Grade 11 Biology Textbook PDF

Textbook Biology CHAPTER 1 INTRODUCTION TO BIOLOGY Grade 11 Learning Outcomes It is expected that students will be able to - learn why knowledge of biology is important for mankind - gain knowledge on how other branches of sciences interrelated to biology and the interdisciplinary of sciences - unde...

Textbook Biology CHAPTER 1 INTRODUCTION TO BIOLOGY Grade 11 Learning Outcomes It is expected that students will be able to - learn why knowledge of biology is important for mankind - gain knowledge on how other branches of sciences interrelated to biology and the interdisciplinary of sciences - understand the concept and uses of classification - construct the dichotomous keys based on distinctive characters to identify the organisms - understand the working of the light microscope and electron microscope and explain the differences between them - differentiate the terms magnification and resolution - define biotechnology and the use of microorganisms in bread making, yoghurt, cheese, wine, beer and biofuel production - learn the concept of fermentation and the working of fermenter - know how to produce biological washing powder and fruit juice using enzyme biotechnology 1.1 THE IMPORTANCE OF BIOLOGY Biology, as most people understand it, is the Science of Life. They regard it as the study of living things, such as plants, animals and microorganisms. What they do not realize is that their very existence depends on their understanding of Biology. So unknowingly they are disturbing the balance of nature. The whole world is now suffering under the impact of infectious disease outbreak and weather changes cause by the effect of global warming. Over fishing, over hunting and deforestation may lead to problems in feeding the world exploding population. Many species of plants and animals have disappeared forever. If people should have more knowledge on biology and understanding of nature, this would never have happened. So it is of utmost importance that mankind should realize that impact of man on nature will always return to them. Nature will give back what it is given to it. Biology is concerned with animal breeding, agriculture and also in the field of medicine just to mention a few. People should realize the importance of biology, for the knowledge of it will help mankind to protect nature, feed the starving nation and leave the world a better place for our future generations. 1.1.1 Links between Biology and Other Branches of Science Biology is a very fundamental and important natural science consisting of many disciplines or branches of study. Some of these branches study the basic facts or principles, such as the study of structure and function of living things. They are regarded as pure science. Examples include morphology, the study of structure and form of organisms and cytology, the study of cell structure and function. Other branches are concerned with applying the basic knowledge to practical application or particular technologies. They are known as applied science. The applied biology includes biotechnology which is application of biology in productive industry, the medicine and veterinary science-restoration and maintenance of health in human and in animals, agriculture and animal husbandry-farming of crops and breeding of livestock for food. Many branches or disciplines arise within biology due to its close association with other sciences. Biology has strong links with physics, chemistry, geology, geography, mathematics and computer science, etc. These sciences help the biologists in their study to understand the vital life processes of the organism and gain information on the working of the biological systems. Biophysics, for example, applies the laws of physics to study the biological processes, like flight of the bird or echolocation in bats. Biochemistry is the study of chemical substances and the chemical processes which occur in the cells and organisms. Biogeography explains how plants and animals are distributed on earth through space and time. These are only a few examples of the link between biology and other sciences that contribute much to the advances in the field of biology. Biology Pure Biology Applied Biology Other Sciences Morphology Biotechnology Biophysis (Bio+Physics) Anatomy Veterinary Science Biochemistry (Bio+Chemistry) Histology Agriculture Biometry (Bio+Statistic) Cytology Animal Husbandry Biogeography (Bio+Geography) 1.2 Figure 1.1 Diagrammatic representations of branches of biology and its link with other sciences IDENTIFICATION AND CLASSIFICATION OF LIVING THINGS Identification in biology is the process in which an organism or specimen is classified and assigned a scientific name. The