Brenda Hoffman, age 11, of Fowler, Mich., for her question:

Are bacteria classed as plants or animals?

A row of 25,000 bacteria measures about one inch. Under a microscope that magnifies 1,000 times, a single bacterium appears to be about the size of a small pinhead. Almost all plants have green chlorophyll with which they manufacture their own food. A bacterium has no chlorophyll, and it depends upon prefabricated food chemicals from its surroundings.

Most biologists, however, classify bacteria in the plant kingdom. Some give them a place in the fungus family, making them small cousins of the toadstools. Other biologists classify bacteria in a special group reserved for living things that are neither plant nor animal.