Plankton are microscopic organisms that area unable to swim against the current. They are an important food source to large ocean animals like whales and fish. Although most plankton are on the microscopic level, including bacteria, algae, and protozoa, they do come as larger organisms such as jellyfish. Plankton are commonly described in relation to their size.
The larger megaplankton, such as jellyfish, measure greater than 20 centimeters, whereas the smallest plankton is the femtoplankton, measuring smaller than .2 micrometers. Plankton live in almost every body of water like oceans, seas, lakes and ponds. Plankton are at the bottom of the oceanic food chain.