Biology Student Textbook Grade 7 PDF

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This will keep the cover in good condition.  BIOLOGY STUDENT TEXTBOOK GRADE 7 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 978-99944-2-261-6  Content Unit 1: Biology and Technology 1 1.1 What is biology? 3 1.2 Industries that Utilize Biological Knowledge 5 1.3 The elevance of Biology to Society 10 1.4 Biology and Technological Innovations 18 1.5 Values in Biology Education 20 hh Unit summary 22 hh Review Exercise for Unit 1 23 Unit 2: Cell Biology 25 2.1 Microscope and its Uses 26 2.2 The Cell 32 2.3 Looking at cells 37 2.4 Cell type, shape and size 42 hh Unit summary 45 hh Review Exercise for Unit 2 45 Unit 3: Human Biology and Health 49 3.1 The Muscular and Skeletal System 50 3.2 Human Dentition 62 hh Unit summary 66 hh Review Exercise for Unit 3 67 IV C o n t e n t Unit 4: Plants 69 4.1 Diversity of plants 71 4.2 Flowering plants 74 hh Unit summary 96 hh Review Exercise for Unit 4 97 Unit 5: Animals 99 5.1 Diversity of Animals 100 5.2 Life histories of some insects 103 5.3 Some economically important insects 107 5.4 Social insects 111 hh Unit summary 122 hh Review Exercise for Unit 5 123 Unit 6: Environment 127 6.1 Habitats 128 6.2 Studying a habitat 133 6.3 Food relationships 139 hh Unit summary 145 hh Review Exercise for Unit 6 146  Unit Biology and 1 Technology Unit Outcomes By the end of this unit, you will be able to: ”” define biology as the study of life; ”” list the branches of biology; ”” state what each of these branches of biology studies about; ”” indicate that all natural sciences are interrelated; Main Contents ”” describe how biological knowledge is 1.1 What is biology? utilized in the fields of agriculture, 1.2 Industries that Utilize medicine and food science; Biological Knowledge ”” explain the relevance of biology to the 1.3 Relevance of Biology to society; Society 1.4 Biology and Technological ”” give examples of technological Innovations innovations derived from biological 1.5 Values in Biology Education knowledge; ŒŒ Unit Review ”” identify values developed in learning science to maintain a more proactive and environmentally conscious population.  2 Biology Grade 7 Introduction In your earlier grades you have studied science, which dealt with all living and non-living things in nature in an integrated form. Science is a systematic method of gaining knowledge about the natural world and the social aspect of human society. Generally, it is divided as social and natural sciences as shown in Figure 1.1. The study of natural science is divided into three major subject areas as Biology, Chemistry and Physics. Which of your Grade 5 and 6 topics were about living things? The survival and well-being of humans largely depend upon knowledge of living things, and their interactions among themselves and with their environment. Science Did You Know? Social Science Natural Science Social science deals with how people think, behave and act; whereas natural science Physics Biology studies about natural things. Chemistry Figure 1.1: Classification of science Do biology and technology interrelate? Biology is a branch of science by which living things Key Terms are studied. On the other hand, technology is the science 55Science: a systematic way of or technique that develops machines, hardware or getting knowledge through instruments used by humans. observation and experimentation so as to understand nature. Biology helps the society in many different aspects, like 55Living things: are organisms which show the properties of life. in medicine, agriculture, environment and population 55Life: is the characteristics of control. For biology to effectively serve the society it organisms that make them alive; it includes characteristics like requires materials and instruments from technological growing, reproducing, sensitivity innovations. to stimuli, metabolizing, and moving by their own. As biology requires the knowledge of technological innovations; so does technology; that is, technology needs the understanding of living systems for its further improvement and progress of techniques to better serve the society. In this unit, you will start studying one branch of natural science known as Biology. You will describe biology as a part of science. You will also identify branches of biology, its relationship with other sciences, its application and relevance to society.  Unit 1: Biology and Technology 3 1.1 What is biology? By the end of this section, you will be able to: ”” define biology as the study of life; Did You Know? ”” list the branches of biology; ¸¸Living organisms range from the smallest ”” state what each of these branches of bacteria to the biggest whale. biology studies about; and ¸¸The smallest bacteria which is the smallest organism is less than 1 micron ”” indicate that all natural sciences (one-millionth of a meter) in diameter. are interrelated. Can you define biology? Biology is the study of living things. Biologists are Word Roots and Origins people who study biology or about living things. Living things range from tiny organisms like bacteria Biology: came from two Greek words ‘bios’ to very large organisms, such as whales, elephants meaning life, and ‘logos’ meaning study. and big trees. Branches of Biology Can you list down branches of biology? Biology is the science that studies about various living Key Terms organisms. A living organism could be a one-celled bacteria or a several-celled organism such as animal 55Biologists: are people who study living things. or plant. Although there are many branches of biology, each focused on different aspects of living things. The three main branches, are shown in Figure 1.2: Zoology (animals), Botany (plants), and Microbiology (microorganisms). See Table 1.1 for some of the major sub-branches of biology and their definitions. Biology Botany Zoology Microbiology Figure 1.2 Classification of Biology based on major groups of organisms it studies  4 Biology Grade 7 Table 1.1: Sub-disciplines in biological sciences Sub discipline Description Botany The scientific study of plants. Cytology The study of cells. Ecology The study of relationships between organisms, and their environment. Evolution The study of the origin and gradual change of organisms in time. Genetics The study of heredity and identity. Microbiology The study of microscopic organisms (micro-organisms). Physiology The biological study of the functions of living organisms and their parts. Taxonomy The science of identification, classification and naming of organisms. Zoology The study of animals. Activity 1.1 Searching for other branches of biology 55 Go to your school library. 55 Find out other branches of biology Present your findings: what do the branches study? The Relationship of Biology with Other Sciences Is biology related to other fields of science? Biology requires knowledge from Geography other fields of science to understand about processes in living things. These overlaps in the study areas of Chemistry Biology Physics biology and other sciences resulted in interdisciplinary studies. The body of living things is composed of Mathematics chemical substances. Understanding Figure 1.3: Overlap of biology with other reactions in living organisms and fields their physical activities needs knowledge of chemistry and physics (Figure 1.3). The overlap of biology with chemistry, for example, forms biochemistry.  Unit 1: Biology and Technology 5 Exercise 1.1 Choose the best answer for each of the following. 1 The word biology is derived from A Two Latin words – bios and logos B Two English words – bio and logos C Two Greek words – bios and logos D Two Greek words – bio and logy 2 Which one of the following is not true about biology: It studies A about all living things B about life C the interaction between organisms D about non-living things 3 The branch of biology that studies about plants is A Zoology C Ecology B Botany D Taxonomy 4 One of the following field of biology examines organisms not seen by unaided eyes? A Taxonomy C Genetics B Microbiology D Ecology 5 The branch of biology which studies animals is known as A Botany C Zoology B Cytology D Micro biology 1.2 Industries that Utilize Biological Knowledge By the end of this section, you will be able to: ”” describe how biological knowledge is utilized in the fields of agriculture, medicine and food science. Knowledge from all branches of biology are utilized directly or indirectly in different areas of human activities. These include agriculture, medicine, and the food industry. In general, the application of biological knowledge and techniques are necessary to the improvements in the quality of life as well as the economic benefits they generate.  