Why are insectivores plants called as partial heterotrophs?
Insectivorous plants like pitcher plant contains chlorophyll; hence it is capable of preparing its own food like green plants. But insectivorous plants grow in swamps or bog areas where the soil is deficient in nitrogen mineral. So, just to fulfill its nitrogen requirement, they trap the insects and utilize their proteins. For this reason they are called partial heterotrophs. They trap prey in a rolled leaf that contain a pool of digestive enzymes or bacteria that help in the digestion of the trapped insects.
Some pitcher plants only act as heterotrophs when they are provided with water on the opening so that the insects could slip in the stomach of the plant. BUT, when there is no rain or water on the opening they have to make their own food using the chlorophyll(by photosynthesis). In this way insectivores plants like pitcher plant is known as partial heterotrophs.