Plankton are microscopic organisms that live in aquatic environments. They are an important part of the food chain, providing food for larger animals such as fish and whales. The term plankton is derived from the Greek word 'planktos' meaning 'DRIFTER'. Plankton can be divided into two main categories: BRIT, which stands for Bacterioplankton, and ALGA and ALGAE, which stand for Phytoplankton. Bacterioplankton are bacteria and other single-celled organisms, while Phytoplankton are photosynthetic organisms such as ALGAE and diatoms. Both types of plankton are essential to the health of aquatic ecosystems.