Foundation Bhawan Bharti Biology

Foundation Science BIOLOGY FOR CLASS 10 N K Mishra, PhD L C Saha, PhD

PREFACE It gives us great pleasure to present this book. It covers, along with our book for class 9, the secondary school biology course of the CBSE. The text has been written in a simple and easy-to-understand style. A lot of information has been presented in tabular and pointwise formats that should aid quick learning, comparison of facts, etc. The diagrams are fairly large, and they have been drawn and labelled as clearly and simply as possible. Wherever possible, photographs have been given. A book for class 10 has special significance because students take the first public examination after this class. Therefore, the content of this book has been prepared to train students for the board examination and beyond. At the end of each chapter points to remember has been given. To help students, the exercises have been divided into three separate groups that have very-short-answer, short-answer and long-answer questions. Apart from these, objective questions, which test a student’s understanding so well, have also been given. Special importance has been given to lab work. A separate chapter, including experiments and short-answer questions for viva voce, has been added. In addition, a separate exercise based on multiple-choice questions has been given. This will prepare students for the written examination based on multiple-choice questions. We would like to thank the editors, proofreaders, artists and typesetter associated with this book. A special word of thanks to the projects manager, who helped in putting all the pieces together. We would like to know whether the book meets the requirement of the students and how it can be improved. We would appreciate feedback and suggestions from teachers and students. Authors (iii)

CONTENTS 1 11 1. Nutrition 20 2. Respiration 30 3. Transportation 38 4. Excretion 50 5. Control and Coordination 64 6. Reproduction 82 7. Heredity and Evolution 94 8. Our Environment 142 9. Practicals Question Bank (v)

1 Nutrition NNuturittriiotinon Before we learn about the various life processes, we should know the defining characteristics of life. How do we understand what is alive and what is not? We see a variety of things such as mountains, land, buildings, plants, insects, birds, animals, etc., around us. How do we differentiate these things? Some of these, like mountains, land and buildings, are nonliving things, while others like plants, insects, birds and animals are living. What are the basic differences between these? All living things carry out various life processes like taking in food, obtaining energy from food, throwing out wastes, and so on. Living things also move, grow, respond to changes in their external and internal conditions, and produce young ones. All living things (organisms) also have an organized (cellular) structure with different levels of organization. An organized and ordered structure with cells, tissues, organs, organ systems, etc., is an important feature that distinguishes the living from the nonliving. If this organization breaks down, an organism is no longer alive as organization is not only confined to the external appearance, but is present in the internal structure as well. Therefore, living things have to repair and maintain their structures through various processes. Let us learn about some of these processes which help maintain life. LIVING THINGS AND LIFE PROCESSES You have learnt that living organisms have tissues, which comprise groups of cells with similar structures and functions. A cell is the basic structural and functional unit of any living thing. Each cell is made up of molecules. The molecules exhibit movement during cellular reactions. Such reactions lead to the cellular life activities. There is an absence of such molecular movements in viruses, which remain nonliving until they infect a living organism. Their molecular movement begins when they use the other organism’s cell molecules and organelles for producing their own proteins and replicating themselves. Let us now discuss how living beings grow and how they maintain and repair their structures. The growth of a living organism starts with the division of its cells. When a cell divides, it forms two daughter cells from a single mother cell. The daughter cells divide and redivide to give rise to tissues and organs. Different life processes of an organism, like growth and maintenance, require energy which is obtained from food by a process called nutrition. Different organisms have varied nutritional processes depending on their environment and specific food requirements. Food is broken down into simpler forms by a stepwise oxidizing–reducing process known as respiration. During this process, oxygen is commonly required by organisms to release energy from food for carrying out various life processes. Generally, in multicellular organisms all the cells are not in contact with the environment. The exchange of gases and the uptake of food occur in specialized tissues. So, food and oxygen have to be transported to all parts of the body. For the movement of food and oxygen from one part to another, there is a transportation system. The carrying out of different life processes 1

2 Foundation Science: Biology for Class 10 involves metabolism (chemical reactions in organisms), which produces harmful waste products that have to be removed from the bodies of living beings. The process of elimination of these waste products of metabolic activity from the body is excretion. In complex organisms a specialized tissue system carries out excretion and a specialized transportation system carries the metabolic waste products to the excretory tissues. The exchange of materials with the environment is accomplished by diffusion in unicellular organisms as the entire surface of the organism remains in contact with the environment. Living things also respond to changes in their environment in a particular manner. They produce new individuals similar to themselves by a process called reproduction. They have a definite life cycle of birth, growth, reproduction and death. From the above discussion it is clear that living things can be easily distinguished from nonliving things as they carry out various life processes such as nutrition, respiration, transportation, excretion, etc. In this chapter we shall discuss the basic concepts of nutrition. Nutrition provides nutrients to the body so that it can obtain energy to carry out the activities required to stay alive. Nutrients are substances that give nourishment, which provides energy to an organism. Cells obtain nutrients from the food taken by the organism. The food taken by the organism is complex, but nutrients are much simpler molecules. The digestive system of an organism breaks down complex food into simpler molecules, so that the cells can take them in and use them for survival, growth and reproduction. Nutrition promotes growth of the body, which involves the formation of new protoplasm. Nutrition meets the energy requirement of the body. Nutrition helps synthesize a variety of substances, like proteins, carbohydrates, lipids, etc., which in turn perform a variety of functions. MODES OF NUTRITION Plants and animals do not obtain food by the same processes. Plants and some bacteria have the green pigment chlorophyll to help synthesize food, while animals, fungi and other bacteria depend on other organisms for food. Based on this, there are two main modes of nutrition: autotrophic and heterotrophic. AUTOTROPHIC NUTRITION The term ‘autotroph’ is derived from two Greek words—autos (self) and trophe (nutrition). In autotrophic nutrition, an organism makes its own food from simple raw materials. Fig.1.1 A summary of nutrition in green plants Photosynthesis Green plants, which are autotrophic, synthesize food through the process of photosynthesis. Photosynthesis is a process by which green plants, having chlorophyll, synthesize the simple

Nutrition 3 sugar (glucose) from the simple raw materials water and carbon dioxide using the energy of sunlight. Oxygen is released in this process. The overall equation of photosynthesis is 6CO2 + 12H2 O ¾S¾un¾lig¾ht ® C6 H12 O6 + 6H2 O + 6O2 Chlorophyll The sugar produced is stored in the form of starch in plants. (In animals food is stored in the form of glycogen.) These food reserves provide energy as and when required by the organism. Since autotrophic plants are able to produce food, they are also known as producers. Site of Photosynthesis Though all green parts of a plant are capable of performing photosynthesis, the leaves are the most suitable organs for this process. The cells of the leaves contain special organelles called chloroplasts, which are the main sites of photosynthesis. These are plastids which contain the light-absorbing green pigment chlorophyll. Requirements for Photosynthesis Photosynthesis requires chlorophyll, carbon dioxide, water and sunlight. 1. Chlorophyll Chlorophylls are green pigments found in all photosynthetic organisms and are responsible for their green colour. In plants, chlorophyll is mainly found in the leaves. Young stems and fruits may also have chlorophyll. In lower plants like algae, the whole plant is green and takes part in photosynthesis. 2. Carbon dioxide Air contains about 0.03% of carbon dioxide. Terrestrial plants use atmospheric carbon dioxide in photosynthesis. Aquatic plants use the carbon dioxide dissolved in water. Plants obtain carbon dioxide through pores called stomata present on the surfaces of leaves. The opening and closing of these pores are regulated by guard cells, which surround them. Cuticle Upper epidermis Chloroplast Xylem Phloem Guard cell O2 Air spaces CO2 Lower epidermis Stoma Fig. 1.2 Anatomy of a leaf. Note how plants obtain CO2 through stomata. 3. Water Water is an important raw material for photosynthesis. Plants absorb water from the soil through their root hairs. The water is then transported up to the leaves through the stem. 4. Sunlight Light energy is used in splitting water molecules into hydrogen and oxygen. The splitting of water in the presence of light is called photolysis. Mechanism of Photosynthesis There are two main stages in the entire process of photosynthesis. The first stage is dependent on light (light reactions). The other stage does not require light (dark reactions). During these two stages, the following events occur. 1. Light energy is first absorbed by chlorophyll molecules found inside the chloroplasts.

4 Foundation Science: Biology for Class 10 2. The absorbed energy causes splitting of water molecules into hydrogen and oxygen. During this process the light energy gets converted into chemical energy. 3. Finally, carbon dioxide is reduced to carbohydrate (the end product of photosynthesis). Factors Affecting Photosynthesis Intensity of light, carbon dioxide concentration in the air, temperature and water are the important external factors that influence photosynthesis. Internal factors include chlorophyll content and the accumulation of the products of photosynthesis. 1. Experiment to demonstrate that starch is formed during photosynthesis Pluck a healthy green leaf of a plant which was in the sunlight. Place it in a beaker containing boiling water for about two minutes. Now transfer the leaf to a beaker containing alcohol. Warm it over a water bath for a few minutes. You will observe that the leaf turns white, indicating that the chlorophyll has been removed. Now wash the leaf carefully in water without damaging it. Place the leaf in a dilute solution of iodine. This will turn the leaf bluish black. The changing of the leaf’s colour to bluish black after it has been treated with iodine solution shows that the leaf contains starch. 2. Experiment to demonstrate that carbon dioxide is essential for photosynthesis Get two healthy potted plants of almost the same size and place them in the dark for 24 hours to destarch the leaves. Now place them on glass plates. Cover the plants with separate bell jars. Keep some crystals of potassium hydroxide (KOH) in a Petri dish and place it under one of the jars. Make the set-up airtight by applying Vaseline at the bottom of the bell jars. Fig. 1.3 Experiment to show that CO2 is essential for photosynthesis Keep the plants in sunlight for photosynthesis to take place. After 3 to 4 hours pluck a leaf from each plant. Boil the leaves in water and subsequently in alcohol, using a water bath, to remove chlorophyll. Now use a few drops of iodine to test for starch in each leaf. Only one leaf turns blue-black showing the presence of starch. This happens because KOH absorbs the CO2 present inside one bell jar. As a result, the leaves do not get CO2 for photosynthesis. Thus the process of photosynthesis is inhibited and starch is not synthesized. 3. Experiment to show that sunlight is essential for photosynthesis Keep a potted plant in the dark for 24 hours. On one of the leaves, stick black paper strips (one below and one above the leaf) with the help of Sellotape. Now, place this plant in sunlight for a few hours. Pluck the leaf and remove the black strips. Boil this leaf, first in water and then in alcohol, to remove chlorophyll. After washing the leaf with water, keep it in a Petri dish. Add a few drops of iodine solution. The leaf turns blue-black except in the region that had been covered. This region did not receive light and

Nutrition 5 hence no starch was formed. The uncovered region received light and starch was formed due to photosynthesis. Black paper Does not turn blue-black Blue-black Fig. 1.4 Experiment to show that sunlight is essential for photosynthesis Plants take up different nutrients like nitrogen, phosphorus, iron, magnesium, etc., along with water through the root. These nutrients contribute not only to the process of photosynthesis but also to the general development of the plants. For example, nitrogen is used in the synthesis of proteins and other compounds. HETEROTROPHIC NUTRITION The word ‘heterotroph’ is derived from two Greek words—heteros (other) and trophe (nutrition). Unlike autotrophs, which manufacture their own food, heterotrophic organisms obtain food from other organisms. As heterotrophs depend on other organisms for their food, they are called consumers. All animals and nongreen plants like fungi come under this category. Consumers which consume herbs and other plants are called herbivores, and those which consume animals are called carnivores. After taking complex organic materials as food, heterotrophs break them into simpler molecules with the help of biological catalysts, or enzymes, and utilize them for their own metabolism. Depending upon the mode of living and the mode of intake of food, heterotrophs may be parasitic, saprophytic or holozoic. Parasitic Parasitic organisms, or parasites, live on or inside other living organisms, called hosts, and obtain their food from them. The host does not get any benefit from the parasite. Different parasites, like Cuscuta (akash-bel), Cassytha (amar-bel), hookworms, tapeworms, leeches, etc., have different modes of feeding, depending upon habit, habitat and modifications. Saprophytic Saprophytic organisms, or saprophytes, derive their food from dead organisms. They secrete enzymes that are released on food material outside their body. These enzymes break down complex food into simple forms. Common examples of saprophytes are fungi (moulds, mushrooms, yeasts) and many bacteria.

