Jane Meadows, age 12, of Huntsville, Ala., for her question:

WHAT FEEDS THE PLANKTON THAT STARTS THE FOOD CHAIN?

We are told that the ocean plankton feeds the tiny fishes that feed the larger and still larger fishes. Obviously the floating plankton must have abundant supplies of its own in order to keep this fantastic food chain going. And so it does. Actually, the basic system is somewhat similar to the great food chains that support all life on the land.

Plankton is a mini world of microscopic plants and animals. In the ocean, the animal kingdom depends for its survival on the plant world. The plants provide food and oxygen for all life on earth  but they need little or nothing from the animals.

This is because the green world can manufacture its own basic supplies fron nonliving raw materials. As we know, green plants contain chlorophyll which uses sunlight to create their basic surgary foods from carbon dioxide, water and certain inorganic chemicals. This is true on land and ocean, where most of the plants are microscopic seaweeds. These single celled alga plants teem in the floating meadows of plankton. Their basic color is chlorophyll green, though this may be tinged with various shades of blue or brown. Most of these floating midgets are dainty diatoms, encased in shells of silica. Under the microscope, they look like ornate little jewel boxes, each lovelier than all the rest.

Diatoms and other single celled algae make up most of the plankton and they are present in astronomical numbers. All of them use sunlight during the daylight hours, which is why the vast plankton meadows float near the surface. They also use dissolved carbon dioxide, the waste gas given off by both plants and animals.

There is no shortage of water  but the floating algae do better when certain chemicals are dissolved in the water. This is why plankton is more plentiful in cool ocean currents, where rich chemicals well up from below. Surrounded by these abundant supplies, the plankton plants thrive and multiply at astronomical rates.

Also present in the plankton are multitudes of strange looking microscopic animals. Naturally they feed on the teeming diatoms and other small algae. Actually, the soupy plankton is a rich seafood salad of meat and plant food. And there is enough of it to start the food chain that feeds all life in the sea.

It takes about 10 pounds of assorted plankton food to produce one pound of meat to a herring. And it takes about 10 pounds of herring type food to add one pound of weight to a human being.