Amoebae are single-celled organisms that grow and reproduce asexually, replicating through both binary fission and sporulation. Binary fission is when a single cell divides into two cells, while sporulation is when a single-celled organism divides into multiple cells.
Because it is a single-celled organism, an amoeba's growth is limited, and it does not have a definite shape. Rather, its shape changes as it moves, absorbs food, or excretes waste.
To absorb food such as plankton or diatoms in its environment, the amoeba must be adjacent to its food. It then forms an extremity called a pseudopodium that extends to envelop and absorb the food. This creates a temporary increase in size when the amoeba forms a food vacuole or cavity around its food. The vacuole contains digestive enzymes that break down the food so that nutrients can be absorbed and waste can be released. Waste elimination reverses some of the increase in size that occurred when the food was initially absorbed.
If environmental conditions are favorable, the cell continues its feeding cycle until it is ready to reproduce, which it will do by simply dividing itself into two amoebae, which can then grow and develop independently.
If environmental conditions become unfavorable, an amoeba can form itself into a tiny ball with a protective shell (a microbial cyst), where it will remain dormant until conditions are once again favorable. While inside its shell, an amoeba can divide into many smaller entities called amoebulae. When conditions are once again favorable, the outer shell will break down and release the new amoeba.