6 Foundation Science: Biology for Class 10 Holozoic In holozoic nutrition complex organic substances are ingested (taken in) without their being degraded or decomposed. After intake, such food is digested by enzymes produced within the organism. Digested food is absorbed into the body and the undigested product is egested (expelled) from the body. This kind of nutrition is found mainly in nonparasitic animals—simple ones like Amoeba and complex ones like human beings. How Organisms Obtain Nutrition Different organisms obtain food in different ways. Nutrition in unicellular organisms, like Amoeba, involves ingestion by the cell surface, digestion and egestion. Amoeba takes in complex organic matter as food. Amoeba first identifies its food. It then throws out a number of small pseudopodia (projections of cytoplasm, also called false feet). These pseudopodia enclose the food particle and prevent it from escaping. The food enclosed in the cell membrane forms a food vacuole. The complex food is broken down into simpler molecules with the help of digestive enzymes of the organelle called lysosome. The digested food is distributed in the cytoplasm and the undigested food is egested through the cell membrane. Fig. 1.5 (a) Amoeba sends out pseudopodia to engulf food. (b) Feeding in Paramoecium In Paramoecium, a unicellular organism with a specific shape, food is ingested through a special opening, the cytostome (cell mouth). Food is brought to this opening by the lashing movement of cilia that cover the entire surface of the cell. HUMAN DIGESTIVE SYSTEM The alimentary canal and the glands associated with digestion constitute the human digestive system.

Nutrition 7 Alimentary Canal The alimentary canal in human beings measures about 8 to 10 metres in length. It extends from the mouth to the anus. It has the following parts. Mouth The mouth consists of the oral cavity, through which food is ingested. It is bounded by lips and cheeks. It contains gums, teeth, a tongue and muscles. The tongue tastes food and moves it into the pharynx. Teeth help in biting, cutting and chewing food. Teeth masticate the food. This makes it easier to swallow food and increases its surface area for various digestive secretions to act on. The four types of teeth are incisors, canines, premolars and molars. Our teeth are covered with a hard protective covering of enamel. The enamel covers the dentine, which is a yellowish substance forming the bulk of the tooth. When we eat sweets, chocolates and ice creams, bacteria act on sugars and produce acids which soften the protective covering. This causes dental caries. Bacterial cells and food particles stick to the teeth and form dental plaque. If the teeth are not brushed properly after meals, bacteria may invade deeper into the teeth. This leads to infection and toothache. The presence of food in the mouth stimulates the three pairs of salivary glands to secrete saliva. Saliva has mucin, which lubricates the mouth and food. Saliva also has salivary amylase, a digestive enzyme that breaks down starch and glycogen to maltose (a simpler sugar). Pharynx The oral cavity opens into the pharynx. The swallowing mechanism guides the masticated food through the pharynx, into a tube called oesophagus. Oesophagus It is a muscular, tubular part of the alimentary canal. The muscular walls of the oesophagus move in a rhythmic wavelike manner, which carries the food down to the stomach. This muscular movement is called peristalsis. Here also salivary amylase acts on starch and glycogen in the chewed food. Mouth Salivary gland Oesophagus Contraction Food Diaphragm Liver Gall bladder Stomach Relaxation Pancreas Ascending colon Transverse colon Small intestine Descending colon Appendix Rectum (a) (b) Fig. 1.6 (a) Alimentary canal and digestive glands of man (b) Food passes down the alimentary canal by peristalsis. Stomach It is located below the diaphragm (the muscular partition between the chest cavity and abdominal cavity). It is a saclike muscular structure. It serves as a storehouse of food where partial digestion takes place. The stomach has an anterior cardiac and a posterior pyloric part. As in other parts of the alimentary canal, columnar cells line the inner wall of the stomach. The inner lining has

8 Foundation Science: Biology for Class 10 sunken pits. Each pit constitutes a gastric gland. The cells lining a gastric pit, or gland, are of three kinds: (1) mucous cells (secreting mucus), (2) parietal, or oxyntic, cells (secreting hydrochloric acid) and (3) chief, or zymogen, cells (secreting the inactive enzyme propepsin). The hydrochloric acid in gastric juice converts propepsin to active pepsin and also kills bacteria ingested with food. The mucus protects the stomach lining and glands from being digested by gastric juice. About 3 L of gastric juice is produced per day. Excess secretion of gastric juice, particularly in an empty stomach, erodes the inner lining of the stomach. This erosion causes lesions or round depressions called peptic ulcer in the stomach walls. Digestion of protein begins in the stomach. Pepsin breaks down proteins into peptones. Gastric lipase partially breaks down lipids. Small intestine The small intestine is about 6 metres in length and 2.5 centimetres in thickness. There are three divisions of the small intestine: duodenum, jejunum and ileum. Duodenum is the first part. It begins from the pyloric stomach, and is C-shaped. In the middle of the duodenum two different ducts open through a common aperture. One of the ducts is the common bile duct and the other is the pancreatic duct. Bile, a yellowish green alkaline juice, is poured into the duodenum through the common bile duct. Liver It is the largest gland of the body. It performs many functions. It secretes bile, which helps in digestion. Bile juice produced by the liver is stored in the gall bladder. There are two main functions of bile. 1. It emulsifies fats, by rendering them soluble and breaking them into small globules. In this form, fats are better exposed to the action of fat-hydrolyzing enzymes. (All digestive enzymes catalyze by breaking water molecules, and are hence called hydrolyzing enzymes.) 2. The acidic food (chyme) coming from the stomach becomes alkaline (chyle) when it is mixed with bile. This is important as the intestinal enzymes catalyze the breakdown of food only in an alkaline medium. Pancreas It secretes pancreatic juice, which is carried by the pancreatic duct into the duodenum. Pancreatic juice contains a number of digestive enzymes such as amylase for the splitting of polysaccharides, lipase for the breakdown of fats, and trypsin and chymotrypsin for the breakdown of proteins. These enzymes catalyze the breakdown of their substrates in an alkaline medium. But the catalysis does not completely break all the substrates into their simplest units. Jejunum is the middle part of the small intestine. It is found only in man. Ileum is the last and main part of the small intestine. The major part of digestion and absorption takes place here. Intestinal glands The complete digestion of the remaining food material takes place in the ileum. There are numerous small glands in the walls of the small intestine. These glands secrete intestinal juice. The digestive enzymes in the intestinal juice break small peptides into amino acids, disaccharides into monosaccharides, lipids into fatty acids and glycerol, and nucleic acids into nucleotides. Large intestine The ileum passes into the large intestine. The large intestine can be divided into two parts: anterior (colon) and posterior (rectum). At the junction of ileum and colon, there is a blind (one end closed) outgrowth called caecum. The caecum ends in the vermiform appendix (Latin vermis = worm; vermiform = worm-shaped). In man, the vermiform appendix has outlived its usefulness; it is a vestigial organ. It is an 8-cm-long blind tube, which sometimes becomes a source of trouble. The colon has an ascending part, a transverse part and a descending part. The last part, or the descending part, opens into the rectum. The terminal part of the rectum is called anal canal. It opens through the anus, guarded by the sphincter muscles. The large intestine allows the passage of residual food mass (faecal matter), which is egested through the anus. As the residue of the food mass passes along the large intestine, a considerable amount of water contained in the residue is absorbed into the blood through the intestinal walls. The specialized longitudinal muscles present in the colon wall regulate the passage of the faecal matter along the colon.

Nutrition 9 Take two clean test tubes. Pour 1 mL starch solution (1%) in each of them. Add 1 mL saliva in one test tube only and keep both the test tubes in a test tube holder undisturbed for half an hour. Now add a few drops of iodine solution in both the test tubes. You will observe that the saliva-containing test tube shows no blue-black colour, while the other test tube does. What does it indicate? It shows that saliva contains some enzyme which has converted starch into some simpler compounds. In fact, salivary amylase present in saliva breaks down starch into maltose. Absorption of Digested Food Fig. 1.7 Villi of small intestine Absorption of completely digested food takes place in the ileum. The wall of the ileum has fingerlike projections called villi that increase the surface area for absorption of digested food. The villi are richly supplied with blood vessels to carry the absorbed food (Figure 1.7). The absorbed food is then brought into the blood capillaries. From the blood capillaries, absorbed materials are transported by veins to the liver and then to the heart for distribution to different parts of the body. Assimilation of Digested Food Intake of digested food by cells of the body is called assimilation. Digested food is utilized by the body in many ways. It is used to obtain energy through the process of respiration. Excess monosaccharides are stored as glycogen. Amino acids are used in the synthesis of proteins. The glycerol and fatty acids either provide energy or get reconverted into fats. These fats are accumulated in different organs below the skin. The absorbed food is also utilized for the formation of new cells and tissues, leading to the growth and development of the body. • POINTS TO REMEMBER • · Living beings can be distinguished from · In photosynthesis, solar energy is absorbed by nonliving things due to their organized structure chlorophyll. The absorbed energy causes and life processes, like nutrition, respiration, splitting of water molecule. O2 is liberated as transportation, excretion and reproduction. by-product. · Nutrition is the process of providing nutrients to · There are various forms of the heterotrophic the body cells. In this, food is taken in by the mode of nutrition such as saprophytic (feeding organism, digested and assimilated. The on dead and decaying organic matter), assimilated food is utilized by the cells for the parasitic (depending upon a living host), and production of energy and the synthesis of holozoic (involving (a) ingestion, (b) digestion, proteins, etc. (c) absorption and (d) egestion). · Nutrition may be autotrophic or heterotrophic. · Amoeba ingests food by the infolding of its cell All green plants are autotrophs. Nongreen membrane around the food. After digestion and plants and animals depend on autotrophs for assimilation, it egests the undigested material. their food and are thus called heterotrophs. · Human digestion begins in the mouth. In the · Chlorophyll pigments in green plants are unique stomach, digestion of protein occurs in an acidic in their property of trapping solar energy and medium. In the duodenum, the food is turned converting it into chemical energy. alkaline by the bile juice and digestion occurs Photosynthesis occurs in the chloroplasts. It with the help of enzymes from the pancreas. In requires sunlight, chlorophyll, water and carbon the ileum, digestion occurs with the help of dioxide. It produces glucose and liberates intestinal juice produced by the intestinal glands. oxygen. · Absorption of digested food occurs in the small intestine with the help of villi. The large intestine helps in water absorption.

10 Foundation Science: Biology for Class 10 • EXERCISES • A. Very-Short-Answer Questions 5. Describe the process of nutrition in Amoeba. 1. Why is diffusion sufficient for transporting food 6. Define the terms ‘nutrition’ and ‘nutrients’. List two and oxygen in unicellular organisms? differences between holozoic nutrition and 2. How can we distinguish the living from the saprophytic nutrition. Give two examples of each of nonliving things? these two types of nutrition. [CBSE] 3. Name the different modes of nutrition. D. Objective Questions I. Pick the correct option. 4. Name the requirements for photosynthesis. 5. What are the two stages in photosynthesis? 1. Which of the following options describes the 6. How do autotrophs obtain CO2 and N2 to make characteristics of a living being? their food? [CBSE] (a) Nutrition (b) Respiration 7. What is the action of saliva on starch? (c) Excretion (d) All of these 8. What is peristalsis? 2. Which of these is not required for photosynthesis? 9. Name the three parts of the small intestine. [CBSE] (a) Sunlight (b) Carbon dioxide (c) Oxygen (d) Water B. Short-Answer Questions 3. Amoeba captures food with the help of 1. Define nutrition. (a) teeth (b) cilia 2. Differentiate between producers and consumers (c) pseudopodia (d) tentacles with examples. 4. The largest gland associated with the human 3. Why are leaves suitable for photosynthesis? alimentary canal is 4. Differentiate between the following. (a) Saprophytic and holozoic digestion (a) stomach (b) liver (b) Herbivore and carnivore (c) pancreas (d) small intestine 5. What do the gastric glands secrete and how do these help in digestion? 5. The mode of nutrition in green plants is 6. What is the role of hydrochloric acid in our (a) autotrophic (b) holozoic stomach? (c) heterotrophic (d) saprophytic 7. Mention any two ways in which digested food is utilized by the body. 6. In humans the process of digestion begins in the (a) oesophagus (b) mouth (c) stomach (d) pharynx II. Fill in the blanks. C. Long-Answer Questions 1. The process by which green plants synthesize their food is called _____. 1. Describe the human digestive system. 2. Organisms that derive their food from decaying 2. Mention the major glands associated with the matter are called _____. alimentary canal of man, and their functions. 3. The mode of nutrition in Amoeba is _____. 3. How will you test for the presence of starch in a leaf? 4. The glands which produce salivary amylase are called _____. 4. Give an account of the process of photosynthesis. 5. The wall of the ileum has fingerlike projections called _____ , which have absorptive cells. Objective Questions • ANSWERS • 5. (a) 1. (d) 2. (c) 3. (c) 4. (b) v 6. (b)

