By Jenny Green
Updated Aug 30, 2022
Amoebas are microscopic, single‑cell organisms that thrive in moist habitats—freshwater, saltwater, soil, and even within animal bodies. Their cell envelope is a clear outer membrane that encloses a granular cytoplasm housing essential organelles and one or more nuclei, depending on the species.
Amoebas reproduce asexually, meaning they do not require genetic material from another individual. The process begins with DNA replication inside the nucleus, followed by mitosis. After the nucleus divides, the cytoplasm and cell membrane undergo binary fission, splitting into two daughter cells, each containing a copy of the original genetic material. The result is two genetically identical amoebas.
During binary fission, a narrow membrane bridge often connects the two nascent cells. Research from the Weizmann Institute has shown that this bridge can sometimes persist, halting division. In such cases, a third amoeba may intervene, inserting itself between the two cells and breaking the tether. Experiments indicate that stressed reproducing cells release a chemical signal that attracts nearby individuals to assist, ensuring successful completion of division.
Scientists at the University of Massachusetts suggest that some amoebae can exchange genetic material through various mechanisms, a process that may have occurred in their evolutionary past. Asexual reproduction can limit genetic diversity, potentially reducing adaptability to environmental changes. Yet, the longevity of amoeboid lineages indicates that alternative strategies—such as occasional genetic exchange—might have helped maintain their resilience over millions of years.
Amoebas propel themselves by extending pseudopodia—protrusions of the cell membrane and cytoplasm—toward their destination. They engulf food particles by engulfment and expel waste through similar protrusions. Oxygen diffuses directly across the membrane, while metabolic waste exits the cell. When environmental moisture drops, amoebas form a protective membrane to retain water; this barrier ruptures once conditions improve.
