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Question
The figure given below represents an experimental setup with a weighing machine to demonstrate a particular process in plants. The experimental set-up was placed in bright sunlight. Study the diagram and answer the following questions:

- Name the process intended for the study.
- Define the above mentioned process.
- When the weight of the test tubes (A and B) is taken before and after the experiment, what is observed? Give reasons to justify your observations in A & B.
- What is the purpose of keeping the test tube B in the experimental set-up?
- What is the purpose of putting oil in the test tube?
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Solution
- Transpiration.
- It is the release of water vapours from the surface of the plant, mainly from the leaves.
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- Before: the weights of A and B are the same.
- After: 'A' gets lighter as it loses water from transpiration; 'B' stays the same since evaporation causes no loss of water as the surface of water is covered with oil.
- 'B' acts as a control to show that transpiration from the aerial parts I leave of the plant causes water to evaporate.
- By adding oil to the test tube, one hopes to prevent water from evaporating from it.
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