2 Respiration All living organisms require energy to carry out life processes. This energy comes from food. However, processes carried out in cells cannot use the energy locked in stored food, fats, etc., directly. Cellular processes get usable energy from a process called respiration. Respiration commonly involves the use of oxygen to break down carbohydrates and other organic molecules, giving usable energy, carbon dioxide and water in the process. RAellsporirgaatnioisnms breathe—a process in which they take in oxygen and give off carbon dioxide. This is called external respiration. Internal respiration, or cellular respiration, takes place inside every living cell. In this process, carbohydrates and other organic molecules are broken down in successive steps to produce energy, which is used to make a compound called adenosine triphosphate (ATP). Cellular processes get energy from ATP. ATP is often called the ‘energy currency’ of the cell. The amount of ATP in a cell indicates how energy-rich it is. Where does this energy come from? During photosynthesis, carbon dioxide and water combine with the help of the energy from the sun to form ca rbohydrates. Energy gets stored in the bonds of the carbohydrates. In respiration, these bonds are broken to release energy and give back carbon dioxide and water. This energy then gets stored in the bonds of ATP. These bonds get easily broken to release energy when required by the cells. We can study cellular respiration by taking the example of the complete oxidation of glucose. This molecule is oxidized and broken down gradually in two distinct stages. The first stage is called glycolysis, which involves anaerobic respiration. This takes place in the cytoplasm of the cell. The second stage involves aerobic respiration, which takes place inside the mitochondria of the cell. The overall reaction can be represented as follows. C6H12 O6 + 6O2 ¾® 6CO2 + 6H2 O + Energy (glucose) Anaerobic Respiration Partial oxidation of food in the absence of oxygen, resulting in the release of some amount of energy, is called anaerobic respiration. Anaerobic means without oxygen or in the absence of oxygen, while aerobic means with oxygen or in the presence of oxygen. Glucose has six carbon atoms joined to each other by covalent bonds. Hydrogen and oxygen atoms are also attached to these carbon atoms. In anaerobic respiration of glucose, some hydrogen atoms are removed from it, resulting in its oxidation. (The addition of oxygen or the removal of hydrogen is oxidation.) At the end of a series of reactions, glucose gets converted into two molecules of pyruvate, which contains three carbon atoms. These reactions also produce two molecules of ATP. The oxidation of glucose in a series of reactions leading to the formation of pyruvate is called glycolysis. 11

12 Foundation Science: Biology for Class 10 Glycolysis means ‘splitting of sugar’. It takes place in all organisms, in the cytoplasm of the cell. It is the first stage of respiration—both aerobic and anaerobic. After glycolysis, its product (pyruvate) gets converted into different compounds depending on whether further reactions take place in the presence or absence of oxygen. Glycolysis is the last energy-producing stage in case oxygen is absent or in low supply, and in cells that lack mitochondria. After glycolysis, further anaerobic reactions produce different products like lactic acid or ethanol (ethyl alcohol) in different situations. This step completes the anaerobic respiration of glucose. Anaerobic respiration resulting in the formation of these products is also called fermentation. Examples of lactic acid fermentation and alcohol fermentation are given below. In a low supply of oxygen, yeast converts pyruvate to ethanol and carbon dioxide. Certain bacteria (which lack mitochondria) convert pyruvate to lactic acid. When our muscles are overworked, blood is unable to supply oxygen fast enough for producing energy through aerobic means. In this low-oxygen condition pyruvate gets converted to lactic acid. Accumulation of excess lactic acid in the muscles causes pain. Fig. 2.1 Different ways in which glucose gets oxidized In aerobic respiration, a different path is followed after glycolysis. In the presence of oxygen, in cells that have mitochondria, pyruvate is oxidized further in a number of steps to produce more energy, carbon dioxide and water. Aerobic Respiration The complete oxidation of food yielding carbon dioxide, water and energy in the presence of oxygen is called aerobic respiration. Aerobic respiration takes place inside the mitochondria. After glycolysis, pyruvate enters the mitochondria and is oxidized in a series of reactions. The products of these reactions include ATP, carbon dioxide and water. The number of molecules of ATP formed in aerobic respiration is 38. Hence the energy made available is much greater than in the case of anaerobic respiration. Inside the mitochondria, when an inorganic phosphate group (PO43- , represented here as Pi ) gets attached to a compound called ADP (adenosine diphosphate), a molecule of ATP (adenosine triphosphate) is formed. ADP + Pi ¾® ATP The bond holding the last (terminal) phosphate group is easily broken when ATP reacts with water. In the process, energy is produced. This energy is used to drive cellular processes that are endothermic (i.e., processes that absorb energy). Processes like protein synthesis, contraction of muscles, etc., get energy from ATP.

Respiration 13 Table 2.1 Differences between aerobic and anaerobic respiration Aerobic respiration Anaerobic respiration 1. Aerobic respiration takes place in the 1. Anaerobic respiration takes place in the presence of oxygen. absence of oxygen. 2. The first step in this process (glycolysis) 2. The complete process takes place in the takes place in the cytoplasm, while the cytoplasm. second step takes place in the mitochondria. 3. Glucose is incompletely oxidized either into carbon dioxide, ethyl alcohol and energy (as in 3. Glucose is completely oxidized into yeast) or into lactic acid and energy (as in carbon dioxide, water and energy. muscle cells). 4. 38 molecules of ATP are produced by 4. Only 2 molecules of ATP are formed in the complete oxidation of one this process. gram-mole of glucose. 1. Take two clean test tubes. Pour freshly prepared limewater in each of them. Keep the test tubes in a test-tube stand. Use a syringe to inject air into the limewater in one test tube. Take the syringe out of limewater. Pull up the piston to fill it with air and inject more air into the limewater. Repeat the process till the limewater turns milky. Note the time taken in this process. Now, use a glass tube to blow air into the limewater in the other test tube. You will find that the limewater in the second test tube turns milky in lesser time. This is because the air we breathe out has more CO2 than does atmospheric air. Syringe Glass tube Test tube Limewater turns CO2 in air milky fast CO2 in exhaled air (a) (b) Fig. 2.2 (a) Injecting air with a syringe (b) Blowing air by mouth 2. Take some fruit juice in a clean conical flask. Add some yeast to it. Pass a bent glass tube through a cork, and fit the cork into the mouth of the conical flask. Place the other end of the glass tube inside a test tube containing freshly prepared limewater. The limewater turns milky. This shows that carbon dioxide is liberated during fermentation by the yeast cells. Glass tube Cork Fruit juice + yeast Limewater turns milky Fig. 2.3 Fermentation produces carbon dioxide.

14 Foundation Science: Biology for Class 10 Exchange of Gases in Plants In plants, oxygen and carbon Fig. 2.4 Stomata dioxide diffuse through the stomata and the intercellular spaces of the leaves, and the lenticels of the bark. In woody plants, the stem is covered with bark. Lenticels are small openings in the pits of the bark. The exchange of gases takes place through the lenticels also, apart from the exchange through the openings in the leaves. The direction of exchange of gases between a plant and its surroundings depends upon the time of the day and the usage of the gases by the plant. Plants respire throughout the day, while photosynthesis takes place only in the presence of sunlight. In daytime, carbon dioxide produced in respiration by the plants is used by them in photosynthesis. So, carbon dioxide is not released into the environment. In fact, plants take in additional carbon dioxide from the air for photosynthesis. Out of the oxygen produced in photosynthesis, some amount is consumed by the plants in respiration. The rest is released into the air through the stomata. At night, when there is no photosynthesis, no oxygen is released. Also, the carbon dioxide produced in respiration is not used by the plants. So, it is released in the air. That is why it is advised not to sleep under trees at night. In summary we can say that in daytime, on the whole, the plant releases oxygen and takes in carbon dioxide. And at night the plant releases carbon dioxide and takes in oxygen. Different parts of the plant respire independently. For example, the root takes in oxygen present in the soil by the process of diffusion. Oxygen diffuses into the root hairs and passes into the other cells of the root. And carbon dioxide released by the root cells diffuses into the soil. Since the root is involved in the exchange of gases, if the root of a land plant remains waterlogged for long, the plant dies. In certain respects, respiration in plants is different from that in animals. For example, plants produce some of the oxygen used by them for respiration. In plants, respiration occurs at a much slower rate than in animals. Also, there is little transport of gases from one part of the plant to another, unlike in animals. Exchange of Gases in Animals In small organisms (e.g., Amoeba, Paramoecium) the exchange of gases occurs through the general surface of the body or the cell membrane. However, larger animals (e.g., birds, mammals) have a much greater requirement of energy. Hence they need much more oxygen than can be met through diffusion across the general surface of the body. Therefore, they have special respiratory organs that have a greatly enlarged surface area through which oxygen can diffuse. For example, the human lungs have millions of air sacs whose surface area is many times that of the body. These air sacs are involved in the exchange of gases. In animals, there are three types of respiratory organs—tracheae, gills and lungs. Insects have a fine system of air tubes reaching all parts of the body. Such a tube is called trachea. Oxygen reaches the tissues through the tracheae. Gills are respiratory organs found in aquatic

Respiration 15 animals. You may have seen the gills of a fish. Reptiles, birds and mammals have lungs for the exchange of gases. Fig. 2.5 Exchange of gases in some organisms Aquatic animals have to use the Fig. 2.6 Respiration in fish oxygen dissolved in water. Hence, they have some special organs such as gills to absorb it. In fish, as water enters the mouth, it passes through the chambers where the gills are present. The exchange of gases takes place through the gills. The blood vessels in the gills absorb the oxygen dissolved in water. Terrestrial animals use the abundant oxygen of the atmosphere for respiration. Since the solubility of oxygen in water is low, there is not much oxygen available for aquatic organisms. Therefore, to make up for the low availability of oxygen, the rate of breathing in aquatic organisms is much higher than that in terrestrial organisms. Observe fish kept in an aquarium. You will see that they open and close their mouth and operculum (gill covering) in quick succession. The rate at which they do this is higher than the rate at which we breathe. The higher rate of breathing is necessary to take in the required amount of oxygen from the limited amount dissolved in the water.

16 Foundation Science: Biology for Class 10 THE HUMAN RESPIRATORY SYSTEM The human respiratory system consists of a pair of lungs and a series of air passages leading to the lungs. The entire respiratory tract (passage) consists of the nose, pharynx, larynx, trachea, bronchi, and bronchioles. Fig. 2.7 Human respiratory system Air enters the nose through the nostrils. When air passes through the nose, it is warmed, moistened and filtered. The hairs present in the nose filter out particles in the incoming air. The air is moistened by the mucus present in the nose, and it is warmed by the blood flowing through the capillaries in the nose. The respiratory tract from the nose to the bronchioles is lined by mucous membranes and cilia. The mucus and cilia act as additional filters. Behind the nose lies the pharynx (throat). There are two passages here—one for food and the other for air. The air passes from the pharynx to the larynx, or the voice box. The opening leading to the larynx is called glottis. It is protected by a lid called epiglottis, which prevents food from entering the passage to the lungs. From the larynx the air goes to the trachea, or the windpipe. The trachea is about 11 cm long. It is guarded by 16–20 C-shaped cartilage rings, which prevent the trachea from collapsing. The trachea divides into two tubes called bronchi. Each bronchus divides and branches out in the form of thinner tubes called bronchioles. The bronchioles enter the lungs and divide further into finer branches called alveolar ducts. These open into extremely thin-walled, grape-shaped air sacs called alveoli. Each alveolus is covered by a web of blood capillaries. The lungs are a pair of spongy Fig. 2.8 Alveoli organs lying in the chest cavity formed by the ribs. The actual exchange of gases between the air and the body takes place in the capillary-covered alveoli inside the lungs. Here, oxygen from the air in the alveoli goes into the blood, and the carbon dioxide in the blood goes out. The oxygen binds to the haemoglobin molecules present in the red blood corpuscles and is taken to different parts of the body.

Respiration 17 The total surface area through which the exchange of gases can take place increases because of the millions of alveoli in the lungs. Their total surface area can be about a hundred times that of the body. The large surface area allows sufficient oxygen intake needed for releasing the large amount of energy required by us. Mechanism of Breathing There are two main steps in breathing: inspiration and expiration. Inspiration Inspiration (inhalation) is the process of breathing in, by which air is brought into the lungs. Inspiration involves the following steps. The muscles attached to the ribs on their outer side contract. This causes the ribs to be pulled out, expanding the chest cavity. The muscle wall between the chest cavity and the abdominal cavity, called diaphragm, contracts and moves downwards to further expand the chest cavity. The abdominal muscles contract. The expansion of the chest cavity creates a partial vacuum in the chest cavity. This sucks in air into the lungs, and fills the expanded alveoli. Expiration After the exchange of gases in the lungs, the air has to be expelled. Expulsion of the air from the lungs is called expiration. In this process, muscles attached to the ribs on their inner side contract, and the diaphragm and the abdominal muscles relax. This leads to a decrease in the volume of the chest cavity, which increases the pressure on the lungs. The air in the lungs is pushed out and it passes out through the nose. When we breathe out, not all of the air in the lungs gets expelled. Some of it remains in the lungs. This keeps the lungs from collapsing and allows more time for the exchange of gases. Transport of Gases In very small organisms, there is no need to have a separate transportation system for gases because all its cells are involved directly in the exchange of gases by diffusion. However, a large multicellular organism needs a mechanism for the transport of gases for its different organs and tissues. Human beings also have a system for transportation of gases. Oxygen is carried by haemoglobin of the red blood cells. Haemoglobin has a great affinity for oxygen—each haemoglobin molecule binds to four molecules of oxygen. The oxygen ‘picked up’ by haemoglobin gets transported with the blood to various tissues. Carbon dioxide is more soluble in Fig. 2.9 The overall process of respiration water than oxygen. So, some of it is transported in the dissolved form in our blood. Some carbon dioxide is also transported by haemoglobin. Not all of the carbon dioxide formed is expelled from the body. Some of it reacts with water to form compounds useful for life processes.

