As they eat bacteria, protozoa release excess nitrogen that can then be used by plants and other members of the food web. They eat the other two types of protozoa, as well as bacteria. Amoebae also can be quite large and move by means of a temporary foot or pseudopod.
Flagellates are the smallest of the protozoa and use a few whip-like flagella to move.
Protozoa play an important role in mineralizing nutrients, making them available for use by plants and other soil organisms. Bacteria eaten by protozoa contain too much nitrogen for the amount of carbon protozoa need. This usually occurs near the root system of a plant. Bacteria and other organisms rapidly take up most of the ammonium, but some is used by the plant. Another role that protozoa play is in regulating bacteria populations.