You have heard about several insectivorous plant that feed on insects

You have heard about several insectivorous plant that feed on insects. Nepenthes or the pitcher plant is one such example which usually grows in shallow water or in marsh lands. What part of the plant is modified into a ‘pitcher’. How does this modification help the plant for food even though It can photosynthesis like any other green plant?

Part modified into pitcher—Lamina.
Uses This modification help plant to provide nitrogen which is deficient in marshy areas.