study and process of classification is known as Taxonomy. Biologists study the differences and unique features of the living things, grouping organisms with similar characters together and placing the dissimilar ones apart. The classification or grouping of living things is arranged in a hierarchical order and is known as hierarchical classification. There are eight taxonomic groups or taxa. At the top of the hierarchical are three domains, Archaea, Bacteria and Eukarya. Each of the three domains is subdivided into seven different levels or taxa they are Kingdom, Phylum/Division, Class, Order, Family, Genus and Species. Another method of classification known as cladistics is also used by modern taxonomists. In this method of classification many techniques are used including comparing of DNA from different species to find out how closely they are related. To carry out the identification of organism, biologists usually use easily identifiable features like morphology and anatomy as keys. Keys provide a simple way to classify organisms. Figure (1.2) represents the processes carried out by biologists using key features in classification. Living things unicellular multicellular nucleus absent nucleus present cell wall absent cell wall present usually found in extreme environment extreme environment not found in chlorophyll present Kingdom Archaeabacteria Eubacteria Protista Animalia Plantae without backbones with backbones non-flowering chlorophyll absent Fungi flowering invertebrates vertebrates spore bearing seed bearing exoskeleton present exoskeleton absent segmented body with jointed limbs Phylum/Division Arthropoda Class Order Insects segmented body with bristle Annelida Earthworm with feathers and beaks Aves Birds pouch and tail present 4 limbs, digits with claws Marsupialia Kangaroos Chordata Pteridophyte Gymnospermae Angiospermae with hair and mammary glands Mammalia Mammals pouch and tail absent 4 limbs, digits with nails Primates Fenns Pines seed with one cotyledon Monocotyledons Paddy soft stem with large unisexual flowers body covered with body covered with Cucurbitales Pumpkin more than one seed seed with two cotyledons Dicotyledons hard woody stems with small bisexual flowers Spindales Family Genus Species thick hair Pongidae Apes single seed short hair sparsely Hominidae Rutaceae Anacardiaceae Citrus plant Homo Mangifera sapiens indica Homo sapiens Human Mangifera indica Mango Figure 1.2 Keys and classification of the six kingdoms 1.2.1 Construction of Dichotomous Keys for Identification Dichotomous keys provide a simple way to put unknown organisms in their proper taxa. Based on easily identifiable characters questions are asked, each question having two possible answers. [The word dichotomous is derived from Greek words meaning "divided into two parts"]. The method of dichotomous keys is to divide the groups of organisms into two categories repeatedly. They often begin with general characteristics and then progress to more specific ones step by step. The characteristics of unknown organisms are compared to that given in the dichotomous keys. If the organism fits into one category you have to go on to the next set of statements. By following the sequence of the given dichotomous keys and making the correct choices the unknown organisms can be identified and placed in their proper taxonomic level. Figure 1.3 and Figure 1.4 show how organisms are identified using dichotomous keys. Plant divisions 1. Vascular system absent Vascular system present 2. No embryo formation Has spores and gametes formation 3. Spore-bearing Seed-bearing 4. Non-flowering plants Flowering plants 2 3 Thallophyta Bryophyta Pteridophyta 4 Gymnospermae Angiospermae Figure 1.3 A dichotomous keys for plant divisions Vertebrate classes 1. Cold-blooded animals Warm-blooded animals 2. Body covered with scales Body not covered with scales 3. Feathers present on body Hair present on body 4. Has fins Has four limbs or without limbs 2 3 4 Amphibian Bird Mammal Fish Reptile Figure 1.4 A dichotomous keys for vertebrate classes 1.3 MICROSCOPY The development of new tools and technology has aided in the advancement of biology. Among the most widely used tools in biology are microscopes. Biologists use these to study cells, cell parts and also organisms that are too small to be seen with naked eyes. Basically there are two main types of microscope, the light microscope and the electron microscope. The light microscope uses light as a source of radiation to form the image of the specimen being studied while the electron microscope uses electron. Two different types of electron microscopes are commonly used the transmission electron microscope or TEM and the scanning electron microscope or