George Dobbs, age 11, of Cleveland, Texas, for his question:

What is meant algae?

It may be an enormous tangle of seaweed, a speck of greenery that helps to becloud a fish pond or a rosy spot of life that helps to tinge a snowy slope with pink. These and numerous other algae are simple members of the plant world. They have no true roots or stems, even though the kelp and other large seaweed algae resemble fronds and foliage. Like the more specialized plants, they contain green chlorophyl and use sunlight to manufacture their basic food from air and water.

Most algae live in salt or fresh water, but some types live in soil and moist shady forests. Many are single celled plants with pigmented material that masks their basic green color, adding tinges of blue or brown or red. The importance of the tiny teeming plants cannot be exaggerated. In the floating plankton of the sea, they contribute enormous amounts of oxygen to the global circulation. They also are part of the basic food chain that feeds all life in the ocean.