One biologist comes up with an idea. Another carries out more experiments, which either support the new idea or suggest it is KEY WORDS wrong. Then more biologists join in until eventually a new idea, or hypothesis, is accepted. Like all scientists, biologists publish their hypothesis an idea or new work (called research) in special magazines called journals. statement that explains Before an idea is published in a journal, several other well-known observed facts and predicts biologists have to read it and check that the research has been done new outcomes to a high standard. This process is called peer review. Sometimes journal a regular biology takes a great leap forward, when a very gifted biologist publication presenting comes along with a big new idea! articles on a particular If you think you would like to be such a biologist, start right now by subject observing living things around you. peer review evaluation of Here in Ethiopia we have some very renowned biologists. Their a person’s work done by work is known and important not just here in Ethiopia but around others in the same field the world. Here are some of their biographies. Grade 9 1 Unit 1: Biology and technology Dr Aklilu Lemma and the battle against bilharzia (schistosomiasis) Schistosomiasis (also known as bilharziasis) is a common parasitic disease. It affects 200–300 million people in Africa (including Ethiopia), South America, Asia and parts of the Caribbean. It is caused by parasitic flatworms which spend part of their lifecycle in freshwater snails and part in humans. Anyone washing, working or playing in shallow fresh water is at risk. Once inside a person, Figure 1.1 Highly magnified the parasites mature and produce eggs which are passed out in the image of the parasitic flatworms urine and faeces. They also infest the blood vessels, liver, kidneys, that cause schistosomiasis bladder and other organs. The body sets up an immune reaction and an infected person can become weakened and ill for many KEY WORDS years. immune reaction a Some of the most important work in finding a way of controlling biological response involving this parasite, which is effective but does not cost too much, was the production of antibodies carried out by Dr Aklilu Lemma, one of Ethiopia’s most renowned biologists. etc. as a reaction to the presence in the body of Dr Aklilu began his work in 1964, when he was investigating the bacteria, a poison, or a freshwater snails that carry the schistosomiasis parasite around transplanted organ Adwa in northern Ethiopia. He saw women washing clothes in the water and he noticed that downstream of the washing party there treated water filtered or were more dead snails than anywhere else he had collected. The disinfected water made safe women were using the soapberry, Endod (Phytolacca dodecandra), for consumption to make washing suds. Dr Aklilu collected some live snails from genetic engineering above the washing party and asked one of the women to give him the deliberate, controlled some of her Endod suds. Not long after the suds were put in the manipulation of the genes snail container, the snails all died. This was the start of years of work in an organism, with the for Dr Aklilu. intent of making that Back in the laboratory he showed that if the Endod berries were organism better dried, crushed and diluted in water they would kill snails at very low concentrations. Other scientists carried out similar investigations and got the same results. If the freshwater snails can be controlled, the spread of schistosomiasis can be greatly reduced. The World Health Organisation recommended a chemical molluscicide (i.e. a compound that kills molluscs including snails) but it was extremely expensive. Endod works well, it is cheap, it is well known by local people who are likely to use it and it is environmentally friendly as it breaks down naturally within about two days. Dr Aklilu Lemma worked for many years to convince scientists all around the world that his ideas would work. Trials using locally collected Endod showed that using the molluscicide worked. Before the water was treated, 50% of children 1–6 years old were infected. After treatment only 7% were infected by the flatworm. Dr Aklilu’s results were published in journals around the world. He found the Figure 1.2 Dr Aklilu Lemma, best species of the soapberry plant and developed programmes for one of Ethiopia’s most renowned local communities to treat their own water. Eventually people were biologists, with the snail-killing convinced and the use of Endod-based molluscicides is spreading soapberries known locally as throughout Africa and beyond. Hopefully a combination of Endod Endod water treatment to kill the snails, improved hygiene, clean water 2 Grade 9  UNIT 1: Biology and technology wells and medicine for affected people will mean that Ethiopia Did you know? can be free of this terrible disease. If we succeed it will be largely due to the work of Dr Aklilu Lemma. He has been honoured and Around 300 million recognised in many different ways both in Ethiopia and around the people are affected by world for his work. schistosomiasis in the tropical and sub-tropical Dr Tewolde Berhan Gebre Egziabher, an ardent lover parts of the world – so the work of Aklilu Lemma of nature could make an enormous Dr Tewolde Berhan Gebre Egziabher was born in 1940. In 2000 difference in many other he won the Right Livelihood Award (often called the Alternative countries as well as Ethiopia. Nobel Prize) “for his exemplary work to safeguard biodiversity and Dr Aklilu recognised this the traditional rights of farmers and communities to their genetic when he said “we found a resources”. poor man’s medicine for a During the 1990s Dr Tewolde Berhan was involved in negotiations poor man’s disease”. at the various biodiversity-related meetings, including the Convention on Biological Diversity (CBD) and the Food and Agriculture Organization. Having built a strong and able team of African negotiators, he managed to help achieve progressive, unified policies for Africa, such as recognition of community rights. Dr Tewolde Berhan was instrumental in securing recommendations from the Organisation of African Unity (OAU) encouraging African countries to develop and implement community rights, a common position on Trade Related Aspects of Intellectual Property Rights, and a clear stance against patents on living materials. He also helped to draft the OAU model legislation for community rights, which is now used across Africa. In January 2000 Dr Tewolde Berhan acted as chief negotiator on biosafety for the Like-Minded Group, made up of most of the G77 countries, in Montreal. Here he was central to achieving an outcome protecting biosafety and biodiversity and respecting community Figure 1.3 Dr Tewolde Berhan rights, against strong US-led representations. Gebre Egziabher Dr Tewolde Berhan also won the United Nations top environmental prize, Champions of the Earth, in 2006. Professor Tilahun Yilma and his vaccines Professor Tilahun Yilma is known internationally for the vaccine he developed to help get rid of the terrible cattle disease rinderpest, and for his work on HIV/AIDS vaccines. Rinderpest arrived in Ethiopia in 1888, carried by three infected cattle brought into the country by Italian soldiers. Within a year 90% of the domestic cattle plus many wild animals such as buffalo, giraffe and antelope died. As a result 30–60% of the people starved. In the 1980s rinderpest became a major problem again. Professor Tilahun worked to develop a vaccine using genetic engineering. He was very successful – his vaccine doesn’t need refrigeration, it is easily scratched onto the animal’s neck or abdomen so cattle don’t need injections from vets and it can be made relatively cheaply in Figure 1.4 Professor Tilahun large quantities. By 1997 the vaccine was ready for use across Africa, Yilma Grade 9 3 Unit 1: Biology and technology including his own country Ethiopia. Now he is working on using similar methods to develop an effective vaccine against HIV/AIDS, which is