18 Foundation Science: Biology for Class 10 • POINTS TO REMEMBER • · Respiration commonly involves the use of · The oxidation of glucose in a series of reactions oxygen to break down carbohydrates and other leading to the formation of pyruvate is called organic molecules, giving usable energy, carbon glycolysis. dioxide and water in the process. · The complete oxidation of food yielding carbon · All organisms take in oxygen from the dioxide, water and energy in the presence of environment and give off carbon dioxide. This oxygen is called aerobic respiration. process is external respiration. Cellular respiration takes place inside the living cell. In this process, · Respiration involves the exchange of gases. In carbohydrates and other organic molecules are plants, the gases diffuse through the stomata, broken down in successive steps to produce ATP, lenticels, and intercellular spaces. In animals, the which provides energy for cellular processes. organs that help in the exchange of gases include gills, tracheae (air tubes) and lungs. · Partial oxidation of food in the absence of oxygen, resulting in the release of some amount of energy, is called anaerobic respiration. • EXERCISES • A. Very-Short-Answer Questions 8. What is the function of the epiglottis in man? Draw 1. Which molecule supplies usable energy for cellular a labelled diagram showing the human respiratory processes? system. [CBSE] 2. Name two end products of anaerobic respiration. 9. How does the total surface area through which the 3. In which part of the cell does aerobic respiration exchange of gases can take place in the lungs take place? become large? What is its advantage? 4. Why do higher animals have special respiratory C. Long-Answer Questions organs with large surface area? 1. What is glycolysis? 5. Name the two steps in breathing. 2. Distinguish between aerobic respiration and 6. Define aerobic respiration. anaerobic respiration. 7. What are the ways in which glucose is oxidized in 3. Explain how the direction of exchange of gases in organisms? plants changes with the time of the day. 8. In which type of respiration is more energy 4. Describe how the exchange of gases takes place in released? the lungs. 9. What happens to the air as it passes through the D. Objective Questions nose? Pick the correct option. B. Short-Answer Questions 1. The energy-rich compound produced during respiration is 1. Differentiate between external and internal (or (a) ATP (b) ADP cellular) respiration. (c) pyruvate (d) AMP 2. What are the steps involved in the formation of 2. The final product of glycolysis is lactic acid from glucose? 3. Why is the rate of breathing faster in aquatic (a) lactic acid (b) glucose organisms than in terrestrial organisms? (c) ethanol (d) pyruvate 4. Differentiate between respiration in plants and 3. The series of reactions resulting in the oxidation of animals. glucose leading to the formation of pyruvate is called (a) fermentation 5. In what forms are oxygen and carbon dioxide transported in the blood? (b) glycolysis 6. How are oxygen and carbon dioxide transported in (c) aerobic respiration human beings? How are lungs designed to maximise the area for exchange of gases? [CBSE] (d) anaerobic respiration 4. The common stage between aerobic and anaerobic 7. Give reasons for the following. [CBSE] respiration is called (a) The glottis is guarded by the epiglottis. (a) oxidation (b) reduction (b) The alveoli in lungs are covered with blood (c) photosynthesis (d) glycolysis capillaries. 5. Aerobic respiration takes place in the (c) The wall of trachea is supported by cartilage (a) nucleus (b) cytoplasm rings. (c) mitochondria (d) vacuole

Respiration 19 6. Which of the following acids is the end product of (a) stomata (b) gills fermentation? (c) lungs (d) alveoli (a) Hydrochloric acid (b) Lactic acid 8. Gaseous exchange in fish takes place through the (c) Pyruvic acid (d) Citric acid (a) trachea (b) lungs 7. Gaseous exchange in plants takes place through the (c) gills (d) alveoli Objective Questions 3. (b) 4. (d) • ANSWERS • 1. (a) 2. (d) 8. (c) 5. (c) 6. (b) 7. (a) v

3 Transportation In orTdrearntsopocartrartyioonut various life processes like nutrition and respiration, organisms require food and oxygen. It is also necessary for the organisms to get rid of the waste products of cellular processes. Food, oxygen and waste products need to be carried from one part of the body to another. In unicellular organisms and many simple multicellular organisms, materials are transported by osmosis and diffusion. In higher organisms this is done by a specialized transport system called the vascular system. TRANSPORTATION IN PLANTS Plants take in some compounds like carbon dioxide through their leaves. They absorb some other materials such as compounds of nitrogen, phosphorus, etc., from the soil through their roots. If the distance between the roots and leaves is very small, food and other materials can be transported by diffusion. But the distances between different plant parts are often quite large, as in tall trees. Therefore, most plants need a proper transport system to carry materials from one part to another. Plants do not move much and have many dead cells in their tissues. Therefore, they do not need much energy. So, they have transport systems slower than those of animals. In plants, the transport system consists of tubelike passages made up of vascular tissue. There are two types of vascular tissues in plants—xylem and phloem. The vascular system extends from the roots through the stem and continues up to the leaves. In the leaves it is clearly seen as a pattern of veins. Water and minerals are transported from the roots upwards through the xylem tubes. Phloem transports synthesized food from the leaves to the rest of the plant body. The transport of water, nutrients and other substances from one part of a plant to another is called translocation. The medium of transport in plants is water. Transport of Water and Minerals The xylem tissue transports water and minerals. It consists of interconnected vessels and tracheids organized into continuous conducting tubes stretching from the roots to the leaves. These tubes carry water and minerals to all parts of the plant. Plants absorb water from the soil through the root and transport it to the stem, leaves and flowers. Roots have root hairs that are unicellular, thin-walled outgrowths of the epiblema (skin of the root). The root hairs are in close contact with the thin film of water surrounding the soil particles. There are mineral salts such as nitrates, chlorides, sulphates, phosphates, etc., dissolved in this water. Water is absorbed by osmosis, while the minerals are absorbed as ions by active transport (transport against the law of diffusion, by spending cellular energy). The cell membrane has transport proteins that allow the ions to cross the membrane. The ions then move upward through the xylem, to the leaves and other aerial parts of the plant. 20

Transportation 21 Ascent of Sap The transport of water and dissolved mineral salts from the roots to the leaves is known as ascent of sap. The cell wall of each root hair is permeable to water and minerals, but its cell membrane and the membrane around the vacuole are semipermeable membranes. The root hair cells take up mineral ions by active transport. This creates a concentration difference of these ions between the root and the soil. Now, the soil solution has higher water content than the cell sap of the root hair. Hence, water from the soil diffuses into the root hair. The root hair cells now become turgid, while the adjacent cells of the cortex have lower water content. This results in the diffusion of water from the root hairs into the cortical cells (Figure 3.1). After passing through the cortical cells by osmosis the water reaches the endodermis (tissue separating the cortex from the vascular tissues). The endodermis forces water into the xylem tubes through passage cells. Fig. 3.1 Absorption of water through root hair The pressure with which water is pushed into the xylem tubes of the root is called root pressure. The water moving upwards forms a column, which is maintained up to a certain height due to root pressure. In tall trees, this type of absorption plays a minor role in transporting water. This process is slow, and it cannot make up for the water lost by transpiration (the evaporation of water from the leaves). Transpiration is rapid during the day. The loss of water due to transpiration creates a suction force that pulls water up through the xylem vessels. This transpiration pull serves as the main force that transports water through the xylem. Root pressure helps in the transport of water at night. Fig. 3.2 Relationship between transpiration and Fig. 3.3 Plants lose excess water by transpiration. absorption. Water absorbed by the root passes up to the leaf through the xylem of the stem. Take a healthy potted plant and enclose some of its leaves in a plastic sheet. Then keep the plant in bright sunlight. After some time, you will observe droplets of water on the inner surface of the plastic sheet. This water was lost through the stomata on the leaves as a result of transpiration. The rate of transpiration is high if the atmosphere is warm and dry.

22 Foundation Science: Biology for Class 10 Transport of Food and Other Substances The food manufactured in the leaves is translocated upwards, downwards and laterally to all parts of the plant through the phloem. The phloem also conducts some other substances such as amino acids. The conducting cells of the phloem are cylindrical cells called sieve tubes, which have sievelike partitions at both ends. These partitions are called sieve plates. A continuous column from the leaves to other parts of the plant is formed by the arrangement of sieve tubes one above the other. Besides sieve tubes, the phloem also has companion cells and phloem parenchyma. Sucrose is the main form of carbohydrate that is translocated in plants. Its translocation into the phloem tissue occurs with the expenditure of energy. When sucrose is synthesized in the leaf cells, the osmotic pressure of the cells increases. As a result, water from the surrounding cells is forced to flow into the leaf cells by osmosis. This causes sucrose to be translocated from the point of its synthesis to the receiving end in the form of a solution. This process is dependent on the requirement of the plant. For example, in the flowering season, when vegetative activity is more at the apex of the plant, sugar in the leaves will be readily consumed. This is the reason for the translocation of sugar to the buds from the storage regions (root, stem, etc.) during spring. Excess food is transported to the storage regions when the vegetative activity of the plant is reduced. Table 3.1 Differences between xylem and phloem 1. Xylem cells are dead, whereas phloem cells are alive. 2. Xylem carries mainly water and minerals, while phloem carries organic compounds such as sugar and amino acids. 3. The flow of liquid in xylem is upward only, whereas the flow of liquid in phloem is in all directions. Fig. 3.4 (a) Xylem vessels (b) Phloem tubes (in longitudinal section) TRANSPORTATION IN ANIMALS In very simple animals, materials are transported through diffusion. In complex animals, there is a special transport system to carry oxygen, carbon dioxide, nutrients, waste products, food and various other substances from one part of the body to the other. This transport system, also called the circulatory system, comprises a blood vascular system and a lymphatic system. The blood vascular system has three components—blood, blood vessels and the heart. The lymphatic system includes lymph, lymph vessels and lymph nodes. Blood—a Fluid Transport Medium Blood is a liquid connective tissue having two main components—plasma and blood corpuscles. Plasma is the liquid part of the blood. It is made up of water with various substances dissolved in it. These include proteins, salts, glucose, nitrogenous compounds, and so on. In many invertebrates, plasma contains the respiratory pigment. Corpuscles are cells floating in the plasma. Red blood cells, a type of corpuscle in vertebrates, contain a red-coloured respiratory pigment called haemoglobin. Heart—a Pumping Organ The heart is a muscular pumping organ. It pumps blood that comes to it from other parts of the body through the circulatory system. It pumps deoxygenated blood to the lungs for oxygenation, and oxygenated blood to all parts of the body.

Transportation 23 Control of the heart The invertebrate heart is generally fully controlled by the nervous system. The vertebrate heart is controlled by a pacemaker system made up of specialized cardiac muscles. Chambers in the heart The heart is divided into chambers in order to prevent the mixing of oxygenated blood with deoxygenated blood. A complete vertical partition of the heart into left and right chambers ensures a complete separation of oxygenated and deoxygenated blood. This type of partition is seen in animals having a double circulation system, with two circuits. These animals (e.g., mammals, birds and crocodiles) have lungs. In one circuit blood flows between the heart and the lungs, and in the second circuit it flows between the heart and the body. The heart has four chambers—two atria (often also called auricles) and two ventricles. Such a heart is called ‘double’ heart. This type of complete separation into chambers provides an ample supply of oxygen to all parts of the body. These animals are quite active, so they have a high rate of respiration and require an efficient supply of oxygen. Birds and mammals, being warm-blooded, need to spend energy to regulate their body temperature. This also requires oxygen. Some vertebrates do not use energy for temperature regulation. Their temperature fluctuates with that of the environment and we call them cold-blooded. In these animals (except crocodiles) there is some mixing of oxygenated and deoxygenated blood in the heart. This does not harm the animals as their energy demands are not very high. In amphibians the heart is three-chambered, having two atria and a single ventricle. Such a heart is called transitional heart. In most reptiles there are two atria and an incompletely divided ventricle. Fish have a single circulation system. Their heart is two-chambered, having one atrium and one ventricle. Such a heart is called ‘single’ heart. The fish heart receives and pumps only impure blood. The impure blood goes to the gills for oxygenation, and from there it goes to different parts of the body. The impure blood returns to the heart for being pumped out to the gills. Therefore, the fish heart is also called venous heart. Blood Vessels In vertebrates the blood vessels are arteries, veins and capillaries. Arteries are more muscular, while veins are more elastic. Capillaries are made up of a single layer of squamous epithelium. In invertebrates the blood vessels are not properly distinguished as arteries and veins. CIRCULATORY SYSTEM IN MAN Blood Blood, as you know, is a liquid connective tissue that circulates in a closed system of blood vessels. An adult man has about five to six litres of blood, while a woman, on an average, has about one litre less. Our blood consists of (i) solid elements—which include red blood corpuscles (RBCs), white blood corpuscles (WBCs), and blood platelets, and (ii) liquid element—the plasma. The corpuscles comprise about 45% and the plasma about 55% of the volume of blood. Plasma Plasma is a straw-coloured liquid in which the RBCs, WBCs and platelets float. It contains mainly water, in which are dissolved various substances such as plasma proteins, food substances (amino acids, glucose, fats), nitrogenous compounds and ions of sodium, potassium, calcium, magnesium and phosphorus. Blood corpuscles Blood is red in colour due to the presence of RBCs. The RBCs contain the red-coloured respiratory pigment haemoglobin. This iron–protein compound transports oxygen from the lungs to the tissues. RBCs also transport carbon dioxide. WBCs protect the body from infection. Platelets help in the clotting of blood.

