Biology Student Textbook Grade 8 PDF

Take Good Care of This Textbook This textbook is the property of your school. Take good care not to damage or lose it. Here are...

Take Good Care of This Textbook This textbook is the property of your school. Take good care not to damage or lose it. Here are 10 ideas to help take care of the RE BL OF IC N PU ATIO IC EDUC ET HIOP IA book: AT CR OF MO STRY L DE MI NI RA DE FE 1. Cover the book with protective material, such as plastic, old newspapers or magazines. 2. Always keep the book in a clean dry place. 3. Be sure your hands are clean when you use the book. 4. Do not write on the cover or inside pages. 5. Use a piece of paper or cardboard as a bookmark. 6. Never tear or cut out any pictures or pages. 7. Repair any torn pages with paste or tape. 8. Pack the book carefully when you place it in your school bag. 9. Handle the book with care when passing it to another person. 10. When using a new book for the first time, lay it on its back. Open only a few pages at a time. Press lightly along the bound edge as you turn the pages. This will keep the cover in good condition.  BIOLOGY STUDENT TEXTBOOK GRADE 8 Authors, Editors and Reviewers: Anteneh Tesfaye(Ph.D) Dereje Mergia (B.Sc, M.A.) Fekadu Worku (M.Sc) Gessesse Assefa (M.Sc) Abebe Getahun(Ph.D) Evaluators: Solomon Belayneh Getachew Bogale Gashaw Kebede FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA MINISTRY OF EDUCATION Published E.C. 2004 by the Federal Democratic Republic of Ethiopia, Ministry of Education, under the General Education Quality Improvement Project (GEQIP) supported by IDA Credit No. 4535-ET, the Fast Track Initiative Catalytic Fund and the Governments of Finland, Italy, Netherlands and the United Kingdom. © 2012 by the Federal Democratic Republic of Ethiopia, Ministry of Education. All rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted in any form or by any means including electronic, mechanical, magnetic or other, without prior written permission of the Ministry of Education or licensing in accordance with the Federal Democratic Republic of Ethiopia, Federal Negarit Gazeta, Proclamation No. 410/2004 – Copyright and Neighbouring Rights Protection. The Ministry of Education wishes to thank the many individuals, groups and other bodies involved – directly and indirectly – in publishing this textbook and the accompanying teacher guide. Copyrighted materials used by permission of their owners. If you are the owner of copyrighted material not cited or improperly cited, please contact with the Ministry of Education, Head Office, Arat Kilo, (PO Box 1367), Addis Ababa, Ethiopia. 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ISBN 978-99944-2-263-0  Content Unit 1: Biology and Technology 1 1.1 Biology for Development 2 1.2 Technological products used in Biology 7 hh Unit summary 16 hh Review Exercise for Unit 1 17 Unit 2: Cell Biology 21 2.1 Looking at Unicellular Organisms 22 2.2 Single Celled Organisms 25 2.3 Levels of Cellular Organization in multicellular organisms 38 hh Unit summary 48 hh Review Exercise for Unit 2 50 Unit 3: Human Biology and Health 53 3.1 The reproductive system 54 3.2 HIV and AIDS 68 hh Unit summary 73 hh Review Exercise for Unit 3 74 II C o n t e n t Unit 4: Plants 77 4.1 Food manufacturing in green plants 79 4.2 Growing trees 87 hh Unit summary 96 hh Review Exercise for Unit 4 96 Unit 5: Animals 99 5.1 Keeping farm animals 100 hh Unit summary 116 hh Review Exercise for Unit 5 117 Unit 6: Environment 119 6.1 Ecosystem 120 6.2 Biological Associations 125 6.3 physical factors of the ecosystem 130 hh Unit summary 143 hh Review Exercise for Unit 6 144  Unit Biology and 1 Technology Unit Outcomes By the end of this unit, you will be able to: ”” explain how biology contributes to country’s development; ”” explain the role of technology for the progress of biology; ”” list at least seven technological products used in biology; and ”” tell the functions of some technological products used in biology. Main Contents 1.1 Biology for Development 1.2 Technological Products used in Biology ”” Unit Review  2 Biology Grade 8 Introduction In your previous grade of biology lessons, you were able to explore the meaning and branches of biology, industries that utilize biological knowledge and its relevance to society. Furthermore, you have studied biology and technological innovations and values in biology education. In this unit you will identify, discuss and explain how biology contributes directly or indirectly in the development of Ethiopia. Biology uses several technological products. You will explore some of the technological products used in biology. 1.1 Biology for Development By the end of this section, you will be able to: ”” explain how biology contributes to the country’s development. Biological studies in general contribute for the development of a country in many aspects. Biology plays a role in the following areas of developmental activity in Ethiopia. Health Care What is the contribution of biology for community health? Relationship of Biology and In a community where health conditions are better, development people live, safer and longer, reduce incidence of Biological knowledge diseases, and produce more. ↓ Health Care-Professionals Biology is the basis for all health care activities. In ↓ Healthy People all health care facilities, skilled professionals work ↓ Work and Produce more in diagnosis, treatment, prevention and control of ↓ diseases. A wide variety of health care practitioners Increased income and standard of living work in health care including, medical doctors, ↓ nurses, laboratory technicians, etc. DEVELOPMENT All physicians, nurses, laboratory technicians and other health professionals are trained in the field of biology. These professionals serve in several hospitals, clinics, and other health care centers in Ethiopia. Activity 1.1 Discussion on the application of biology in health Procedure: in group, discuss how the services of clinical laboratory and vaccination in your community require biological knowledge. 55 Present the out comes of your discussion to your class  Unit 1: Biology and Technology 3 Agriculture What is the role of biology in Agriculture? Agriculture plays an important role in the Key Terms Ethiopian Economy. Our country generates its 55Agrochemcials: chemicals used income by exporting a number of agricultural for agriculture as fertilizers, weed products such as coffee, grains, flowers and and pest killers. fruits. Agriculture is an activity of producing 55Selective breeding: a practice during crops and raising animals. Improving quality which selected two individuals mate and produce offspring with improved of crops and animals needs knowledge of qualities. biology so that to increase their productivity 55Hybrid: an individual that has superior (See Figure 1.1). qualities than that found in either of selected parent. What is the use of Agro-chemicals? Increasing productivity using Agro-chemicals like fertilizers, herbicides (weed-killers), and pesticides is made possible by using biological principles. However, agro - chemicals can be accumulated in the body of plants. As plants are consumed by other animals the concentration of these chemicals increase by many folds. The accumulation of these chemicals in the body of animals including humans causes more serious health problems. Agro-chemical residue is the agricultural chemical Figure 1.1 Improved crop found in the food to be consumed. plantation by the use of agrochemicals What is selective breeding? Selective breeding of animals is an important practice in which biological knowledge is used in animal husbandry. Animals with the desired characteristics such as giving more milk, resistance to disease, giving more meat etc. Can be selected and reproduced in large numbers. Selective breeding practices are also conducted to produce plants with desired qualities. Breeding is a practice of selective controlled mating in plants and animals to produce organisms that better serve human needs for food, work, sport, or aesthetics. Breeding involves crossing distinct strains or even species to produce hybrids that contain a combination of traits that is superior to that found in either parent. Hybrid varieties have many superior qualities, especially in yield and vigor. Genetically modified crops (GM crops) are crops produced by means of genetic engineering in order to get desired characteristics of crops such as high yield from small plot of land.  4 Biology Grade 8 Activity 1.2 Investigating the role of biology in agricultural products Procedure: 55 in group discuss how agricultural products (egg, milk, crops, hens, cattle) require biological knowledge to increase productivity. 