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:

1. Name the process intended for the study.
2. Define the above mentioned process.
3. 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.
4. What is the purpose of keeping the test tube B in the experimental set-up?
5. What is the purpose of putting oil in the test tube?

Answer 1

1. Transpiration.
2. It is the release of water vapours from the surface of the plant, mainly from the leaves.
3. • 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.
4. 'B' acts as a control to show that transpiration from the aerial parts I leave of the plant causes water to evaporate.
5. By adding oil to the test tube, one hopes to prevent water from evaporating from it.