Adam Wlodek Jr., age 13, of Pittsburgh, Pa., for his question:

WHAT IS PLANKTON?

In bodies of water you'll find a mass of small, drifting animals and plant life that is called plankton. The name comes from the Greek word for wandering.

Plankton is made up mainly of small animals such as protozoans, larval fishes and crustaceans. During the day 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 also consists of small plants, such as algae. Three types of drifting plant life can also be found in plankton.

Plankton in the oceans is important as food for larger animals, such as whales, herring and mackerel.