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10, , Respiration in, Organisms, , O, , ne day Boojho was eagerly, waiting, to, meet, his, grandparents who were coming, to the town after a year. He was in a real, hurry as he wanted to receive them at the, bus-stop. He ran fast and reached the, bus-stop in a few minutes. He was, breathing rapidly. His grandmother asked, him why he was breathing so fast. Boojho, told her that he came running all the way., But the question got stuck in his mind., He wondered why running makes a, person breathe faster. The answer to, Boojho’s question lies in understanding, why we breathe. Breathing is a part of, respiration. Let us learn about respiration., , 10.1 WHY, , DO, , W E RESPIRE?, , In Chapter 2 you learnt that all, organisms ar e made of small, microscopic units called cells. A cell is, the smallest structural and functional, unit of an organism. Each cell of an, organism performs certain functions, such as nutrition, transport, excretion, and reproduction. To perform these, functions, the cell needs energy. Even, when we are eating, sleeping or reading, we require energy. But, where does this, energy come from? Can you say why, your parents insist that you should eat, regularly? The food has stored energy,, which is released during respiration., , Therefore, all living organisms respire, to get energy from food. During, breathing, we breathe in air. You know, that air contains oxygen. We breathe out, air which is rich in carbon dioxide. The, air we breathe in is transported to all, parts of the body and ultimately to each, cell. In the cells, oxygen in the air helps, in the breakdown of food. The process, of breakdown of food in the cell with the, release of energy is called cellular, respiration. Cellular respiration takes, place in the cells of all organisms., In the cell, the food (glucose) is broken, down into carbon dioxide and water using, oxygen. When breakdown of glucose, occurs with the use of oxygen it is called, aerobic respiration. Food can also be, broken down, without using oxygen. This, is called anaerobic respiration., Breakdown of food releases energy., in the presence of oxygen, , Glucose , →, carbon dioxide + water + energy, You should know that there are some, organisms such as yeast that can survive, in the absence of air. They are called, anaerobes. They get energy through, anaerobic respiration. In the absence of, oxygen, glucose breaks down into alcohol, and carbon dioxide, as given below:, , 108, , in the absence of oxygen, , Glucose →, alcohol + carbon dioxide + energy, SCIENCE, , 2020-21

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Yeasts are single-celled organisms., They respire anaerobically and during, this process yield alcohol. They are,, therefore, used to make wine and beer., Our muscle cells can also respire, anaerobically, but only for a short time,, when there is a temporary deficiency of, oxygen. During heavy exercise, fast, running (Fig. 10.1), cycling, walking for, many hours or heavy weight lifting, the, demand for energy is high. But the, supply of oxygen to produce the energy, is limited. Then anaerobic respiration, takes places in the muscle cells to fulfil, the demand of energy:, in the absence of oxygen, , Glucose , →, (in muscle), , Have you ever wondered why you get, muscle cramps after heavy exercise? The, cramps occur when muscle cells respire, anaerobically. The partial breakdown of, glucose produces lactic acid. The, accumulation of lactic acid causes muscle, cramps. We get relief from cramps after a, hot water bath or a massage. Can you, guess why it is so? Hot water bath or, massage improves circulation of blood., As a result, the supply of oxygen to the, muscle cells increases. The increase in, the supply of oxygen results in the, complete breakdown of lactic acid into, carbon dioxide and water., , 10.2 BREATHING, Activity 10.1, , lactic acid + energy, , CAUTION, Do this activity under the supervision, of your teacher., , Fig. 10.1 During exercise, some muscles may, respire anaerobically, , Close your nostrils and mouth, tightly and look at a watch. What did, you feel after some time? How long were, you able to keep both of them closed?, Note down the time for which you could, hold your breath (Fig. 10.2)., So, now you know that you cannot, survive for long without breathing., Breathing means taking in air rich, in oxygen and giving out air rich in, carbon dioxide with the help of, respiratory organs. The taking in of air, rich in oxygen into the body is called, inhalation and giving out of air rich in, carbon dioxide is known as exhalation., It is a continuous process which goes, , RESPIRATION IN ORGANISMS, , 109, , 2020-21