55 Present the outcomes of your discussion to the class. Food Production What is the contribution of biology in food production? The food that we consume is produced by living things; plants and animals. Biology studies the living things and the processes in the production of nutritional substances (See Figure 1.2). Biology provides the means for keeping quality of foods during processing, transport and storage. Then industrial process, transport and storage of food require biological knowledge to keep quality of foods. Biological studies are essential in determining nutritional requirements and provision of nutrition for people. Biologists study the nutritional content of food, as well as the interaction of food components with each other, with air, and with packaging materials, and the preservation of quality during Figure 1.2 some nutritional processing, transporting and storage. foods Activity 1.3 Discussion on the contribution of biology in food processing Procedure: 55 in group, discuss the contribution of biological knowledge in making, transporting and storing biscuits. 55 present the outcomes of your discussion to the class.  Unit 1: Biology and Technology 5 Improvemenet of our Environment What is the importance of biology for the improvement of our environment? The conservation of natural environment, D Y id ou now K ? vegetation, and wildlife is important for our ¸¸Effective conservation of wildlife and vegetation is survival. The study of biology contributes to important for tourism industry. the improvement of the environment and how humans can live in harmony with the environment. Good or friendly environmental practices are important to reduce the impact of negative human activities on the environment. Good environment is suitable for living. It is a practice through which consumption of natural resources is reduced and introduction of harmful chemicals to the environment is minimized. Activity 1.4 Discussion on the role of biological knowledge in wildlife. Procedure: 55 in group, discuss the contribution of biological knowledge to wildlife conservation 55 Role of biological knowledge in tree planting campaign during Ethiopian millennium. Natural Products W is the importance of biology in using natural products (remedies and cosmetics?) Biological knowledge and techniques are also important for production of medicinal substances and cosmetics from natural resources. For example, Kosso is used as medicine for tape worm infection (see Figure 1.3). Activity 1.5 Discussion on remedies and cosmetics Procedure: 55 in group, discuss on the economic and biological importance of remedies and cosmetics.  6 Biology Grade 8 Figure 1.3 Hagenia abyssinica (Kosso)tree (left) and its preparation for use as remedy for tape worm disease(Right). What are natural products and their uses? Cosmetic is a general term applied to all preparations used externally to condition and beautify the body. It is done by cleaning, coloring, softening; and used for protecting Did You Know? the skin, hair, nails, lips and eyes. More than 80% of modern medicines are prepared from natural products, mainly from plants. Natural products used for beauty include: 55 “Hinna” used to stain hair 55 “Ensosilla” used to stain skin Local herbal medicines include: 55 “Kosso” used to treat Tapeworm. 55 “Enkoko” used to treat Tapeworm. 55 “Meterae” used to treat Tapeworm and Ascaris. 55 “Dingetegna” used to treat sudden illnesses 55 “Yemitch medehanit” used to treat common cold and related diseases. Several modern drugs are prepared from plants and other natural products produced from Key Terms plants include: 55Natural products: are products that 55 Rubber are obtained in nature. 55Cosmetics: substances used for 55 Gum body beauty. 55 Incense- “Itan” 55Remedies: substances used for treatments. 55 Dyes  Unit 1: Biology and Technology 7 Exercise 1.1 I Choose the best answers for the following questions 1 Biology is used in agriculture to produce A Pests attacking plants C Disease causing plants B High yielding animals D Weeds 2 Biological knowledge is needed to improve A Food qualities C Food storage B Food packaging D All of the above 3 Which of the following biological knowledge is useful to improve the environment? A Protection of vegetation C Damaging natural things B Destruction of wildlife D B and C 4 The desirable characteristics of plants or animals can be developed for Ethiopian farmers through A Selective breeding C Conservation B Natural breeding D All of the above 5 Biological knowledge enables us to know all, but not A The use of agrochemicals C The method of pest control. B The destruction of natural D The method of used control products 1.2 Technological Products used in Biology At the end of this section, you will be able to: 55 explain the role of technology for the progress of biology; Some Technological products 55 list at least seven technological used in biological studies: products used in biology; and ˆˆ Microscope and hand lens ˆˆ Thermometer 55 tell the functions of some technological ˆˆ Binoculars products used in biology. ˆˆ Stethoscope ˆˆ Sphygmomanometer Biological studies use various technological ˆˆ Incubator products. These equipment are products of ˆˆ Refrigerator and freezer other sciences such as Mechanical, Electrical, ˆˆ Balances and Electronic technologies. ˆˆ Centrifuges  8 Biology Grade 8 Microscope What is Microscope? A microscope is an instrument which is used to study smaller objects. It magnifies and revolves the object under study. Biologists study smaller organisms and cells using microscope (Figure 1.4). Figure 1.4 A Binocular microscope Activity 1.6 Labelling parts of a microscope 1 1 Refer to Grade 7 Biology Unit 1 2 and label the parts of Figure 1.5. 2 What is the difference between a 3 4 microscope and a hand lens? 5 7 6 9 8 11 10 12 Figure 1.5 A microscope What is the use of microscope? Microscopes are tools used to enlarge images of small objects so as they can be studied. Word Roots and Origins Microscopes allow us to look at things that The word microscope is derived from two Greek words are too small to be seen with our eyes. The “Micro” meaning tiny and “scope” meaning to view or microscope Figure 1.5 above is the most common look at. type of microscope, the compound microscope. Compound microscopes can magnify objects up to about 1,000 times.  Unit 1: Biology and Technology 9 Activity 1.7 Observing samples under a Microscope Materials you require: 55 Microscope 55 A small cup of yogurt (sample) 55 Slide and cover slip 55 Droppers with teat Procedure: Observation under compound light microscope 1 Place a drop of thin yogurt at the center of the microscope slide and cover it with a cover slip. Avoid Figure 1.6 Using the microscope trapping of air bubbles. 2 Place the slide at the center over the stage opening on the stage of the microscope and fix it with clippers. 3 Adjust the amount of light using the iris diaphragm on the condenser (Figure 1.6). 4 Focus with the coarse adjustment knob using first the low power objective, and then with medium power objective using the fine adjustment knob to get a clear view. 5 Observe and search for organisms by moving the slide in all directions, left to right, and back to forth. 6 Draw and label what you observe. Binocular Key Term 55Prism: a block of clear glass which What is a Binocular? separates light in to different color Field glasses or binocular telescopes are Main focus instruments used to observe distant or far (thumbscrew) objects. Binocular is a pair of field glass Independent Ocular lenses which is made up of two small telescopes focus (eyepiece) joined with a single focusing device. It is designed for simultaneous use by both Prisms eyes. It allows viewer to use both eyes when viewing distant objects (Figure 1.7). Objective lens Figure 1.7: A binocular  10 Biology Grade 8 Activity 1.8 Observing distant objects through binocular Materials you require: 55 Binocular Procedure: 55 Look first with your naked eyes at the distant object (bird or other animal) 55 Use the binocular and look at the same bird or animal you see with your naked eyes. 55 Using the binocular look at sites where you were not able to see clearly with your eyes. Question: What is the difference between naked eye and binocular observation? Many different abbreviations are used for binoculars, including glasses, binos and bins. Thermometer What is a thermometer? It is an instrument used to measure and indicate temperature. It typically consists of a graduated glass Figure 1.8: Thermometer tube that contains mercury or alcohol which expands when heated(Figure 1.8). Activity 1.9 Measuring temperature using thermometer Material you require: 55 Thermometer, 70 % alcohol, cotton, stove, beaker, water. Procedure: 55 Add water to a beaker. 