affecting people all around the world including millions of Africans. Professor Tilahun has been given many international awards and honours over the years. He is also very active in encouraging young scientists and establishing the highest quality research establishments here in Africa. Professor Yalemtsehay Mekonnen: The first female professor from AAU Professor Yalemtsehay Mekonnen is a biologist and an academic member of staff at the Department of Biology, Faculty of Science, Addis Ababa University. She has worked in this Department for the last 30 years. She received her PhD, specialising in human physiology, from the University of Heidelberg in Germany. Figure 1.5 Professor Yalemtsehay One of her research areas is the assessment of the impact of Mekonnen working in the chemical pesticide hazard on humans. This research covers almost Biomedical Laboratory, Addis all government farms including the Upper Awash Agricultural Ababa University farms and some private horticultural farms in the Rift Valley region. The other area of her research is in the use of plants as medicine against human and animal diseases. Professor Yalemtsehay Mekonnen served as Head of the Department of Biology from 1993 to 1995 and as the Director of the Aklilu Lemma Institute of Pathobiology from February 2003 to October 2007. In leadership positions she was involved and has initated a number of national and international research networks and collaborations. She is a member of many professional societies, such as the Biological Society of Ethiopia, the Safe Environment Association, the Ethiopian Wildlife and Natural History Society, the New York Academy of Sciences and the Third World Organization for Women in Science. She has served as President of the Biological Society of Ethiopia. She has been awarded research grants and fellowships nationally from the Ethiopian Science and Technology Commission and the Ethiopian Agricultural Research Organization, and internationally from the British Council, the International Foundation for Science, Third World Academy of Sciences, the German Academic Exchange Service and the Alexander von Humboldt Foundation from Germany. Dr Melaku Worede Dr Melaku Worede was born in 1936 and he has worked for many years to save the genetic diversity of Ethiopia’s domestic plants. He is an internationally acclaimed plant genetics researcher. Dr Melaku set up the Plant Genetic Resources Centre in Addis Ababa. Our country is noted for its great genetic diversity but Figure 1.6 Dr Melaku Worede, an modern farming methods and problems such as drought can internationally acclaimed plant affect this badly. Dr Melaku Worede has preserved many different genetics researcher traditional crop varieties and developed ways of farming that 4 Grade 9  UNIT 1: Biology and technology produce high yields without commercial fertilisers. Dr Worede’s methods are now widely used both in other areas of Africa and in Asia. He was the first chair of the African Committee for Plant and Genetic Resources and has been Chair of the United Nations Food and Agriculture Organisation’s Commission on Plant Genetic Resources. He has also won the Right Livelihood Award (often called the Alternative Nobel Prize) in 1989 for outstanding vision and work and in 2008 he received the Outstanding International Contribution Award from the National Green Award Foundation. Dr Gebissa Ejeta When Dr Gebissa Ejeta was born in a small rural village his mother was determined her son would receive a good education. He walked 20 miles to school every Sunday evening, returning home on Friday after a week of studying. It all paid off as he gained a place at Jimma Agricultural and Technical School and then Alemaya College where he took his first degree. He specialises in plant breeding and genetics. Dr Gebissa Ejeta did his research on sorghum – he got his PhD from Purdue University in the USA where he still holds a professorship. He has helped to develop Africa’s first commercial hybrid strain of sorghum. This not only needs less water and so is Figure 1.7 Dr Gebissa Ejeta who resistant to drought, but it also yields more grain than traditional has been honoured for his work varieties. Dr Gebissa Ejeta developed other strains of sorghum in developing new, high yielding which are also resistant to the parasitic Striga weed, which can strains of sorghum which grow destroy a big percentage of a crop. Dr Ejeta’s work has made a very well in our conditions big difference to the food availability in many areas of Ethiopia and other African countries – his varieties yield up to ten times more than the original strains. In 2009 Dr Gebissa Ejeta was awarded the World Food Prize, which is the most important agricultural prize in the world! He has also been awarded the National Hero award of Ethiopia for his work in science and technology. These are just some of many renowned Ethiopian biologists who have carried out work of great value both in our own country and across the world. You will have the opportunity to find out more about some of the other scientists with your teacher in activity 1.1. Here are some more examples of Ethiopian biologists. Professor Beyene Petros is a biomedical scientist and long serving professor at Addis Ababa University. Professor Beyene Petros, in addition to his distinguished academic career, served as Chairman, Advisory Committee on Health Research and Development, WHO/AFRO, 1997–2000; as vice minster of Education (1991–1993) and many other scientific societies. He has produced more than 43 publications in reputable scientific journals and Published books. Professor Beyene has won Gold Medal Award from Ethiopian Health Association; Fellowships from Fulbright and from Centers for disease control and prevention, Atlanta, USA. Professor Sebsebe Demissew is a plant taxonomist. He is now the Director of the National Herbarium and the leader of the Ethiopian Flora Project (EFP). Grade 9 5 Unit 1: Biology and technology Dr Zeresenay Alemseged discovered a 3.3 million-year-old Activity 1.1: Discovering humanoid child fossil in 2006. Ethiopian biologists Dr Tsehaynesh Meselle was the Director General of the Ethiopian It is inspiring to know what Health and Nutrition Research Institute (EHNRI) during great work is being done the writing of this book and leads research in human health, by Ethiopian biologists including HIV/AIDS. today. Here you have the Dr Berhane Asfaw is an Ethiopian scientist whose team opportunity to do some discovered two 160 000-year-old human skulls, some of the research and find out about oldest that have ever been found. His discoveries were published some of the people who in the famous scientific journal Nature. They have had a great are active in biology in our impact on the study of human evolution around the world. country. Professor Legesse Negash is a Professor of Plant Physiology in You can choose a the Department of Biology, Faculty of Science, Addis Ababa biologist from the list University. He is a pioneer in the propagation of Ethiopia’s on pages 5 and 6, find indigenous trees and is the Founder and Leader of the Center out more about one of for Indigenous Trees Propagation and Biodiversity Development the biologists already in Ethiopia. Professor Negash is a winner of several awards, mentioned in this chapter including that from the Stockholm-based International or write about a biologist Foundation for Science. you have discovered for yourself. If you look at Professor Mogessie Ashenafi works at the University of Addis the research institutions Ababa and leads international research into food microbiology. mentioned in the rest Professor Ensermu Kelbessa is one of the leading systematic of this chapter you will botanists who has discovered and named many new plants. be able to find lots of Ethiopian biologists to choose from! Review questions Use any resources you Select the correct answer from A to D. have available. You may 1. Biology is: find out about Ethiopian A the study of matter biologists in books, B the study of life and living organisms magazines, journals, leaflets, in the news or C the study of how living organisms interact even on the internet if it D the study of the way atoms and molecules react together is available. 