6 Biology Grade 7 Agriculture How is biological knowledge utilized in agriculture? Agriculture is one of the human activities to which biological knowledge and skills are very essential. Agricultural practices include cultivation of soil, growing and harvesting crops, breeding and raising livestock, forestry, etc. (see Figure 1.4a−d) for the illustration of some of the terminologies used here. Figure 1.4 Different agricultural activities. a) spraying pesticide to crop plantation, b) crop plantation, c) dairy cow and d) plowing with oxen. Is biological knowledge important to study plant nutrients? Did You Know? Plants require different factors for their growth. These ¸¸Plants use essential nutrients which are include temperature, inorganic nutrients, water, light, available in the soil. and air. Plants obtain substances such as inorganic ¸¸Primary nutrients include nitrogen, potassium nutrients and water from the soil. Therefore, biological and phosphorous. knowledge is essential to understand the role of ¸¸Soil is a non-renewable natural resource which is composed of minerals, water, nutrients in plant growth. organic matter and living organisms including microorganisms and worms. ¸¸The top soil that contains much of the organic Is biological knowledge necessary to matter is the fertile layer of a soil. study soil composition? ¸¸Different soil conservation practices (vegetation Soil plays a major role in determining the kinds covering, avoiding overgrazing, exercising good farming practice, etc.) protect the top of plants that grow on it. Biologists study growth soil from being easily eroded out. requirement of crops, analyze soil composition and ¸¸Inorganic nutrients include major soil design ways of increasing productivity. nutrients like nitrogen, phosphorus, calcium, potassium, magnesium and sulfur.  Unit 1: Biology and Technology 7 Is biological knowledge necessary to study agro-chemicals ? Biological knowledge is used to increase productivity of crops in many ways. Agricultural industries use agro-chemicals like fertilizers, herbicides (weed-killers), and pesticides to increase productivity. See different types of agro-chemicals in Figure 1.5. Biological knowledge is utilized for the preparation and use of the right quantities and qualities of agrochemicals. Key Terms a) 55Fertilizer: a chemical or natural substance added to soil to increase its fertility. 55Pesticide: a substance used for destroying insects or other pests of plants or animals. 55Herbicide: a chemical substance used to destroy unwanted vegetation or weeds from farming sites. Figure 1.5: Agrochemicals used by large farms in Ethiopia: a)atrazine (herbicide), b)acetochlor herbicide, b) c) d) c)hand spray and d)claearys 3336F (fungicide) Does crop rotation practice require biological knowledge? Crop rotation consists of growing different crops in succession on the same land. For instance, a farmer can possibly rotate corn, bean and teff in succession. The rotation of crops helps to reduce the effect of pests and keep the soil fertile; moreover, it increases the yield. Does preservation of soil require biological knowledge? Poor agricultural practices like overgrazing, burning the vegetation cover, over fertilizing, and vertical ploughing of steep land reduce soil fertility. So, protecting the top surface of the soil from effects, such as erosion, is very important in agriculture. Medicine How is biological knowledge and skill utilized in medicine? Medicine is the science and art of diagnosing, treating Word Roots and Origins and preventing disease and injury. Medical scientists engage themselves in a constant search for new drugs, Medicine from a Latin word ‘medicus’ which effective treatments, and more advanced technology. means physician. Biology is one of the central foundations for knowledge and techniques in medicine.  8 Biology Grade 7 Does the study of effect and use of drugs require biological knowledge? Biological knowledge and skills are found to be important to analyze the effects of drugs on human body. A drug is a medicine or any substance which has a marked physiological effect when taken into or applied on the body. Antibiotics (Greek anti, “against”; bios, “life”) are chemical compounds used to kill or inhibit the growth Did You Know? of bacteria. All antibiotics share the property of Tobacco smoke contains about 4000 chemicals; selective toxicity: They are more toxic to an invading one of which is nicotine and it stimulates nerves organism than to an animal or human host. These and makes the heart beat faster. drugs are used to fight diseases. Does the practice of correcting drug abuse require biological knowledge? Drug abuse is a pattern of using a substance that leads to significant problems or distress. It can be taking more than the recommended dose of prescribed drugs such as stimulants or depressants without medical supervision and it can also be taking antibiotics without prescription. The major drug abuse, however, is illegally using substances like marijuana, cocaine, heroin, or other illegal substances that are not allowed by governments. Food How is the biological knowledge utilized in food industries? Food production and processing industries utilize biological knowledge and skills to produce good quality food and to keep it safe and longer. Food is anything nutritious and taken into the body in order to maintain life. Food is made up of compounds known as nutrients, which can be used by organisms after the process of digestion. Biological knowledge is needed to know the end products of digestion, absorption and utilization by our body. Food producing and processing industries utilize biological knowledge and skills to provide safe and quality foods. Does the understanding of deficiency diseases require biological knowledge? The food we eat should contain the nutrients in a balanced proportion. The increase or decrease of nutrients in the diet causes diseases. Deficiency diseases are diseases caused by a lack of nutrients in the diet. See Table 1.2 for some of the deficiency diseases that result due to lack of minerals, vitamins or other nutrients in the diet of a person. See also Figure 1.6 for the effect of some of the deficiency diseases.  Unit 1: Biology and Technology 9 Table 1.2 Lack of nutrients in diet and their associated deficiency diseases Deficient Nutrient Deficiency disease Iodine Goiter Iron Anemia Vitamin A Night blindness Vitamin B (thiamine) Beriberi Vitamin B (niacin) Pellagra Vitamin D Rickets Vitamin C Scurvy Carbohydrate Marasmus Protein Kwashiorkor a) Rickets b) Kwashiorkor c) Marasmus Figure 1.6 Effects of lack of nutrients in the food Does the study of agro-chemical residues on / in food need biological knowledge? Agro-chemical is a general name given to those chemicals used commonly during agricultural practices and these include fertilizers and pesticides. These chemicals have been used for long to increase productivity in agriculture. However, most of the chemicals used remain as residues on plants and can cause health problems when consumed by people. Furthermore, when plants with chemical residues are consumed by other animals and when the animals are eaten by people, the concentration of the chemical increases several times and cause more serious health problems. Does the practice of selective breeding require biological knowledge? Selective breeding is a practice of controlled mating in plants and animals. It is done to produce organisms that better serve human needs. It is a technique by which offspring are made to have superior quality (high yield, disease resistant, drought tolerant, etc.) to that found in either parent. Exercise 1.2 Choose the best answer among the given alternatives. 