55 Insert a thermometer and measure the temperature. 55 Heat the water on a stove for 10 minutes. 55 Insert a thermometer and read the thermometer. Question: 1 What was the temperature before and after heating? 2 What is the difference in temperature between the two?  Unit 1: Biology and Technology 11 Stethoscope What is the use of stethoscope? A stethoscope is a medical instrument used to listen to sounds produced in the body, especially from the heart and lungs. It is designed to be used Figure 1.9 Stethoscope with both ears. It contains two flexible rubber tubes running from a valve to the ear pieces. The Key Terms valve is connected to the chest piece. The chest 55Heart beat: the rhythmic contraction and relaxation of the heart to pump piece is either a bell-shaped piece to pick up low blood through out the body of an sounds or a flat disk for higher frequencies. Most animal. stethoscopes have Y-shape (Figure 1.9). 55Blood pressure: the pressure of circulating blood from the heart to the rest of the body. Sphygmomanometer What is sphygmomanometer? A sphygmomanometer or blood pressure meter is a device used to measure blood pressure. It is always used in combination with a means to determine at what pressure blood flow start and at what pressure it is unimpeded. Manual sphygmomanometers are used together with a stethoscope (Figure 1.10). Figure 1.10 Sphygmomanometer Activity 1.10 Measuring heart beat and blood pressure. Material you require: 55 Stethoscope, Sphygmomanometer Procedures: 55 With your teacher go to the nearby clinic and observe how a stethoscope Did You Know? ¸¸The human heart beats 70 times in average every and Sphygmomanometer are used. minute. Or invite a health worker to your classroom and ask him/her to demonstrate the use of these instruments to you, and 55 Record and compare heart beat and blood pressure of the group member.  12 Biology Grade 8 Incubator What is an incubator? Incubator is a device for maintaining an organism in an environment that encourages its growth (Figure 1.11). The instrument commonly maintain a constant temperature and, a constant humidity level in poultry (chicken farm). Incubators are used to keep eggs warm until they hatch and to warm the young chicks after Figure 1.11 Incubator hatching. Did You Know? Refrigerator An infant incubator is used to keep pre mature newborns in a controlled temperature. What is a refrigerator? A refrigerator (often called a “fridge”) is a cooling instrument. It contains a thermally insulated compartment and a heat pump to transfer heat from it to the external environment. Then it cools the contents kept in to a temperature below the room temperature. Refrigerators are extensively used to store foods, and prevent bacterial spoilage if this device maintains a temperature a few degrees above the freezing point of water. A similar device which maintains a temperature below the freezing point of water is called a “freezer”. Most freezers operate around −18oC (Figure 1.12). Figure 1.12 Refrigerator  Unit 1: Biology and Technology 13 Activity 1.11 Examing food items kept at different incubation conditions. Materials you require: 55 Three pieces of meat (fresh), 55 Three small plastic containers, 55 Freezer refrigerator. Procedure: 55 Smell each piece of meat and make sure it is not spoiled (Or they can be cooked). 55 Place one piece in each plastic container. Label: 1 Freezer 2 Refrigerator 3 Room 55 Place label 1, in freezer, label 2 in refrigerator label 3 in one corner of the laboratory. 55 Each day, smell all of them and return to their places. 55 Continue smelling until one of them smells bad. 55 Note the day, and continue until the second smells bad. Question: 1 Which sample goes bad first and after how many days? 2 Which sample was spoiled next, and after how many days? 3 Which sample stayed long-unspoiled? 4 What is your conclusion? Balance What is a balance? A weighing scale (balance) is a measuring instrument for determining the weight or mass of an object. The balances are used in many industries and laboratories to measure the weight or mass of an object or a substance (Figure 1.13). Specialized medical scales and bathroom scales are used to measure the body weight of human beings. Figure 1.13 Balance  14 Biology Grade 8 Activity 1.12 Measuring weight Materials you require: 55 Bathroom balance Procedure: 55 Place the balance on a leveled surface. 55 Adjust the weight indicator to zero by positioning your eyes in 90o line. 55 Without shoe and heavy clothes, mount yourself on the balance. 55 Let other students take the reading (look as above). 55 Compare your weight with the weight of other students. Question: Reading from the side is not correct, why? Activity 1.13 Field Visit Visit the nearby health care facility and do the following. 1 Identify the type of instruments used? 2 Identify the purpose of each instrument? 3 Explain how each instrument is used? Present a report of your visit in table format using the following template. Type of Instrument Purpose How it is used Centrifuge What is centrifuge? A centrifuge is a device used to separate two or more substance of different mass by rotating at a central axis. It is able to separate different substances from each other because the materials with heavier mass moving faster to the bottom of the tube than the lighter one.  Unit 1: Biology and Technology 15 It is used in industries and scientific laboratories to separate different substances with different weight or mass (Figure 1.14). Figure 1.14 Centrifuge Exercise 1.2 Choose the best answers for the following questions. 1 Stethoscope is used by physicians A To listen blood pressure C To measure temprature B To listen heart beat D To measure weight 2 What instrument is used by physicians to measure blood pressure? A Centrifuge C Sphygmomanometer B Incubator D Thermometer 3 A centrifuge separates contents from a solution by A Heating C Pressurizing B Spinning D Cooling 4 What do you use to measure your body temperature? A An incubator C Beam balance B A thermometer D Sphyg momanometer 5 An incubator is used to control A Temperature C Light B Pressure D Gravity  16 Biology Grade 8 U n i t S u m m a r y ŒŒ Biology plays an important role and contributes for development of our country in community health, agriculture, food production and other useful aspects. ŒŒ Health professionals that diagnose, treat and cure diseases are trained in biology. ŒŒ Biological knowledge is needed to increase productivity of crops and animals. ŒŒ Biology plays role in improving the nutritional values of foods. ŒŒ Biology is important to safe guard the environment by providing the ways of conservation. The following flowchart shows how biological knowledge is related to development BIOLOGY FOR DEVELOPMENT Biological Knowledge Health Care HEALTHY PEOPLE Work and Produce more Environment Agriculture Biological Knowledge Food Natural Products Other activities Increased income and standard of living DEVELOPMENT  Unit 1: Biology and Technology 17 ŒŒ Technological products have played a significant role in the progress of biology as science. ŒŒ Microscope is the most important tool used in biology. ŒŒ Other technological products used in biology include centrifuge, thermometer, refrigerator and incubator. Some technological products used in biology are summarized in the following table Technological Product Use in Biology Microscope and hand lens To enlarge and see objects Thermometer To measure temperature Binoculars To see far objects Stethoscope To listen internal body sound Sphygmomanometer To measure blood pressure Incubator To grow or keep at a required temperature Refrigerator To keep materials cold (0-5oC) Freezer To keep materials cool (below 0oC) Balances To measure weight Centrifuges To separate components in a solution ? Review Excises for unit 1 Ajsjsdf AjsjsdfAjsjsdf AjsjsdfAjsjsdf Ajsjsdf AjsjsdfAjsjsdf Ajsjsdf AjsjsdfAjsjsdf Ajsjsdf AjsjsdfAjsjsdfAjsjsdf Aj Ajsjsdf AjsjsdfAjsjsdf Ajsjsdf AjsjsdfAjsjsdf AjsjsdfAjsjsdf Ajsjsdf AjsjsdfAjsjsdf Ajsjsdf AjsjsdfAjsjsdf Ajsjsdf.......................................... Ajsjsdf Part I: For the following questions choose the best answer among the choices given. 