2. Bilharzia is caused by: Write a report about your A snails biologist and prepare to B bacteria give a brief talk on him C viruses or her to the rest of the class. D parasitic flatworms 3. Dr Tewolde Berhan Gebre Egziabher is a biologist who researches into: A HIV/AIDS B genetic engineering C environmental protection and diversity D human evolution 6 Grade 9  UNIT 1: Biology and technology 1.2 Biological research in Ethiopia By the end of this section you should be able to: Explain how scientific institutions contribute to scientific research. Name some Ethiopian institutions involved in biological research. Explain the activities and contributions of some of these Ethiopian research institutions. Biologists, like other scientists, do not work alone. A biologist needs equipment, laboratories and other biologists to discuss ideas with and develop theories. Biologists work in many different areas, from plants to animals, and from medicine to classification and genetics. Ethiopia has a number of well-known institutions that are involved in biological research. Our country continues to invest in these institutions and to develop more. Our biologists have international reputations in many fields. Biologists from other African nations and from other continents come to our institutions to take part in the research programmes, and our biologists also travel to other countries. Sharing knowledge across the world is an important part of science and Ethiopia plays her part in this. Here are some of the institutions that play an important part in biological research in Ethiopia. Addis Ababa University (AAU) Biology Department Addis Ababa University (AAU) is a very large university with an international reputation and the Biology Department is no exception. A top university, AAU is one of the major centres of biological research in the country and it is also home to the Aklilu Lemma Institute of Pathobiology (see the next page). The university entrance is impressive and the Department of Biology contains much modern and high-level equipment to help Figure 1.8 Addis Ababa biologists in their research. University is home to much Addis Ababa University is not the only renowned university in internationally recognised Ethiopia. There are many others, including Haramaya University, research. Mekelle University, Jimma University, Hawassa University, Gonder University and Bahir Dar University. They all have active biology departments where teaching and research takes place. Grade 9 7 Unit 1: Biology and technology Armauer Hansen Research Institute (AHRI) When Armauer Hansen Research Institute (AHRI) was first set up in 1969 it was sited next to a big hospital dedicated to patients with leprosy and it carried out research only into leprosy. However, in the years since 1969 leprosy has become a disease that we can treat quite effectively. Since 1996 AHRI has widened its research to include tuberculosis (TB, which has become a big threat with the rise in HIV/AIDS), leishmaniasis, malaria and HIV/AIDS, as well as leprosy. Aklilu Lemma Institute of Pathobiology (ALIPB) The department of pathobiology at Addis Ababa University has been renamed the Aklilu Lemma Institute of Pathobiology (ALIPB) in honour of Professor Aklilu Lemma (see page 2). The institute sets out to be a centre of excellence for biomedical research and training. ALIPB carries out research in five major areas. They have Figure 1.9 The AHRI buildings a microbiology research programme into the major infectious and some of the workers who diseases, they look into vectors of diseases and how to control them, work there some of the biologists are focused on human parasitic diseases and others work on animal health and disease. Finally, some of the biologists are carrying out research into Endod and other plants, which may be useful as medicines. The institute also plays an important role in training new Ethiopian pathobiologists. Students with a first degree in biomedical sciences (i.e. biology, human medicine, veterinary medicine, laboratory technology) can apply to do a Masters degree in tropical and infectious diseases at the institute. Ethiopian Health and Nutrition Research Institute (EHNRI) The Ethiopian Health and Nutrition Research Institute (EHNRI) is an organisation that carries out research into health and nutrition issues which affect public health. Its role is both to identify problems and to help everyone in the country become aware of how to overcome the problems and improve their levels of nutrition and health. The laboratory facilities at EHNRI are good and are well equipped for research into immunology and viral diseases. At the moment EHNRI is carrying out a lot of work into HIV/ AIDS in Ethiopia. For example, biologists working with EHNRI are following the progression of HIV/AIDS in two populations of factory workers (about 2000 people) over a long period of time – the research began in 1994! They are planning to work with more people in the future, and are also hoping to set up trials of a possible HIV vaccine. EHNRI is also very active in the battle against TB and it houses the National TB Reference Laboratory. It is involved in rapid diagnosis of TB. EHNRI is also involved in many other projects including issues such as the nutritional state of mothers and babies in the country as well as infectious diseases. 8 Grade 9  UNIT 1: Biology and technology Ethiopian Institute of Agricultural Research (EIAR) also known as Institute of Agricultural Research (IAR) Agriculture – farming crops and livestock – is the life force of our country. We must grow food to eat. The EIAR (IAR) is the institute where biologists with a passion for improving agriculture and supporting everyone who cultivates the land or raises livestock in Ethiopia carry out research. There are five main areas of research. Biologists working on crop technology are working to help us achieve food security and Figure 1.10 Farming is vital to nutritional quality, so that we always have sufficient food. They Ethiopia. Biologists with the EIAR are looking at different crops and ways of improving the crops work hard to improve our crops, we already grow. Other biologists are focusing on our livestock, our animals and our soil. looking at ways of managing our animals’ breeding and feeding programmes to make sure that they grow as quickly and as well Did you know? as possible. They also look at ways of improving the health of our Farming is vital to livestock. Ethiopia. About 90% of Biologists working on crop technology have improved crops like our exports and around maize, teff and sorghum. Two of these are shown here. 80% of our economy Another important area of research is with regard to the soil and depends on agriculture. water. Biologists are looking into ways of improving the fertility of the soil, particularly ways of avoiding buying expensive inorganic fertilisers. Other scientists are also looking at ways to water the land more effectively. Forestry is also an area of research. Biologists are very involved in rehabilitating, restoring and conserving some of our forest ecosystems. Finally, the institute also looks at ways of mechanising farming. Biologists research into the species of crop plants that are most suitable for mechanised harvesting. The Institute of Biodiversity Conservation (IBC) Biodiversity – the range of living organisms in an area – is internationally recognised as one of the biggest issues in biology today. Here in Ethiopia we have a tremendous range of biodiversity, particularly in our plants. There are also many species which are found only in Ethiopia (endemic). So in world terms, when it was Figure 1.11 An agronomist decided to set up gene banks to conserve the genetic material of as examining sorghum crop many plants as possible, Ethiopia was given the highest priority. The Institute of Biodiversity Conservation (IBC) started off conserving the genes