Welcome dear students! Today we are going to learn about Respiration in Organisms from Class 7 Science. One day, a student named 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.
In Chapter 2 you learnt that all organisms are 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, which is 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. 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.
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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, 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 place in the muscle cells to fulfil the demand of energy. 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.
Let us move to breathing. Activity six point one begins with an interesting fact: yeasts are single celled organisms. They respire anaerobically and during this process yield alcohol. They are, therefore, used to make wine and beer. Please note the caution: do this activity under the supervision of your teacher. 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. 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 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.
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Would 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 Activity six point two. 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, which is the number of breaths per minute, after a 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. In Table six point one, you will record the name of each classmate along with their breathing rate under normal conditions, after a brisk walk for ten minutes, after running fast for one hundred meters, and at rest. From the above activity, you must have realised that whenever a person needs extra energy, he or she breathes faster. As a result more oxygen is supplied to our cells. It speeds up the breakdown of food and more energy is released. Does this explain why do we feel hungry after a physical activity? When you feel drowsy, does your breathing rate slow down? Does your body receive sufficient oxygen? 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? Think about what happens to the oxygen and carbon dioxide levels in your lungs when you hold your breath, and consider why your body demands rapid breathing immediately after.
Activity six point three shows various activities carried out by a person during a normal 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. 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. This cavity is surrounded by ribs on the sides. A large, muscular sheet called diaphragm forms the floor of the chest cavity. 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. These movements in our body can be felt 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. Everyone was boasting that she or he could expand it the maximum. How about doing this activity in the class with your classmates?
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Activity six point four asks you to take a deep breath. Measure the size of the chest with a measuring tape and record your observations. In Table six point two, you will record the size of the chest in centimeters during inhalation and during exhalation for some classmates, and calculate the difference in size. 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. Activity six point five instructs you to take a wide plastic bottle and 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. 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. To understand the expansion of the lungs, pull the rubber sheet from the base downwards and watch the balloons. Next, push the rubber or plastic sheet up and observe the balloons. Did you see any changes in the balloons? What do the balloons in this model represent? They represent the lungs. What does the rubber sheet represent? It represents the diaphragm. Now, you should be able to explain the mechanism of breathing.
On an average, an adult human being at rest breathes in and out fifteen to eighteen times in a minute. During heavy exercise, the breathing rate can increase up to twenty five 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. Yawning helps take in more oxygen when the body is drowsy and breathing slows down. The air around us has various types of unwanted particles, such as smoke, dust, and pollens. 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 dust free, 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. Smoking damages lungs. Smoking is also linked to cancer. It must be avoided.
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Let us look at what we breathe out. Activity six point six asks you to take a slender, clean test tube or a glass or 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 the hole in the lid in such a way that it dips in lime water. Now blow gently through the straw a few times. Is there a change in the appearance of lime water? Can you explain this change on the basis of what you learnt in Chapter 5? The lime water turns milky, which indicates the presence of carbon dioxide. 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? They come from the water vapor present in our exhaled breath. Boojho wants to know how much air a person can hold in the lungs. The percentage of oxygen and carbon dioxide in inhaled and exhaled air is as follows. Inhaled air contains twenty one percent oxygen and zero point zero four percent carbon dioxide. Exhaled air contains sixteen point four percent oxygen and four point four percent carbon dioxide. Breathe for Better Life tells us that regular traditional breathing exercise, known as 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.
Let us explore breathing in other animals. Animals such as elephants, lions, cows, goats, frogs, lizards, snakes, and birds have lungs in their chest cavities like human beings. How do other organisms breathe? Do they also have lungs like those of human beings? Let us find out. A cockroach has small openings on the sides of its body. Other insects also have similar openings. These openings are called spiracles. 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. Recall from Chapter 6 of Class 6 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.
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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 6 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 for exchange of gases. 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? They come to the surface to breathe air because they have lungs and cannot extract oxygen directly from water like fish. Like other living organisms, plants also respire for their survival as you have learnt in Class 6. They also take in oxygen from the air and give out carbon 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. 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. Can you guess what would happen if a potted plant is overwatered? Overwatering fills the air spaces in the soil with water, cutting off the oxygen supply to the roots, which can cause the plant to die.