1 One of the following aspects of agriculture does not need biological knowledge? A studying requirements for plant growth B preservation of soil C the use of a tractor D the use of manure 10 Biology Grade 7 2 Antibiotics are drugs used to A reduce pain C cure disease B avoid infection D prevent diseases 3 Drug abuse is the use of A drugs to fight diseases B drugs to reduce pain C drugs with out the order of doctors D drugs with the order of doctors 4 Deficiency diseases are caused by a lack of A lack of agro-chemicals in food C lack of drugs B lack of balanced diet D A and B 5 Biology is useful in food industries to improve A quality of food C preservation of food B safety of food D all of the above 1.3 The Relevance of Biology to Society By the end of this section, you will be able to: ”” explain the relevance of biology to society. Biology contributes to society in many different ways. Biologists use their knowledge of organisms and their Did You Know? interaction to make contributions in medicine, Acid rain or acid deposition, is air pollution agriculture, nutrition, population control, conservation from burning fossil fuels. Fossil fuel burning and many other industries. Biotechnology is the applied releases large amounts of acid chemicals that branch of biology that uses living organisms and rain down as acids. bioprocesses in engineering, technology, medicine, agriculture, and environment. Health Is biology relevant to study drugs that combat diseases in our body? Biology is involved in understanding the human body Key Terms and describes its normal and abnormal conditions. All professionals in medicine study biology. The study of 55Disinfectant: a substance used for destroying germs from non- biology is necessary to understand the normal body living surfaces. processing, cause of diseases, methods of prevention, to identify the causes of diseases, and to develop drugs.  Unit 1: Biology and Technology 11 Drugs are used to fight diseases by curing sick people or Word Roots and Origins by preventing diseases before they occur. Some people may use drugs without the instruction of physicians Antibiotics: from two Greek words ‘anti’ or illegally. The use of drugs illegally or too much of meaning against and ‘bios’ meaning life. instructed drugs is known as drug abuse. The knowledge and techniques in biology are useful to discover drugs (antibiotics), analyze their interaction with the body, and their action against disease causing organisms. Antibiotics have the property of magic effects. Drugs like penicillin is a well-known antibiotic that has been used to fight many infectious diseases, including syphilis, gonorrhea, and tetanus. Is biology relevant to characterize effects of antiseptics and disinfectants? Antiseptics and disinfectants are antimicrobial chemical substances, which reduce potential germs. Antiseptics D Y id ou now K ? are antimicrobial substances that destroy potential ¸¸Antibiotics are chemicals used to kill germs. Disinfectants are chemical substances that are disease causing bacteria. used to destroy microorganisms that contaminated nonliving objects. These chemical substances are necessary for us to keep our places free of potential germs. The preparation and testing the effects of these chemical substances against potential germs require the knowledge of biology. Is biology relevant to describe the healthy status of an individual? Biology is involved in analyzing the human body and describes its normal and abnormal conditions. Healthy people are those people whose body parts properly work, have good mental status and interact with other people properly. Unhealthy people are those either their body parts, mental condition or interaction with other people is affected in a negative way, or all of them are affected. Analyzing the body weight of and describing the health status of an individual requires knowledge of biology. Nutrition Is biology relevant to nutrition? Nutrition is a branch of biology that studies different aspects of food we eat. The studies in nutrition include how organisms obtain food, digest it, its composition and its uses to the body of an organism. Biologists study foods and their contents. We depend on biological knowledge to analyze nutrition and its health impacts. Our body requires food to grow, reproduce, and maintain good health. Without food, our bodies could not stay warm, build or repair tissue, or maintain a heartbeat. Eating the right foods can help us avoid certain diseases or recover faster when we are ill. These and other important functions of our body are fueled by chemical substances in our food called nutrients. Nutrients are classified as carbohydrates, proteins, fats, vitamins, minerals, and water. 12 Biology Grade 7 Is biology relevant to identify major groups of foods? All foods at least contain one of the six basic nutrients: carbohydrates, lipids, proteins, vitamins, mineral and water. Each nutrient plays a different role in keeping an organism healthy. Knowledge from biology is required to understand the composition food, digestion and function of food that is consumed by organisms. Techniques from biology are also required to test the presence and amount of these nutrients in the food. Fats and sweets Milk, yogurt Meat, chicken, and cheese fish and egg Fruits and vegetables Breads, grains and other starches Figure 1.7 The five major food groups Did You Know? Based on their function biologists classify foods The daily requirement of the five major food into five groups. These groups of food include meat groups are: and legumes, milk and cheese, fruits and vegetables, ¸¸Group A (milk and cheese) – 300-600 gm. bread and cereals, and fats and sweets (Figure 1.7). ¸¸Group B (fruit and vegetables) – Four Each group of food contains the six nutrients in servings (Example: 1 fruit is one serving). different proportions. So, the food that an individual ¸¸Group C (meat and legumes) – Two consumes should contain the five groups in a servings (Example: 55-85 gm of meat is one serving). balanced form as balanced diet. Knowledge of ¸¸Group D (bread and cereals) – Four biology is necessary to identify the major groups of servings (Example: 2 slices of bread is foods, their sources and workout the balanced diet one serving). an individual requires consuming. ¸¸Group E (fats and sweets) – in small amounts.  Unit 1: Biology and Technology 13 Activity 1.2 Constructing a balanced diet 1 Look at the picture (Figure 1.8) and classify the food components into nutrient groups. 2 In a group, list down food items in the food you had for your breakfast; from the list prepare a balanced diet combination Figure 1.8 Ethiopian dish and discuss with the other groups. Environment Is biology relevant to study environment? With growing population, rapid industrialization Key Terms and urbanization the use of all resources is rising. Bad farming practices and deforestation created 55Resource: any natural or artificial substance, energy or organism, additional problems as well. It is feared that unless which is used by human being for proper measures are taken to conserve them in time, living. we will face serious problems like loss of species and 55Environment: the surroundings or conditions in which organisms pollution of the environment. live and operate. 55Conservation: the proper Biologists study the environment, organisms and their management of a natural resource interaction. We rely on biological knowledge and to prevent its exploitation, destruction or degradation. skills not only to investigate environmental problems 55Biodiversity: variety of organisms but also to find their solutions. living at a given region. 55Deforestation: is clearing away of trees and vegetation that hold Is biology relevant to increase water and soil in place. agricultural productivity? 55Pollution: is contamination of the environment with materials Farming is a collection of activities done in an area that harm health, quality of of land and its buildings to grow crops and to rear life or the natural functioning of living organisms and their animals. The main activities in farming include surroundings. cultivation of soil, growing plants, and animal 55Population: all inhabitants of a husbandry practices. These practices can either be particular place. good (friendly) or bad (unfriendly) to the environment. Loss of top soil reduces the fertility of the soil and agricultural productivity. Biological knowledge is necessary to examine whether the farming practices techniques in biology can also be used to reduce problems associated with bad farming practices. 14 Biology Grade 7 The bad farming practices consist of: 55 cutting trees to get space of crop cultivation, 55 plowing horizontally steep lands, 55 monoculturing (growing a single crop in a given area year after year), 55 burning vegetation cover and 55 allowing overgrazing. Good farming practices, on the other hand, protect the soil from erosion and increase agricultural productivity of the land. The good farming practices contain: 55 planting trees, 55 contour farming (farming step land horizontally), 55 terracing, 55 crop rotation, 55 reduce overgrazing. 