1 Which one of the following is not the contribution of biology for community health A Tracing of health professionals B Production of fertilizers C Prevention of disease D Knowing causes of diseases 2 Herbicides are agrochemicals used A To kill insects attacking crops B To fertilize the soil C To inhibit growth of weeds D To inhibit growth of crops  18 Biology Grade 8 3 The agriculture sector develops more when biology plays role in A Keeping soil fertility B Increasing plant and animal productivity C the use of agrochemical production D All of the above 4 Food production requires biological knowledge to A Determine nutrient content B Improve food storage C Increase food production D All of the above 5 Which of the following is not a natural product? A Plastic B Oil C Silk D Rubber 6 Consciousness in biology and its application makes environment A Safe to humans B Harmful to humans C Unhealthy to live D All of the above 7 Reproducing plants and animals which have desirable traits is called A Genetic modification B Fertilization C Selective breeding D Agrochemical using 8 A natural product used for colouring hair in Ethiopia is A Kosso B Ensosilla C Hinna D Metere  Unit 1: Biology and Technology 19 Part II: Match descriptions in column B with the items in column A lased on function Column A Column B 9 Centrifuge A used to observe far objects 10 Incubator B used to measure blood pressure 11 Stethoscope C used for growing bacteria 12 Sphygmomanometer D used to heart beat 13 Binocular E used for spinning materials at high speed Part III: Fill in the blank 14 The instrument used to know the weight of materials is called 15 Body temperature is measured by 16 Health care providers such as and are trained in biology 17 Products used for beauty care are called 18 Analysis of the Nutrient of food needs knowledge. Part IV: Give short Answer 19 What are the development areas in which biological knowledge is used? 20 How can biology contribute to the safety of our environment?  20 Biology Grade 8 Part V: Copy the crossword puzzle and use the numbered clues to complete and solve the puzzle. 1 2 3 4 5 The numbers in bracket indicates the number of letters in each word. Across 1 An instrument used for spinning solutions (10) 4 An instrument used to see very small objects (10) 5 An instrument used to keep temperature below zero degree centigrade (7) Down ward 2 An instrument used to measure temperature (11) 3 An instrument used to listen heart beat (11)  Unit Cell Biology 2 Unit Outcomes By the end of this unit, you will be able to: ”” use hand lenses and microscopes to observe unicellular organisms and name some unicellular organisms; ”” describe the structure, habitat, locomotion, nutrition, reproduction and importance of some unicellular organisms; ”” name different types of cells, tissues, organs, and systems and state their Main Contents functions; 2.1 Looking at Unicellular ”” describe organism as the highest level Organisms of organization; 2.2 Single Celled Organisms ”” demonstrate scientific enquiry 2.3 Levels of Organization in skills: observing, comparing and Multicellular Organisms contrasting, drawing conclusions, ”” Unit Review communicating, inferring, problem solving, comparing and contrasting.  22 Biology Grade 8 Introduction In Unit 1, you have discussed the contribution of biology to development by its role in community health, agriculture, food production, use and conservation of the environment. These contributions of biology for societal development are the outcomes of studying and understanding living things or life. Every living thing from the tiniest bacterium to the largest whale is made of one or more cells. Many of the chemical reactions that keep organisms alive (metabolic functions) take place in cells. All organisms are made of cells. A cell is the basic unit of structure and function of living things. The cell is the smallest unit that carries on all life processes. Unicellular organisms like bacteria, protozoa, algae, and yeasts are organisms that are made Did You Know? up of one cell. Living organisms such as some ¸¸Unicellular organisms perform the algae, most fungi, plants and animals are made same life processes as multicellular up of many cells and are called multicellular organisms. organisms. In multicellular organisms all cells ¸¸Scientists estimate that our bodies work together and make the organism alive. contain from 75 to 100 trillion (1012= 106 X 106) cells. Some of these cells are of the same type and collectively form a tissue. These cells of a tissue do the same job. For example, muscle tissues in animals effect movement and vascular tissues in higher plants transport materials. In the following sections you will learn more about different unicellular organisms, which are very small to be seen with the naked human eye. Thus, you need to use a hand lens or microscope to study these organisms. 2.1 Looking at Unicellular Organisms By the end of this section, you will be able to: ”” use hand lenses and microscopes to observe unicellular organisms; ”” name amoeba, paramecium, euglena, bacteria and yeast as unicellular organisms.  Unit 2: Cell Biology 23 Can you see unicellular organisms with your naked eyes? The term unicellular organism indicates that the organism is made of a single cell. These single Did You Know? celled organisms carry out the functions like ¸¸Unicellular organisms that are feeding, locomotion, expelling wastes, neither animals, plants, bacteria nor reproduction, and so on by the single cell. These fungi are called ‘Protists’. unicellular organisms include amoeba, euglena, paramecium, bacteria and yeasts. Many of these Key Terms organisms are commonly found in water bodies like lakes, ponds, and river water. In most cases, 55Unicellular organism: an they are minute sized or microscopic and organism which is made up of only one cell. require microscopes to observe them. 55Multicellular organism: an Because of their movement, unicellular organisms organism which is made up of like amoeba and paramacium are generally many cells that work together. known as animal-like single celled organisms. 55Tissue: a group of similar or different cells that perform the Because they are photosynthetic, unicellular same function (blood tissue algae like chlorella are known as single-celled consists of red blood cells, white plants. Whereas unicellular organisms, like blood cells and platelets). euglena, which moves and feeds like animals and also prepares its own food like plants can neither be a plant nor an animal. All these microorganisms are known as Protists. The diversity of single-celled organisms is surprising. These differences are apparent for both the structure and function of the organisms. Single-celled organisms range greatly in their size, from less than 1 micron (one-millionth of a meter) in diameter for the smallest bacteria, to more than 100 microns for some protozoans. Activity 2.1 Examining different water samples and prepared slides for the presence of organisms In the first part of this activity, you will examine prepared slides of unicellular organisms under a compound microscope (Figure 2.1). In the second part of this activity, you will prepare a wet mount of amoeba culture. Materials you will require: 55 Hand lens, 55 Water samples from pond, river, lake, well or standing water, 55 Compound light microscope, 55 Prepared slides of amoeba, euglena, paramecium, bacteria, yeast, and unicellular algae.  24 Biology Grade 8 Procedures: I Observation using a hand lens 1 Collect water samples in open mouth container (beakers). 2 Observe the surface of each sample with a hand lens for the presence of living organisms. 3 Can you observe anything moving? Please, draw it. II Observation of prepared slides 1 Place a prepared slide of amoeba on the stage of the microscope. 2 With your microscope on low power, observe the slide. 3 Move the slide around on the stage until you find some cells. 4 Now, using the medium- or high-power objective lens, focus on one cell and observe and draw what you see. 5 Label all visible structures. 6 Repeat steps 1 – 5 for prepared slides of Paramecium, euglena, yeast and bacteria. 7 For each organism you view, be sure to include the name of the organism and the total magnification used. N.B: Total magnification = Magnification of ocular lens × Magnification of objective lens After completing these practical activities, compare your drawings with the figures given below (Figure 2.2). Key Terms 55Mounting: Placing a sample on glass slides and preparing it for observation under a microscope. 55Wet mount: A process during which water is used as a mounting medium. 55Prepared slide: (also known as permanent slide): a sample prepared without water to be used for longer and many times. 