of Ethiopian plants. Now the institute is involved in the conservation of plants, animals and micro-organisms in Ethiopia. Research into the management of the ecosystem is also an important part of the work. Current research in the IBC looks at many areas including forest and aquatic plants, medicinal plants, animal genetic resources, biotechnology and safety, and ecosystem conservation. The institute Figure 1.12 Scientists have also holds one of the leading gene banks in the whole of Africa with improved crop production of over 300 plant species represented. Quncho, an improved teff. It is a hybrid crop now yielding more than 30 quintals per hectare. Grade 9 9 Unit 1: Biology and technology Activity 1.2: Discovering Activity 1.3: Making a table of research institutions more about research in Make a table to summarise the biological research institutions Ethiopia in Ethiopia that are mentioned in this book. Add any that you There are many great or your classmates have discovered. Draw a table as shown institutions in Ethiopia below and complete it: carrying out biological research. You have learnt a Institution Focus of research little about some of them. Now you can find out more. Investigate the biology department at the university nearest to your school or any other institution with biologists working there. Find out as much as you can about the research they carry out and the biologists who are there. Investigate one other Review questions biological research Select the correct answer from A to D. institution in Ethiopia. You may choose to 1. EHNRI carries out research into: find out more about A health and nutrition issues one of the institutions B farming highlighted in this book or you may find another C biodiversity different one. D soil and water Use any resources you 2. Before it widened its research the Armauer Hansen Research have available. You may Institute studied only: use books, magazines, A HIV/AIDS journals, leaflets, B tuberculosis university prospectuses or reports in the news or C leprosy even on the internet, if it D cervical cancer is available. 3. ALIPB is world-renowned for research into: Write a report about your A different diseases and their control local university biology B improved agricultural practices department and one other Ethiopian research C human evolution institute and prepare to D environmental conservation give a brief talk on them to the rest of the class. 10 Grade 9  UNIT 1: Biology and technology Summary In this unit you have learnt that: Biology is the study of life and living organisms. Scientific research is based on the ideas of scientists. They design experiments to test these ideas. Results of these experiments are published in peer-reviewed journals, which are read by scientists around the world. Ethiopia has some renowned biologists whose work is known both in Ethiopia and internationally. They include Dr Aklilu Lemma, Professor Tilahun Yilma, Professor Yalemtsehay Mekonnen, Dr Melaku Worede, Dr Legesse Woldeyes, Dr Gebissa Ejeta, Dr Berhane Asfaw, Professor Legesse Negash, Professor Mogessie Ashenafi, Professor Ensermu Kelbessa and many others. Most biological research is linked to a research institution that has the facilities which are needed. There are a number of well-known Ethiopian biological research institutions. End of unit questions 1. a) Name two Ethiopian biologists who have made internationally recognised contributions in their field. b) Describe the main work of both of the biologists you have chosen and explain why it is so important. 2. What are the main advantages of using Endod in the battle against bilharzia? 3. Why is Professor Yalemtsehay Mekonnen internationally renowned? 4. What is rinderpest? 5. Why is the work of Dr Gebissa Ejeta so important? 6. Why are scientific institutions important to biological research? 7. a) Name three institutions involved in different types of biological research in Ethiopia. b) Summarise the areas of biological research carried out by each institution. Grade 9 11 Unit 1: Biology and technology Copy the crossword puzzle below into your exercise book (or your teacher may give you a photocopy) and solve the numbered clues to complete it. 1 2 3 4 5 6 7 8 9 Across 2 Professor Tilahun Yilma developed a vaccine against this disease (10) 4 The Ethiopian scientist who has helped make food more available with his new breeds of sorghum is Dr Gebissa ***** (5) 7 What type of trees are planted in Ethiopia by Professor Legesse Negash? (10) 8 The Armauer Hansen Research Institute (4) 9 The surname of the Ethiopian scientist who discovered a way to prevent bilharzia (5) Down 1 A new scientific idea (10) 3 What is studied at the EIAR (IAR)? (11) 5 What is the name of the plant which kills the snails which cause bilharzia? (5) 6 What do we call a special magazine where scientists publish their research? (7) 12 Grade 9 Cell biology Unit 2 Contents Section Learning competencies 2.1 The microscope Name different types of microscopes. (page 13) Distinguish between the magnification and resolution of a microscope. State the functions of different types of microscopes. Compare the different resolutions and dimensions of light and electron microscopes. Explain and demonstrate basic techniques using a light microscope. Explain the purpose of staining cells. Use the microscope to study cells. Compare the way materials are prepared for the electron microscope and the light microscope. 2.2 The cell State the cell theory. (page 22) List the structures of cells and describe their function. Draw and label diagrams and compare typical plant and animal cells. Describe the types, shapes and sizes of a variety of cells using diagrams. 2.3 The cell and Describe the permeability of the cell membrane. its environment Describe the process of diffusion and its importance in living organisms. (page 33) Demonstrate diffusion experimentally. Explain the process of osmosis and its importance in living organisms. Demonstrate osmosis experimentally. Show that plant cells become flaccid when they lose water and turgid when they absorb water by osmosis. Explain plasmolysis and turgor pressure. Explain passive and active transport across cell membranes. Discuss the advantages and disadvantages of diffusion, osmosis and active transport for moving substances into and out of cells. 2.1 The microscope By the end of this section you should be able to: Name different types of microscopes. Distinguish between the magnification and resolution of a microscope. State the functions of different types of microscopes. Compare the different resolutions and dimensions of light and electron microscopes. Explain and demonstrate basic techniques using a light microscope. Explain the purpose of staining cells. Use the microscope to study cells. Compare the way materials are prepared for the electron microscope and the light microscope. Grade 9 13 UNIT 2: Cell biology Biologists use different tools to help them study living organisms. Did you know? One of the most important is the microscope. Many important The largest single cell in organisms are very small and biologists need to be able to see them. the world is an ostrich The building blocks of life are called cells and scientists need to be egg – they are about able to see cells to understand living organisms. Most cells cannot 18 cm long and weigh be seen without some kind of magnification. You will be discovering around 1.2 kg. Most cells the secrets of cells revealed with the help of a microscope. In this are much harder to see! section you will learn more about microscopes and how they work. In the next section you will be learning more about the structure of cells and how they work. Seeing cells There are some cells that can be seen very easily with the naked eye. Unfertilised birds eggs are single cells, most cells are much smaller than this. Everything we know about the structure of cells has depended on the development of the microscope. For over 300 years we have been able to look at cells, and as microscopes have improved, so has our knowledge and understanding