55 manuring or using fertilizer If good farming practices are not used and soil erosion is allowed to continue at its current rate in Ethiopia, it will lead to continuous loss of the top fertile soil. Knowledge and techniques in biology are needed to reduce soil erosion and conserve the top fertile soil. Conserving the top fertile soil is important to increase agricultural productivity. Is biology relevant to conserve natural resources? Conservation is the wise use and protection of the environment. The environment consists of natural resources including plants, animals, minerals, soils, water air and fossil fuels. The environment is conserved for its biological, economic, and recreational value, as well as its natural beauty and importance for survival of human beings. In general, conservation of natural resources requires understanding of basic biological concepts. Therefore, the conservation of natural resources requires knowledge from biology. The way in which one natural resource is managed has a direct effect upon other natural resources. For instance, cutting a forest near a river increases erosion, loss of top soil, and can lead to flooding. Appropriate conservation methods are used to conserve different natural resources. These include reducing planting trees, practicing good farming activities like terracing (Figure 1.9a), reusing or recycling natural resources, and protecting or preserving when necessary. The actual practices of these conservation activities require biological knowledge. Is biology relevant to control the effect of deforestation? Deforestation is a human activity that leads to removing plant cover from a given land for agricultural, firewood or settlement purposes (Figure 1.9b). These practices expose the soil and lead to loss of top soil due to wind erosion and water erosion. On the other  Unit 1: Biology and Technology 15 hand, forestation or planting tree (Figure 1.9c) has many advantages like reducing soil erosion. Plants Did You Know? are also an important defense against global climate ¸¸The Ethiopian Red Fox is found at Simen and change. Forests produce life saving oxygen and Bale Mountains. It is the most endangered consume carbon dioxide and reduce global warming. Fox with only about 550 adults remaining. Knowledge of biology is necessary to select and grow the appropriate plant suitable for a given area and to care as well for the growing plant. a) b) c) Figure 1.9 Good farming practices. a) Planting trees; b) Terracing; c) Crop rotation Is biology relevant to study the effects of atmospheric pollution? Pollution is contamination of the Library Research environment with materials that harm Go to the library and answer the following health, quality of life or the natural questions. functioning of living organisms and 1 List activities that you consider as their surroundings. Kinds of pollution harmful to the environment. include air (atmosphere), water and 2 Describe the importance of planting land pollution. Among the major trees and the effects of deforestation. sources of pollution are power and heat 3 List down the effects of population growth on the environment. generation, the burning of solid wastes, industrial processes, and, especially, transportation (Figure 1.10). Evaluation of the effects of pollution to human, other organisms and the environment requires knowledge from biology. The solution towards reducing the effect of practices that increases the rate of pollution needs an understanding of biological concepts. 16 Biology Grade 7 a) b) c) Figure 1.10 Sources of air pollution: a) Cars, b) Industries and c)Burning forest Activity 1.3 Discussion on harmful activities to the environment Method: in groups, ”” discuss and list activities that are harmful to the environment, ”” discuss and describe the importance of tree planting and effects of deforestation. ”” discuss the effects of population growth on the environment. ”” present your summary to the class. Population Is biology relevant to control growth of world population? A population refers to the total number of individuals of the same kind that are living in a specified space. Biologists commonly use the term population to refer to the number of the same kinds of animals, plants or other living things. But, most of the time, population refers to human beings. For instance human population means the number of humans living at a given area (such as in the village, town, city, country or the Earth). Since human population has a very strong effect on the environment than any other living things, here we will consider human population. The effects of population growth are different and vast. Population growth may be beneficial to a certain Did You Know? extent, like increasing labor force. But, there may ¸¸The prevalence of Female Genital Mutilation come a time when the number in the population (FGM) in Ethiopia is reported to be 62% exceeds the natural resources available to feed and between ages of 15-19, (estimates of house it. The consequences of such an event are Population Bureau, 2010 (2002 EC)). severe. Therefore, controlling the number of ¸¸In Ethiopia, 19% of girls were married by age population is necessary. Knowledge of biology is 15 (Population Council, July 2004 (1996 EC)). relevant in designing the activities that are used to control the number of population.  Unit 1: Biology and Technology 17 Is biology relevant to develop vaccine? Immunization is one of the most effective weapons available to combat the spread of infectious disease. Immunization is the process of making the body resistant or immune to a specific disease by using a vaccine. A vaccine is a chemical substance that stimulates the body to create antibodies to fight a specific disease causing organism. It is the process of safe and effective Figure 1.11 Immunization: A child use of a small amount of a weakened receiving a vaccine virus or bacteria to prevent infection (Figure 1.11). For instance vaccines developed to fight many infectious by biologists include tetanus vaccine, meningitis vaccine, small pox vaccine, polio vaccine, hepatitis vaccine and many others. Knowledge of biology is relevant to develop vaccine and to immunize the population against different communicable diseases. Is biology relevant to reduce the rate of harmful traditional practices in Ethiopia? Harmful cultural practices that are commonly practiced by many societies include female genital mutilation, early marriage, rape and illegal abortion. These traditional practices are common in Ethiopia. In Ethiopia it is possible to relate these practices to low level of education and poverty. Education as a whole and biology education in particular is relevant to reduce the extent of these harmful traditional practices. Exercise 1.3 Choose the best answers for the following questions. 1 Biology is relevant to society to ensure A over population C pollution B health D deforestation 2 Biology is important to solve social problems of A harmful traditional practices C recycling natural resources B poor diet D All of the above 3 Which of the following agricultural practices is harmful? A overgrazing C reforestation B crop rotation D contour farming 4 Which of the following can not be the effect of over population? A increasing famine C increasing stress B increasing poverty D increasing quality of life 18 Biology Grade 7 5 Tree planting reduces A oxygen production C soil fertility B global warming D CO2 consumption 1.4 Biology and Technological Innovations By the end of this section, you will be able to: ”” give examples of technological innovations derived from biological knowledge. From early times in history, humans have been studying other living things and tried D Y id ou now K ? to copy what they are doing. After observing New robotic cars avoid collisions by using sensors the processes and features in living systems based on bumble-bee’s compound eyes. humans tried to apply knowledge and biological principles to meet practical needs. Some of the discoveries made in the past were copied from the understandings of biological principles; these include the invention of camera, airplane and submarines. You can easily recognize how valuable the discoveries are and their importance in changing the living pattern of humans. Human Eye and Camera How is a camera related to a human eye? A human eye and a camera share a number of features. Both the retina film human eye and a camera are iris diaphragm composed of comparable parts, pupil aperture such as a lens, iris/diaphragm, lens lens pupil/aperture, retina/film and choroid black point choroid/black paint, which actually work in different ways. Refer to Figure 1.12 to observe Figure 1.12 A camera and a human eye the common parts that a human eye and a camera share. Activity 1.4 Look at Figure 1.12 and describe similarities and differences between a camera and a human eye in a tabular form.  