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on all the time and throughout the life, of an organism., The number of times a person, breathes in a minute is termed as the, breathing rate. During breathing, inhalation and exhalation take place, alternately. A breath means one, inhalation plus one exhalation. Would, , Fig. 10.2 Holding breath, , Boojho noticed that when he, released his breath after holding, it for some time, he had to, breathe heavily. Can you tell, him why it was so?, , you like to find out your breathing rate?, Do you want to know whether it is, constant or it changes according to the, requirement of oxygen by the body? Let, us find out by doing the following, activity., , Activity 10.2, Generally we are not aware that we are, breathing. However, if you try you can, count your rate of breathing. Breathe, in and out normally. Find out how many, times you breathe in and breathe out, in a minute? Did you inhale the same, number of times as you exhaled? Now, count your breathing rate (number of, breaths/minute) after brisk walk and, after running. Record your breathing, rate as soon as you finish and also after, complete rest. Tabulate your findings, and compare your breathing rates under, different conditions with those of your, classmates., From the above activity, you must, have realised that whenever a person, needs extra energy, he/she breathes, faster. As a result more oxygen is, , Table 10.1 Changes in breathing rate under different conditions, Name of the classmate, Normal, , Breathing rate, After a brisk, After running, walk for 10, fast 100 m, , At rest, , minutes, , Self, 110, , SCIENCE, , 2020-21

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On an average, an adult human being, at rest breathes in and out 15–18, times in a minute. During heavy, exercise, the breathing rate can, increase upto 25 times per minute., While we exercise, not only do we, breathe fast, we also take deep breaths, and thus inhale more oxygen., , Paheli wants to know why, we yawn when we are, sleepy or drowsy., , supplied to our cells. It speeds up, the breakdown of food and more, energy is released. Does this explain, w h y do w e f e e l h u n g r y a f t e r a, physical activity?, When you feel drowsy, does your, breathing rate slow down? Does your, body receive sufficient oxygen?, , Activity 10.3, Figure 10.3 shows the various activities, carried out by a person during a normal, , Fig. 10.3 Variation in the breathing rate during, different activities, , day. Can you say in which activity, the, rate of breathing will be the slowest and, in which it will be the fastest? Assign, numbers to the pictures in the order of, increasing rate of breathing according, to your experience., , 10.3 HOW, , DO, , WE BREATHE?, , Let us now learn about the mechanism, of breathing. Normally we take in air, through our nostrils. When we inhale, air, it passes through our nostrils into, the nasal cavity. From the nasal cavity,, the air reaches our lungs through the, windpipe. Lungs are present in the, chest cavity (Fig. 10.4). This cavity is, surrounded by ribs on the sides. A large,, muscular sheet called diaphragm forms, the floor of the chest cavity (Fig. 10.4)., Breathing involves the movement of the, diaphragm and the rib cage., During inhalation, ribs move up and, outwards and diaphragm moves down., This movement increases space in our, chest cavity and air rushes into the, lungs. The lungs get filled with air., During exhalation, ribs move down and, inwards, while diaphragm moves up to, its former position. This reduces the size, of the chest cavity and air is pushed out, of the lungs (Fig. 10.5). These, movements in our body can be felt, , RESPIRATION IN ORGANISMS, , 111, , 2020-21

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easily. Take a deep breath. Keep your, palm on the abdomen, feel the, movement of abdomen. What do you, find?, After having learnt that during, breathing there are changes in the size, of the chest cavity, children got involved, in the chest expansion competition., , Smoking damages lungs. Smoking is, also linked to cancer. It must be, avoided., Everyone was boasting that she/he, could expand it the maximum. How, about doing this activity in the class, with your classmates?, Nasal passage, , Pharynx, , Oral cavity, , Trachea, , Lungs, , Ribs, , Diaphragm, , Fig 10.4 Human respiratory system, , The air around us has various types of unwanted particles, such as smoke, dust,, pollens, etc. When we inhale, the particles get trapped in the hair present in our, nasal cavity. However, sometimes these particles may get past the hair in the, nasal cavity. This may irritate the lining of the cavity, as a result of which we, sneeze. Sneezing expels these foreign particles from the inhaled air and a dustfree, clean air enters our body., TAKE CARE: When you sneeze, you should cover your nose so that the foreign, particles you expel are not inhaled by other persons., 112, , SCIENCE, , 2020-21