of cell structure. There are two main types of microscopes in use, the light microscope and the electron microscope. The light microscope uses a beam of light to form the image of an object, while the electron microscope uses a beam of electrons to form an image. You are going to learn about both. Figure 2.1 Ostrich with eggs Magnification and resolving power The reason microscopes are so useful is because they magnify KEY WORDS things, making them look bigger. Magnification means increasing microscope an instrument the size of an object. The best light microscopes will magnify up for magnifying specimens to around 2000 times. Light microscopes have given us a lot of information about the structure of cells, but in the last 50 years or light microscope a so we have also been able to use electron microscopes. An electron microscope that uses a microscope can give you a magnification of around 2 000 000 times. beam of light to form the Using electron microscopes makes it possible for us to learn a lot image of an object more about cells and the ways in which they become specialised for electron microscope a particular functions. microscope that uses a The biggest problem with the light microscope is the limited detail beam of electrons to form it can show. There is a minimum distance between two objects for an image them to be seen clearly as separate. If they are closer together than magnification increase the this they are seen as one thing. This distance is known as the limit size of an object of resolution. Resolution is the ability to distinguish between two separate points and it is the resolving power of a microscope that resolution ability to affects how much detail it can show. The greater the resolving power distinguish between two of the microscope, the more detail it can show. For the optical light separate points microscope the limit of resolution is approximately 200 nanometres resolving power how much (1 nm = 1 × 10–9 m). In comparison, the human eye can only resolve detail the microscope is down to about 0.1 mm (1 mm = 1 × 10–2 m) (see figure 2.2). Objects able to show closer than 0.1 mm are seen as one by human eyes. The magnification we can get with a light microscope is limited by the resolving power possible using the wavelength of light. To see 14 Incomplete advance copy Grade 9  UNIT 2: Cell biology more detail clearly we need an electron microscope where an electron Did you know? beam is used to make the image. As the wavelength gets smaller, the resolving power is increased. An electron microscope has a resolving If you magnified an power around a thousand times better than a light microscope, about average person by the 0.3 nm. Objects that are 0.3 nm apart can be seen as separate by an same amount as the best electron microscope, demonstrating that the resolving power of an light microscopes (×2000) electron microscope is greater than that of a light microscope. they would be about 3.5 kilometres tall. Magnified by an electron microscope Functions of different types of microscopes (×2 000 000), the average person becomes about We will now look in more detail at the different types of microscope 3500 kilometres tall! and how they are used. The light microscope KEY WORD To look at a biological specimen using a light microscope you will stains chemicals added to often use a slide of cells, tissues or individual organisms. These are slide tissues to make the often very thin slices of biological material that have been specially cells easier to see treated and stained, but you can look at living material directly through a light microscope as well. Often chemicals known as stains are added to the tissue on the slide to make it easier to see particular cells, or parts of a cell. When you are looking at stained cell samples it is important to remember that the cells are dead. The cells have been treated with chemicals or ‘fixed’ so they do not decay. The tissue has also been sliced very thinly. These things can damage or change the cells. Living cells have not been treated in this way, but are less easy to see. Below is a list of commonly used stains. Table 2.1 Application of commonly used stains Type of stain Type of cells Main organelles stained Haematoxylin Animal and plant Nuclei stained blue/ cells purple or brown Methylene Animal cells Nuclei stained blue blue Acetocarmine Animal and plant Staining the Figure 2.2 The lines that make up cells chromosomes in dividing this diagram are actually a mass nuclei of dots on the page. The resolving power of your eyes means that Iodine Plant cells Any material containing you see the dots merged together starch to make lines because you can’t resolve the dots individually. If you magnify the line, you can How does a light microscope work? see the dots. In the same way, In a light microscope, a specimen is placed on the stage and what you can see through the illuminated (lit) from underneath. The light passes through the light microscope is limited by the specimen and on through the lenses to give an image at the eyepiece resolving power of the microscope lens which is greatly magnified, upside down and right to left. itself. Grade 9 Incomplete advance copy 15 UNIT 2: Cell biology To calculate the magnification of the specimen, you multiply the Did you know? magnification of the objective lens by the magnification of the Electron beams have a eyepiece lens. So if the magnification of the objective lens is ×10, shorter wavelength than and the eyepiece lens is also ×10, the overall magnification of the light. microscope is 10 × 10 = ×100. If you move the objective lenses round and use the ×40 lens, the overall or total magnification will become 40 × 10 = ×400. eyepiece lens tube coarse focusing knobs rotating nosepiece fine Did you know? objective lenses stage stage clips A light microscope with iris diaphragm (under stage) two lenses – the eyepiece lens and the objective mirror lens – is known as a compound microscope. It produces much better magnification than is Figure 2.3 A compound microscope has two sets of lenses (objective possible with a single lens. and eyepiece lenses) which are used to magnify the specimen. These microscopes are widely used for looking at cells. Activity 2.1: Learning to use a microscope You will need: 4. Now look through the eyepiece lens and a microscope adjust the iris diaphragm until the light a lamp is bright but doesn’t dazzle you. The illuminated area you can see is known as a piece of graph paper the field of view. a prepared slide of stained human cheek 5. Looking at your microscope from the side cells (see figure 2.4), or look on page (not through the eyepiece lens) and 18 to find out how to make a slide for using the coarse focusing knob, move yourself the objective lens down slowly so it is Method as close as possible to the paper without Remember, microscopes are delicate pieces of touching it. equipment so always take care of them and 6. Now look through the eyepiece lens again. handle them safely. Turn the coarse focusing knob very gently 1. Set up your microscope with the lowest in the opposite direction to move the power lens (the smallest lens) in place. objective lens away from the slide. Do this while you are looking through the eyepiece 2. Clip the prepared slide into place on the lens and the lines on the graph paper will stage using the stage clips. Position the gradually appear in focus. Once you can piece of graph paper over the hole in see the specimen clearly, use the fine the stage. focusing knob to get the focus as sharp as 3. If your microscope has a built-in lamp, you can. switch it on. If it has a mirror, adjust the 7. You may find that if you now shut the iris angle of the mirror until the specimen is diaphragm down further, so that the hole illuminated. for the light to pass through gets smaller, you will see the specimen better (the contrast is greater). 