An experiment was set up as shown in the figure below. After some time, the water level in test tube A fell down but not in test tube B. Why was there a fall in the water level of test tube A and not in that of test-tube B?

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Solution

In test tube A, the water level falls because the water was absorbed by the plant through its roots dipped in water.
There is no loss of water from the surface because of oil on the water surface which prevents the evaporative loss of water. In test tube B the water level stays unchanged as it does not contain a rooted plant. Moreover, the oil on the water surface prevents the water from evaporating.

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Standard VII Biology

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