Question

A potted destarched plant was taken in order to prove that light is necessary for photosynthesis.
(i) What is meant by 'destarched plant'? How can it be destarched?
(ii) Using the destarched plant describe step by step how you would proceed to prove that in the absence of light the leaf cannot manufacture starch.

Answer 1

(i) Destarched plant means a plant from which starch has been removed. A plant can be destarched by keeping it in dark for at least two days.

(ii) Take one leaf of a destarched plant kept in dark and one leaf of a normal plant kept in light. Boil them separately in water and treat them with alcohol to remove chlorophyll. Add iodine solution in both of them. The leaf of the plant that was kept in light will turn blue-black on addition of iodine solution, showing the presence of starch, while the other leaf will not. This shows that light is needed for photosynthesis.