16 Incomplete advance copy Grade 9  UNIT 2: Cell biology 8. To use the higher magnifications, rotate 10. Return the microscope lenses to their the nosepiece so that the next lens clicks original positions. Now look at a slide into place. Do not adjust the focusing of stained human cheek cells and practise knobs at this point as the specimen should focusing on what you see. still be in focus and, with the coarse focusing knob in particular, it is very easy to break a slide. It is good to practise this using graph paper, which will not break! If you do need to adjust the focus, use the fine focusing knob only with higher magnifications. Take great care to avoid letting the lens touch the slide/paper. You may want to adjust the iris diaphragm as well. 9. Make simple drawings to show how much of the graph paper you can see at each magnification. This will help you to get an idea of how much the microscope is magnifying what you are seeing. Notice Figure 2.4 Human cheek cells stained with how the appearance of the smooth lines methylene blue (×100) changes as you see them at greater magnification. Advantages and disadvantages of the light microscope One of the biggest advantages of using a light microscope is that we can see living plants and animals or parts of them directly. It is very important to observe living cells. It lets us check if what we see on prepared slides of dead tissue is at all like the real living thing. Any biologist working in a hospital, industrial or research lab will have a light microscope readily available to use at any time. School and university students around the world also rely on light microscopes to enable them to learn about the living world of cells. Light microscopes can also be used without electricity, which means they can be used anywhere in the world. Light microscopes are relatively small and not very heavy, so Figure 2.5 (a) Typical green they can be moved around easily. They are quite delicate so they plant cells seen under the light need to be protected, but with care biologists can even take light microscope microscopes out into the field with them to do their research. The biggest disadvantage of light microscopes is that their resolving power is limited by the wavelength of light. As you saw earlier, this limits their powers of magnification. Also we can’t usually magnify living cells as much as we can dead tissue, which limits what we can learn from living cells. Grade 9 Incomplete advance copy 17 UNIT 2: Cell biology Using the light microscope Figure 2.5 (b) Using the light In the next section of this book you will learn how the light microscope. microscope can be used to examine many different types of animal and plant cells. It is important to learn how to mount a specimen on a slide to use with a light microscope. Sometimes you may need to add stain to the specimen so that it can be seen more easily. The activity below explains exactly how to carry out this process. Activity 2.2: Making a slide of plant cells The prepared slide you looked at in Activity 3. Using the mounted needle (or a sharp 2.1 showed animal cells that were dead and pencil), lower the cover slip very gently stained to make them easier to see. In this over the first specimen. Take great care activity you are going to learn how to make a not to trap any air bubbles – these will slide of living tissue and stain it so that the show up as black ringed circles under the cells are easier to see. microscope. You will need: a microscope lower cover slip slowly to mounted needle avoid air bubbles becoming trapped beneath it microscope slides cover slips cover-slip forceps a mounted needle specimen glass slide mounting medium a pipette Figure 2.6 Making a slide a lamp 4. Remove any excess liquid from the slide a piece of onion skin and place it under the microscope. iodine solution 5. Repeat this process with the other slide, adding a drop of iodine solution instead Method of water. Remember, microscopes are expensive and 6. Starting with the slide mounted in water delicate pieces of equipment so always take and using the lowest power objective lens, care of them and handle them safely. follow the procedure for looking at cells Onion cells (the sample taken) do not contain described in activity 2.1. Use the higher any chlorophyll so they are not coloured. You power lenses to look at the cells in as can look at them as they are, or stain them much detail as possible. You can judge how using iodine, which reacts with the starch in well you have mounted the tissue – the cells and turns blue-black. it should be a single layer thick and there 1. Take your piece of onion and remove should be NO air bubbles! a small piece of the thin skin (inner 7. Repeat this process looking at the cells epidermis) on the inside of the fleshy part stained with iodine solution. What using your forceps. It is very thin indeed difference does the stain make? and quite difficult to handle. 8. Make a labelled drawing of several of 2. Place the epidermis onto a microscope the cells you can see. When you make a slide and add a drop of water. Make drawing of cells, you try and show another identical slide and add a drop of clearly and simply what is seen under the iodine very gently from a pipette. microscope (see figure 2.7). 18 Incomplete advance copy Grade 9  UNIT 2: Cell biology Use a pencil for your drawing and always show the magnification. nucleus cell wall (a) mag x100 (b) Figure 2.7 (a) Onion epidermis cells stained with iodine x100 (b) Illustration of some sample onion epidermis cells You can get even more information from the light microscope by KEY WORD using the light in different ways. Dark-field illumination, which is where the background is dark and the specimen illuminated, can be wavelength the distance useful for showing tiny structures inside cells. between neighbouring wave There is one big problem to bear in mind when you are working with crests microscopes. Unless you are looking at living material, or have the use of a scanning electron microscope (see below), all the cells that you see appear flat and two-dimensional. But cells are actually three- dimensional – spheres, cylinders and strange three-dimensional (3-D) shapes. You need to use your imagination when you look at cells and see them as the living things that they really are. The electron microscope The electron microscope was developed in the 1930s and came into regular use in the 1950s. It has greatly increased our biological knowledge. Instead of relying on light with its limit of resolving power, an electron beam is used to form an image. The electrons behave like light waves, but with a much smaller wavelength. The resolving power is increased as the wavelength gets smaller, and as a result, the electron microscope can resolve detail down to 0.3 nm. Samples of material have to be specially prepared for the electron microscope. They are fixed, stained and sliced very thinly in a similar way to the preparation of samples for the light microscope but the materials and stains used are very different. How does an electron microscope work? The image in an electron microscope is formed as electrons, which cannot be seen by the human eye, scattered by the biological material, in much the same way as light is scattered in the light microscope. The electron beams are focused by magnetic lenses. A series of magnifications gives you an image. However, you do not simply look into an electron microscope. Complex electronics Grade 9 Incomplete advance copy 19 UNIT 2: Cell biology cathode (–) produce the image on a television screen, which can then be These produce the beam of electrons recorded as a photograph known as an electron micrograph or EM. anode (+) The most common type of electron micrograph you will see is magnetic lens produced by a transmission electron microscope, but the scanning electron microscope produces spectacular images of the surfaces of cells and organisms. It shows the surface of structures, greater depth specimen of focus, and a three-dimensional view of the object (see figure 2.9). magnetic lens – the magnification can be varied by altering Advantages and disadvantages of the electron microscope the current in these lenses We can see much more detail using an electron