SEM. In the TEM, electron is passed through the specimen and allow us to see thin sections of the specimen, and thus the inside cells. In SEM the electron beam is passed back and forth over the surface of the specimen. Only the reflected beam is observed and three dimensional appearance is obtained. How the light microscope works - Usually substage illumination is the light source. Light must come only from substage position. - By adjusting the iris diaphragm, the amount of light reaching the specimen is controlled. - Condenser focuses the light onto the specimen on the slide. - Light passing through the specimen is collected by the objective lens and a magnified image is produced. This lens is responsible for both the magnification and resolution. - Eyepiece lens magnifies but does not resolve the image formed by the objective lens. - Eyepiece lens focuses the image onto the eye. How the electron microscope works - The electron beam, the specimen and the fluorescent screen must be in the vacuum. - Electron gun and anode emit high velocity electron beam. - Condenser electromagnetic lens focuses the electron beam onto the specimen. - Objective electromagnetic lens focuses and magnified the first image. - Projector electromagnetic lenses focus the magnified image onto the screen. - The image of the specimen in black and white is recorded on the screen or photographic plate. Table 1.1 A comparison of light and electron microscopes No. Light Microscope 1. Uses light as a source of radiation. 2. The image is projected on the eye or on photographic film. 3. Preparation of specimen simple, not complicated. 4. Magnifies up to 2000 X 5. Either dead or alive specimen can be examined. 6. Inexpensive to purchase and operate. Electron Microscope Uses electron as a source of radiation. The image is projected on a screen or on photographic film. Preparation of specimen lengthy and complicated. Magnifies up to 500,000 X Only dehydrated and dead specimen can be examined. Expensive to purchase and operate. Magnification and Resolution Students studying biology have already learnt how to use a microscope in Grade 10. Now they should understand the magnification and resolution of the microscope. Magnification To magnify means to make things bigger. Hence magnification is the ability to increase the size of the image of the object being studied so that microscopic organisms become visible. Magnification can also be defined as the number of times larger an image is, compared with the real size of the object. Resolution Where If two of these values are known the third one can be calculated. Resolution is the ability to distinguish between two objects that are close together. If the two objects cannot be resolved they will be seen as a single object. Resolving power shows up the smallest detail that a microscope can resolve when imaging an object. One important fact of difference between magnification and resolution should be noted. An increase in magnification does not always produce a more detail image. It might increases in size but not in detail. In fact the image may become blur. But with resolution, the greater the resolution, the greater the detail. 1.4 BIOTECHNOLOGY Biotechnology is a branch of applied biology which combines biological sciences with engineering technologies. 1.4.1 What is Biotechnology? Biotechnology is a technology which apply the use of living systems and organisms to produce useful chemicals and products or to carry out industrial work for mankind. Although this branch of biology is well-known technology of our modern world, our ancestors had been practicing it for hundreds of years making wine, bread, cheese and breeding livestock and crops without any scientific knowledge. Now understanding of scientific basis of the techniques has led to the application of biotechnology in the fields of food production, agriculture, animal breeding and medicine etc. 1.4.2 Traditional Biotechnology It can be said that traditional biotechnology came into use thousands of years ago when people unknowingly discovered the usefulness of microorganisms like bacteria and yeast. It was known that seven thousand years ago, people in Mesopotamia used bacteria to convert wine into vinegar. For centuries mankind had been practicing the methods handed down by their forefathers to prepare their meals. Examples of this traditional biotechnology includes making wine, cheese, yoghurt, bread and beer. 1.4.3 Modern Biotechnology The scientific study of the biochemical processes that has developed in the past few decades contributes much to the advancement of the biotechnology. The range of materials produce by modern biotechnology techniques is vast, ranging from medicines like