Topic outline

    • Respiration in Organisms

      Q47. How do the cockroaches breathe?

      Ans. A cockroach has small openings on the sides of its body. These openings are called spiracles. They 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.


      Q48. Why does an athlete breathe faster and deeper than usual after finishing the race?

      Ans. During fast running the demand for energy is high. But the supply of oxygen to produce the energy is limited. Our muscle cells can also respire anaerobically, but only for a short time, when there is a temporary deficiency of oxygen. Thus, an athlete breathes faster and deeper than usual after finishing the race so that more oxygen is supplied to the cells. This speed up the breakdown of food and more energy is released.


      Q49. Why do we respire?

      Ans. 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. The food has stored energy, which is released during respiration. Therefore, we respire to get energy from food.

      Q50. List the similarities and differences between aerobic and anaerobic respiration.

      Ans. Similarities

                                i.        Both aerobic and anaerobic respirations are types of cellular respiration.

                               ii.        Both generate energy by breaking down glucose and produces byproducts.


      Aerobic Respiration

      Anaerobic respiration

      1. It occurs in the presence of oxygen.

      1. It occurs in the absence of oxygen.

      2. Large amount of energy is released.

      2. Small amount of energy is released.

      3. Glucose breaks down into water and carbon dioxide.

      3. Glucose breaks down into alcohol and carbon dioxide.

      4. It is a slow process.

      4. It is a fast process.

      5. It occurs in most of the plants and animals.

      5. It occurs in human muscles cells, yeast, bacteria etc.


      Q51. How do we breathe?

      Ans. 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.

      Q52. Take three test-tubes. Fill ¾ th 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?

      Ans. Snail breathes in oxygen and breathes out carbon dioxide. Hence concentration of CO2 increases in the test tube. Therefore, Test tube A will have high concentration of carbon dioxide.

      In test tube B water plant uses carbon dioxide for synthesizing food and hence there will be less concentration of carbon dioxide compared to test tube A.

      In test tube C, carbon dioxide produced by snail is utilized by plant for synthesis of food and oxygen released by plant is utilized by snail for respiration. Hence, concentration of carbon dioxide is least in test tube C.


      Q53. Write one word for the following:

                                  i.        The air tubes of insects - Trachea

                                 ii.        Skeletal structures surrounding chest cavity - Ribs

                                iii.        Muscular floor of chest cavity - Diaphragm

                                iv.        Tiny pores on the surface of leaf - Stomata

                                 v.        Small openings on the sides of the body of an insect - Spiracles

                                vi.        The respiratory organs of human beings - Lungs

                vii.        The openings through which we inhale - Nostrils

                viii.        An anaerobic organism - Yeast

                                ix.        An organism with tracheal system - Ant

      Q54. 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?

      Ans. Whales and dolphins are mammals and breathe air into their lungs, just like we do. They cannot breathe under water like fish can as they do not have gills. They breathe through a nostril, called a blowhole, located right on top of their heads. This allows them to take breaths by exposing just the top of their heads to the air while they are swimming or resting under the water. After each breath, the blowhole is sealed tightly by strong muscles that surround it, so that water cannot get into the dolphin’s lungs.

      When they surfaces for air, they breathes out (exhales) first and then breathes in (inhales) fresh air. The water spray is not coming from theirs lungs; it is just water sitting on top of their head around the blowhole being blown away before they inhale.


      Q55. Explain the mechanism of breathing with the help of an activity.

      Ans. 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. 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. The volume of the cavity increases. This causes the pressure to decrease. Air rushes in to equalize the pressure, causing the balloons to inflate. Next, push the rubber/plastic sheet up. The volume of the cavity decreases. This causes an increase in pressure within the bottle, the air rushes out of the balloons causing them to deflate.

       Image from NCERT


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