microscope than with a light microscope. It gives us much higher magnification and resolution. This is its biggest advantage. Biologists have discovered many structures inside cells since electron microscopes magnetic lens were developed. The electron microscope has also shown us the complicated structures inside cell organelles (see next section) and this helps us understand how they work. There are several disadvantages to the electron microscope. All the specimens are examined in a vacuum because air would scatter the electron beam. This means it is impossible to look at living material. final image – formed on a screen or photographic plate Some scientists question how useful the images are because the tissue is dead, sliced very thinly, treated with strong chemicals and Figure 2.8 A diagram of an put in a vacuum before we look at it. electron microscope and how it works Electron microscopes are very expensive. They take up a lot of space and are usually kept in a separate room. They have to be kept at a constant temperature and pressure and have an internal vacuum. They rely on a constant source of electricity. Few scientists outside of the top research laboratories have access to electron microscopes and so their use for the majority of biologists is limited. Figure 2.9 The transmission Preparing samples for microscopes electron microscope shows the Materials must be prepared in different ways depending on what inside details of a cell (right) and type of microscope you are using. the scanning electron microscope can show us three-dimensional Tissue has to be prepared and stained in different ways for light and shapes (blood cells above). electron microscopes: for light microscopes staining is done using 20 Incomplete advance copy Grade 9  UNIT 2: Cell biology coloured dyes to reflect light, whereas for electron microscopes heavy metals such as lead and uranium are used to reflect electrons. For light microscopes only non-living materials need fixation, while living materials are not fixed: specimens are always fixed with electron microscopes. Summary In this section you have learnt that: is around 1000 times greater than the Light microscopes and electron microscopes resolving power of a light microscope. are widely used by biologists. Using a light microscope takes skill and Microscopes magnify both living and dead practice. tissue so you can observe the features of Dead specimens are fixed, stained and the cells and tissue. sliced before mounting on slides to be Magnification involves increasing the size observed under the microscope. Living of an object. To work out the magnification specimens are mounted on slides and stains of a microscope you multiply the may be added. magnification of the objective lens by the Stains are used to make parts of cells (e.g. magnification of the eyepiece lens. the nucleus) or types of cells show up Resolution is the ability to distinguish better under the microscope. between two separate points. Tissue has to be prepared carefully before The resolving power of a microscope is it can be used in the electron microscope. dependent on the wavelength used, so the Only dead tissue can be used in the resolving power of an electron microscope electron microscope. Review questions Select the correct answer from A to D. 1. The maximum magnification of a light 3. Which of the following is not an advantage of microscope would make a person: the light microscope? A 3.5 m tall A It can be used anywhere without B 35 m tall electricity. C 3.5 km tall B Its resolving power is limited by the D 35 km tall wavelength of light. 2. The largest single cell is: C It is relatively light so can be carried out into the field for research. A an amoeba D It is relatively cheap. B a jelly fish 4. Which of the following is the main advantage C an unfertilised ostrich egg of the electron microscope? D an unfertilised human egg A It’s very expensive. B Specimens are examined in a vacuum so must be dead. C It needs a constant temperature and pressure. D It gives a greatly increased magnification and resolution over the light microscope. Grade 9 Incomplete advance copy 21 UNIT 2: Cell biology 2.2 The cell By the end of this section you should be able to: State the cell theory. List the structures of cells and describe their function. Draw and label diagrams and compare typical plant and animal cells. Describe the types, shapes and sizes of a variety of cells using diagrams. The planet we live on is covered with a wide variety of living organisms, including animals, plants and microbes. All living organisms are made up of units called cells. Some organisms, such as amoeba, consist of single cells. Others, such as ourselves, are made up of many millions of cells all working together. Organisms that contain more than one cell are known as multicellular. Cell theory Figure 2.10 An organism like Cells were first seen over 300 years ago. In 1665, the English this Paramecium carries out all scientist Robert Hooke designed and put together one of the first the characteristic reactions of life working optical microscopes. He examined many different things within a single cell. including thin sections of cork. Hooke saw that these sections were made up of many tiny, regular compartments, which he called cells. It took many years of further work for the importance of cells to be recognised. In 1839 Matthias Schleiden and Theodore Schwann introduced an idea known as the cell theory. The cell theory states that cells are the basic units of life and by the 1840s this idea was KEY WORDS accepted by most biologists. cells the basic structural All living organisms have certain characteristics, which they carry and functional units in all out regardless of whether they have one cell or millions. When we living organisms look at cells we can see how all of these functions are carried out. cell theory states that cells The seven life processes that are common to most living organisms are the basic units of life are: nutrition food substances Nutrition – all living organisms need food to provide them with needed by the body the energy used by their cells. Plants make their own food by photosynthesis, whereas animals eat other organisms. respiration process whereby living organisms Respiration – the process by which living organisms get the obtain energy from their energy from their food. food Excretion – getting rid of the waste products produced by the excretion removal of cells. poisonous waste products Growth – living organisms get bigger. They increase in both size produced by cells and mass, using chemicals from their food to build new material. growth increase in size and Irritability – all living organisms are sensitive to changes in their mass of an organism surroundings. 22 Incomplete advance copy Grade 9  UNIT 2: Cell biology Movement – all living organisms need to move to get near to KEY WORDS things they need or away from problems. Animals move using muscles, plants move more slowly using growth. irritability sensitivity of Reproduction – producing offspring is vital to the long-term an organism to changes in survival of any type of living organism. surroundings movement the need to get near to or away from Cell structures and functions things reproduction the There are some basic similarities between all cells, animal and plant alike. For example, almost all cells have a nucleus, a cell membrane, production of offspring to mitochondria, ribosomes, endoplasmic reticulum and cytoplasm. ensure the survival of a Other features are often seen in plant cells, particularly from type of organism the green parts of the plants, but not in animal cells. This has nucleus controls all cell led scientists to develop a picture of the basic structure of an activity and contains unspecialised animal cell and an unspecialised green plant cell. chromosomes Although there are not many cells which are quite this simple, the cell membrane outer idea of unspecialised animal and plant cells gives us a very useful layer of living cell that base point with which to compare other, more