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Activity 10.4, , Activity 10.5, , Take a deep breath. Measure the size, of the chest with a measuring tape, (Fig. 10.6) and record your observations, in Table 10.2. Measure the size of the, chest again when expanded and, indicate which classmate shows the, maximum expansion of the chest., We can understand the mechanism, of breathing by a simple model., , Take a wide plastic bottle. Remove the, bottom. Get a Y-shaped glass or plastic, tube. Make a hole in the lid so that the, tube may pass through it. To the forked, end of the tube fix two deflated balloons., Introduce the tube into the bottle as, shown in Fig. 10.7. Now cap the bottle., Seal it to make it airtight. To the open, base of the bottle tie a thin rubber or, plastic sheet using a large rubber band., , Air is, drawn in, , Air forced out, , Ribs move, back, , Ribs move, out, , Diaphragm, moves down, , Diaphragm, moves back, , (a) Inhalation, , (b) Exhalation, , Fig. 10.5 Mechanism of breathing in human beings, , Table 10.2: Effect of breathing on the chest size of some classmates, Name of the, classmate, , Size of the chest (cm), During inhalation, During exhalation, , RESPIRATION IN ORGANISMS, , Difference in size, , 113, , 2020-21

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the hole in the lid in such a way that it, dips in lime water. Now blow gently, through the straw a few times (Fig., 10.8). Is there a change in the, appearance of lime water? Can you, explain this change on the basis of what, you learnt in Chapter 6?, You are aware that air we inhale or, exhale is a mixture of gases. What do, we exhale? Do we exhale only carbon, dioxide or a mixture of gases along with, it? You must have also observed that if, you exhale on a mirror, a film of, moisture appears on its surface. From, where do these droplets come?, , Fig. 10.6 Measuring chest size, , To understand the expansion of the, lungs, pull the rubber sheet from the, base downwards and watch the balloons., Next, push the rubber/plastic sheet up, and observe the balloons. Did you see, any changes in the balloons?, What do the balloons in this model, represent? What does the rubber sheet, represent?, Now, you should be able to explain, the mechanism of breathing., , 10.4 WHAT, , DO, , WE BREATHE, , Boojho wants to know how, much air a person can hold in, the lungs., , Plastic, bottle, , OUT ?, , Activity 10.6, , Balloons, , Take a slender, clean test tube or a, glass/plastic bottle. Make a hole in its, lid and fix it on the bottle. Pour some, freshly prepared lime water in the, test-tube. Insert a plastic straw through, , Ruber, sheet, , Fig 10.7 Model to show, mechanism of breathing, , Breathe for Better Life, Regular traditional breathing exercise (pranayama) can increase the capacity of, lungs to take in more air. Thus more oxygen can be supplied to the body cells, resulting in release of more energy., 114, , SCIENCE, , 2020-21

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Boojho wants to know if, cockroaches, snails, fish,, earthworms, ants and mosquitoes, also have lungs., Straw, , These openings are called spiracles, (Fig. 10.9). Insects have a network of air, tubes called tracheae for gas exchange., Oxygen rich air rushes through spiracles, into the tracheal tubes, diffuses into the, body tissue, and reaches every cell of, the body. Similarly, carbon dioxide from, the cells goes into the tracheal tubes and, moves out through spiracles. These air, tubes or tracheae are found only in, insects and not in any other group of, animals., , Lime water, Fig 10.8 Effect of exhaled air on lime water, , The percentage of oxygen and carbon, dioxide in inhaled and exhaled air., Inhaled air, Exhaled air, 16.4% oxygen, , 21% oxygen, , Tracheae, , Lungs, 0.04% carbon, dioxide, , 10.5 BREATHING, , 4.4% carbon, dioxide, IN, , OTHER ANIMALS, , Animals such as elephants, lions, cows,, goats, frogs, lizards, snakes, birds, have, lungs in their chest cavities like the, human beings., How do other organisms breathe? Do, they also have lungs like those of human, beings? Let us find out., Cockroach: A cockroach has small, openings on the sides of its body. Other, insects also have similar openings., , Fig.10.9 Tracheal system, , Earthworm: Recall from Chapter 9 of, Class VI that earthworms breathe, through their skins. The skin of an, earthworm feels moist and slimy on, touching. Gases can easily pass through, them. Though frogs have a pair of lungs, like human beings, they can also, breathe through their skin, which is, moist and slippery., , RESPIRATION IN ORGANISMS, , 115, , 2020-21

