A chloroplast is the organelle.
It contains chlorophyll inside which does photosynthesis, coverting light energy into food such as starch.
Chloroplast is mostly found in leaf cells, especially palisade mesophyll cells, though other cells in the leaf contains too, such as guard cells, but the quantity is a lot less.
For example, a palisade mesophyll cell may contain around 17 chloroplasts, but guard cells may only have 1 or 2.
Photosynthesis is necessary for plants to survive since they have to make food themselves, not like animals who hunt for food.
