Describes different types of single-celled organisms and their role in the world's ecosystems.

Includes index.

Classifying living things -- Just one cell -- Bacteria: simplest of all -- Cyanobacteria: blue-green algae -- Protozoa: on the move -- Euglena: best of two worlds -- Algae: producers -- Slime molds and water molds: decomposers -- Harmful and helpful -- Living and nonliving.