What is a plankton and what are some examples of plankton?

Plankton are very small organisms that live in the world's oceans. There are two main categories of plankton; phytoplankton and zooplankton. Phytoplankton are small plants that cause the color of the oceans in some places to be green. They also make up the largest single biomass in the world. Zooplankton are small animals that eat phytoplankton.