Glen Marshall Deis, age 12, of Houston, Texas, for his question:

What is the life span of a protozoan?

All the numerous species of one celled animals live their own lives. Some multiply by a merging of opposite sexes, or by budding daughter cells. These types may sometimes multiply by dividing. Cell division is the most common method of reproduction in almost all the protozoa. It occurs when a protozoan is well fed and in suitable surroundings. This is the mayor factor that determines its life span.

The chromosomes that determine the nature of the tiny protozoan are in the nucleus of its single cell. During cell division, the chromosomes duplicate themselves. The cell stretches and breaks apart. Each half takes a complete duplication of the original nucleus and soon completes the formation of a new cell. The two new cells are identical twins and there are no parents left behind to grow old and die. A protozoan can divide any number of times and, barring accidents, it could be immortal.