Q16 of 70 Page 73

All life owes its existence to chlorophyll. Give reason.

All living organisms require oxygen and give out carbon dioxide during respiration. Photosynthesis is the process by which all green plants replace the carbon dioxide in the atmosphere with oxygen. Green plants are able to initiate this vital process only because of the presence of chlorophyll which traps light energy. This light energy helps in the production of oxygen molecules. This is the reason why all life owes its existence to chlorophyll.

Explanation: The first step in the process of photosynthesis is activation of chlorophyll by absorbing light energy. This absorbed light energy helps in the splitting of a water molecule to release hydrogen and oxygen. Hydrogen is used further in the process to produce NADPH, but oxygen is released in its molecular form. This is the oxygen all living organisms depend on.


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Complete the following food chains by writing the names of appropriate organisms in the blanks.

(i) Grass → ……… → Snake →………


(ii) ........... → Mouse ........... → Peacock

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How do non-green plants such as fungi and bacteria obtain their nourishment?

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Complete the following by filling the blanks 1 to 5 with appropriate words/terms/phrases:

To test the leaf for starch, the leaf is boiled in the wafer to ................... (1). It is next boiled in methylated spirit to ................... (2). The leaf is placed in warm water to soften it. It is then placed in a dish and ................... (3) solution is added. The region, which contains starch, turns ................... (4) and the region, which does not contain starch, turns……………. (5).

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A candidate studied the importance of certain factors in photosynthesis. He took a potted plant and kept it in the dark for over 24 hours. In the early hours of the next morning, he covered one of the leaves with dark paper in the centre only. Then he placed the plant in sunlight for a few hours and tested the leaf which was covered with black paper for starch.

(a) What aspect of photosynthesis was being investigated?


(b) Is there any control in this experiment? If so, state it.


(c) Why was the plant kept in the dark before the experiment?


(d) Describe step by step, how the candidate proceeded to test the leaf for the presence of starch.