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. Let us review the key points. Respiration is essential for survival of living organisms. It releases energy from the food. The oxygen we inhale is used to breakdown glucose into carbon dioxide and water. Energy is released in the process. The breakdown of glucose occurs in the cells of an organism, which is cellular respiration. 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. During heavy exercise when the supply of oxygen to our muscle cells is insufficient, food breakdown is by anaerobic respiration. 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. During inhalation, our lungs expand and then come back to the original state as the air moves out during exhalation. Increased physical activity enhances the rate of breathing. In animals like cow, buffalo, dog and cat the respiratory organs and the process of breathing are similar to those in humans. In earthworm, the exchange of gases occurs through the moist skin. In fishes it takes place through gills and in insects through the tracheae. 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. The keywords for this chapter are aerobic respiration, anaerobic respiration, breathing rate, cellular respiration, diaphragm, exhalation, gills, lungs, inhalation, spiracles, tracheae, and ribs.
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Now let us solve the exercises. Question one: Why does an athlete breathe faster and deeper than usual after finishing the race? Answer: During a race, the muscles work very hard and need a large amount of energy. To produce this energy quickly, the body requires more oxygen. Therefore, the athlete breathes faster and deeper to take in more oxygen and supply it to the muscle cells for aerobic respiration, which releases the required energy. Question two: List the similarities and differences between aerobic and anaerobic respiration. Answer: Similarities: Both processes break down food to release energy. Both occur in the cells of organisms. Differences: Aerobic respiration requires oxygen, while anaerobic respiration occurs without oxygen. Aerobic respiration completely breaks down glucose into carbon dioxide and water, whereas anaerobic respiration partially breaks down glucose into alcohol and carbon dioxide in yeast, or into lactic acid in muscle cells. Aerobic respiration releases more energy compared to anaerobic respiration.
Question three: Why do we often sneeze when we inhale a lot of dust laden air? Answer: When we inhale dust laden air, the unwanted particles like dust and smoke may get past the hair in the nasal cavity. This irritates the lining of the cavity, which triggers a sneeze. Sneezing expels these foreign particles from the inhaled air so that dust free, clean air can enter our body. Question four: Take three test tubes. Fill three fourths 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 carbon dioxide? Answer: Test tube A will have the highest concentration of carbon dioxide. The snail in test tube A will respire and release carbon dioxide into the water. In test tube B, the water plant will perform photosynthesis and use carbon dioxide, so the concentration will be low. In test tube C, the carbon dioxide released by the snail will be used by the plant for photosynthesis, so the net concentration will be lower than in test tube A.
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Question five: Tick the correct answer. Part a: In cockroaches, air enters the body through. The correct answer is three, spiracles. Part b: During heavy exercise, we get cramps in the legs due to the accumulation of. The correct answer is two, lactic acid. Part c: Normal range of breathing rate per minute in an average adult person at rest is. The correct answer is two, fifteen to eighteen. Part d: During exhalation, the ribs. The correct answer is two, move downwards. Question six: Match the items in Column one with those in Column two. Yeast matches with alcohol. Diaphragm matches with chest cavity. Skin matches with earthworm. Leaves match with stomata. Fish matches with gills. Frog matches with lungs and skin. Question seven: Mark T if the statement is true and F if it is false. Part one: During heavy exercise the breathing rate of a person slows down. This is false. Part two: Plants carry out photosynthesis only during the day and respiration only at night. This is false, because plants respire continuously. Part three: Frogs breathe through their skins as well as their lungs. This is true. Part four: The fishes have lungs for respiration. This is false. Part five: The size of the chest cavity increases during inhalation. This is true.
Question eight: Given below is a square of letters in which are hidden different words related to respiration in organisms. Find the words for your respiratory system. The clues and answers are: The air tubes of insects is Tracheae. Skeletal structures surrounding chest cavity is Ribs. Muscular floor of chest cavity is Diaphragm. Tiny pores on the surface of leaf is Stomata. Small openings on the sides of the body of an insect is Spiracles. The respiratory organs of human beings is Lungs. The openings through which we inhale is Nostrils. An anaerobic organism is Yeast. An organism with tracheal system is Ant. Question nine: The mountaineers carry oxygen with them because. The correct answer is b, the amount of air available to a person is less than that available on the ground.
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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. Let us look at extended learning activities and projects. First, 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. This shows that fish continuously take in water through the mouth, pass it over the gills to extract dissolved oxygen, and expel it through the gill flaps. Second, visit a local doctor to learn about the harmful effects of smoking. You can collect material on this topic from other sources. Find out the percentage of people in your area who smoke. If you have a smoker in your family, confront him with the material that you have collected. Third, visit a doctor to find out about artificial respiration. Ask the doctor when a person needs artificial respiration, whether the person needs to be kept on artificial respiration temporarily or permanently, and from where the person can get supply of oxygen for artificial respiration. Fourth, measure the breathing rate of the members of your family and some of your friends. Investigate if the breathing rate of children is different from that of adults, and 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.
Thank you for listening! Keep revising and practicing. Goodbye! [CHAPTER_COMPLETE]