Protozoa are a large group of single- or multi-celled organisms without a rigid cell wall.

1. Protozoa are larger than bacteria.
2. Protozoa are found in freshwater, marine habitats, and soil.
3. Though in general protozoa do not cause disease, some are pathogenic and can lead to intestinal infection in humans including: Malaria, diarrhea, and amebic dysentery.