24 Foundation Science: Biology for Class 10 Visit a diagnostic centre. Give your blood sample. Get it checked for the level of haemoglobin. The normal range of haemoglobin in humans is 120–180 g/L, or 12–18 g/dL, of blood. Check your blood report to see if your haemoglobin level falls in this range. But haemoglobin levels also depend on age, sex and ethnic values of a place. For example, females have a lower normal value of haemoglobin level than males. A below-normal level of haemoglobin may indicate anaemia due to a number of possible causes. Low haemoglobin level could be from actual loss of blood from haemorrhage, vitamin deficiencies, lack of iron in the diet or a disease. This indicates that the person’s cells are not getting enough oxygen for energy production. Such anaemic persons always feel tired and weak. You can even obtain the normal range of haemoglobin level in animals such as cows, buffaloes, goats, etc., by visiting a veterinary clinic. This value is lower in these animals than in humans. The normal haemoglobin level in cows lies in the range of (5.9 ± 1.54) g/dL of blood. Blood clotting by platelets You must have noticed that after a cut the skin bleeds for a while, and then the blood thickens to form a clot. This process takes place as a result of a series of reactions in the blood. These reactions are started by the release of an enzyme by the circulating platelets. The clot, which forms at the point of the wound, is a microscopic network of insoluble fibrous protein. It minimizes the loss of blood. If blood is lost, it leads to a loss of pressure by the pumping heart. Functions of blood 1. Transport of respiratory gases Blood carries oxygen from the lungs to the tissues. It also carries carbon dioxide from the tissues to the lungs. 2. Transport of nutrients Nutrients absorbed in the small intestine enter the blood capillaries. Blood carries these nutrients and distributes them to all parts of the body. 3. Transport of waste products Waste products of the body, such as urea, uric acid, etc., are carried by blood to the excretory organs. 4. Regulation of water content of cells Blood regulates the water content of the cells. When the water content in cells increases, blood takes up the excess amount of cellular water. Blood provides water to cells when they need it. 5. Regulation of body temperature Increased body temperature resulting from the excess respiration of a particular tissue is equalized by circulation of blood. 6. Defence against infection Blood protects the body against infection. 7. Prevention of bleeding Clotting of blood prevents excess bleeding. Blood Vessels Fig. 3.5 Route of blood circulation Three types of blood vessels, namely, arteries, veins and capillaries, are involved in blood circulation. They are all connected to form one continuous closed system. Arteries The arteries are wide, elastic and thick-walled vessels as they carry blood

Transportation 25 away from the heart to the limbs and organs of the body. They have thick, elastic walls to withstand the high pressure of the blood emerging from the heart. Veins Veins bring back blood from the tissues and organs to the heart. The blood in veins flows under less pressure than that in arteries. Therefore, veins do not have thick walls. But veins can accommodate more blood. Veins have valves that allow blood to flow in one direction only. Capillaries Arteries branch out into smaller and thinner blood vessels called arterioles. These divide into still smaller vessels to provide blood to all the cells. The thinnest blood vessels are called capillaries. Their walls have just one layer of squamous cells. These walls are permeable, so that water and dissolved substances pass in and out, exchanging oxygen, carbon dioxide, dissolved nutrients and waste products with the tissues around the capillaries. The capillaries form a dense network, reaching out to each and every part of the body. The flow of blood is very slow in capillaries. They join to form venules and veins, which return blood from organs and tissues to the heart. The Human Heart Structure The heart is a muscular, conical and dark red organ that plays the role of a pump in the circulatory system. Its pumping action maintains the circulation of blood. In man, the heart weighs about 0.43 per cent of the body weight. It is located in the middle of the thoracic cavity, but its apex is tilted towards the left side. The heart is enclosed in the pericardium, a tough, inflexible membrane. Between the heart and the pericardium is a fluid which reduces the friction produced during heartbeat. The heart is made up of cardiac muscles. These muscles contract with considerable force, squeezing the blood out into the arteries. The heart beats nonstop throughout one’s life. It is due to the rhythmic contraction and relaxation of the heart muscles. There are four chambers in the heart—two atria, with thin walls, and two ventricles, with thick walls. Working of the heart Blood from different parts of the body comes to the right atrium when it expands. This impure blood is brought from the upper part of the body through the superior vena cava and from the lower part of the body through the inferior vena cava. As the right atrium contracts, the blood goes to the right ventricle, which dilates. The atrioventricular aperture is closed by a valve after the blood transfer. Valves prevent the backflow of blood when the atria or ventricles contract. When the right ventricle contracts, the blood is forced out to the lungs for oxygenation through the pulmonary artery, guarded by another valve. In the lungs, there is an exchange of oxygen and carbon dioxide. After the blood has received oxygen from the lungs and given off carbon dioxide, the oxygenated blood returns to the left atrium. Pulmonary veins bring this oxygenated blood from the lungs to the left atrium, as it relaxes. When the left atrium contracts, blood is transferred to the left ventricle, which expands. The aperture between the left atrium and left ventricle is guarded by a valve. The wall of the left ventricle is three or four times thicker than the wall of the right ventricle, as it pumps blood to the body. When the left ventricle contracts, the oxygen-rich blood is pumped into the aorta for circulation to different parts of the body. The opening of the aorta is also guarded by a valve. Deoxygenated blood is collected from different parts of the body by small veins. These open into larger veins, which bring the blood back to the right atrium.

26 Foundation Science: Biology for Class 10 Fig. 3.6 Internal structure of the human heart Cardiac cycle One sequence of the filling of the heart with blood and its pumping is called the cardiac cycle. The phase of contraction of the ventricle is called systole and its relaxation phase is called diastole. Blood pressure As blood flows, it exerts a force on the walls of the blood vessels. This is much greater in the arteries than in the veins. The pressure of flow of blood in the aorta and its main branches is defined as blood pressure. The heart has to develop a high pressure so that blood can be pumped through the arteries, capillaries and veins. During the ventricular contraction, or systolic phase, it is equal to that exerted by a column of 120 mm of mercury. During the ventricular relaxation, or diastolic phase, it is about 80 mmHg. Thus, the normal blood pressure is said to be ‘120/80’. However, the blood pressure varies from person to person and is affected by age, sex, heredity, physical and emotional states, and other factors. An instrument called sphygmomanometer is used to measure blood pressure. Abnormally high blood pressure is called hypertension. It may be associated with a disease or may occur due to anxiety. During hypertension, the arterioles get constricted and increase resistance to blood flow. High blood pressure can cause the rupture of blood vessels, internal bleeding or stroke. If a blood vessel is ruptured in the brain, that part does not get blood, oxygen and nutrients, and loses its function. Fig. 3.7 Measuring blood pressure (here ‘120/70’) by a sphygmomanometer

Transportation 27 The Lymphatic System Lymph is another type of fluid that takes part in transportation. Blood containing oxygen and food flows under tremendous pressure in the arteries, which divide into arterioles and eventually into capillaries. When the blood from an arteriole enters a capillary, it is under so much pressure and the capillary walls are so thin that a clear liquid is forced out of the capillary walls into the spaces between the surrounding cells. This liquid is called tissue fluid. Tissue fluid carries with it oxygen, food and other useful substances to the cells. It also takes away carbon dioxide and waste products from the cells. If tissue fluid were to accumulate in the tissues and organs, it would cause swelling. So, it is returned to the bloodstream through another system of vessels, called the lymphatic system. The lymphatic system consists of lymph, lymph vessels and lymph nodes. Most of the tissue fluid drains into lymph vessels and flows as lymph. Lymph is similar to blood except that it does not have RBCs and blood platelets, and has a lesser amount of proteins. Therefore, lymph is colourless or slightly yellowish and is similar to blood plasma. The lymphatic system maintains the balance between tissue fluid and blood. Lymph carries digested fat from the intestine and drains excess fluid from the intercellular spaces back into the blood. Before lymph enters the blood, it passes through a number of lymph nodes. These are small globular masses of lymphatic tissue. Lymph nodes produce WBCs that prevent infection. • POINTS TO REMEMBER • · In higher plants, the transport system (vascular The left atrium receives oxygenated blood from system) consists of tubelike structures made up of the lungs. This blood is sent to the left ventricle, xylem and phloem tissue. Water and minerals are which pumps the blood to different organs. The transported from the roots upwards through right atrium receives deoxygenated blood from xylem tubes. Phloem transports synthesized food different parts of the body. It sends this blood to from the leaves to the rest of the plant body. the right ventricle, which pumps it to the lungs for oxygenation. · Water and dissolved minerals are absorbed by the root hairs. Water from the root hairs diffuses · The heart pumps blood through arteries to the through the cortical cells and is pushed into the different parts of the body. From the different xylem vessels with the help of root pressure. parts of the body, the blood is collected by veins and brought back to the heart. · The blood vascular system of higher animals consists of blood, heart and blood vessels. · Blood performs several important functions— transport of respiratory gases, nutrients, waste · Blood consists of liquid plasma and solid products, etc., regulation of water content, corpuscles (RBCs, WBCs and platelets). RBCs carry prevention of infection, and so on. oxygen. WBCs prevent infection. Platelets help in blood clotting. · The lymphatic system consists of lymph, lymph vessels and lymph nodes. It maintains the · The human heart is a four-chambered pumping balance between tissue fluid and blood by organ, consisting of two atria and two ventricles. returning tissue fluid to the blood circulation. • EXERCISES • A. Very-Short-Answer Questions 5. Name the three types of blood corpuscles. 1. What is translocation? 6. Why are red blood cells red in colour? 2. What do you mean by ascent of sap in plants? 7. What is the main function of white blood cells? 3. Which tissue plays the most important role in 8. Name the two major veins that carry blood from upward transportation in plants? different parts of the body to the right atrium. 4. Name the vascular tissue which transports food 9. Which blood vessels bring oxygenated blood from from the leaves to different parts of the plant. the lungs to the left atrium?

28 Foundation Science: Biology for Class 10 10. What is the difference between the systolic and 6. Which of the following animals has a single diastolic phases of the cardiac cycle? circulation system? 11. Where is lymph finally drained? (a) Frog (b) Bird (c) Crocodile (d) Fish B. Short-Answer Questions 1. How is water absorbed by the roots of plants? II. Fill in the blanks. 2. What are the major differences between arteries and 1. Blood is a liquid _____ tissue. veins? 2. The iron-rich compound in RBCs is _____. 3. Why is RBC suitable for transport of oxygen in the body? 3. Oxygenated blood leaves the heart through the _____, for circulation to different parts of the body. 4. Name the constituents of blood. White blood 4. The blood brought into the heart by the pulmonary corpuscles are called the ’soldiers’ of the body. veins is rich in _____. Why? [CBSE] 5. The capillaries are made up of a single layer of _____ epithelial cells. 5. How does blood clot? 6. The normal blood pressure of a young person is 6. What is lymph? _____. 7. What is plasma? 7. Blood pressure is measured by an instrument called _____. 8. Write one function each of the following components of the circulatory system in humans. (a) Blood vessels (b) Blood platelets (c) Lymph (d) Heart [CBSE] E. Diagrammatic Question C. Long-Answer Questions 1. The diagram below shows the internal structure of 1. Briefly describe the structure of the human heart. the human heart. Label the chambers and the major 2. Mention any five functions of blood. blood vessels shown. D. Objective Questions I. Pick the correct option. 1. In plants, the transportation of food materials is carried out by (a) xylem (b) phloem (c) root hair (d) palisade cells 2. In plants, water and minerals are transported by (a) xylem (b) phloem (c) leaves (d) lenticels 3. The capillaries join to form (a) arterioles (b) arteries (c) veins (d) venules 4. What is blood pressure? (a) The pressure of blood on the heart muscles (b) The pressure of flow of blood exerted on the walls of arteries and veins (c) The pressure of blood on the walls of veins only (d) The pressure of blood on the walls of arteries only 5. Which of the following blood vessels have thick, elastic walls? (a) Veins (b) Capillaries (c) Arteries (d) All of these Objective Questions • ANSWERS • 1. (b) 2. (a) 3. (d) 4. (d) 5. (c) 6. (d)

Transportation 29 • POSTSCRIPT • · The heartbeat is controlled by a pacemaker recording done by this instrument is called an system. It consists of a sinoatrial (SA) node, electrocardiogram (ECG). The graphic pattern atrioventricular (AV) nodes, bundle of His, and reveals the condition of the heart. The pattern of Purkinje fibres. The nodes are specialized cardiac electrical activity of the heart can also be seen on muscles that produce electrical impulses (or an oscilloscope screen. current). The SA node is buried in the upper wall of the right atrium, close to the opening of the R superior vena cava. This node is called the pacemaker, and it produces the mild electric PT impulse which initiates the contraction of the heart muscles. QS · The instrument used to record the electrical Fig. 3.8 ECG tracing of one cardiac cycle of a normal- impulse starting from the SA node to the Purkinje functioning heart. The five waves are fibres is called the electrocardiograph. The graphic customarily named (P, Q, R, S, T). v