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dioxide. In the cells oxygen is used to, break down glucose into carbon dioxide, and water as in other organisms. In, plants each part can independently take, in oxygen from the air and give out, carbon dioxide. You have already learnt, in Chapter 1 that the leaves of the plants, have tiny pores called stomata for, exchange of oxygen and carbon dioxide., , Boojho has seen in television, programmes that whales and, dolphins often come up to the, water surface. They even release, a fountain of water sometimes, while moving upwards. Why do, they do so?, , 10.6 BREATHING, , UNDER, , Paheli wants to know whether, roots, which are underground, also take in oxygen? If so, how?, , WATER, , Can we breathe and survive in water?, There are many organisms which live in, water. How do they breathe under water?, You have studied in Class VI that, gills in fish help them to use oxygen, dissolved in water. Gills are projections, of the skin. You may wonder how gills, help in breathing. Gills are well supplied, with blood vessels (Fig. 10.10) for, exchange of gases., , Like all other living cells of the, plants, the root cells also need, oxygen to generate energy. Roots take, up air from the air spaces present, between the soil particles (Fig. 10.11)., , Gills, , Soil particles, , Root hair, Fig. 10.10 Breathing organs in fish, , 10.7 DO PLANTS, , ALSO, , Air space, , RESPIRE?, , Like other living organisms, plants also, respire for their survival as you have, learnt in Class VI. They also take in, oxygen from the air and give out carbon, 116, , Fig. 10.11 Roots absorb air from the soil, SCIENCE, , 2020-21

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Can you guess what would happen, if a potted plant is overwatered?, In this chapter you learnt, that respiration is a vital biological, , process. All living organisms need, to respire to get the energy needed, for their survival., , Keywords, Aerobic respiration, Anaerobic respiration, Breathing rate, Cellular respiration, , Diaphragm, Exhalation, Gills, Lungs, , Inhalation, Spiracles, Tracheae, Ribs, , What you have learnt, n, , Respiration is essential for survival of living organisms. It releases energy, from the food., , n, , The oxygen we inhale is used to breakdown glucose into carbon dioxide, and water. Energy is released in the process., , n, , The breakdown of glucose occurs in the cells of an organism (cellular, respiration)., , n, , If the food is broken down with the use of oxygen, it is called aerobic, respiration. If the breakdown occurs without the use of oxygen, the, respiration is called anaerobic respiration., , n, , During heavy exercise when the supply of oxygen to our muscle cells is, insufficient, food breakdown is by anaerobic respiration., , n, , Breathing is a part of the process of respiration during which an, organism takes in the oxygen-rich air and gives out air rich in carbon, dioxide. The respiratory organs for the exchange of gases vary in different, organisms., , n, , During inhalation, our lungs expand and then come back to the original, state as the air moves out during exhalation., , n, , Increased physical activity enhances the rate of breathing., , n, , In animals like cow, buffalo, dog and cat the respiratory organs and the, process of breathing are similar to those in humans., , n, , In earthworm, the exchange of gases occurs through the moist skin. In, fishes it takes place through gills and in insects through the tracheae., , n, , In a plant the roots take in air present in the soil. Leaves have tiny pores, called stomata through which they exchange gases. The breakdown of, glucose in the plant cells is similar to that in other living beings., , RESPIRATION IN ORGANISMS, , 117, , 2020-21

