Protists

Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy. Protists live in almost any environment that contains liquid water. Many protists, such as algae, are photosynthetic and are vital primary producers in ecosystems, particularly in the ocean as part of the plankton. Others are saprophytes, or organisms that decompose dead organisms, and parasites, which harm their host.

Classification

Protists were traditionally subdivided into several groups based on similarities to the "higher" kingdoms such as:

• Protozoa, which includes amoebae, flagellates, ciliates, sporozoans, and many other forms of unicellular organisms.
• Algae, which are photosynthetic protists.
• Fungus-like protists, which include slime molds and water molds.

However, modern classifications attempt to assign protists into monophyletic groups, which are sets of species containing all the descendants of a common ancestor.

Characteristics

Protists are a diverse group of organisms, with a wide range of characteristics. Some protists are unicellular, while others are multicellular. Some protists are autotrophic, meaning they can produce their own food, while others are heterotrophic, meaning they must consume other organisms for food. Some protists reproduce sexually, while others reproduce asexually.

Ecology

Protists play a key role in many ecological processes. They are an important source of nutrition for many other organisms. In aquatic environments, protists form the base of the food chain. Some protists are also important decomposers, breaking down dead organic material and recycling nutrients in the ecosystem.

Human health

Some protists are harmful to human health. For example, the protist Plasmodium is the cause of malaria, a disease that affects millions of people worldwide. Other protists, such as Giardia and Cryptosporidium, can cause disease when they contaminate drinking water.

See also

• Eukaryote
• Protozoa
• Algae
• Fungus-like protists

Protists Resources
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