55Budding: reproduction by forming a side growth from the mother cell. 55Algae: photosynthesizing unicellular Figure 2.1 Student making an organisms. observation using microscope  Unit 2: Cell Biology 25 Nucleus Flagellum cell Stigma Reservoir membrane Pseudopod Nucleolus Nucleus Pseudopods Food being Chloroplast engulfed by Pellicle Contractile pseudopods vacuole Cytoplasm a) amoeba b) euglena c) chlorella (algae) Food vacuole Cilia Anal Oral groove pore d) paramecium e) bacteria (rod shaped) f) yeast (budding) Figure 2.2: Pictures of different unicellular organisms Exercise 2.1 I Give short answers for the following questions. 1 Explain why organisms are called unicellular. 2 Based on your examination discuss the similarity and differences between each unicellular organisms. 3 Name unicellular organisms. 2.2 Single Celled Organisms By the end of this section, you will be able to: ”” describe the structure, habitat, locomotion, nutrition, reproduction and importance of amoeba, paramecium, euglena, bacteria and yeast. In the previous section, you have observed different types of organisms which are made up of one cell only: those organisms are commonly known as single-celled organisms. Some microscopic organisms, such as bacteria, amoeba, euglena, paramecium, yeast or uni- cellular and some algae are unicellular. Plants, animals, and most fungi are multicellular; that is, they are composed of many cells working together. But whether it makes up an entire bacterium or is just one of trillions in a human being, the cell is an amazing thing of plan and efficiency. A closer study of single celled organisms shows how they are organized to perform various life activities. Generally, a cell consists of different parts, commonly known as sub-cellular structures. Word Roots and Origins Amoeba Protozoa: made up of two Greek words proto, which means ‘first’ and, zoa, meaning What does a cell of amoeba ‘animals’. Protozoa or protozoan for singular. look-like? Amoeba is a unicellular organism, which is found in nearly all freshwater habitats. It does not have a definite shape. Its shape depends on the condition.  26 Biology Grade 8 This animal-like unicellular organism is commonly known as protozoan. Amoeba can be identified Key Terms with its unique mode of locomotion. It moves by 55Pseudopodia: extended cell membrane for movement. means of extension of the plasma membrane 55Habitat: a place where an known as pseudopodia. The amoeba consists of organism lives. cellular parts like cell membrane, cytoplasm, 55Life activities: activities like nucleus, food vacuole and contractile vacuole. growth, movement, reproduction, metabolism, response to stimuli which characterize living things. Where do amoeba live? 55Parasitic: an organism that lives A habitat is a place where an organism lives. on or in the host and harms it. Amoebas (sometimes spelled amoebas or 55Free living: an organism which amoeba) are either free living or parasitic is not dependent on another organism to survive. organisms. The free living amoeba live in fresh water (ponds, rivers and lakes), mud including 55Cell membrane: cellular structures serving as boundary of the cell to ditches, salty water and soil. Certain amoebae are move materials in and out. parasites that are living inside other organisms. 55Cytoplasm: jelly like substances enclosed by cell membrane. How do amoebae move? 55Nucleus: used to control all life activities. Can be one or more Amoeba moves by pushing its cytoplasm nuclei. out to the direction of movement and by 55Food vacuole or granule: used to contain food for digestion. extending the cell membrane outwards. 55Contractile vacuole: used to This outward projection (finger like remove excess water. projection) of the cytoplasm is called pseudopodia meaning false feet. By a flowing motion of the cytoplasm within the cell and the pseudopodia, the whole Did You Know? cell moves forward on the surface. ¸¸The pseudopodia of amoeba can form at any point on the cell membrane so that it can move in any direction. What do amoebae feed? Amoeba commonly feed on bacteria, microscopic algae and other protozoa, Word Roots and Origins which are enqulfed by pseudopodia Pseudopodia: made up of two Greek words from. pseudo, meaning ‘false’ and, podia, meaning ‘feet’. How do amoebae feed? Amoeba uses its pseudopodia to engulf food particles and takes it into the food vacuole (Figure 2.3). The process of engulfing solid food is called Phagocytosis. When an amoeba approaches a food particle, it extends its pseudopodia forward on either side of the food particle and then by flowing around the food particle; the pseudopodia engulf it within a food vacuole.  Unit 2: Cell Biology 27 The food vacuole containing the food particle receives digestive enzymes from the cell Key Terms cytoplasm. Then the food digested is broken 55Sub-cellular structures: cellular down into small nutrient molecules that can parts that perform the many physiological functions needed to pass out of the vacuole into the cytoplasm of maintain the life of the organism. the organism. Unused parts are removed out 55Engulf: take in solid food by cell. through the cell membrane. Food Food particle particle Pseudopod Extendedd Food pseudopodium vacuole Figure 2.3: The feeding of amoeba using its pseudopodia How do amoebae reproduce? Amoeba reproduces and produces new amoebae (daughter amoebas) asexually (see Figure 2.4). Acve (feeding Inacve (cyst, Depending on the condition of living as good and moving protected (favourable) or bad (unfavourable) an amoeba passes phase) phase) through two major stages. During its life period, the passing of an amoeba through good and bad living conditions forms its life cycle. The life cycle of Figure 2.4: The life cycle amoeba includes two phases, the active (moving and of amoeba feeding) and cyst (inactive and protected) phase. A B C D E F Figure 2.5: Binary fission in amoeba: a) Amoeba stops moving and rounds off. b) The nucleus begins to divide. c) The nucleus has divided and the cytoplasm starts to constrict. d) and e) The construction continues to divide the cytoplasm. f) The daughter amoebae separate. This is a form of asexual reproduction called binary fission. There is no evidence of sexual reproduction in this species of Amoeba.  28 Biology Grade 8 During favorable condition an amoeba exists and lives in an active state. While in its active Did You Know? phase an amoeba reproduces by a type of asexual ¸¸During sporulation an amoeba cyst reproduction, known as binary fission forms as many as 500-600 spores, (Figure 2.4). Binary fission means a process in those which develop into active which a cell divides into two equal parts and amoebae when condition is favorable for an active life. forms two daughter cells. The formed structure, the cyst, is resistant to dessication, low Key Terms temperatures, and process of binary fission 55Sporulation: asexual reproduction continues as long as the condition is suitable or by forming spore favourable. 55Cyst: a hard cover enclosing an inactive cell in unfavourable conditions. Cyst A B Nucleus C Spore The release of active amoebae D E Figure 2.6 Sporulation of amoeba: a) Active amoeba; b) cyst; c) nucular division in the cyst; d) the covering of each nucleus with a spore membrane and the formation of spore; e) breaking of the cyst and the release of active amoebae. Is Amoeba important? There are several species of amoeba, both free living and parasitic. The fresh water species of amoeba is a useful experimental animal. However, Entamoeba histolytica is a parasitic species of amoeba that negatively impacts the human body, resulting in the infectious disease known as amebiasis. It is most common in developing countries that have poor sanitary conditions.  Unit 2: Cell Biology 29 Activity 2.2 Examining different water samples for the presence of living organisms In the previous section you have observed prepared slide of amoeba, now you will bring water sample from places nearby your school and you will observe live samples. Materials you will require 55 Compound light microscope, 55 Pond, river, lake water, 55 Slides and cover slip, standing water or hay infusion. 55 Dropper, Procedures: 1 Using a clean eyedropper place a drop of sample at the center of microscope slide and cover it with a cover slip. Avoid trapping of air bubbles by tapping the slide gently to remove any air bubbles. 2 Place the slide at the center of the hole on the stage of the microscope and fix it with clippers. 3 Adjust the amount of light using the iris diaphragm on the condenser. N.B: Since amoeba will be inactivated when exposed to light, either adjust the light so that it will not be much for them or take a few minutes till they get activated. 4 Use the coarse-adjustment knob to focus on the cells under the low power. 5 Switch to medium power and use the fine adjustment knob to bring the cells into focus once more. 6 Draw what you observe and compare it with picture of amoeba in Figure 2.3. 