antibiotic penicillin to chemicals like enzymes and fuel. Nowadays, with the development of gene technology scientists are able to modify or manipulate living organisms by transferring genes from one organism to another, usually an unrelated species. In this way genes for herbicides resistance are put into crop plants and human insulin producing genes are put into bacteria and cultured to produce insulin. Genetic engineering carried out on some plants and animals have enabled them to produce substances that are not part of their normal metabolism. They are known as transgenic plants and animals. Transgenic goats produce antibodies and blood clotting agent in their milk and transgenic plants are engineered to produce vaccine. 1.4.4 Microorganisms and Biotechnology Microorganisms or microbes are small organisms that can only be seen with the microscope. The term microorganisms include protists, archea, fungi, bacteria and viruses. Of these, archea and bacteria are prokaryotes whereas protists and fungi are eukaryotes. The viruses are not cellular and they do not have the characteristic of living things but they can reproduce inside the living cell of other organisms by using the genetic materials of the host. Protists are single-celled organisms usually found in the wet surrounding. Fungi have hyphae or filamentous cells but yeasts, an unusual family of fungi, have single spherical cells. These microbes are harness by biotechnologists to run their biotechnological processes in manufacturing useful products for man. The advantages of using microorganism in the industrial field are many. They can be cultured easily by using fermenters where they can reproduce profusely as they can be kept in optimum conditions. As they are not affected by outside conditions, like climate, they grow rapidly and can produce large amount of product in a short time. The nutrients they need are quite cheap and sometimes they can be fed with waste products of other industrial processes. They are put to use in food technology, baking and brewing industries, in drug production, textile and mining, and production of biological washing powder and biofuel. 1.4.5 Making of Biofuels, Bread, Yoghurt, Cheese, Wine and Beer The making of biofuel Raw or unrefined sugar obtained from sugarcane or cane wastes are used as nutrient for the anaerobically respiring yeasts. This fermentation process produces ethanol which is distilled to obtain pure ethanol. It is then mix with petrol to get gasohol which is used for driving cars. In Brazil, Zimbabwe and in USA some cars are already using ethanol and gasohol as energy sources and they cause less pollution than petrol. Biofuel can also be produced by using oil from rapeseeds or sunflower seeds. The single-celled fungi yeast is used in the making of bread. - First flour, water, oil and yeasts are mixed together and kneaded (folded and stretch repeatedly). - Water activates the amylase enzymes to act on the starch in the flour breaking it down to sugar. - Then the yeasts ferment (respire anaerobically) the sugar to carbon dioxide and ethanol. - The dough is left to ferment at about 27 C for a few hours. - A sticky protein gluten holds the carbon dioxide gas bubbles in the dough and make it rise almost to twice of its original size. - After that, the dough is baked in the oven at 200 C. Baking kills the yeasts and evaporates the ethanol and the expanding gas bubbles give the bread a light cellular texture. Making yoghurt and cheese Both yoghurt and cheese are made from milk. First milk is pasteurized at about 90 C degree to kill the bacteria in it. Then it is homogenized to break up the fat globules. At 40 °C-45 C a starter culture of two species of bacteria (Streptococcus thermophilus and Lactobacillus bulgaricus) is added which turn the lactose, milk sugar, in milk to lactic acid. This acid coagulates the milk protein casein and thick creamy yoghurt is produced. In the making of cheese the basic processes are the same as yoghurt. But after the coagulation of milk protein casein, a mixture of enzymes called rennet is added which causes further coagulation of the milk casein and solid lumps called curds are formed. The liquid whey is drained off and the solid curds are partially dried and compressed. Then the cheeses obtain are allowed to ripen and mature. Making wine and beer To make wine, grapes are crushed and the extracted juice is placed in a large vessel or vat and treated with sulphur dioxide to kill the natural occurring yeast. A starter culture of yeast (Saccharomyces cerevisiae) is added which respire aerobically at first until the oxygen is used up. Then the yeast cells start to respire anaerobically fermenting the grape sugar (glucose) to