specialised cells. controls the movement of substances in and out Structures and functions in unspecialised mitochondria carry out animal cells cellular respiration All cells have some features in common and we can see them clearly ribosomes organelles in typical unspecialised animal cells (like the ones on the inside involved in protein synthesis of your cheek). They contain small units called organelles. Many of these organelles contain enzymes and chemicals to carry out endoplasmic reticulum specialised jobs within the cell. links the nucleus of a cell The nucleus controls all the activities of the cell. It also contains with the cell membrane the instructions for making new cells or new organisms in the cytoplasm liquid gel which form of long threads known as chromosomes. This is the genetic contains all the organelles material. You will find out more about this in Grade 10. of a cell The cytoplasm is a liquid gel in which most of the chemical organelles the small units reactions needed for life take place. About 70% of the cytoplasm inside a cell of a cell is actually water! The cytoplasm contains all the other chromosome strand of DNA organelles of the cell where most of the chemical reactions take carrying genetic information place. The cell membrane forms a barrier like a very thin ‘skin’ around the outside of the cell. The membrane controls the passage of Did you know? substances such as carbon dioxide, oxygen and water in and out of the cell. Because it lets some substances through but not Human beings contain an others it is known as selectively permeable. enormous number of cells. Estimates range from The mitochondria (singular: mitochondrion) are the 10 million million cells powerhouse of the cell. They carry out most of the reactions (1012) to 100 million of respiration, whereby energy is released from the food in a million (10012) cells – no form your cells can use. Whenever cells need a lot of energy – one has counted accurately! such as muscle cells and secreting cells – you will see a lot of mitochondria. Grade 9 Incomplete advance copy 23 UNIT 2: Cell biology The endoplasmic reticulum is a three-dimensional system of tubules that spreads right through the cytoplasm. It links the nucleus with the cell membrane. The ribosomes are found on the endoplasmic reticulum in your cells. They are vital for protein synthesis, the process by which your body makes all the enzymes that control the reactions of your cells. mitochondria nucleus cell membrane cytoplasm Human cheek cells Figure 2.11 A simple animal cell like this shows the features that are common to almost all living cells. Mitochondria, endoplasmic reticulum and ribosomes cannot be seen easily with a light microscope. They are much clearer using an electron microscope. Activity 2.3: Using the microscope to look at animal cells You will need: a microscope a lamp prepared microscope slides of human cheek cells/ epidermal cells Method Remember, microscopes are expensive and delicate pieces of cell membrane equipment so always take care of them and handle them safely. 1. Use the instructions for using the microscope, which you ×400 learnt in the previous section. You will be provided with nucleus slides of human cheek cells and simple epithelial cells. cytoplasm 2. Human cheek cells and simple epithelial cells are very Figure 2.12 Micrograph and similar to your diagram of an unspecialised animal cell. a drawing of simple cuboidal Draw some of the cells you see and label them as well epithelial cells as you can. Remember you will NOT see ribosomes and mitochondria under normal light microscopes. 24 Incomplete advance copy Grade 9  UNIT 2: Cell biology Why do cells have organelles? KEY WORDS All of the processes of life take place within a single cell. Imagine enzyme protein molecule 100 mixed reactions going on in a laboratory test tube – chemical that acts as a catalyst in chaos and probably a few explosions would be the result! But this is the level of chemical activity going on in a cell at any one time. Cell cells chemistry works because each reaction is controlled by an enzyme, cell wall outer layer in a protein designed to control the rate of a very specific reaction plant cells and bacteria that and ensure that it takes place without becoming mixed up with any is freely permeable other reaction. What is more, the enzymes involved in different cellulose complex chemical processes are usually found in different parts of the cell. carbohydrate that makes up So, for example, most of the enzymes controlling the reactions of plant cell walls respiration are found in the mitochondria. The enzymes controlling the reactions of photosynthesis are found in the chloroplasts and vacuole a fluid-filled cavity the enzymes involved in protein synthesis are found on the surface inside a cell of the ribosomes. These cell compartments or organelles help to keep your cell chemistry well under control. cell membrane vacuole Structures and functions in unspecialised plant cells cell wall (inside cell wall) Plants are very different from animals – they do not move their whole bodies about and they make their own food by photosynthesis. So, whereas plant cells have all the features of a typical animal cell – nucleus, cell membrane, cytoplasm, mitochondria, endoplasmic reticulum and ribosomes – they also have structures that are needed for their very different way of life. The cell wall is made mainly of a carbohydrate called cellulose, which strengthens the cell and gives it support. It is found outside the cell membrane. The cell wall structure contains large holes so substances can move freely through it in either direction – it is freely permeable. Many (but not all) plant cells also have other features. Chloroplasts are found in all of the green parts of the plant. They contain the green pigment chlorophyll, which gives the plant its colour. As a result of the chlorophyll they can absorb energy nucleus chloroplasts from light to make food by photosynthesis. mitochondria cytoplasm A permanent vacuole is a space in the cytoplasm filled with cell sap, a liquid containing sugars, mineral ions and other chemicals Figure 2.13 A photosynthetic dissolved in water. The vacuole is important for keeping the cells plant cell has many features in rigid to support the plant. The vacuole pushes the cytoplasm common with an animal cell, but against the cell wall, which keeps the whole structure firm. A others that are unique to plants. permanent vacuole is often a feature of mature (adult) plant cells. Grade 9 Incomplete advance copy 25 UNIT 2: Cell biology Activity 2.4: Making a slide of plant cells The prepared slides you have looked at show Activity (b) – red pepper animal cells that are dead and stained to Repeat the instructions for the onion cells make them easier to see. In this activity except this time remove a thin epidermal you are going to look at one of a number layer of the pepper. Again these cells do not of different types of plant cells – either (a) contain chlorophyll, but they are red so you onion (as you used in the previous section), do not need to use iodine on them. (b) red pepper or (c) pondweed. You will need: Activity (c) – pondweed such as Elodea a microscope (Canadian pondweed) microscope slides These plant cells contain chloroplasts. If you cover slips watch very carefully when you have the cells under a high power of magnification you may forceps well see the chloroplasts moving about in the mounted needles living cytoplasm of the cell. pipette 1. Take a single leaf from a piece of a lamp pondweed and cut a very small section a piece of (a) onion, (b) red pepper or about 2 mm2. (c) pondweed, e.g. Elodea or Canadian 2. Place the leaf sample onto a microscope pondweed slide and add a drop of water. Method 3. Using the mounted needle (or a pencil!) Remember, microscopes are expensive and lower the cover slip very gently over the delicate pieces of equipment so always take specimen, taking care not to trap air care of them and handle them safely. bubbles. 4. Remove any excess liquid from the Activity (