Unit 1: Biology and Technology 19 Birds versus Airplane Key Terms 55Submarine: war-ship that moves underwater for a long Do birds and airplanes share features? period. The desire to fly dated back to the pre-historic period. Many stories from olden times involve flight, such as Did You Know? the Greek legend of Icarus and others. Long in history humans were attracted by the flying of birds, and they A number of anatomical, physiological and behavioral adaptations enabled birds to meet tried to fly like birds. Wings made of feathers or the requirements of flight. lightweight would be attached to arms to test their ability to fly. The results were often disastrous as the ¸¸Have hollow bones that reduce weight. muscles of the human arms are not strong like birds. ¸¸Have strong keel-shaped breast bone (sternum), to which the flight muscle is The first successful piloted flight with self-powered attached to. aircraft was done in 1903 by Orville Wright and Wilbur ¸¸Have feathers, which are light, and smoothly shaped body. Wright (Figure 1.13). ¸¸Have efficient four chambered heart. a) b) c) Figure 1.13 a) showing air lifting, b) an airplane, c) a bird flying Fish versus Submarine Do submarines relate to fish? The practice of human swimming has been known since prehistoric times. The earliest record of swimming dated back to Stone Age paintings from around 7,000 years a) ago. The first submarine appeared during the 19th century (Figure 1.14). Obviously, fish came earlier than the submarines, which are constructed by humans. Beyond doubt, humans tried copying the body plan, structures and functions of fish into submarines long ago. b) Figure 1.14 a)A swimming fish and b)Submarine 20 Biology Grade 7 Activity 1.5 Library reading. Go to your school library ”” in group, research on the study of Icarus. ”” research the early attempts made by people who worked under water in huge bells containing air. Exercise 1.4 Choose the best answers for the following questions. 1 Which of the following functions like our eyes? A microscope C camera B handlens D A and B 2 Which of the following is made possible by observing birds? A submarine C Car B an aeroplane D B and C 3 Which of the following machines moves like a millipede? A tank C train B excavator D A and B 4 A boat looks like a A duck C frog B tortoise D Lizard 5 A robot is analogous to A dog C human B monkey D cat 1.5 Values in Biology Education By the end of this section, you will be able to: ”” identify values developed in learning science; ”” maintain a more proactive environmentally conscious Did You Know? population. ¸¸Values in education are principles, rules or standards of behavior that are Both the theoretical and practical activities during realized in school life and afterwards. biology lessons will give you the opportunity to ¸¸Biology education similar to other develop different values. Biology, as an experimental science is intended to achieve the three science, involves activities like critical thinking, major educational objectives, which reasoning and problem solving. include the development of values, skill and knowledge.  Unit 1: Biology and Technology 21 Nowadays, biology education has Openness Cooperation received special attention due to its Curiosity Freedom rapid progress and its influence on our Value daily lives. Love Reasoning Honesty Respect Biology raises a wide range of issues (for Tolerance Humility example, ethics in relation to using animals during experiment, conservation of nature, environmental protection, sustainable development). These issues Figure 1.15 Values developed can serve as a base for an economically in biology education efficient, socially reasonable and environmentally sustainable development (see Figure 1.15 and Table 1.4). Table 1.3 Values you can develop by learning biology Curiosity Curiosity is the strong desire of learning more, which is the driving force to develop skills that enable success in the study of the subject and beyond. Love Biology gives the chance to value life, living things and the environment. While learning biology we develop love and compassion for life, humanity, living things and environment. Freedom As a branch of science, while you are studying biology you will practice the freedom of thinking and expression of your observation. Honesty Honesty is very important in science. As a young science student you have to honestly collect, organize, analyze and summarize your data. Respect Learning about living things and environment at school is usually being done in groups, during which you learn and practice how to interact with others and respect the ideas of others. Cooperation Group activities in a class while learning science are strong foundations for the collaborative nature of scientific and technological works. It is important to develop respect for others and to learn from one another. Tolerance While working in a group during biology lesson you will develop the quality of tolerating the view of others. Humility Humble way of listening to what others are saying, respecting and accepting the view of others: and accepting ones mistakes and weakness. Reasoning In science to make a conclusion or a summary one needs to critically evaluate and develop sense of pattern among pieces of information collected. Openness During science lesson you should not restrict yourself to what you are only told, without examining it. You should be open-minded to learn more than limiting yourself to what you only learn in the class. 22 Biology Grade 7 Exercise 1.5 Choose the best answers for the following questions. 1 The interest that one develops to know about things around is known as A humility C reasoning B curiosity D cooperation 2 The determination that one shows to keep going until getting a solution is A honesty C tolerance B respect D love 3 The values that you give to the natural environment and people around you is ______. A respect C freedom B openess D all of the above 4 The loyality and humbleness that one shows in all activities is called A freedom C cooperation B openess D respect 5 The power to be critical of yourself and the information that you collect is called ______. A cooperation C humility B reasoning D honesty Unit Summary ŒŒ Biology is a natural science that studies living things (life). ŒŒ Biology is divided into many branches, such as botany, zoology, micro biology, cytology, ecology, physiology and genetics. ŒŒ Biology is related with chemistry, physics, geology and other sciences. ŒŒ Biological knowledge is utilized in various industries such as agriculture, medicine and food science. ŒŒ In agriculture, biological knowledge is useful to utilize fertilizers, pesticides and weed killers to increase crop productivity. Biology is also useful in determining soil composition, identifying plant growth requirements, practicing crop rotation and soil preservation. ŒŒ In medicine biological knowledge is utilized in making drugs to combat diseases, and in food industries, to supply the right quality and quantity of nutrients in the diets. ŒŒ Biology is relevant to human society in aspects of health, nutrition, environment and population. ŒŒ In relation to health, biology is useful in using drugs against diseases, effect of drug abuse, recognizing the physiology of healthy people, determine the effects of antiseptics and disinfectants. ŒŒ Regarding nutrition biology plays important roles to classify foods, identify nutrients, determine sources of nutrients and balanced diet.  Unit 1: Biology and Technology 23 ŒŒ Biology is relevant for the environment in many ways including practice in good farming, preventing species loss, avoiding deforestation, preventing pollution and also in conserving natural resources. ŒŒ Biology is relevant to world population growth and enables provision of medical care, immunization and avoiding harmful traditional practices. ? Ajsjsdf AjsjsdfAjsjsdf AjsjsdfAjsjsdf Ajsjsdf AjsjsdfAjsjsdf Ajsjsdf AjsjsdfAjsjsdf Ajsjsdf AjsjsdfAjsjsdfAjsjsdf Aj Ajsjsdf AjsjsdfAjsjsdf Review Exercise for Unit 1 Ajsjsdf AjsjsdfAjsjsdf AjsjsdfAjsjsdf Ajsjsdf AjsjsdfAjsjsdf Ajsjsdf AjsjsdfAjsjsdf Ajsjsdf.......................................... Ajsjsdf Part I: Choose the best answers for the following questions 1 The study of living things is the concern of A Chemistry C Biology B Physics D Geology 2 The concern of taxonomy is A Classifying living things C Identifying living things B Naming living things D All of the above 3 Which branch of science studies the chemical substances in nature? A Physics C Mathematics B Chemistry D Taxonomy 4 Which of the following field of studies does not require the knowledge of biology? A Agriculture C Medicine B Electricity D Nutrition 5 Biology is needed for a human society to improve A health C life style B nutrition D all of the above 6 Which of the following innovations is derived from biological knowledge? A Bicycle C Train B Airplane D Television 7 A good scientist has to be A curious C incooperative B dishonest D intolerant 8 All natural sciences are A interacting C interrelated B overlapping D all of the above Part II: Match the items in column ‘B’ with items in column ‘A’ Column A Column B 9 Antiseptic A Aspirin 10 Disinfectant B Global 11 Drugs C Reasoning 12 Value D Alcohol 13 Pollution E Shisha 24 Biology Grade 7 Part III: Fill in the blanks with appropriate terms. 