alcohol and carbon dioxide. When the alcohol content reach 15%, the yeast cells die and the juice become wine. Beer is made from barley grains. The seeds are wetted and allowed to germinate thus activating the starch-digesting enzymes. Then the seeds are dried at temperature which kill the seed but do not destroy the enzymes. The dried grains known as malted barley are crushed and mixed with water and starch extracted from wheat or rice is added. The barley enzymes digest starch to maltose and glucose and 'wort', a sugary solution is obtained. Wort is filtered and boiled with hops which give beer a bitter flavour. Yeast is added which act on maltose and glucose to produce ethanol. Fermentation takes 5-15 days after which beer is obtained. 1.4.6 Fermentation and Fermenters Fermentation Respiration is a chemical reaction carried out by all living organisms to get energy out of food. Living things usually respire in the presence of oxygen but most microorganisms do not need it as they can respire anaerobically. The anaerobic respiration is a process that breaks down glucose to alcohol and carbon dioxide and this process is also known as alcoholic fermentation. This chemical reaction provides the microorganism with energy needed for their living processes. Louis Pasteur, a French biologist (1822- 1895) had described alcoholic fermentation as "life without air" but nowadays fermentation is defined as chemical changes in organic substances brought about by microorganisms in the presence or absence of oxygen. Fermenters Fermenters are large containers that maintain an optimum environment for culturing microorganisms, usually bacteria and fungi, to promote large scale fermentation processes and to manufacture commercially, products like enzymes, antibiotics, alcohol beverages etc. As the waste produce by microorganisms are acidic, the fermenter tanks are usually made of stainless steel or special alloy to withstand the corroding effect. Figure (1.9) represents a diagrammatic typical fermenter and steps taken to run the fermenter are shown below. - First hot steam is passed into the fermenter through steam inlet under high pressure to sterilize it. - Next nutrients are put into the tank from another inlet and the microorganisms to be cultured are added. - Air, which is filtered to prevent contamination, is passed through the air inlet if the microorganisms need to respire aerobically. If the reaction is going to be anaerobic this step is not necessary. - Temperature and pH are monitored through probes and optimum environment for the culture such as oxygen, carbon dioxide and nutrient supply are also maintained. To keep the pH constant, alkali or acid is added as needed. - Fermentation process produces heat. So to prevent the fermenter from overheating and damaging the culture, cold water is circulated through the water jacket surrounding it. - Build-in stirring paddles are used to stir the contents to keep the temperature even throughout the tanks. It also keeps the microorganisms suspended in the medium to get more exposure to the nutrient. - The products are collected from the harvesting outlet when the fermentation process is finished. In commercial fermentation there are two types of culture: batch culture and continuous culture. The volume of culture medium and microorganisms are fixed in batch culture at the beginning of the process and when the maximum products accumulate, it is collected. The fermenter is shut down, cleaned out and prepared for reuse. However, in continuous culture once the fermentation process has started. the fermenter is kept running for extended period adding fresh nutrients while the products are harvested continuously. 1.5 ENZYMES USE IN INDUSTRY Enzymes are protein molecules formed in the living cells. They are biological catalysts and all the metabolic processes of the living things are catalysed by them. Enzymes that are isolated from the cell still retain their ability to function. This property of enzymes is put to use in industrial processes which require high temperature or pressure to work. They are much cheaper to use and the cost for industrial processes are reduced as they do not require expensive fuel to maintain high temperature to function. Many enzymes used in industries are obtained from microorganisms mostly from fungi or bacteria. Application of useful enzymes is seen in many industries like baking and brewing industries, dairy industry and textile industry. Even in medicine and pharmaceutical industry microbial trypsin is used to treat blood clotting and pancreatic trypsin is used for treatment of inflammation. 