4 Excretion ChemExiccraeltiroenactions occur in the cells of living organisms all the time to carry out the life processes. The sum of these reactions is called metabolism. Metabolism produces useful products as well as toxic (poisonous) by-products. These toxic substances have to be removed as they are harmful if allowed to accumulate. The removal of metabolic waste products from the body of an organism is known as excretion. The major excretory products are carbon dioxide, excess water, and nitrogenous compounds like ammonia, urea, uric acid, etc. Carbon dioxide and water are produced in the process of tissue respiration. Nitrogenous compounds are formed from the breakdown of proteins and amino acids. Water and salts in excess of the body’s needs are also excreted. We acquire most of the water with our food and drink and some by metabolism, e.g., the water produced during cellular respiration. Other excretory products include chemicals from medicines, toxic substances, and circulating hormones that have already served their purpose. We will learn how metabolic wastes get eliminated. EXCRETION IN ANIMALS Many unicellular organisms like Amoeba throw out their wastes by diffusion from their body surface. Protozoans have no organs for excretion. As they live in an aquatic habitat, their wastes are eliminated by diffusion through the plasma membrane. Simple multicellular organisms like Hydra throw out solid waste matter through their mouth. Higher multicellular organisms have well-defined specialized excretory organs. These organs could be simple tubular structures as in flatworms and leech. The excretory organs of insects (e.g., grasshopper, cockroach and housefly) are also tubular. They remove nitrogenous wastes from the body fluid and help in maintaining the water balance in the body. In vertebrates, the main organs of excretion and maintenance of water balance are the kidneys. EXCRETION IN HUMAN BEINGS Although the kidneys are the main organs of excretion, the skin, lungs and liver also help in excretion. Skin Our skin has sweat glands, through which we excrete small amounts of water, urea and salts. 30

Excretion 31 Liver The liver excretes bile, which contains bile pigments. These are produced by the breakdown of old RBCs in the liver. As haemoglobin breaks down, its iron is retained, while the pigment (haem) is excreted with the bile. The liver also excretes cholesterol. Lungs The lungs help in getting rid of carbon dioxide, formed as a result of cellular respiration, through exhalation. Excretory System in Man Our excretory system consists of kidneys, blood vessels that join them, ureters, urinary bladder and urethra. They help produce and excrete urine. There are two bean-shaped kidneys that lie in the abdominal cavity, one on either side of the vertebral column. The kidneys are reddish brown. Each of them is about 10 cm long and weighs about 150 g. Although they weigh less, they receive a lot of blood for filtration. A volume of blood nearly equivalent to that in the whole body passes through the kidneys every four or five minutes. The kidneys produce urine to filter out the waste products, like urea and uric acid, from the blood. Fig. 4.1 (a) Excretory organs of man (b) Internal structure of a kidney Urine leaves each kidney through a tube called ureter. The ureters from both the kidneys are connected to the urinary bladder that collects and stores urine. Ureters carry urine from the kidneys into the urinary bladder. The urethra is a canal that carries urine from the bladder and expels it outside the body. Internal Structure of a Kidney Each kidney is enclosed in a thin, fibrous covering called the capsule. A renal artery brings blood into the kidney, along with nitrogenous waste materials. After filtration in the kidney, the purified blood leaves the kidney through a renal vein. Two distinct regions can be seen in the section of a kidney—(1) an outer, dark, granular cortex and (2) an inner, lighter medulla. The hollow space from where the ureter leaves the kidney is called the pelvis. Each kidney is made up of numerous (about one million) coiled excretory tubules, known as nephrons, and collecting ducts associated with tiny blood vessels. A nephron is the structural and functional unit of a kidney, having three functions— filtration, reabsorption and secretion. A cluster of thin-walled blood capillaries remains associated with the cup-shaped end of each nephron tubule. These capillaries bring blood from the body to the nephron for filtration. The network of capillaries spreads over the nephron tubules also. These capillaries finally carry purified blood to the body.

32 Foundation Science: Biology for Class 10 Structure and Function of a Nephron A nephron consists of a long coiled tubule and the Malpighian corpuscle. The tubule of the nephron is differentiated into the proximal convoluted tubule, Henle’s loop and the distal convoluted tubule. The distal tubule opens into the collecting duct. At the proximal end of the nephron is the Malpighian corpuscle, which consists of Bowman’s capsule and the glomerulus. Bowman’s capsule is a double-walled cuplike structure which surrounds the dense network of blood capillaries called the glomerulus. Fig. 4.2 Different parts of a nephron The process of excretion in nephron The process of excretion may be divided into three stages—filtration, selective reabsorption and tubular secretion. Filtration Filtration of blood occurs under high pressure in the nephrons of the kidney. Blood enters the glomerulus through the afferent arteriole (with a wider lumen) and leaves through the efferent arteriole (with a narrow lumen). Therefore, blood passes through the glomerulus under pressure. This results in filtration of blood. Water and small molecules are forced out of the walls of the capillaries of the glomerulus and Bowman’s capsule and enter the tubule of the nephron. Large molecules remain in the blood of the glomerulus. The filtrate contains water, glucose, salts, urea, vitamins, etc. It is called the glomerular filtrate. Selective reabsorption Some molecules of the glomerular filtrate are selectively reabsorbed into the blood. The glomerular filtrate flows through the proximal convoluted tubule, the U-shaped Henle’s loop and the distal convoluted tubule. It contains many useful substances such as glucose, amino acids and salts. These are reabsorbed by a process, which requires energy. Without reabsorption, these nutrients could have been lost with the urine. The filtrate now contains urea, some salts and water. Reabsorption of solutes into the blood increases the water concentration of the filtrate. Then water is reabsorbed into the blood by the process of osmosis, and the osmotic balance is restored. The amount of water reabsorbed depends on the amount of excess water in the body and that of the dissolved waste to be excreted. This reabsorption of water from the filtrate to maintain the water balance of the body fluid is known as osmoregulation. In this way the kidneys serve as water-conserving organs. After reabsorption from 180 L of filtrate in the kidney, only 1–2 L of urine is produced.

Excretion 33 Tubular secretion Some nitrogenous waste products like creatinin and some other substances like potassium ions are removed from the blood by the distal convoluted tubule, and are then added to the urine. This is called tubular secretion. Control of excretion The urine that is formed continually collects in the urinary bladder. As the bladder expands, its pressure creates an urge to pass urine through the urethra. As the bladder is muscular, the urge to urinate is under voluntary nervous control. Fig. 4.3 Blood supply to a nephron Kidney Failure and the Survival Kit—Haemodialysis The kidneys may be damaged due to infection, injury, diabetes, and extremes of blood pressure. A damaged kidney cannot function efficiently to remove urea, ions, water, etc., from the blood. This malfunctioning results in the accumulation of toxic wastes like urea (uraemia), which can lead to death. One of the ways to treat kidney failure is to use a ‘dialysis machine’ that acts as an artificial kidney. It has a long tubelike structure made of Cellophane suspended in a tank (dialyser) of a fresh dialysis fluid (dialysate). The Cellophane tube is partially permeable and therefore allows solutes to diffuse through. The dialysis fluid has the same concentration as normal tissue fluid, but nitrogenous wastes and excess salts are absent. During dialysis, the blood of the patient is withdrawn from an artery and cooled at 0°C. It is maintained in a liquid state by adding an anticoagulant and by other special treatments. It is pumped through the dialysis machine. Here, the nitrogenous waste products from the blood diffuse into the dialysis fluid. The purified blood is then warmed to the body temperature and pumped back into the patient’s body through a vein. The dialyser is specific for each patient to avoid infections. Dialysis through an artificial kidney has to be carried out at frequent intervals. This process of purification of blood is called haemodialysis.

34 Foundation Science: Biology for Class 10 A dialysis machine works like a kidney except that no selective reabsorption takes place in the former. An artificial kidney (1) helps remove harmful wastes, extra salts and water; (2) controls blood pressure; and (3) maintains the balance of sodium and potassium salts in a patient whose kidneys have failed. Fig. 4.4 (a) Haemodialysis (b) Dialyser EXCRETION IN PLANTS Compared to animals, plants do not have a well-developed excretory system to remove nitrogenous waste materials. This is because of the differences in their physiology. Therefore, plants use different strategies for excretion. The gaseous waste materials produced during respiration (carbon dioxide) and photosynthesis (oxygen) diffuse out through stomata in the leaves and through lenticels in other parts of the plant. Excess water evaporates mostly from stomata and also from the outer surface of the stem, fruits, etc., throughout the day. This process of getting rid of excess water is called transpiration. The waste products, like oxygen, carbon dioxide and water, are the raw materials for other cellular reactions. The excess of carbon dioxide and water are used up in this way. The only major gaseous excretory product of plants is oxygen! Many plants store organic waste products in their permanent tissues that have dead cells, e.g., in heartwood. Plants also store waste within their leaves or barks. These wastes are periodically removed as the leaves and barks fall off. Some of the waste products are stored in special cells or cellular vacuoles. Various waste products such as tannins, essential oils, gums, resins, etc., are produced during catabolic processes. Tea leaves, amla and betel nuts (supari) contain tannin. Tannins are found also in the barks of trees. The leaves of many plants, like Eucalyptus, lemon, sacred basil (tulsi), etc., contain essential oils. The rind of oranges and lemons and the petals of flowers like rose and jasmine also contain oils. Some plant wastes are stored as a thick, white fluid. You may have seen a white fluid ooze

Excretion 35 out when you pluck a papaya or a fig or the leaves of yellow oleander (pila kaner). This white fluid is called latex. Gums are a group of sticky, water- soluble wastes found in the common gum tree (babul). Resins are another group of wastes found commonly in the stems of conifers (e.g., pine, fir). Alkaloids are a group of toxic waste products. But some of these are useful to us. Quinine and morphine are medicines derived from alkaloids stored in Cinchona bark and opium poppy flowers respectively. Caffeine found in coffee seeds and nicotine in tobacco leaves are also alkaloids. Organic acids, which might prove Fig. 4.5 Waste products in the leaves of yellow oleander harmful to plants, often combine with excess cations and precipitate out as insoluble crystals that can be safely stored in plant cells. Calcium oxalate crystals accumulate in some tubers like yam (zamikand). Aquatic plants lose most of their metabolic wastes by direct diffusion into the water surrounding them. Terrestrial plants excrete some waste into the soil around them. • POINTS TO REMEMBER • · The removal of metabolic waste products · Each part of the nephron has a distinct function. from the body of an organism is known as The functions include filtration, reabsorption and excretion. secretion. · Vertebrates have kidneys as the main organs of · Osmoregulation is the process of controlling the excretion. water content and the ion concentration in the body of an animal. It helps an organism maintain · The nephron is the structural and functional its osmotic pressure. unit of a kidney. It consists of the Malpighian corpuscle, the proximal convoluted tubule, · Plants use different strategies for excretion. They Henle’s loop and the distal convoluted tubule. store waste products in cell vacuoles. Waste products like gum, resin, latex, etc., are removed when leaves or barks fall off. • EXERCISES • A. Very Short-Answer Questions B. Short-Answer Questions 1. Name three main excretory products of human 1. What is the basic filtration unit in the lungs and in beings. the kidneys? [CBSE] 2. Which part of the body is responsible for excretion in (a) Amoeba and (b) Hydra? 2. What is the fate of the glucose that enters the nephron along with the filtrate? 3. Name the excretory unit of a kidney. 3. How is the amount of urine produced controlled? 4. Mention the three main functions performed by the nephron. 4. Why is the blood in the glomerulus under high pressure? 5. Name the blood vessel which enters the glomerulus and the one that leaves it. 5. Why does selective reabsorption take place as the glomerular filtrate passes through the nephron? 6. What are the excretory products of plants? 6. What do you mean by ‘artificial kidney’? 7. Which procedure is employed in the working of an artificial kidney? C. Long-Answer Questions 1. What is a nephron? Describe its main parts.

