Protist (noun, “PRO-dest”)
Protists are a group of eukaryotes — organisms whose cells package their DNA inside a nucleus. Three groups of eukaryotes you may be familiar with are animals, plants and fungi. Protists are eukaryotes that do not fit into any of these three categories.
Nearly all protists are made up of one cell. But some contain multiple cells. Examples of protists include slime molds (which look just like their name sounds), amoebas and certain algae.
Some one-celled protists live in groups called colonies. Sometimes those colonies are so organized that you might even mistake them for a plant or animal. For instance, some types of slime molds form colonies made of many individual cells.
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But a handful of protists are multicellular. Consider kelp — tall, leafy-looking protists that live in the ocean. Kelp looks like a bunch of underwater trees. Clusters of kelp are even called “kelp forests.” Kelp are one of the few examples of multicellular protists. They carry out photosynthesis, just like plants.
Protists come in all shapes, sizes and lifestyles. While some protists like kelp carry out photosynthesis, others must find organic matter to eat. Examples include slime molds and free-living ciliates, such as Paramecium caudatum.
Most protists are harmless to people. But a few cause problems. For example, a parasitic protist called Plasmodium causes malaria. This deadly disease gets passed to humans through bites from infected mosquitos.
Other protists can help humans. Algae-type protists do photosynthesis, which helps our environment by removing carbon dioxide from the air. And slime molds — which might look icky— help all life on Earth by breaking down dead organic matter and recycling their nutrients.
In a sentence
Though protists are usually microscopic, their total biomass is greater than all the birds and mammals on Earth combined.