14 Humans invented __________ by copying the flying of birds. 15 As retina is to an eye a film is to __________. 16 A food that contains a healthy proportion of the six nutrients is __________. 17 Humans invented a __________ by copying the swimming ability of fish. Part IV: Give short answer to the following questions. 18 Define biology? 19 List down bad agricultural practices. 20 What is the risk of trying to fly like birds? Why? Part V: Word search. Think about some words related to the relevance of biology to the society. Can you find them in the word search table below? Look down, diagonally and sideways. Be careful, some words overlap and some are written diagonally. C B G Z D S T A E T T P I U R X C W N E X D O M U E J U P C D U M I G W T K Q H V U M L Q R E M R N S H U W I L X T Y O V B O T A N Y S X L A S I Y L P N T M O H O N E S T Y Z I G N T E X V O L D N Y Unit Cell Biology 2 Unit Outcomes By the end of this unit, you will be able to: ””define microscopes; ””classify them into simple and compound; ””identify their parts and tell the functions of each part; ””define cell, list parts of plant and animal cells seen under a compound microscope; ””tell the functions of each part and compare a plant cell with an animal cell; ””examine plant and animal cells under a microscope and draw and Main Contents label the structures seen under a 2.1 Microscope and its Uses microscope; and 2.2 The Cell ””show types, shapes, and sizes of 2.3 Observation of Cells cells using diagrams. 2.4 Cell Type, Shape and Size ŒŒ Unit Review  26 Biology Grade 7 Introduction Is discovery of cells related to invention of microscope? Biologists use different types of instruments to study life and life systems. Microscope is one of the most important tools that biologists use to study living things. In fact, it is the invention of microscope that led to the discovery of cells. Cells are the smallest units from which all life forms are made. Both multi-cellular organisms, like you, and an eucalyptus tree, and single-celled organisms like amoeba, paramecium and bacteria are made up of cells. Microscope is a very useful instrument which is used to observe and study different types of cells. With a microscope biologists not only observe cells but also identify their type, shape and size. In the following sections you will learn more about the types, parts and uses of compound light microscope. 2.1 Microscope and its Uses By the end of this section, you will be able to: ”” define microscope; Did You Know? ”” classify microscope into simple and ¸¸Electron microscope magnifies up to compound; 100,000 x of the sample size under study. ”” identify parts of a microscope; ¸¸Most cells are less than 50 µm (micrometer ”” tell the functions of parts of a = 1/1000 mm) in diameter, much smaller microscope. than the dot at the end of this sentence. When were cells first detected? Today we commonly get used to think of living things Word Roots and Origins as being composed of cells. However, the word was not used until the seventeenth century. The first Microscope: is made up of two smaller Greek observation of cells was made in 1665 by the English words. Micro which means small and, scope scientist Robert Hooke. Hooke, using a microscope of meaning to ‘look’ or ‘see’. his own invention, observed and named it cell. But, he did not understand its significance. In 1673, Anton van Leeuwenhoek, a Dutch merchant pioneered the invention of one of the best microscopes of the time. He was the first to observe, draw, and describe a variety of cells including bacteria, other one-celled organisms and sperm cells.  Unit 2: Cell Biology 27 What is a microscope? A microscope is an instrument that is used to observe objects too small to be seen clearly with the naked eye. Microscope uses lenses or system of lenses to produce a magnified image of an object under study. The science of investigating small objects using such an instrument is called microscopy. Microscopic means invisible to the eye unless aided by a microscope. Have you ever had a chance to see and use a microscope? Tell your experience to the class. What is the use of a microscope? A microscope offers a chance to closely study and learn more about smaller organisms. Even if biology is one of the oldest in the history of science, recognition of cells came very late. The use of magnifying lenses was vital for their recognition and study (see Figure 2.1). Figure 2.1: Students observing a sample under a microscope Types of Microscopes A microscope enlarges the size of the object observed so that it looks bigger than its actual size. This is Key Terms called magnification. 55Monocularcompound microscope: A compound There are two types of microscopes. These are simple microscope with single eye piece lens. microscope and compound microscope (see Figure 2.2). 55Binocular compound microscope: A compound microscope with two eye pieces. 55Microscope: an optical instrument used to observe very small objects. B 55Microscopic: very small A objects which are only C viewed with microscope. D E 55Magnification: ability of a microscope to enlarge the size Figure 2.2: Different types of simple of the specimen. microscopes: A) and B) magnifying lenses; 55Lens: a piece of glass used to C) reading lenses; D) binocular two eyepieces and E) monocular (single eye piece) converge or diverge light and form optical images. 28 Biology Grade 7 What is a simple microscope? Did You Know? A simple microscope consists of a single convex When an object is magnified with a microscope, it looks bigger, but its true size remains the lens that is capable of magnifying an object. A same. microscope which consists of only one curved lens is simple microscope. A hand lens is an example of simple microscope. The magnifying glass, reading lens and hand lens magnify between 10 times to 20 times (usually written as 10X to 20X). It means that the object you are looking through these simple microscopes will appear 10X larger than its normal size (see Figure 2.3). Figure 2.3: Observation of sample with a hand lens Activity 2.1 Observing different plants using hand lens Materials you require: ;; Hand lens ;; Flowers from different plants (from rose and chrysanthemum plant) ;; Leaves from different plants ;; Body parts of small insects (like house fly, ants and grasshopper) Procedure: 1 Collect flowers and leaves from different plants and bring samples of insects to the laboratory. 2 Pick your hand lens and the objects you are going to observe. 3 Sit in an area with good lighting or sunlight. 4 Observe the flower from a rose plant (try to observe the anther and the stigma) with your naked eyes and note what you observe. 5 Hold the rose plant flower on the opposite side of the hand magnifier from your eyes. 6 Move the object or the hand lens until you are able to see clearly through the lens and draw what you see. Important: while you look through the lens, hold the object close to the hand lens or magnifier, probably less than an inch away (see Figure 2.3). 7 Do the same for the other samples you have brought to the class or laboratory; and note the difference between what you have observed with your naked eyes and with the hand lens. Also observe the skin at the back of your hand, and note the difference between your observation with the hand lens and with your naked eye.  