1.5.1 Biological Washing Powders Commercial fermentation produces many enzymes that are useful to man. They include proteases. the protein-digesting enzymes and lipases, the fat-digesting enzymes. These enzymes are used to make biological washing powder and stains in clothes cause by blood, egg, gravy and grease can be removed easily. The enzyme proteases act on red haemoglobin and break it down into smaller molecules which are colourless and dissolve in water. Both the protein and fat molecules are large but the proteases and lipases digest them into small, soluble substances which pass out of the fabric and are washed away. 1.5.2 Extracting Fruit Juice Fungi produce the pectinases enzymes which are used in extracting fruit juices. The enzymes break down pectin, a jelly like substances between the cell walls and separate the fruit cells making it much easier for extracting the juice. During the break down process many kinds of polysaccharides (such as cellulose and starch) are also released causing the juice to become cloudy. Pectinases continue to break them down to sugar making the juice sweeter and clearer. Review questions 1. Why is knowledge of biology important for mankind? 2. Give a few examples of the link between biology and other sciences? 3. Based on easily identifiable features draw a key to classify the six kingdoms. 4. The diagram below shows the underground storage organs of five plants. Use the key to identify which storage organ, shown in the diagram, is produced by which plant. Write the letter of each storage organ on the correct line in the key. Key Name of plant Letter of storage organ 1. (a) Approximately round go to 2 (b) Longer than it is wide go to 3 2. (a) Has a ring of roots at the base Allium (b) No ring of roots Colocasia 3. (a) Has shoots or leaves go to 4 (b) No shoots or leaves 4. (a) Branched (b) Not branched 5. The diagram below shows seven species of arachnid. Cassava Zingiber Solanum Referring to the diagram in the box, use the key to identify each species. Write the letter of each species (A to G) in the correct box beside the key. One has been done for you. Key 1. (a) Abdomen with a tail (b) Abdomen without a tail Abaliella dicranotarsalis E go to 2 (a) Legs much longer than abdomen and cephalothorax go to 3 2. (b) Legs not much longer than abdomen go to 4 and cephalothorax (a) Hairs on legs Tegenaria domestica 3. (b) No hairs on legs Odielus spinosus (a) Cephalothorax or abdomen segmented Chelifer tuberculatus 4. (b) Cephalothorax or abdomen not go to 5 segmented (a) Abdomen and cephalothorax about the Poecilotheria regalis 3. same size (b) Abdomen larger than cephalothorax (a) Body covered in long hairs 4. (b) Body not covered in hairs 6. The diagram below shows five mammals. Use the key to identify each of these mammals. Write the letter for each mammal in the table. tail more than half that of body length 1. tail less than half that of body length ears at top of head, with thick tail 2. ears at side of head, with thin tail nose pointed, nose length longer than its depth 3. nose blunt, nose length shorter than its depth front legs as wide or wider than long 4. front legs longer than wide go to 6 Tyroglyphus longior Ixodes hexagonus go to 2 go to 4 Sciurus caroliniensis go to 3 Sorex araneus Clethrionomys glareolus Talpa europaea Oryctolagus cuniculus Name of animal Letter Clethrionomys glareolus Oryctolagus cuniculus Sciurus caroliniensis Sorex araneus Talpa europaea 7. Explain what is meant by the term magnification and resolution. 8. Outline the working of the light microscope. 9. Make a table comparing the advantages and the disadvantages of the light and electron microscopes. 10. Define and discuss the term biotechnology. 11. Write briefly on the advantages of using microorganisms in biotechnology. 12. Give a brief account on the making of biofuel. 13. Describe in outline the stages in bread making. 14. What are curds and whey? 15. Give a brief account on making of wine. 16. Explain the processes in making of yoghurt and cheese. 17. Describe the steps taken to brew beer. 18. Name three microorganisms used in food production and state their fermentation products. 19. How is the fermenter sterilized before use? 20. Why is cold water circulated through the water jacket of the fermenter during the fermentation process? 21. Explain what would happen to the microorganisms in the fermenter if the paddles stopped working. 22. State the role of enzymes in the biological washing powder. 