55 Have you seen amoebae? 55 How are they moving? Paramecium What does a cell of paramecium look-like? Paramecium is a unicellular organism with Key Terms a shape of a print of shoes. This colorless and 55Conjugation: a process in slipper-like protozoan consists of cellular parts which unicellular organisms are temporarily united and exchange such as, cell membrane, cytoplasm, macro and genetic material. micro-nuclei, food vacuole, contractile vacuoles, 55Binary fission: a type of cell division anal pore, gullet and oral groove and cilia during which the cell divides into (Figure 2.7). two equal cells.  30 Biology Grade 8 Anterior contractile vacuole Food vacuole Micronucleus Macronucleus Gullet pellicle cilia Posterior contractile vacuole Figure 2.7: Paramecium and its cellular parts Where does paramecium live? Paramecium is living in fresh water habitats including ditches, rivers and lakes as free living Key Terms organism. 55Macro nucleus: large nucleus which is related to metabolism and development of Paramecium. How does a paramecium 55Micro nucleus: smaller nucleus move? which is responsible for the reproduction of Paramecium. Paramecium uses its cilia for movement. The 55Oral groove: a mouth-pore, whole surface of a Paramecium is covered with through which a Paramecium feeds. cilia that beat and create water currents and then 55Anal pore: an opening through which a Paramecium removes move it towards a food source. The oral groove waste material. of the Paramecium also contains cilia that create 55Gullet: the passage through which currents and which draw the food into an oral food passes from mouth (oral cavity. groove) into the cytoplasm. 55Cilia: fine hair-like extensions that beat and move the organism How does a paramecium through liquid. feed? 55Pellicle: a thin protective membrane that covers the whole Paramecium is able to feed on bacteria and surface of the cell membrane of a algae which are brought into the oral groove and Paramecium. carried to the cytoplasm by the beating action of the cilia. The food from the oral groove is moved down a gullet and enters the food vacuoles for digestion. Following digestion, the soluble nutrients are absorbed by the cytoplasm, and the undigested food is eliminated at the anal pore. How does paramecium reproduce? Paramecium is capable of reproducing both asexually and sexually (Figure 2.8a and b). During asexual reproduction, Paramecium first divides its micronuclei. Then, it divides its cytoplasm and divides into two paramecia through binary fission.  Unit 2: Cell Biology 31 Sexual reproduction in Paramecium involves conjugation. During conjugation, each of the two paramecia divide their micronuclei and form four micronuclei. In each paramecium three of the micronuclei disappear and only one survives. Then, each nucleus in each paramecium divides and forms two nuclei. The macronuclei brake down and disappear. Then after, the two paramecia join together and exchange one of the two nuclei. The new and the old nuclei in each paramecium fuse (unit) and form a zygote. The paramecia separate and the nucleus in each paramecium divides into eight. Afterwards, each paramecium undergoes binary fission twice to form four new individuals. LIfe cycle of paramecium sexual asexual conjugation mitotic fission Figure 2.8: Reproduction in paramecia. Activity 2.3 Examining the reproduction of Paramecium. In groups discuss the types of reproduction in Paramecium. Draw the sequence of events that occurs during the reproduction of the species. Is paramecium important? Paramecium feeds on bacteria and algae; thereby they play significant role in the carbon cycle. These free living protists are in turn eaten by other protozoan and invertebrates, which in turn are eaten by other higher animals. As a result they are part of the food relationship among organisms in the ecosystem. Euglena What does a cell of euglena look–like? Euglena is an oval-shaped unicellular organism. It shows both plant and animal like features. The cell of euglena consists of cell membrane, nucleus, contractile vacuole, flagellum, eye spot (stigma) and chloroplast.  32 Biology Grade 8 Key Terms flagellum 55Flagellum: slender whip-like stigma structure used for movement in water, to swim. 55Eye spot (stigma): light sensitive nucleolus nucleus structure usually found behind the flagellum. 55Chloroplast: part of a plant cell chloroplasl that contains chlorophyll and in contractile vacuole which photosynthesis takes place. pellicle 55Preying: a process of hunting and feeding. Figure 2.9: Euglena and its cellular parts Where does an euglena live? Euglena is living in freshwater habitats such as ditches and ponds, especially those contaminated by urine and feces. How does an euglena move? Euglena moves by propelling its flagellum. When the long flagellum rotates, the euglena is able to move in a wave- like motion in the direction it wants to go. How does an euglena feed? Because of the presence of chloroplast, euglena can prepare its own food using sun light. In the absence of light it can feed by preying. How does an euglena reproduce? Euglena are capable of reproducing asexually only. The type of asexual reproduction is binary fission that involves the division of the nucleus and the length wise division of the cytoplasm to produce new daughters of Euglena. Is an euglena important? Did You Know? Euglena lives in freshwater habitats especially ¸¸Euglena like an animal ingests its food in those contaminated by urine and feces. In the and like plants it photosynthesizes. absence of light euglena feed on bacteria; and ¸¸Euglenas are unique unicellular or in the presence of light they photosynthesize. single-celled organisms with both These characteristic give them especial place in plant and animal features. the ecosystem. They serve as primary producers in the presence of light and as heterotrophs in the absence of light. As a result they play important role in the food relationship among organisms in the ecosystem.  Unit 2: Cell Biology 33 Activity 2.4 Examining the movement of Euglena under the microscope. Materials you will require 55 Compound light microscope 55 Slides and cover slip, 55 Dropper, 55 Standing water or hay infusion. Procedures 1 On a clean slide add a drop of hay infusion and cover it with a cover slip. 2 Observe your sample first under the lower power and then observe it under the medium power. 3 Draw what you observe and compare it with the picture of amoeba in Figure 2.9. 55 Have you seen Euglena? 55 How do you differentiate Euglena from Paramecium? Bacteria What are bacteria? Bacteria are very small, unicellular organisms that have nuclear material, but without distinct Did You Know? nucleus. They have cellular structure such as cell ¸¸Bacteria are prokaryotic organisms. Prokaryotes are organisms in which wall, cell membrane, nuclear material (nucleoid), their nuclear material is not enclosed cytoplasm, slime envelope and flagellum (see within a nuclear membrane. Figure 2.10). ¸¸Since bacteria are very small, I µm Nucleoid Capsule (0.001 mm), it takes more than one million of them to cover a pinhead. plasma Cell Flagellum membrane wall Figure 2.10: A generalized bacterial cell.  34 Biology Grade 8 Activity 2.5 Library research in different shapes of bacteria. Go to the library and investigate the major shapes of bacteria. Together with the major shapes among bacteria give one or two representative examples for each shape. Submit your report to your teacher. Where do bacteria live? Bacteria are found in a wide variety of habitat, almost everywhere. They are found in air, water, soil, and in or on the body of other living things. Bacteria can exist in single, in pairs or in chains. Bacteria are so small that they can normally be seen only through a powerful microscope by experts working in a laboratory. Because bacteria are so small, the experts grow them in the laboratory until there are many of them. These groups or pile of bacteria are called colonies (Figure 2.11). What do bacteria feed on? Because of their existence in a wide range of habitats, they show different types of feeding. Some bacteria are photosynthetic and are able to make their own food using sun light or inorganic substances. Other types of bacteria feed by decomposing organic matters. The remaining others absorb materials from their hosts being parasites. Figure 2.11: Bacterial colonies on a plate. How do bacteria reproduce? Bacteria reproduce asexually by binary fission which involves the division of the nuclear materials within the nucleoid. During binary fission the cell stops moving, and then the genetic material divides. Following this, the cytoplasm divide and finally two bacterial daughter cells will be formed. How do bacteria move? Some bacteria are able to move by means of their flagella. These flagella when they rotate cause the bacteria to move forward. Are bacteria important to us? Bacteria are important in many aspects. Some bacteria are useful to us like in making food (yoghurt [ergo] and cheese [ayib]) and to make medicine. As photosynthetic organisms they provide food for other organisms. Being decomposers they supply nutrients in a cyclic way.  