A control set-up is exact the same set-up as the experimental except for one difference - the variable being tested.
Given alongside is the diagram of an experimental set-up to demonstrate a certain phenomenon in plants.
(a) Name the phenomenon being demonstrated.
(b) What is the purpose of putting oil in the test tube ?
(c) What is the purpose of the spring balance in the set-up ?
(d) Would it make a difference if the experimental set-up is kept in bright sunshine ?