23. Describe the use of pectinase enzyme in fruit juice extraction. Concept map Biotechnology Microscopy Traditional Biotechnology Introduction to Biology of Living Things The working of light and electron microscope Construction of Dichotomous Key Identification and Classification H The Importance of Biology Link between Biology and Other Branches of Science Comparison of light and electron microscope Magnification and Resolution Modern Biotechnology Microorganism and Biotechnology Making yoghurt and cheese Enzymes use in industry Biological washing powder 15 Making wine and beer Extraction fruit juice Biofuels and bread making Fermentation and fermenter Textbook Biology CHAPTER 2 BIOLOGICAL MOLECULES AND MOVEMENT IN AND OUT OF CELL Learning Outcomes It is expected that students will be able to - explain the main basic groups of molecules in living organisms - know the compositions and structures of different biomolecules - realize the structure of hereditary biomolecules - describe the structure of a cell membrane and the role of each component - clarify the processes of passive and active transport - comprehend the importance of water potential 2.1 BIOLOGICAL MOLECULES OF THE CELL A biological molecule (biomolecule) is a chemical compound that naturally occurs in living organisms. Some are inorganic molecules (such as water) and some are organic molecules. Carbon is an element present in all organic biological molecules. Carbon atoms can join to form chains or ring structures. So biological molecules can be very large often by polymerization (macromolecules), often constructed of repeating sub-units (monomers). Other elements always present are oxygen and hydrogen. Nitrogen is sometimes present. When macromolecules are made of long chains of monomers held together by chemical bonds, they are known as polymers. Examples are carbohydrates, proteins and nucleic acids. Lipids are not polymers but important biomolecule. Cells need chemical substances to make new cytoplasm and to produce energy. Therefore, the organism must take in food to supply the cells with these substances. Of course, it is not quite as simple as this; most cells have specialized functions and so have differing needs. However, all cells need water, oxygen, salts and food substances and all cells consist of water, carbohydrates, lipids, proteins including enzymes and nucleic acids. 2.1.1 Water Water is a good solvent and many substances move about the cells in a watery solution. It is the most important biochemical of all living things. Water is the medium for various enzymatic and chemical reactions in living cell. Without water, life would not exist on this planet. It is important for two reasons: first, it is a major component of cells, typically forming between 70% and 95% of the cells. About 60% present in human. If water contents fall, the cells will die. Second, it provides an environment for aquatic organisms. Despite these, water has some unusual properties. Properties of water Water molecules are made up of two 'H' atoms bonded to an 'O' atom. 'H' atom possesses a slight positive charge and O' atom has a slight negative charge. Therefore, water molecules have two poles i.e. a positive hydrogen pole and a negative oxygen pole, it is termed as polarity and water is a polar molecule. A bond called hydrogen bond (H-bond), which formed in liquid state of water providing useful and significant properties of water in the living organisms (Figure 2.1). 1. Water has a high specific heat. Specific heat is the amount of heat that must be absorbed in order for 1 g of a substance to change its temperature 1 °C. This means that large bodies of water, like oceans, absorb a lot of heat and resist changes in temperature. As a result, they provide a stable environment for the organisms that live in them. In addition, coastal areas exhibit relatively little temperature change because the oceans moderate their climates. 2. Water has a high heat of vaporization. This means that a relatively great amount of heat is needed to evaporate water. As a result, evaporation of sweat significantly cools the body surface. 3. Water is the universal solvent. Because water is a polar molecule, it dissolves all polar and ionic substances. All the reactions of metabolism occur in solution. Also, food, hormones and other substances are transported in solution either in the blood of animals or in the sap of plants. 4. Water exhibits strong cohesion tension. This means that molecules of water tend to stick to each other. This results in several biological phenomena. Water moves up a tall tree from the roots to the leaves without the expenditure of energy by what is referred to as transpirational-pull and/or cohesion tension. Strong cohesion also results in surface tension that allows insects to walk on water without breaking the surface. 5. Water has high adhesion properties. Adhesion is an attraction between two different molecules. Water molecules exhibit the attraction to the inside of the vascular tube. This force of adhesion contributes to capillary action, which helps water flow up from the roots of a plant to leaves. It plays an important role in the survival of plants. 