Scott Stiles, age 10, of Monroe, La., for his question:

WHAT EXACTLY IS PLANKTON?

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

The animals in plankton include protozoans, larval fishes and crustaceans. During the day, the plankton animals usually swim as deep as 600 feet below the surface of the ocean. But at night, they rise to the upper levels of the water.

The tiny plants in plankton include algae. There are actually three groups of drifting plant life: the diatoms, the oeridinians and the coccospheres.

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

The life in or on the bottom of bodies of water is called "benthos." The animals of larger sizes that swim freely, and independently determine their movements in the body of water, are called nekton.