Unit 2: Cell Biology 35 Some bacteria are harmful and spoil our food. They make it go rotten hence taste and smell bad. Moreover they cause diseases to plants and animals. For instance, they can cause diseases such as cholera, pneumonia, typhoid, and syphilis in humans. Activity 2.6 Library study on some human bacterial diseases. Go to the library and investigate the bacterial agents responsible to cholera, pneumonia, tuberculosis, typhoid, and syphilis. In your investigation include the ways of transmission and major control methods. Yeast What does a yeast cell look-like? Yeast is an oval unicellular microscopic fungus. The yeast cell is composed of cell membrane, nucleus and cytoplasm (Figure 2.12). Cell wall Key Terms Nucleus Cytoplasm 55Fungi: organisms that include yeasts and moulds. They have cell wall like plants, but unlike plants and animals they obtain their foods Chromosome through absorption. Plasma membrane 55Fermentation: biochemical process during which raw food material (like teff flour and water) is Figure 2.12: A yeast cell. converted into fermented products (like fermented teff dough, beer, wine, tella). Where do yeasts live? 55Fermented dough: biochemical conversion of thick malleable Yeasts are found normally on the skin surface mixture of flour and liquid , which of fruits such as grapes and also in fermented is going to be baked into bread, pastry or enjerra dough (enjerra dough) and other local fermented products like tella and tej. Yeasts are also found on the skin surfaces and in the intestinal tracts of warm-blooded animals. What do yeasts feed on? Yeasts commonly feed on sugary materials present in fruits and grains. When they feed on sugar or glucose, in the absence of oxygen they convert it into alcohol (ethanol) and carbon dioxide (Figure 2.13). This process is known as fermentation.  36 Biology Grade 8 Glucose Ethanol + CO2 Figure 2.13: Equation showing ethanol and CO2 production from glucose. How do yeasts reproduce? A yeast cell reproduces asexually by budding (Figure. 2.14). When a yeast cell reaches full size and matures, its nucleus divides into two nuclei. Then an outgrowth starts forming on one side as a bud. Then one of the nuclei migrates into the growing bud. Finally the bud Key Terms detaches itself from the parent cell and becomes 55Budding: an asexual process of a new yeast cell. reproduction in yeasts by forming an outgrowth, a bud. 55Bud: an outgrowth from a mother yeast that finally separate and form a new individual. 55Biofuel: fuel directly produced from living things. Figure 2.14: Budding yeast Activity 2.7 Looking at yeast cells under the microscope. Materials you require: 55 overnight grown yeast culture 55 eye droppers 55 compound microscopes 55 clean slides and cover slips Procedures: 1 To a clean slide add a drop of yeast and cover it with a cover slip. 2 Observe your sample first under the low power and then observe it under the medium power. 3 Draw what you observe and compare it with picture of budding yeast in Figure 2.13. 55 Have you observed a budding yeast?  Unit 2: Cell Biology 37 Are yeasts important? Yeasts are the most important members of Fungi that are used for industrial production of food and alcohol drinks. The ethanol produced during yeast fermentation (Figure 2.14) is important for the alcohol and taste beer, wine, tella and tej. Moreover, the ethanol produced serves as a biofuel. The CO2 produced by yeast cells during fermentation of dough is important for the rising of bread (including Diffo dabo) and enjerra. Activity 2.8 Discussion on unicellular organisms. In groups compare and contrast the unicellular organisms you have discussed so far. Present your report to the class. Exercise 2.2 Choose the best answer for each of the following questions. 1 Amoeba does not have a definite A nucleus B shape C contractile vacuole D A and B 2 Paramecium is identified by its A macro and micronuclei B flagellum and oral groove C slipper-like shape D A and C 3 Like a plant cell, euglena has A chloroplast C eye spot B flagellum D A and B 4 All bacterial cells are without A cell walls C cell membranes B nucleus D flagella 5 A yeast cell does not A make its own food C have nucleus B feed sugar D reproduce  38 Biology Grade 8 2.3 Levels Cellular Organization of in Multicellular Organisms By the end of this section, you will be able to: ”” name different types of cells; ”” state the functions of different types of cells; ”” name some plant and animal tissues; ”” state the functions of some plant and animal tissues; ”” name some plant and animal organs; ”” state the functions of some plant and animal organs; ”” name some plant and animal systems; ”” state the functions of some plant and animal systems; ”” describe organism as the highest level of organization in multi- cellular organisms. What are the different types of cells in multicellular organisms? In the previous section you have learnt that all organisms are made up of small structural and D Y id ou now K ? functional units known as cells. All cells have ¸¸All multicellular organisms start as a basic similarities. On the basis of number of single cell in their life cycle.. cells they are made from, organisms are categorized as unicellular and multicellular organisms. Organisms that are composed of one Key Terms cell are known as unicellular organisms. These 55Unicellular organisms: organisms that are made up of one cells that organisms are usually smaller in size, and are include organisms like amoeba, simple types. Multicellular organisms are paramecium, euglena and others. composed of many cells. Plants, animals and 55Multicellular organisms: organisms some fungi are multicellular organisms. In these that are made up of many cells that include organisms like plants and organisms, there are different types of cells that animals. vary in their shapes, sizes and functions. What types of cells are found in plants? Plants are multicellular organisms. A plant body is made up of many and different types of cells. For example, types of cells in different parts of a plant body include leaf epidermal cells; leaf palisade cells; and root tip cells. These different types of cells have different functions. Leaf epidermal cells cover the upper and lower surfaces of a leaf (Figure 2.15).  Unit 2: Cell Biology 39 The leaf epidermis protects the internal part of the leaf from any mechanical damage. The Key Terms leaf palisade cells are found below the upper 55Leaf epidermal cells: are flat cells that are found on the upper and epidermal layer. As their name is indicating, the lower surface of leaves. root tips cells are found at the tip of plant roots. 55Leaf palisade cells: type of cells that are located just below the upper epidermis and contain large number of chloroplast. Due to the presence of chloroplast they are sites at which photosynthesis is taking place in plants. 55Root tip cells: these are cells that are found at the tip of roots. Activity 2.9 Identifying different types of plant cells In groups, list down different types of plant cells and give their possible functions to the plant. Present your report to the class. root hair zone Upper epdermis Palisade cell opening for CO2 lower epidermis to enter leaf root cap a. Root tips b. Leaf cross section Figure 2.15: Different types of plant cells What types of cells are present in the body of animals? Animals including humans are made up of many cells, and are known as multicellular organisms. There are different types of cells in human body. The cells that form our body include skin cells, nerve cells, muscle cells, blood cells, sperm cells, ova (egg cells) and others (Figure 2.16). These cells vary in their shapes and sizes. In addition to variations of these cells in their shapes and sizes, they also differ in their functions.  