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 :

What is the purpose of keeping the test tube Bin the experimental set-up?

Explanation

It is a control experiment where the purpose of using test tube B is to compare the level of water in both test tubes. Test tube B is used here as a control.