36 Foundation Science: Biology for Class 10 2. Name the main steps in the process of excretion in II. Fill in the blanks. the nephron. How does filtration of blood take 1. The cup-shaped capsule in a nephron is place in the glomerulus? called _____. 2. The dense network of capillaries in a Malpighian 3. How do plants get rid of excretory products? corpuscle is called _____. 3. The bag in which urine is collected is called _____. 4. Describe the mechanism of urine formation. 4. Each kidney is connected to the urinary bladder by a tube called _____. 5. (a) Draw a diagram of the human excretory 5. The kidneys excrete nitrogenous waste in the form system and label the following: of _____ . (i) Kidney (ii) Ureter E. Diagrammatic Questions 1. Name the blood vessels and the excretory organs (iii) Urinary bladder (iv) Urethra shown in the diagram below. (b) Name the two major components of normal 2. In the diagram below, label the glomerulus, human urine. Bowman’s capsule, the proximal convoluted tubule, the distal convoluted tubule and the collecting duct. D. Objective Questions Also indicate the afferent and efferent arterioles. I. Pick the correct option. 1. Which of the following is not a part of a nephron? (a) Henle’s loop (b) Proximal convoluted tubule (c) Distal convoluted tubule (d) Cortex 2. Which statement is correct about a human kidney? (a) It is cylindrical. (b) It is bean-shaped. (c) It has 1000 nephrons. (d) It has two ureters. 3. In the glomerulus of a kidney, (a) the afferent glomerular capillaries are wider than the efferent glomerular capillaries (b) the afferent glomerular capillaries are narrower than the efferent glomerular capillaries (c) the afferent glomerular arteriole is narrower than the efferent glomerular arteriole (d) the afferent glomerular arteriole is wider than the efferent glomerular arteriole 4. The network of capillaries in a nephron is (a) the Malpighian corpuscle (b) Bowman’s capsule (c) the glomerulus (d) none of these 5. Uraemia is a condition developed when (a) a large amount of water is lost in urine (b) there is an increase in urea concentration in blood (c) the urine output is decreased (d) the blood pressure in the afferent arteriole decreases 6. Which of the following substances is/are completely reabsorbed from the filtrate in the renal tubule under normal conditions? (a) Uric acid (b) Glucose (c) Salts and water (d) Urea Objective Questions 4. (c) • ANSWERS • 1. (d) 2. (b) 3. (d) 5. (b) 6. (b)

Excretion 37 • POSTSCRIPT • · An adult skin weighs about 3 kg and has about · About 130 mL of filtrate is formed per minute in 8 million sweat glands. During hot weather, we the glomeruli of the two kidneys of man. can lose up to 12 L of water and 30 g of salt in a day through sweating. · About 99% of the water of the filtrate is reabsorbed as it passes down the nephron. · One million nephrons are present in each kidney. Each nephron is approximately 5 cm long. · Body salts excreted with human urine may amount to 2.2% and urea 6% of the volume of urine. · An adult excretes about 1.6 L of urine every 24 hours. · The yellow colour of urine is due to a pigment called urochrome. v

5 Control and Coordination cOcuccrcCbcoocncdctyrcociscl camcncadcdcCeccoucopcrcdocfcincbacictllicioconcncsccocfccceclclcsctchcactccgcectcocrcCgcocancnctirczocecldcacinncdctocCcdcociofcfrcedcricencnactctitcoicsncscucecsc.cDccicffcecrcecncct ctciscscuceccs constitute organs, and different organs constitute systems such as the digestive, respiratory and circulatory systems. In order to perform a particular function the component organs of each system depend on each other and work in harmony. In the absence of such working in harmony, an organism cannot do many things that it normally does. For example, when we run, our muscles require greater energy, which can be produced when there is a greater supply of oxygen. To increase the oxygen supply, the rate of breathing increases. When we stop running, our muscles do not need so much energy. Consequently, there is no need for extra oxygen and the rate of breathing comes down to the normal level. All these activities are coordinated and well organized. The working together of various systems in the body is called coordination. Response and Coordination in Plants and Animals The ability of an organism to detect changes and make appropriate responses is called sensitivity. Anything to which an organism responds and reacts is called a stimulus. In animals the responses are quicker and more obvious. Unicellular animals respond to stimuli either by moving towards them or away from them. In multicellular animals, the process of responding to stimuli is different. The responses occur within seconds, but through a complex network of communication which involves several life processes like movement, locomotion, transport, respiration, etc. For example, when you step out in bright sunlight, you partly close your eyes to keep out the bright light. You may start sweating as the temperature rises. These are coordinated responses to stimuli. Response and coordination in animals involve the sense organs, nervous system and chemical messengers called hormones. Plants also react to specific environmental conditions. However, they have no nervous system and their responses are in the form of slow modified growth or movements called turgor movements, caused due to the distension (swelling) of cells. Let us first examine the phenomena of response and coordination in plants. RESPONSE AND COORDINATION IN PLANTS Continuous Movements of Plants As a plant grows, the stem tip does not grow upwards in a straight line but follows a curved path. This movement, known as nutation, occurs when at any given time, one part of the apical meristem grows faster than the rest of the stem. The region of more rapid growth moves slowly round the apex. This type of movement is more pronounced in climbing plants such as pea, whose stem tips (or tendrils) twine themselves around a support. The part of the tendril in contact with the support does not grow as rapidly as the part of the tendril away from the object. As a result, the tendril encircles the object and clings to it. 38

Control and Coordination 39 Fig. 5.1 Tendrils in pea Quick Movements of Plants Rapid movements are uncommon in plants, but some plants do display such movements in response to stimuli. Touch the tip of a sensistive plant (Mimosa pudica) gently. Only a few leaflets close. When you touch it roughly, all the leaflets close. Fig. 5.2 Response to touch in Mimosa pudica In Mimosa pudica, the leaflets fold up quickly if any leaflet is touched. How does it happen? It happens because the touch triggers a sudden and rapid loss of water (turgor changes) from cells at the base of the leaflets. These movements of sensitive plants in response to touch are very quick. All quick movements are not so quick. For example, the leaves of many plants, including those of Mimosa pudica, remain open during day. When darkness falls, the leaves fold up. Many flowers open after sunrise and close after sunset. All these movements are directed neither towards nor away from the stimulus. Such movements are called nastic movements. Stomatal Movements The opening and closing of stomata is controlled by changes in the turgor pressure of guard cells and is coordinated with light and darkness. Tropic Movements The movement of an organism in the direction of a stimulus or away from it is called tropic movement, or tropism. A tropic movement is said to be positive if it is directed towards the source of stimulus and negative if directed away from the source of stimulus. The plant responds by growth or turgor changes, so that parts of the plant bend towards or away from the direction

40 Foundation Science: Biology for Class 10 of stimulus. Tropic movements are of different types in response to different stimuli. Growth-related movement of plants is quite slow. Phototropism Phototropism is the tropic response of organisms to light. When a young green plant receives light from one direction only, the stem grows towards the light source. The stem is said to be positively phototropic because the stem tip grows in the direction of light. In order to observe the response of plants to light, you can try the following activity. Take a big cardboard box with a large window cut near its top edge. Keep a small potted plant at the bottom of the box. Take a piece of cardboard with a small window near one edge and fix it in the box as shown in the figure. Cover the box so that light enters only through the window on the top. You will observe that the plant grows towards the light. It will first grow out of the small window in the cardboard. Then it will bend towards the top window and grow out through it. Fig. 5.3 Phototropism Sunflower buds exhibit a special type of phototropism in which the buds turn slowly through the day so that they always face the sun. This movement is caused by turgor changes. Geotropism Geotropism is the tropic response of organisms to gravity. When a growing portion of a plant is placed horizontally, the stem tip grows away from the pull of gravity, while the root tip grows towards it. Thus, the stem is said to be negatively geotropic and the root positively geotropic. Place a potted plant horizontally on the ground. After a week, you will see that the stem has bent upwards to grow away from gravity. And if you break the pot and remove some of the soil gently, you will notice that the root has bent downwards to grow in the direction of the pull of gravity. Fig. 5.4 The stem is negatively geotropic, while the root is positively geotropic.

Control and Coordination 41 Hydrotropism The growth of plant parts towards or away from water is called hydrotropism. Roots are positively hydrotropic, i.e., they grow towards water in the soil. Do you know that the positive hydrotropism of roots is stronger than their positive geotropism? This can be demonstrated by the following activity. Take a sieve or a trough with perforations at the bottom. Put some moist sawdust in it and place germinating seeds on the sawdust. Raise the trough above the surface by keeping a brick under each edge. After a few days you will see that the radicles of the seedlings grow downwards through the pores due to geotropism. These radicles then grow towards the moist sawdust in the trough due to hydrotropism. Perforated trough Moist sawdust Germinating seed Radicles of seeds Brick Fig. 5.5 Demonstration of hydrotropism Due to hydrotropism, the roots of roadside trees often block leaking sewage drains. Chemotropism The tropic response of organisms to chemicals is known as chemotropism. For example, pollen tubes grow towards a chemical produced by the ovule during fertilization. Thigmotropism The tropic response of organisms to touch or contact with a solid surface is called thigmotropism. The climbing parts of a plant that twine around a support are positively thigmotropic. When such a plant part touches a support, the side of its apical meristem in contact with the support grows slower than the other side. This is how tendrils coil around a support. Plant Hormones Responses and growth in plants are controlled by chemical substances called plant hormones, or phytohormones. These substances are found in very minute quantities in plant tissues. A hormone is produced in specific cells of the plant and is transferred to another part where it influences a specific physiological process. While some plant hormones such as auxins, gibberellins and cytokinins stimulate growth, some others such as abscisic acid retard it. Plant hormones control directional growth in plants and also bring about growth in carefully controlled ways. For example, they help plants to grow leaves only at the nodes and not at other parts of the body. Auxins Auxins are a group of plant hormones synthesized in the apical meristem of the root tips and shoot tips. When a shoot tip receives light, the hormone auxin is synthesized and diffuses towards the shady side of the shoot. This leads to enhanced growth on this side. Thus, the plant bends towards the light. The twining of a tendril around a support is also due to auxins. In many plants, the apical meristem suppresses the growth of lateral, or axillary, buds. The strong influence of the apical bud on the growth of the lateral buds can be seen by removing the apical bud from the plant. Take two potted Coleus plants of almost the same size. Cut off the shoot tip of one plant, but do not disturb the other. Observe and compare the growth of both plants for about ten days. The plant with the nipped-off shoot tip acquires a bushy appearance due to the increased growth of lateral branches. The other plant grows taller with a lesser degree of lateral growth due to the dominance of the apical bud. Regular pruning of the hedges in gardens removes the apical buds and promotes the growth of lateral buds, giving the plants a bushy appearance. Auxins promote cell elongation, root formation, cell division, respiration and other physiological processes like protein synthesis, water uptake, etc.

42 Foundation Science: Biology for Class 10 Gibberellins Gibberellins stimulate stem elongation, seed germination and flowering. The maximum concentration of gibberellins is found in fruits and seeds. Gibberellins oppose the effect of abscisic acid, which inhibits growth. Cytokinins Cytokinins are chemicals which promote cytokinesis (cell division). They are produced in dividing cells throughout the plant. In mature plants, cytokinins are produced in the root tips and are transported to the shoots. They also help in breaking dormancy and regulating phloem transport. Abscisic acid Abscisic acid is a growth inhibitor that reverses the growth-promoting effects of auxins and gibberellins. It causes dormancy of seeds, tubers and bulbs. It promotes leaf and fruit fall. It helps in the closure of the stomata to decrease the loss of water. COORDINATION IN ANIMALS Coordination of the body functions in animals is brought about by the endocrine glands and the nervous system. The substances produced by endocrine glands are called hormones. Some characteristics of animal hormones are as follows: 1. Hormones are different compounds such as proteins, steroids, etc. 2. Hormones are chemical messengers which are discharged in the blood by endocrine glands, from where they reach different parts of the body. 3. A hormone will go to a particular organ and influence its functions. The organ that is influenced by a particular hormone is called the target organ of that hormone. A hormone acts as a trigger or switch. Endocrine glands are directly or indirectly controlled by the nervous system, which receives information about changes in the external environment or internal conditions in the form of stimuli. Control and coordination in animals depend on two things for information transmission— chemical signals of hormones and nerve impulses (electrical impulses). If they depended only on electrical impulses through nerve cells, a limited range of tissues would be stimulated. Since they get chemical signals in addition to the nerve impulses, a large range of tissues are stimulated. As a result, animals can show wide-ranging changes in response to stimuli. Human Endocrine Glands Hormones are secreted by the endocrine glands, which are ductless glands. We shall now learn about some important endocrine glands in the human body. These are shown in Figure 5.6. Pituitary gland The pituitary is a small gland attached to Fig. 5.6 Diagram showing the positions of endocrine the ventral side of the brain. The pituitary glands. In the pancreas, testis and ovary, there is the most important endocrine gland, as it are specialized areas for endocrine function. secretes a number of hormones that The thymus gland has not been shown because regulate various functions of the body. It this gland is degenerated or lost in the adult. If also controls the functioning of the other present, it is located near the heart. endocrine glands. Therefore, it is called the master gland of the body. The pituitary gland consists of two main parts—the anterior lobe and the posterior lobe. The anterior lobe secretes various hormones. One of these is the growth hormone which regulates growth