Unit 2: Cell Biology 29 What is a compound microscope? A compound microscope is a microscope that uses two lens systems at the same time. The two lens systems Did You Know? are the eyepiece (ocular) lens and the objective lenses. Recent models of compound microscope can The eyepiece lens usually magnifies ten times and is have a total magnification up to 2,000X. labeled 10X. The objective lenses magnify four to hundred times. The total magnification is the product of the eye lens and objective lens magnifications. For example, if the magnification of the eye lense is 10X and the magnification of the objective lense is 4X, then the total magnification is 40X. Activity 2.2 Discussing total magnification. In groups, discuss the total magnification of a compound microscope. Take as an example a medium power objective and an eyepiece lens with a 10X magnifcation. Parts of a Compound Microscope The compound light microscope Ocular lens (Eyepiece) is a type of microscope Body tube which is commonly used in many laboratories. This light microscope consists of different Revolving parts through which the sample nosepiece Arm under study is magnified and Objectives observed. Stage Table 2.1 is based on the diagram Stage clips of the compound microscope. Coarse adjustment Diaphragm knob The column on the left lists the Fine adjustment knob parts, and the column on the Light source right gives its function. See also Figure 2.4 to help you identify Base the parts. Figure 2.4: Compound light microscope and its parts 30 Biology Grade 7 Table 2.1: The compound microscope parts Structure (part) Function (job) Ocular (eyepiece lens) A convex lens used to magnify the image (usually 10X) Body tube (barrel) Supports the eyepiece and the nosepiece. Coarse adjustment knob Moves the tube up and down and produce a rough focus of the image. Fine adjustment knob Moves the tube up and down by very small amount and produce a sharp focus of the image. Arm Used to carry the microscope. Nosepiece Contains the high- and low-power objectives. Low-power objective lens (LP) A convex lens used to magnify the image (usually 4X) Medium-power objective (MP) A convex lens used to magnify the image (usually 10X) High-power objective lens (HP) A convex lens used to magnify the image (usually 40X) Oil immersion objective A convex lens used to magnify the image (usually 100X) Stage Supports the glass slide and contains the specimen being observed. Stage clips Hold the slide in place. Diaphragm (iris) Adjusts the amount of light passing through the stage. Light source (lamp or mirror) Illuminates the specimen. Base The bottom of the microscope, used for support. N.B: Your teacher will provide you with a microscope so that you can identify the parts and their functions. Mounting: is preparing a specimen for observation under a microscope. Focusing: is adjustment of focus to observe specimen clearly. Activity 2.3 Practicing mounting and focusing Materials you require: ;; Clean slide and cover slip Caution ;; A dot on a piece of paper FFSpecimen to be observed under a microscope should be thin enough to pass light through it. ;; Dropper with nipple FFSlides and cover slips should be clear because ;; Forceps dirt can interfere and confuse the observation. ;; Water in a beaker FFIf your specimen is too thick, then the cover slip ;; Compound light microscope will swing on top of the sample like a see-saw.  Unit 2: Cell Biology 31 Procedure: 1 Lay down the piece of paper with a dot on a clean microscope slide as shown in the diagram. (Figure 2.5) Figure 2.5: Illustration showing how to place the cover slip on the sample 2 Place one drop of water directly over the specimen and cover it with a cover slip. 3 If you put too much water over the specimen, cover slip will float on top of the water. This makes it harder to observe the specimen! This process, if done correctly, there should be no air bubble trapped in the water between the slide and the cover slip. 55 Air bubbles confuse the observer. 55 Cover slips protect objective lens and keep the specimen in position. 4 Place the slide on the microscope stage, with the specimen directly over the center of the glass circle on the stage (directly over the light). 5 Always start and end with Low Power objective. Lower the objective lens to the lowest point, then focus using first the coarse knob, then with the fine focus knob. 6 Adjust the Diaphragm as you look through the Eyepiece, and you will see that more detail is visible when you allow in less light! Too much light will give the specimen a washed-out appearance. Try it out!! 7 Once you have found the specimen on low power, then, without changing the focus knobs, switch it to medium power. Move the object or the hand lens until you are able to see clearly through the lens. 8 Once you have it on Medium and High Power remember that you only use the fine focus knob! (Never use the oil immersion lens). 9 Click the high power objective lens in position and only use the fine adjustment knob to focus on specimen. At this point, if the specimen is too light or too dark, try adjusting the diaphragm. 10 Then, focus using the fine adjustment for sharp focusing. Do not use the coarse adjustment/ 11 Is the dot compact or diffused? Draw it. 32 Biology Grade 7 Exercise 2.1 Choose the best answer for each of the following questions 1 One of the following is not the function of a microscope. A Magnifying the image of the sample. B Showing the details of the sample. C Enabling one to observe something difficult to see with naked eye. D Enlarging the size of the sample. 2 Which of the followings is a simple microscope? A Compound binocular microscope. B Compound monocular microscope. C Hand lens. D A microscope with eye piece and objectives. 3 Why are a hand lens and a compound microscope known as light microscopes? A Because they produce light. B Because they use light as a source of energy. C Because they are not heavy in their weight. D None of the above. 4 A simple microscope consists of? A three lenses C one lens B two lenses D four lens 5 Magnification power of a microscope is related to its ability to: A increase the size of the image. B showing the fine details of the sample. C resolving the image. D all of the above. 2.2 The Cell By the end of this section, you will be able to: ”” define cell as the smallest unit of life; Word Roots and Origins ”” list parts of plant and animal cells The word “Cell” come from Latin word, cellula, seen under a compound microscope; means “small room”. ”” tell the functions of parts of plant and animal cells seen under a compound microscope; ”” compare a plant cell with an animal cell.  Unit 2: Cell Biology 33 The cell is the basic structural and functional unit of all living organisms. Most cells are very small in size. Did You Know? Since they are so tiny they can only be seen with the Our body is made up of trillion (1013) of cells aid of a microscope. Your body is composed of billions of cells! Can you estimate the number of cells in an elephant? What is a cell? A cell is the smallest unit of life and is often called the building block of life. All plants and animals are made up of one or more cells. Based on the number of cells they have, organisms can be grouped as unicellular (consisting of a single cell) or multicellular (made up of many cells). Unicellular organisms are those organisms composed of one cell. Examples of unicellular organisms include different bacteria, most algae and protozoans such as, amoeba and paramecium (see Figure 2.6). a) Chlamydomonas (an alga) b) Paramecium (a protozoa) c) Yeast (Fungi) d) Rod shaped bacteria e) Amoeba (a protozoa) f) Euglena (Protozoa) Figure 2.6: Different unicellular organisms Multicellular organisms: plants and animals are examples of multicellular organisms. Within your body, cells have different functions. You have blood cells, skin cells, brain cells, heart cells and many types of other cells. Plants are multicellular organisms, for instance, a rose plant has also different types of cells: like stem Did You Know? cells, root cells, and many other types. Despite their Every living thing - from the smallest bacterium differences, cells in living organisms have similar to the largest whale - is made of one or more structures and functions. cells. 34 Biology Grade 7 Under a compound microscope a cell is observed Key Terms to have three main parts. These are cell membrane Unicellular organism: an 55 or plasma membrane, cytoplasm and nucleus (see organism which is made up of Figure 2.7). a single cell. Multicellular organisms: an 55 Plasma membrane organism which is made up of many cells. Cell membrane: part of a cell, 55 Nucleus which is very thin and delicate Cytoplasm envelope (membrane) that covers and contains the internal parts of a cell. Cytoplasm: the internal fluid 55 Figure 2.7: Common parts of cells component of the cell. (structure of an animal cell) Nucleus: part of a cell and 55 found within the cytoplasm. It is membrane bound structure which contains the genetic material of the cell. Activity 2.4 Comparison of unicellular and multicellular organisms 55 In groups, discuss the differences and similarities between unicellular and multicellular organisms. You may consider the difference between yourself and an amoeba. 55 What is the difference between you and an amoeba? 