Question

Why is the production of starch is used as a measure of photosynthesis in leaves

Answer 1

Because by the process of photosynthesis starch is formed. So, by observing the amount of starch produced we can measure the rate of photosynthesis in the leaves.

Answer 2

Starch is a type of carbohydrate. Plants can turn the glucose produced in photosynthesis into starch for storage, and turn it back into glucose when it is needed for respiration. We need to know the production rate of starch to know the rate of photosynthesis in the leaves.