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| Experiments on Respiration |
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| To Demonstrate Aerobic Respiration |
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| The apparatus shown is called the respiroscope that is used to demonstrate respiration. |
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| Few germinating seeds are taken in the bulb of the respirometer. The tube is inserted into a beaker containing mercury. A pellet of KOH is introduced into the set-up. |
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| Another experiment is set up without any seeds but with the KOH pellet. This acts as the control. |
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| After a day, the mercury level is found to be raised in the tube. |
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| Why does the level of the mercury go up? |
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| The oxygen in the apparatus is used up in respiration. This lowers the air pressure inside the bulb raising the level of mercury. |
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| Why is the KOH pellet introduced? |
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| KOH absorbs carbon dioxide. It is to rule out that carbon dioxide may be absorbed by the seeds. |
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| To Demonstrate Evolution of Carbon Dioxide During Respiration |
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| The experiment is set up as shown. Bottle C is covered with a black cloth to prevent photosynthesis. |
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| On opening the stop cork near the aspirator, the lime water in D turns milky after sometime. However, the lime water in B does not turn milky. |
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| Why does the lime water in D turn milky? |
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| The lime water in D turns milky because the air given out from the seeds contains carbon dioxide. |
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| Why does the lime water in B remain clear? |
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| This is because the soda lime in A absorbs the carbon dioxide and it is this air that is entering the flask B. |
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| Breathe gently on to a cold surface. Minute droplets of water can be observed. This shows that expired air has more water vapour than the inspired air. Thus, water is lost during respiration. |
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| Flask A that contains germinating seeds will show rise in temperature after sometime whereas flask B will not. Why? |
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| Experiment to Demonstrate that Heat is Liberated During Respiration |
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| The seeds in B have been boiled. This destroys the enzymes and kills the seeds. Thus, respiration cannot take place. In A, the temperature rises because heat is liberated during respiration. |
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| Kuhne's Tube |
| (Glucose Solution + Yeast) |
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| The above apparatus is called the Kuhne's fermentation vessel. It is filled with 10% glucose solution along with yeast. The vertical tube is filled completely and the bulb is half-filled. After sometime, the level in the bulb goes up and the level in the tube comes down. Why? |
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| This is because, a gas is liberated. This displaces the liquid and being lighter, it occupies the top of the tube. |
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| How is the gas proved to be carbon dioxide? |
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| A KOH pellet is introduced into the solution. It rises up through the solution to the top of the tube and absorbs the gas. This proves that it is carbon dioxide. |
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