A diverse group of minute animals (zooplankton) and plants (phytoplankton) that freely drift in the water - Source

Minute floating forms of microscopic plants and animals in water which cannot get about to any extent under their own power. They form the important beginnings of food chains for larger animals - Source

Plankton are microscopic organisms that float freely with oceanic currents and in other bodies of water. Plankton is made up of tiny plants (called phytoplankton) and tiny animals (called zooplankton). The word plankton comes from the Greek word "planktos" which means "drifting."

Phytoplankton are primary producers (also called autotrophs). As the base of the oceanic food web, they use chlorophyll to convert energy (from sunlight), inorganic chemicals (like nitrogen), and dissolved carbon dioxide gas into carbohydrates.

Zooplankton are microscopic animals that eat other plankton. Food Web: Plankton is the first link in the marine food chain; it is eaten by many organisms, including mussels, fish, birds, and mammals (like baleen whales). Source

Plankton consist of any drifting organisms (animals, plants, archaea, or bacteria) that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. Plankton are defined by their ecological niche rather than their genetic classification. They provide a crucial source of food to aquatic life. Source

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What is Plankton: Plankton is made up of animals and plants that either float passively in the water, or possess such limited powers of swimming that they are carried from place to place by the currents.