Question 36: Name the following:
(a) The process in plants that links light energy with chemical energy
(b) Organisms that can prepare their own food
(c) The cell organelle where photosynthesis occurs
(d) Cells that surround a stomatal pore
Answer: Guard cells
(e) Organisms that cannot prepare their own food
(f) An enzyme secreted from gastric glands in stomach that acts on proteins.
Question 37: "All plants give out oxygen during day and carbon dioxide during night". Do you agree with this statement? Give reason.
Answer: This statement does not show the complete picture. In fact, plants carry out respiration throughout the day and night; like other living beings. Hence, they keep on emitting carbon dioxide all the time. Photosynthesis takes place only in the presence of light and hence, oxygen is released by plants only during the day.
Question 38: How do the guard cells regulate opening and closing of stomatal pores?
Answer: Guard cells control the opening and closing of stomatal pore by change in turgidity. When water enters the guard cells, they become turgid and the stomatal pore opens. On the other hand, when water exits from the guard cells; they become flaccid and the stomatal pore opens.
Question 39: Two green plants are kept separately in oxygen free containers, one in the dark and the other in continuous light. Which one will live longer? Give reasons.
Answer: The plant which is kept in continuous light would live longer. The plant which is kept in the dark is unable to carry out photosynthesis and hence the container would be filled with carbon dioxide within a short span of time. Lack of oxygen in the container would kill the plant. On the other hand, the plant being kept in light would be able to carry out photosynthesis and thus would be able to convert the carbon dioxide into oxygen. Hence this plant would live for a longer duration.
Question 40: If a plant is releasing carbon dioxide and taking in oxygen during the day, does it mean that there is no photosynthesis occurring? Justify your answer.
Answer: Most of the carbon dioxide released during respiration exits from the plant cells through various openings. The carbon dioxide; required for photosynthesis is taken through stomata. So, even if a plant keeps on taking in oxygen and releasing carbon dioxide during the day; it does not mean that no photosynthesis is happening in the plant.
Question 41: Why do fishes die when taken out of water?
Answer: Fishes are able to take oxygen which is dissolved in water; through their gills. The gills of a fish are not equipped to take in oxygen from air. Hence, when a fish is taken out of water; it is unable to inhale oxygen rich air and so dies quickly.
Question 42: Differentiate between an autotroph and a heterotroph.
Answer: An autotroph is an organism which prepares its own food, while a heterotroph takes food from another organism. Autotrophs do not show locomotion because they don’t need to move in search of food. On the other hand, most of the heterotrophs show locomotion because they need to move in search of food.
Question 43: Is ‘nutrition’ a necessity for an organism? Discuss.
Answer: Every organism needs energy to perform various activities. This energy comes from cellular respiration during which food is oxidized. Additionally, each organism needs raw materials for growth and development. Such raw materials also come from food. So nutrition becomes a necessity for survival of an organism.
Question 44: What would happen if green plants disappear from earth?
Answer: It would mean a total disaster for the ecosystem. Green plants are the main channel through which solar energy is transferred to other organisms. All other organisms directly or indirectly depend on green plants for food. In the absence of food no organism would be able to survive. This would result in extinction of life from the earth.
Question 45: Leaves of a healthy potted plant were coated with vaseline. Will this plant remain healthy for long? Give reasons for your answer.
Answer: The layer of Vaseline would make an impervious layer on the leaves. This would clog the stomata and would stop exchange of gases and transpiration. The leaves won’t be able to get the necessary raw materials for photosynthesis. Thus the plant would not be able to prepare its food. The plant would die a slow death; as a result.
Question 46: How does aerobic respiration differ from anaerobic respiration?
|Aerobic respiration||Anaerobic respiration|
|Happens in presence of oxygen||Happens in absence of oxygen|
|Carbon dioxide and water are the end products.||Ethanol/lactic acid and carbon dioxide are the end products.|
|Complete oxidation of glucose happens.||There is incomplete oxidation of glucose.|
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