40 Biology Grade 8 Activity 2.10 Observing prepared slides under microscope Key Terms Material you will require: 55Muscle cells: cells that are pointed at both ends and form the muscles ”” prepared slides of different of the body. Due to their ability to animal cells (skin cells, nerve contract and relax, they play role in moving body parts or the whole cells, blood cells, muscle cells, body. and others) 55Nerve cells: long and branched cells ”” compound light microscope that are involved in transmitting nerve message in the body. Procedures: 55Blood cells: circular cells that are 1 Observe each prepared slide first involved in transporting oxygen under low power and then under and carbon dioxide; and defending medium power. the body from disease causing organisms. 2 Draw what you have observed and 55Skin cells: flat and thin cells that compare it with pictures in Figure 2.16. cover our body. ”” Have you observed differences 55Sperm cells: male reproductive cells that are involved in fertilizing female among the cells? reproductive cells and initiate the ”” What type of variations have process of reproduction. you observed? 55Egg cells (ova): female reproductive cells that are fertilized by male ”” What do you think is the reason reproductive cells during the for these variations among cells process of reproduction. of multicellular organisms? A. skin cells B. blood cells C. muscle cells dendrite axon Cell body ending D. Egg cell (ovum) axon E. sperm cell F. nerve cell Figure 2.16: Different types of human body cells  Unit 2: Cell Biology 41 Tissues What are tissues? Multicellular organisms are made up of many cells and have different type of cells that are Key Terms specialized to perform various functions. In 55Tissue: a group of cells that have the fact, they are not simply a collection of many same shape and size which carry out the same function. cells. Rather, cells in the body of multicellular 55Epithelial tissue: a tissue made organisms are organized at different levels up of cells that cover the external of functional groups. A group of cells that is surfaces of the body (the skin) and similar in shape, size and that carries out the lining the surfaces of the structures like mouth, heart, liver and eyes. same function is called a tissue. 55Muscle tissue: a tissue made up of a group of muscle cells and forms the muscle that are found at different parts of the body. What are the types of plant tissue? 55Blood tissue: a tissue which is made of blood cells and fluid that fills the Plants are one group of multicellular organisms. space in blood vessels tub. In plants, cells with the same structure and 55Nervous tissue: a tissue which is made of a group of nerve cells that performing similar function are organized as form the brain, spinal chord, and the tissue. Tissues in plants include epidermal peripheral nervous system. tissue, conducting tissue, photosynthetic tissue (mesophyll tissue) and strengthen tissue (Figure 2.17). Activity 2.11 Identify tissues in plants In groups, identify tissues that are found in plants, specify their locations and give their functions. Submit a written summary of your discussion to your teacher.  42 Biology Grade 8 intrcellular spaces cell walls Upper epidermis vascular tissue }photosynthetic tissue Lower epidermis a. Photosynthetic tissues b. Parenchyma c. Collenchymas water and food cell walls with lignin one way only water and stone cell minerals no end walls between cells fiber lumen xylem vessel phloem vessel e. Sclerenchyma d. Conducting tissue (xylem and phloem) Figure 2.17: Different types of tissues in plants. What are the types of animal tissues? Key Terms Similar to plants, in animals including humans a group of similar cells that performs the same 55Epidermal tissue: a tissue found at the external surfaces of plant function is organized as a tissue. Generally, bodies. The tissue is involved in there are four basic types of tissue in the body protecting the plant surface from of human. The four basic tissue types of a external damage, it involves in gas exchange, and reducing water loss human body are epithelial tissue, muscle tissue, from the body of the plant. connective tissue, and nervous tissue. Blood is 55Conducting tissue: a tissue made an example of connective tissue. Connective up of cells that transport water, tissue is a type of tissue characterized by few photosynthetic product and mineral in the plant body. It is made up cells separated by space and large amount of of mainly from xylem (water and extracellular material (Figure 2.18). mineral transporting cells) and phloem (food transporting cells). 55Photosynthetic tissue (mesophyll tissue): a tissue found in plant leaves that contains chloroplasts and is involved in the process of photosynthesis. 55Strengthen tissue: a tissue which is made up of cells with thick-wall and is involved in providing mechanical strength to the body of a plant.  Unit 2: Cell Biology 43 a. connective tissue c. epithelial tissue b.muscle tissue d.nervous tissue Figure 2.18: Different types of tissues found in the body of animals including human. Activity 2.12 Discussion on types of tissues in human body In groups, identify different types of tissues that are found in human body and specify their functions. Present the summary of your discussion to your class. Organs Key Terms 55Organ: a functional unit which is made up of different types of tissues What are Organs? that work together. 55Leaf: an organ found in the body In the body of multicellular organisms different of plants. It is made up of different tissues are grouped together to form structural tissues and mainly carries out photosynthesis, transpiration and and functional unit known as an organ. An gaseous exchange. organ is made up of different types of tissue that 55Stem: an organ found in the body of work together to achieve one or more functions plants. It consists of different tissues within the organism. and mainly involved in supporting the aboveground part of the plant. It is also involved in transporting What organs are there in plants? photosynthetic product, water and mineral in the plant body. A plant body is made up of different tissues 55Root: an organ found in the body of that are organized into functional units known plants. It contains different tissues and mainly anchors the plant as organs. In plants stems, leaves, flowers, into the soil. It absorbs water and and roots are all organs (Figure 2.19). These minerals from the soil and transports organs are made of different types of tissues them up to the aboveground part of the plant. and perform specified function or functions. 55Flower: an organ found in the body For instance, leaf is an organ which is made of flowering plants. It is made up of of tissues like epidermal, photosynthetic, and different tissues and is involved in conducting tissues. sexual reproduction of flowering plants.  44 Biology Grade 8 flower stem shoot system leaves roots root system Figure 2.19: The major organs and organ systems of plants What organs are there in animals? Different tissues are organized to form larger structures, such as the skin, stomach, eye, lung, Key Terms ear and heart in the body of animals including 55Brain: an organ found in the body humans (Figure 2.20). These structures are of animals. It is made up of different called organs. For example the heart is an organ, types of tissues. It coordinates and controls overall activities of the which contains cardiac muscle, connective animal body. tissue, epithelial tissue and nerve tissue. Other 55Heart: an organ found in the body organs found in a human body include the skin, of animals. It contains different types of tissues and pumps blood to stomach, brain, lungs, intestines, eyes, liver and different parts of the body. others. 55Stomach: an organ found in the body of animals. It consists of different types of tissues and is involved in the digestion of food substances ingested by the animal. 55Lung: an organ found commonly in animals. It is made up of different a. Brain b. heart types of tissues and mainly involved in breathing process. 55Eye: an organ found in the body of animals. It is made up of different types of tissues and involved in visual process. 55Ear: an organ found commonly in c. Stomach d. Lung animals. It contains different types of tissues and mainly involved in hearing process. e. Eye f. Ear Figure 2.20: Some of the organs of our body  Unit 2: Cell Biology 45 Activity 2.13 Observing plant and animal organs. In groups, 55 collect plants (small-sized) identify their organs, and specify the types of the tissues that each organ is made from. 55 jot down different organs of the human body and specify their major functions. 55 present your summary to the class. Organ System What are systems? Organs never work alone. Two or more organs work together to perform certain task and form an organ system or a biological system. An organ system is a biological system in which different organs are coordinated to perform major activities of the body. What are the types of systems in plants