Amoeba
An amoeba is a small, single-celled eukaryotic organism that can be found in various environments around the world, both terrestrial and aquatic. These organisms are part of the protist kingdom and are characterized by their irregular shapes and unique method of movement known as pseudopodia, which allows them to change form and move in any direction. While many amoeba species are harmless, some can be parasitic to mammals, leading to serious health issues such as amoebic dysentery and even life-threatening conditions like those caused by Naegleria fowleri, the so-called "brain-eating amoeba."
Amoebas feed by engulfing prey, which typically includes bacteria and other small organisms. They capture food using their pseudopods, forming a food vacuole where digestion occurs through enzymatic action. The complexity of identifying different amoeba species is compounded by their lack of distinct physical traits. Overall, amoebas play a significant role in their ecosystems but can also pose risks to human health when interacting with contaminated water or food sources. Understanding amoebas can provide insights into both microbiology and environmental science.
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Amoeba
An amoeba is a small, usually single-celled organism. Amoebas are found throughout the world. They can survive in both terrestrial and aquatic environments. Amoebas are characterized by their inconsistent, non-uniform shape, their lack of a head or tale, and their novel method of movement.
Scientists have identified a large number of amoeba species. Identification of amoeba species is often complicated by their lack of discernable features. Most species are harmless to humans, but a small number are parasitic to mammals. The parasitic species cause severe diseases, such as amoebic dysentery, when ingested. Complications from parasitic amoebas are difficult to diagnose and treat.
Background
An amoeba is a tiny eukaryotic organism usually composed of a single cell. Unlike prokaryotic organisms, eukaryotic organisms have cells with a well-defined nucleus. The nucleus is a special structure located in the center of the cell. It essentially serves as the control center of the cell. Like it does in most single-celled organisms, the nucleus in an amoeba stores DNA.
An amoeba has a thin layer of protein and fat called a cell membrane, which keeps its cytoplasm and organelles intact. Cytoplasm is the material that fills the cell, and organelles are tiny structures within the cell that serve specific purposes. Many of an amoeba's organelles, such as the contractile vacuole and the food vacuole, are used to process food and waste. An amoeba can form a pseudopod, which is a unique, foot-like structure that it uses to move.
Overview
All amoebas are classified as protists. Protists are single-celled eukaryotic organisms that cannot be classified as fungi, bacteria, plants, or animals. Amoebas are scientifically classified as protists that have no fixed shape. They have no front or back end and may move in any direction at any time. Amoebas have no defined head, tail, arms, or legs, though they do form pseudopods to help them move. Many amoeba species exist, but their lack of easily discernable characteristics makes them difficult to distinguish.
Amoeba proteus is a large species of amoeba. Many members of this species can be viewed without a microscope. An even larger amoeba species, Chaos carolinense, can commonly be viewed with the naked eye. Amoebas from the genus Chaos are harmless to humans.
Some amoebas are parasitic in nature. These amoebas cause health problems when humans or other mammals ingest them. The diseases amoebas cause spread differently than many traditional diseases. Most diseases spread from host to host, through bodily fluids or skin-to-skin contact. Certain symptoms, such as coughing or sneezing, help spread the disease from one living host to another. With amoebas, infection occurs when an otherwise healthy individual ingests a parasitic amoeba. In many cases, parasitic amoebas are found in aquatic environments. They enter an individual through the mouth or nose while he or she is drinking or swimming in contaminated water.
One deadly species of amoeba, Naegleria fowleri, is found in lukewarm water. This species of amoeba passes through three stages during its life cycle: an immobile cyst, a highly mobile trophozoite, and a flagellate amoeba. The trophozoite enters a host through the nasal cavity and travels through the brain. Once in the brain, it begins reproducing, beginning an amoeba colony. The colony feeds on brain tissue, causing inflammation and eventual death. For this reason, this type of amoeba often is called the "brain-eating amoeba." While Naegleria fowleri infection is rare, it is almost always fatal.
A more common parasitic amoeba, Entamoeba histolytica, is responsible for amoebic dysentery. This amoeba infects the intestines instead of the brain. Infections occur when an individual consumes a contaminated food or drink. Entamoeba histolytica moves through the digestive system with the food or drink and eventually begins to breed in the intestines. The amoebas attack the intestinal walls, causing bleeding and ulcers. Initially, amoebic dysentery may cause only stomach cramps and diarrhea. If left untreated, however, the amoebas may spread to other organs, becoming painful and debilitating.
Amoebas move in a unique fashion. Because they hold no defined shape, amoebas are able to manipulate their form in beneficial ways. To move, amoebas form parts of their body into pseudopods. Pseudopods protrude from the amoeba's main body. They help push and pull the amoeba toward food.
Many amoebas eat other organisms. Some common forms of prey for amoebas include bacteria, plant cells, algae, and protozoa. When an amoeba senses food nearby, it begins to form pseudopods to move itself toward the food. Upon reaching the food, the amoeba goes through a startling transformation. It forms new pseudopods, which stretch out in a wide curve. Over time, these pseudopods stretch all the way around the prey. The amoeba then engulfs its prey, closing the pseudopods around it and reforming its own cell wall. The prey is then trapped inside the amoeba.
Once inside the amoeba, the prey is contained in a food vacuole or gastric vacuole. The cell's cytoplasm moves the vacuole, pushing it deeper into the amoeba. The vacuole is moved to the lysosomes, which are organelles that contain enzymes. Enzymes are specialized materials that speed up specific chemical reactions. The amoeba's enzymes allow it to break down its prey at a rapid pace. The enzymes in the lysosomes turn the prey into a liquid. This liquid absorbs directly into the cell's cytoplasm, which then transports the nutrients to wherever they are necessary. As the prey breaks down, the vacuole containing it shrinks. Once the vacuole finishes shrinking, the prey is fully digested.
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