Amoeba

Amoeba is a common name for several species of unicellular, free-living or opportunistic protists in the group Amoebozoa. Most are heterotrophic and lack a rigid cell wall, allowing them to change shape as they move. Movement is accomplished by extending temporary cytoplasmic projections called pseudopodia, or false feet, which also enable the organism to engulf prey.

Anatomy and feeding are geared toward flexibility. The cytoplasm is often described as having an outer, clearer ectoplasm and an inner, granular endoplasm. Nutrition occurs mainly by phagocytosis: a surrounding pseudopodium envelops food particles, forming a food vacuole where digestive enzymes break down the material. Mitochondria generate energy, and many freshwater species use contractile vacuoles to regulate water balance.

Reproduction is typically asexual, most often by binary fission, producing two genetically identical cells. Some species can form dormant cysts to withstand unfavorable conditions, re-emerging as active trophozoites when conditions improve.

Ecology and significance vary by species. Amoebae are common in soil, freshwater, and marine environments, where they contribute to decomposition and nutrient cycling. They can serve as indicators of environmental health and are used in studies of cell motility and phagocytosis. A few species are pathogenic to humans and other animals; Entamoeba histolytica causes amebic dysentery, Naegleria fowleri can cause fatal brain infections, and Acanthamoeba species are associated with keratitis and encephalitis. Overall, amoebae represent a diverse and ancient lineage of single-celled eukaryotes.