Protozoans

Protozoans are a diverse group of unicellular eukaryotic organisms, many of which are motile. Originally, protozoans were defined as single-celled organisms with animal-like behaviors, such as motility and predation. The group is often regarded as the kingdom Protozoa, although this grouping is declined by many researchers in favor of a more complex hierarchical classification.

Characteristics

Protozoans are eukaryotes, meaning their cells have a nucleus and other specialized organelles. They are also unicellular, but unlike bacteria and archaea, they are not prokaryotes. Protozoans exhibit a range of sizes and shapes, from microscopic amoebae to large ciliates. Many protozoans are motile, using structures such as flagella, cilia, or pseudopodia to move.

Classification

The classification of protozoans has been a subject of debate for many years. They were traditionally subdivided into several groups based on their mode of locomotion: the flagellates, the amoebae, the sporozoans, and the ciliates. However, modern classifications propose splitting the protozoa into about seven phyla, which are then further divided into classes, orders, families, genera, and species.

Ecology

Protozoans play important roles in the fertility of soils. By controlling the abundance of soil bacteria, they contribute to the decomposition of organic material and the cycling of nutrients. Some protozoans are also important parasites of humans and other animals.

Human disease

Several species of protozoans cause diseases in humans. For example, species of the genus Plasmodium cause malaria, and Trypanosoma species cause sleeping sickness.

See also

• Amoeba
• Ciliate
• Flagellate
• Sporozoan

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