They range in size and shape from an amoeba, which can change shape, to Paramecium, which has a fixed shape and sophisticated structure.
The life cycle of protozoa
Proliferative phases (such as trophozoites) are paired with resting cysts in the life cycles of some protozoa.
Cysts are caused by protozoa being exposed to severe temperatures or harmful substances or going without food, water, or oxygen for long periods of time.
The protozoan cell is responsible for all of the processes required to sustain and reproduce life, including nutrition, growth, reproduction, excretion, and movement.