Question

if the Pitcher plant is green and carries out photosynthesis then why does it feed on insects ?

Answer 1

To complete its requirement of nitrogen as it grows in nitrogen deficient soil

Answer 2

Pitcher plant feed on insects although it carries out the process of photosynthesis as by the process of photosynthesis the requirement of nitrogen is not fulfilled and also it grows where there is deficiency of nitrogen so to fulfill the need of nitrogen it feed on insects.
Hope it helps!!