Amoebas are microscopic, single-celled organisms, a diverse group of protozoans. They are found globally in various environments, from aquatic settings to soil.
Defining Features
Amoebas are characterized by their constantly changing, amorphous shape, due to their flexible cell membrane and dynamic cytoplasm. They form temporary extensions of their cytoplasm called pseudopods, or “false feet.” These pseudopods are used for both movement and feeding.
Internally, an amoeba contains a nucleus that regulates its functions. The cytoplasm is differentiated into a clear outer layer (ectoplasm) and a granular inner portion (endoplasm). Within the endoplasm are food vacuoles, where ingested particles are digested, and a contractile vacuole, which expels excess water to regulate water balance.
How Amoebas Live
Amoebas move by extending their pseudopods, a process known as amoeboid movement. The cytoplasm flows into these extensions, causing the cell to effectively “crawl” or “slide” across surfaces. This method of locomotion also allows them to engulf food particles, a process called phagocytosis. When an amoeba encounters food, its pseudopods surround and enclose the particle, forming a food vacuole where digestion occurs.
Amoebas inhabit diverse environments, including freshwater, saltwater, and moist soil. They are often found in decaying vegetation in ponds and slow-moving streams. Many species are free-living, consuming bacteria, algae, and other microscopic organisms. Reproduction in amoebas primarily occurs through binary fission, an asexual process where a single amoeba divides into two identical daughter cells under favorable conditions.
Amoebas and Human Health
While many amoeba species are harmless, a few can cause diseases in humans. One notable example is Entamoeba histolytica, a parasitic amoeba responsible for amoebiasis, an intestinal illness. This infection typically spreads through contaminated water or food containing cysts from human feces. Symptoms can range from mild diarrhea to severe dysentery, and in some cases, the parasite can spread beyond the intestines to organs like the liver, causing abscesses.
Another amoeba of concern is Naegleria fowleri, often referred to as the “brain-eating amoeba”. Though rare, infection with Naegleria fowleri can lead to primary amebic meningoencephalitis (PAM), a severe and often fatal brain infection. Infections occur when water containing the amoeba enters the nose, usually during swimming or diving in warm freshwater bodies like lakes or hot springs. It cannot be contracted by swallowing contaminated water. Prevention involves avoiding swimming in warm freshwater known to harbor the amoeba, using nose clips, and ensuring proper chlorination in recreational water facilities.