Eric Schwartz, age ~10, of Marquette, Mich., for his question:

WHAT IS PLANKTON?

Plankton is the mass of small, drifting plant and animal life that lives in bodies of water. The word plankton comes from the Greek word for wandering.

In the ocean, plankton is made up mainly of small animals such as protozoan, larval fishes and crustaceans. During the day, the plankton animals usually swim as deep as 600 feet below the surface, but at night they rise to the upper levels of the water.

Plankton is also made up of tiny plants, such as algae. The life in or on the bottom of bodies of water is called benthos. The animlas of larger size that swim freely and independently determine their movements in the body of water, are called nekton.