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Exercises, 1. Why does an athlete breathe faster and deeper than usual after, finishing the race?, 2. List the similarities and differences between aerobic and anaerobic, respiration., 3. Why do we often sneeze when we inhale a lot of dust-laden air?, 4. Take three test-tubes. Fill ¾th of each with water. Label them A, B and, C. Keep a snail in test-tube A, a water plant in test-tube B and in C,, keep snail and plant both. Which test-tube would have the highest, concentration of CO2?, 5. Tick the correct answer:, (a), , In cockroaches, air enters the body through, (i), , lungs, , (iii) spiracles, (b), , carbon dioxide, , (iii) alcohol, , (iv), , skin, , (ii), , lactic acid, , (iv), , water, , Normal range of breathing rate per minute in an average adult, person at rest is:, (i), , 9 –12, , (iii) 21–24, (d), , gills, , During heavy exercise, we get cramps in the legs due to the, accumulation of, (i), , (c), , (ii), , (ii), , 15–18, , (iv), , 30–33, , During exhalation, the ribs, (i), , move outwards, , (ii), , move downwards, , (iii) move upwards, , (iv), , do not move at all, , 6. Match the items in Column I with those in Column II:, Column I, , Column II, , (a), , Yeast, , (i), , Earthworm, , (b), , Diaphragm, , (ii), , Gills, , (c), , Skin, , (iii), , Alcohol, , (d), , Leaves, , (iv), , Chest cavity, , (e), , Fish, , (v), , Stomata, , (f), , Frog, , (vi), , Lungs and skin, , (vii), , Tracheae, , 118, , SCIENCE, , 2020-21

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7. Mark ‘T’ if the statement is true and ‘F’ if it is false:, (i), , During heavy exercise the breathing rate of a person slows, down. (T/F), , (ii), , Plants carry out photosynthesis only during the day and, respiration only at night. (T/F), , (iii), , Frogs breathe through their skins as well as their lungs. (T/F), , (iv), , The fishes have lungs for respiration. (T/F), , (v), , The size of the chest cavity increases during inhalation. (T/F), , 8. Given below is a square of letters in which are hidden different words, related to respiration in organisms. These words may be present in any, direction — upwards, downwards, or along the diagonals. Find the words, for your respiratory system. Clues about those words are given below, the square., S, , V, , M, , P, , L, , U, , N, , G, , S, , C, , Z, , G, , Q, , W, , X, , N, , T, , L, , R, , M, , A, , T, , I, , D, , O, , T, , C, , I, , Y, , R, , X, , Y, , M, , S, , R, , A, , B, , R, , H, , I, , A, , N, , T, , A, , Y, , S, , T, , P, , T, , B, , Z, , R, , C, , E, , M, , I, , A, , M, , T, , S, , I, , H, , A, , S, , P, , I, , R, , A, , C, , L, , E, , S, , N, , E, , D, , K, , J, , N, , S, , A, , T, , (i), , The air tubes of insects, , (ii), , Skeletal structures surrounding chest cavity, , (iii), , Muscular floor of chest cavity, , (iv), , Tiny pores on the surface of leaf, , (v), , Small openings on the sides of the body of an insect, , (vi), , The respiratory organs of human beings, , (vii) The openings through which we inhale, (viii) An anaerobic organism, (ix), , An organism with tracheal system, , 9. The mountaineers carry oxygen with them because:, (a), , At an altitude of more than 5 km there is no air., , RESPIRATION IN ORGANISMS, , 119, , 2020-21

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(b), , The amount of air available to a person is less than that available, on the ground., , (c), , The temperature of air is higher than that on the ground., , (d), , The pressure of air is higher than that on the ground., , Extended Learning — Activities and Projects, 1. Observe fish in an aquarium. You will find flap like structures on both, sides of their heads. These are flaps which cover the gills. These flaps, open and close alternately. On the basis of these observations, explain, the process of respiration in the fish., 2. Visit a local doctor. Learn about the harmful effects of smoking. You can, also collect material on this topic from other sources. You can seek help, of your teacher or parents. Find out the percentage of people of your, area who smoke. If you have a smoker in your family, confront him with, the material that you have collected., 3. Visit a doctor. Find out about artificial respiration. Ask the doctor:, (a), , When does a person need artificial respiration?, , (b), , Does the person need to be kept on artificial respiration temporarily, or permanently?, , (c), , From where can the person get supply of oxygen for artificial, respiration?, , 4. Measure the breathing rate of the members of your family and some of, your friends. Investigate:, (c), , If the breathing rate of children is different from that of adults., , (d), , If the breathing rate of males is different from that of females., , If there is a difference in any of these cases, try to find the reason., , Did you know?, For us oxygen is essential, but for those organisms which do not use it,, oxygen is toxic. In fact, for humans and other organisms it may be, dangerous to breathe pure oxygen for long., , 120, , SCIENCE, , 2020-21