A pitcher plant is a carnivorous plant. Carnivorous plants are plants that eat insects and other small animals. Carnivorous plants grow in soil that has little nitrogen. All living things must have nitrogen. Carnivorous plants get nitrogen from the insects they eat.
Pitcher plants catch (get) insects in a cup of liquid. The walls of the cup make nectar (sweet liquid) . The nectar attracts insects. When an insect lands on the wall, it falls down into the liquid. The insect cannot get out of the cup because the walls are smooth and slippery and the walls have hairs pointing down. After the insect is dead, its body rots. Rotting releases (lets loose) the nitrogen from the insect's body. The nitrogen then goes into the liquid and the plant takes in the nitrogen from the liquid.