Question

3. Why does pitcher plant feed on insects even though it is green and carries out photosynthesis?​

Answer 1

The insectivorous plants grow in soil which do not contain sufficient nitrogen mineral. These plants (e.g. pitcher plant) are green and carry out photosynthesis to obtain a part of the food required by them. ... So, insectivorous or carnivorous plants feed on insects to obtain the nitrogen needed for their growth.

Answer 2

Pitcher plant contains chlorophyll and it is capable of preparing its own food but pitcher plant eats insects because it grows in swamps where the soil is deficient in nitrogen mineral. For this reason it feed on insects and hence  called as insectivorous plant .