55 What are the common feature(s) between you and an amoeba? Structures of Plant and Animal Cells What are the common cellular parts of both animal and plant cells? Cells, the tiny structural units of life, are made up of different parts. The parts of cells are known as sub-cellular structures or organelles. Different sub-cellular structures carry out different functions in cells. When observed under compound microscope, both animal and plant cells have common cellular parts (see Figure 2.8a and b). The three main parts that can be seen under a compound microscope are: 55 the cell membrane (plasma membrane) 55 an inner region called the cytoplasm and 55 the nucleus In fact, animal and plant cells share some more common features like the cell membrane, nucleus and cytoplasm. The cell membrane controls materials that get in and out of the cell. The nucleus controls reproduction and the activities of the cell. The cytoplasm contains different sub-cellular structures in which chemical processes take place.  Unit 2: Cell Biology 35 Chloroplasts Cell wall Plasma membrane Nucleus Central Vacuole Cytoplasm a) Animal cell b) Plant cell Figure 2.8: Parts of animal and plant cells Comparing Plant and Animal Cells Did You Know? Do animal and plant cells have Cells differ from each other within the body of different parts? an organism according to their function. Animal and plant cells have some key similarities Key Terms (Figure 2.7) and differences as well (Figure 2.8; 55Vacuole: a smaller cavity which Table 2.2). One of the primary differences between is both found in animal and animal and plant cells is that plant cells have a plant cells. cell wall made up of cellulose. Plant cells have 55Large vacuole: large-sized which is only found in mature plant cells. chloroplast, which contains the chlorophyll pigment 55Cell wall: a rigid and protective in which they make their own food in the process external cover of plant cells, known as photosynthesis. Although both animal and which is made up of cellulose. plant cells have vacuoles, the vacuoles in plant cell 55Chloroplast: sub-cellular part of plant cells which contains merge together at maturity and form large vacuole. chlorophyll and in which photo- synthesis takes place. Table 2.2: Differences between plant and 55Chlorophyll: a green pigment animal cells found in chloroplast and Animal cells Plant cells responsible for absorption of light by plants to provide energy yyCells are smaller in size yyCells are larger in size for photosynthesis. yyHave no cell wall yyHave cell wall 55Photosynthesis: the process in yyHave no large central which plants use sunlight energy vacuole yyHave large central vacuole to synthesize food from carbon yyHave no chloroplast yyHave chloroplast dioxide and water. 36 Biology Grade 7 Activity 2.5 Comparison of Animal and Plant Cells ;; In groups, compare and contrast animal and plant cells. Show your comparison (similarities and differences) in a table form. ;; What do you think is the possible reason for the absence of chloroplast in root cells? Exercise 2.2 Choose the best answer for each of the following questions. 1 One of the following is true about cells. A Cells are generally too small to be seen with the naked eye. B Cells are the structural and functional units of all life forms. C Cells are the smallest units that carry out all process of life. D All of the above 2 One of the following is part of a cell and only found in a plant cell? A Cell membrane B Cell wall C Cytoplasm D Nucleus 3 One of the followings is a characteristic of a unicellular organism. A It is made up of many cells. B It is made up of a single cell. C It requires the assistance of other cells for its biological activities. D It is seen with the naked eyes. 4 One of the followings is a unicellular organism. A A tree B A cat C A man D A bacterium 5 One of the following parts of a cell is common to all type of cells. A Cell wall B Large vacuole C Small vacuole D Chloroplast  Unit 2: Cell Biology 37 2.3 Looking at Cells By the end of this section, you will be able to: ”” examine plant and animal cells under a microscope; ”” draw and label the structures of plant and animal cells seen under a microscope. In the previous sub-unit you have been familiarized with parts of a microscope and their functions. Now, you will practice observing different cell samples obtained from different organisms under compound light microscope. This will give you the opportunity to observe different types of cells. Precaution to be Exercised When a Using Microscope 55 Make sure the working table is clean and without any unnecessary items. 55 When the microscope is not in use, place the low power objective in position. 55 Avoid tilting the microscope and do not touch lenses with your finger. 55 Carry the microscope by the arm with one hand and support its base with the other hand. 55 Treat your microscope respectfully and according to proper instructions. General Procedures on How to Set a Microscope 55 Put the microscope on the working table, keeping the arm towards yourself and stage away. 55 The base of the microscope should be kept several centimeters away from the edge of the table. 55 Rotate the nosepiece to make the low power objective in line with the body tube. 55 By using the coarse adjustment, raise the body-tube about 2 cm above the stage. 55 Open the diaphragm of the condenser for passing the light on the stage. 55 Look through the eyepiece, adjust the light source so that it is directed upwards. 55 Do not use coarse adjustment when viewing through the high power objective. 55 Keep the microscope always in upright position. What are pollen grains? Pollen grains are male reproductive cells of plants, which are equivalent to the mammalian sperm cells. 38 Biology Grade 7 Activity 2.6 Observing pollen grains under a microscope. Materials you require: 55 Compound microscope 55 Microscope slides 55 Flowers 55 Cover slip 55 Beaker with dropper Procedure: 1 Gather some pollen from a flower. 2 Place it on a slide. 3 Cover with cover slip and observe the pollen under the microscope. 4 Draw the cells you see on your note book. Activity 2.7 Key Terms 55Scanning objective: the low Making a Wet Mount power objective used to scan the slide in order to spot the specimen to be observed. Materials you require: 55Specimen: a sample to 55 Compound microscope be examined under the 55 Microscope slides microscope. 55 Flowers 55Stain: a dye used to color and 55 Cover slip make visible the whole or 55 Beaker with dropper part of specimen under the microscope. 55 Water 55Wet mount: a process during Procedure: which water is used as 1 Gather some pollen from a flower. mounting medium to examine specimen under study. 2 Place it on a slide and add a drop of water. 55Pollen grains: are male 3 Cover with cover slip and observe the reproductive cells of plants, pollen under the microscope. the botanical equivalent of the mammalian sperm. 4 Draw the cells you see on your note book. What are Stains? Not all parts of cells are observed clearly while examining cellular samples under a microscope. Certain parts of cells will be observed clearly only when samples are stained. Stains are coloring agents. Staining is the process of adding stains or dyes to specimen while observing the specimen under a microscope. Adding stains make the whole or parts of the sample colored and render it easy to be examined.  Unit 2: Cell Biology 39 What are plant epidermal cells? Generally, the surface of the leaf is covered by Did You Know? thin layers, which are tough skin cells (called the An onion is an edible bulb, which is made up epidermis); the upper and lower epidermis. The of many layers of modified leaves. The surface epidermis is made of a single layer of cells. of each leaf is covered by a thin layer of cells, the epidermis. Activity 2.8 Observing onion epidermal cells Materials you require: ;; Compound microscope ;; Onion ;; Forceps ;; Eye dropper ;; Microscope slides ;; Cover slips ;; Iodine solution ;; Beaker with water Procedure: 1 Place a drop of water in the middle of a clean slide. 2 Using forceps, gently remove a section of the skin from the inside layer of the onion and place it on the slide on a drop of water. 3 Put the cover slip over the top gently using the forceps to hold it. 4 Observe through the microscope (by first using low-power and then focusing under medium-power). 5 Did you see cells? 6 Put two drops of iodine solution closer to one side of the cover slip, and leave the solution to diffuse for some minutes. 7 Observe under low and medium power objectives. Compare your specimen with Figure 2.9 below. 8 Which structures of a cell can be seen under a light microscope? 9 Draw one cell and label all the parts identified. Figure 2.9: Image of onion epidermal cells see under a microscope 40 Biology Grade 7 Activity 2.9 Observing the Epidermis of Elodea (Water Plant) Materials you require: 55 Compound microscope