Control and Coordination 43 and development of the body. It promotes the growth of bones and muscles when the body is growing. An excessive secretion of this hormone leads to gigantism, an abnormal condition of excessive growth. On the other hand, insufficient secretion of the growth hormone in childhood retards growth, leading to dwarfism, an abnormal condition of stunted growth. The anterior lobe of the pituitary gland also secretes hormones that influence the secretion of milk in the mammary glands, the production of sperms in males and the maturing of ova (eggs) in females. Two types of hormones are secreted by the posterior lobe of the pituitary. One of these helps in childbirth and the other influences the reabsorption of water in the kidney. Pineal gland It is a small gland attached to the dorsal side of the brain. It has light-sensitive cells. It controls the biological clock (the timing mechanism by which an organism controls regular activities such as sleeping). Thyroid gland Thyroid is a large gland located behind the larynx (voice box) in the neck. The main hormone secreted by this gland is thyroxine, which contains iodine. Thyroxine controls the metabolism of carbohydrates, fats and proteins, and brings about balanced growth. Excessive secretion of thyroxine is called Fig. 5.7 An enlarged thyroid gland is hyperthyroidism. It increases the general metabolism of due to goitre. the body. As a result, fat stored in the body is depleted and there is a loss of body weight. Insufficient thyroxine secretion is called hypothyroidism. It lowers the general metabolism of the body and increases body weight. By slowing down metabolic activity, hypothyroidism retards body growth and brain development in children. When the thyroid gland becomes overactive and secretes excess thyroxine, it becomes enlarged. As a result, the neck swells up and the eyeballs bulge outward. This is called exophthalmic goitre. Swelling of the thyroid may also be due to the deficiency of iodine in the diet. This is called simple goitre. To prevent this it is important for us to have iodized salt in our diet. Iodine is needed for the synthesis of thyroxine. Parathyroid glands These are two pairs of small glands buried in the thyroid gland. They secrete parathormone, which increases the level of calcium in the blood by taking out calcium from the bones. A certain amount of calcium in the blood is essential for functions such as muscular activity and blood clotting. Thymus gland This gland, located near the heart, is present in newborn babies. It gradually becomes smaller with age and is degenerated or lost in the adult. It produces WBCs which fight infection. Islets of Langerhans The pancreas is a digestive gland located in the C-shaped bend of the duodenum (Figure 5.6). Inside this gland there are groups of hormone-secreting cells. These groups are called the islets of Langerhans. Among the hormones produced by them, insulin is the most important. Insulin controls the rate of oxidation of glucose. It helps the liver and muscle cells to absorb glucose from the blood. It also controls the formation of glycogen from glucose in the liver.

44 Foundation Science: Biology for Class 10 People who are unable to secrete sufficient insulin suffer from a condition called diabetes mellitus. The level of glucose in their blood keeps on rising, and after a limit the kidney lets the extra glucose be excreted with urine. Doctors advise diabetics to take less sugar in their diet. Some diabetics are advised to take injections of insulin, if they have very high levels of blood sugar. High levels of blood sugar harm the body in many ways. Adrenal glands We have two adrenal glands, one on each kidney. The adrenal glands secrete the hormone called adrenaline or epinephrine. This hormone is secreted when an individual is under great physical or emotional stress or feels threatened by some kind of danger. Excitement generally stimulates adrenaline secretion. Adrenaline increases the heartbeat, rate of respiration and blood pressure. More air is inhaled as the diaphragm and the rib muscles contract, expanding the chest cavity. Adrenaline constricts all the blood vessels except those that supply blood to the heart muscles and skeletal muscles. As the small arteries around the digestive organs constrict, blood is diverted to the skeletal muscles to carry out a response. Adrenaline is called ‘fight and flight’ hormone because there is a surge of adrenaline when a person is fighting or preparing to fight or running away from danger. The changes caused by adrenaline prepare the body to react during an emergency. Hence, adrenaline is also called the ‘emergency hormone’. Testis The main function of the testis is to produce sperms. The testes also synthesize the male sex hormone testosterone. Testosterone secretion begins at the onset of puberty (age of sexual maturity), at 10–12 years of age. It helps in the development of secondary sexual characters in males, e.g., moustache, beard, etc. Ovary At the onset of puberty the ovaries begin to secrete oestrogen, a female sex hormone. Oestrogen produces secondary sexual characters in females and prepares the body for pregnancy. During pregnancy, the ovaries secrete special hormones that help in the development of the baby. Control of Hormone Secretion We have a feedback mechanism for controlling the precise quantity and timing of hormone secretion. For example, when we take a meal, our blood sugar level rises. The response to this stimulus is the secretion of the required amount of insulin. The insulin carries glucose to the tissues. As a result, the blood sugar level falls and insulin secretion is reduced. Such control of hormone secretion helps maintain a state of balance in the body. THE HUMAN NERVOUS SYSTEM The nervous system performs the following three Fig. 5.8 A nerve cell (neuron) functions. 1. Sensory input, that is, the detection of stimuli by the receptors, or sense organs (e.g., eyes, ears, skin, nose and tongue) 2. Transmission of this input by nerve impulses to the brain and spinal cord, which generate an appropriate response 3. Motor output, that is, carrying out of the response by muscles or glands, which are called effectors Two types of cells constitute the nervous system— neurons and neuroglia. The neurons conduct impulses and the neuroglia support and protect the neurons. A neuron consists of a cell body called cyton, and two types of processes—dendrite and axon.

Control and Coordination 45 Dendrites or dendrons These are hairlike processes connected to the cyton. They receive stimulus, which may be physical, chemical, mechanical or electrical, and pass it on to the cyton. Cyton It is the cell body, with a central nucleus surrounded by cytoplasm. Axon From one side of the cyton arises a cylindrical process filled with cytoplasm. This process is called axon. It is the longest part of the neuron. It transmits impulse away from the cyton. Its tip has a swelling called axon bulb. Generally, a neuron has one axon. The ending of an axon may be branched. These endings are called synaptic terminals. The gap between a synaptic terminal and the dendrite of another neuron or an effector cell is called a synapse. How do we feel a hot or cold object? How do we feel pain? Why do different things have different smells and tastes? There are thousands of receptor cells in our sense organs. They detect stimuli such as heat, cold, pain, smells and tastes. There are different types of receptors such as algesireceptors (for pain), tangoreceptors (for touch), gustatoreceptors (for taste), olfactoreceptors (for smell), and so on. The stimulus received by a receptor is passed on in the form of electrical signals through the dendrites of a neuron to the cyton of the neuron. The cyton transmits only strong impulses. Weak impulses are not further transmitted. An impulse passed on by the cyton travels along the axon of the neuron. When it reaches the end of the axon, it causes the axon bulb to release a chemical which diffuses across the synapse and stimulates the dendrites of the adjacent neuron. These dendrites in turn send electrical signals to their cell body, to be carried along the axon. In this way, the sensation from the receptor is passed on to the brain or spinal cord. A signal from the brain is similarly passed on to the effector, which carries out the appropriate response. Eat some sugar. You will find it tastes sweet. If you block your nose with your fingers there is no difference in its taste. It still tastes sweet because sugar has no smell that can also contribute to the taste. Block your nose again while eating lunch. You will find that the blocked nose makes a difference in appreciating the taste of various food items. When an item has taste as well as smell, it needs the gustatoreceptors on the tongue as well as the olfactoreceptors in the nose to transmit its stimuli to the brain for the full appreciation of its taste. For example, you may not be able to distinguish between mashed papaya and mashed banana with your nose blocked and eyes closed. The gustatoreceptors and olfactoreceptors together make us appreciate any food better. This is the reason why food seems tasteless when you have a cold and your nose is blocked. In humans and vertebrates, the nervous system may be divided into the (1) central, (2) peripheral, and (3) autonomic nervous system. Central nervous system The central nervous system consists of the brain and the spinal cord. Brain It is the most important coordinating centre in the body. It is lodged in the brain box, or cranium, which protects it. The brain is covered by membranes called meninges. Between the membranes and the brain and also inside the brain, there is a characteristic fluid, called cerebrospinal fluid. This also protects the brain. The brain may be divided into three parts—forebrain, midbrain and hindbrain. 1. The forebrain (cerebrum) is the anterior part, consisting of two large hemispheres divided by a longitudinal fissure. The surface of the hemispheres has many folds and is called cerebral cortex. The cerebral cortex consists of numerous neurons, and the folds serve to increase the surface area so that the maximum number of neurons can be present. The cerebral hemispheres are seats of intelligence and voluntary action. The forebrain also contains olfactory lobes, which are the centres of smell; and the diencephalon, which has centres of hunger, thirst, etc. To the floor of the diencephalon is attached the pituitary gland. 2. The midbrain includes optic lobes, which are the centres of vision. 3. The hindbrain is the posterior part, located below the forebrain. It consists of the cerebellum, pons and medulla oblongata. The cerebellum is the coordination centre, and maintains the body’s posture and balance. It also controls some precise voluntary actions such as those involved in writing and speech. The medulla oblongata in the brain stem is

46 Foundation Science: Biology for Class 10 the centre of involuntary actions, like swallowing, coughing, sneezing, salivation, vomiting, heartbeat and breathing. The medulla oblongata is continued into the spinal cord. The pons relays information between the cerebellum and the cerebrum. Fig. 5.9 Section through the human brain Spinal cord It is a long cord which arises from the medulla oblongata and runs through the vertebral column (backbone). The vertebral column protects the spinal cord. The spinal cord is also covered by meninges. A cross section of the spinal cord shows the central canal, which is filled with cerebrospinal fluid. Around the canal are clusters of cytons, which form the grey matter. The peripheral part has mainly axons and is called white matter. From each side of the spinal cord two roots, the dorsal and the ventral root, arise. The dorsal root is joined by a nerve called sensory nerve, which picks up sensations from the sense organs (receptors). From the ventral root arises the motor nerve, which takes messages from the spinal cord to the muscles or glands (effectors). Fig. 5.10 Cross section of the spinal cord, showing how the impact of the hammer was sent to the dorsal root through the sensory nerve and how the motor nerve brought the message from the ventral root to pull the leg downward. This is an example of reflex action. Reflex action What happens when you touch something hot or your finger is pricked by a needle? You immediately pull your hand away, without even thinking why you are doing so. Such sudden involuntary responses to stimuli are examples of reflex action. The response may be different when

Control and Coordination 47 your conscious thought process is involved. For example, when a doctor pricks you with an injection needle to inject a medicine into your arm, you do not withdraw your arm immediately. Your conscious thinking tells you that the medicine is being administered to cure your disease. In this case, a message from the spinal cord goes to the cerebrum, the thinking part of your brain, and your thinking brain directs your arm to bear the pain and not pull away. The spinal cord is the centre of reflex action. Reflex actions are produced by reflex arcs, which may be formed anywhere along the spinal cord, nearest to the receptor and effector. A reflex arc is formed by a sensory nerve and a motor nerve joined by a connecting nerve present in the spinal cord. As the impulses do not have to travel all the way to the brain and back, the detection of stimuli and the completion of responses are faster. Reflex action is an extremely quick action, which does not involve any thinking by the brain. If someone hits your leg with a hammer the leg is immediately withdrawn. In this type of reflex action the impact of the hammer (stimulus) received by the receptor is sent to the spinal cord through the sensory nerve. The message is received by the connecting nerve in the spinal cord. The connecting nerve then sends a response through the motor nerve to the muscles (effectors) to pull the leg away (Figure 5.10). Thus, reflex action is a sudden, involuntary motor response to a stimulus. The flow of food in the alimentary canal, blinking in strong light or in response to a sudden movement in front of the eye, sneezing, coughing, yawning, hiccupping, shivering, etc., are also reflex actions. Peripheral nervous system The peripheral nervous system includes 12 pairs of cranial nerves arising from the brain and 31 pairs of spinal nerves arising from the spinal cord. The nerves from the brain and the spinal cord connect the skeletal muscles and control their activity according to the directions and demands of the body. These nerves are, therefore, related to voluntary acts, i.e., they act according to our will. Autonomic nervous system The autonomic nervous system controls and integrates the functions of internal organs like the heart, blood vessels, glands, etc., which are not under the control of our will. The autonomic nervous system has two subdivisions: sympathetic and parasympathetic. The organs receive both sympathetic and parasympathetic nerves. The two types of nerves have opposite effects on the organs, i.e., if one is stimulatory, the other is inhibitory. How does the nervous tissue cause the muscles to act? When an electrical signal from a nerve cell reaches a synapse it causes the axon bulb to release a chemical. This chemical, which is discharged at the junction between the nerve cell and the muscle cell, causes the cell membrane of the muscle cell to move some ions in the muscle cell. This triggers a series of changes, ultimately causing the muscle to contract or relax. • POINTS TO REMEMBER • · The working together of the various systems in · Plant responses and growth are controlled by the body is called coordination. chemical messengers called hormones. The main plant hormones and their functions are: · Chemical coordination is seen in plants and animals. 1. Auxins promote cell elongation, cell division, etc. · Response and coordination in plants are in the 2. Gibberellins are growth hormones of plants. form of slow growth and turgor movements. 3. Cytokinins promote cytokinesis. · The movement of organisms in the direction of a stimulus or away from it is called tropic 4. Abscisic acid inhibits growth. movement. Tropic movements are in response to light (phototropism), gravity (geotropism), water · Response and coordination in animals involve (hydrotropism), chemicals (chemotropism) and the sense organs, the nervous system and touch (thigmotropism). hormones. · A feedback mechanism regulates the action of hormones.