6. Density or specific gravity of water is highest at 4 °C. As water cools to 4 °C, it reaches its maximum density. As it cools further, the molecules become less dense and change into solid form. The low density of ice causes it to float at the surface of liquid water, such as an iceberg in the sea or the ice cubes in a glass of water. In lakes and ponds, ice forms on the surface of the water creating an insulating barrier that protects the animals and plant life in the pond from freezing. Without this layer of insulating ice, plants and animals living in the pond would freeze in the solid block of ice and could not survive. 2.1.2 Carbohydrates Carbohydrates are organic molecules composed of carbon (C), hydrogen (H) and oxygen (O). They supply the living organism with food and energy and also play an important role in structure and shape of plant cells. Carbohydrates mainly originated from plant materials. Carbohydrates are divided into three groups; namely monosaccharides (simple sugars), disaccharides and polysaccharides. The word 'saccharide' refers to sugar or sweet substance. Monosaccharides Monosaccharides are used to produce and store energy for the living organisms. Monosaccharides are simple sugars in which there is one oxygen atom and two hydrogen atoms for each carbon atom in the molecule. A general formula for this can be written (CH₂O). 'n' is a number of carbon atoms. Triose sugars (n=3) have three carbon atoms and the general formula CHO, such as glycerol, glyceraldehyde and dihydroxyacetone. They are important in mitochondria, where the respiration process breaks down glucose into triose sugars. Pentose sugars (n=5) have five carbon atoms and the general formula CHO. Ribose and deoxyribose are important pentose sugars in the nucleic acids ribonucleic acid (RNA) and deoxyribonucleic acid (DNA), which make up the genetic materials (Figure 2.2). Hexose sugars (n=6) have six carbon atoms and the general formula CHO. They are the best- known monosaccharides, often taste sweet and include glucose, galactose, mannose and fructose. Ring structure has two isomers (different forms): a and ẞ such as a-glucose and B-glucose. Most living things create energy by breaking down the monosaccharide 'glucose' and harvest the energy released from chemical bonds of glucose. Any glucose in the food that has been eaten can be absorbed and used directly in the cells (Figure 2.3). Disaccharides Disaccharides are made up of two monosaccharides joined together by a glycosidic linkage, which a covalent bond. For example, maltose is made up of two glucose units joined; found in germinating seed such as barley. Sucrose, a table sugar is made up of one glucose molecule joined with one fructose molecule. Lactose, a milk sugar is made up of one galactose unit joined with one glucose (Figure 2.4). Polysaccharides Polysaccharides are formed by many monosaccharides units joined together by covalent bonds. They are insoluble and serve as reserve food and structural materials (Table 2.1). Table 2.1 Types of polysaccharides Starch Cellulose Amylose Source Plant Plant Subunit B-glucose a-glucose Bonds 1-4 1-4 Branches No No Diagram Amylopectin Plant a-glucose 1-4 and 1-6 Yes (~per 20 subunits) Glycogen Animal a-glucose 1-4 and 1-6 Yes (~per 10 subunits) Shape Cellulose is a polysaccharide made up of several molecules of glucose joined by B1-4 glycosidic linkages. It is insoluble in water and main component of cell wall in plants. It is a fiber found in protective cell wall of plants. Starch is made up of millions of glucose molecules by photosynthesis process of green plants. The basic chemical formula of the starch molecule is (CHO). It is composed of two portions: (i) Amylose-linear portion containing glucose units joined by a1-4 glycosidic linkages. It is more soluble in water and its content in starch is about 20%. (ii) Amylopectin - it is a branched chain polymer of glucose units joined by a1-4 glycosidic linkages as well as by a1-6 glycosidic linkages. It is less soluble in water but soluble in hot water. Its content in starch is about 80%. It is abundantly found in plants, seeds, fruits and tubers. Glycogen is made up of millions of glucose molecules and formed the main storage carbohydrate. It is found in animal and fungi. In mammals, glycogen molecules are stored in the liver and muscle cells. 2.1.3 Lipids Lipids are another group of important biological molecules present in all cellular organisms and some viruses. Unlike the other groups, they are highly heterogeneous in chemical nature. The simple lipids include fats, oils and