What are Protists? (with photos)

Plant-like forms of protists include algae.

Protists is an umbrella term used to describe all eukaryotic organisms – that is, those that have cells with nuclei – in addition to animals, plants, and fungi. Examples include unicellular animal-like protozoa, slimy fungus-like fungi, and plant-like protophytes. These organisms were previously considered to belong to a kingdom in their own right, like plants and animals, but it is now known through DNA analysis that many of them are not closely related to each other, and that some may be closer to organisms. within other realms than their fellow protists. The term derives from the Greek protistan, meaning “first of all”. These organisms are often microscopic and are unicellular or an undifferentiated multicellular mass.


Paramecia is a type of protist.

The superficial similarities and differences between protists can be misleading. As more analyzes were performed at the molecular level, surprising relationships emerged. For example, kelp that can reach 50 meters in length turns out to be more closely related to microscopic diatoms than to some other seaweeds, while green algae are more closely related to members of the plant kingdom than to other apparently similar protists such as the red algae. It is generally recognized that some sort of reclassification between this category of life forms is necessary; this may result in them splitting into multiple kingdoms, or some types being grouped with other kingdoms. Classifying protists is still an ongoing area of ​​research and may be subject to further revisions as more information emerges, but on a slightly less scientific basis these organisms can be grouped into animal-like, plant-like, and the less numerous fungal-like types.

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animal-like shapes

Protists is a term used to describe all eukaryotic organisms that do not classify themselves as animals, plants or fungi.

These types are all unicellular and are usually capable of independent movement. Most actively hunt for food or are parasites that infect other organisms, although some generate their own food by photosynthesis. They include the life forms generally known as protozoa, as well as a number of other organisms.

Those who are capable of locomotion use one of three methods. Ciliates, like the well-known paramecium, use tiny moving strands of hair, known as cilia, to travel through water. Flagellates use a long whip-like structure called a flagellum to propel themselves, while amoeba-like forms have a flexible, soft cell membrane and are able to move over flowing surfaces, producing pseudopods – foot-like projections. Some types can switch between a flagellate and an amoeba-like form, while some parasitic forms, such as plasmodium, which causes malaria, and toxoplasma, which causes toxoplasmosis, are incapable of independent movement and often have complex life cycles. that involve more than one host.

Algae, a type of protist, seen through a microscope.

Another interesting group are the dinoflagellates. These mobile freshwater and marine organisms move using flagella, but like plants and algae, many create their own food through photosynthesis. Some types exhibit bioluminescence and, if present in large numbers, can produce a visible glow in seawater at night. Other types produce powerful toxins and are responsible for the “red tide” that can kill fish and other organisms – the red color comes from the photosynthetic pigment they use.

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plant-like shapes

Seaweed, a eukaryotic organism, is a protist.

This group consists mainly of non-motile photosynthetic organisms. Red and green algae are perhaps the best known types, although the category includes some very different looking life forms. They range from microscopic single-celled organisms to very large multicellular forms such as seaweed.

Red algae got their name from a red pigment called phycoerythrin, which performs the same photosynthetic function as chlorophyll in green algae and plants, but absorbs blue light. This allows them to live at greater depths than green algae, as light in the blue end of the spectrum penetrates deeper into the water. Red algae includes several types of algae, some of which are edible. Certain types produce a calcium carbonate crust around them and are important in reef formation in some areas.

Green algae resemble members of the plant kingdom in that they use the same forms of chlorophyll. They are, in fact, considered the ancestors of green plants. They range from unicellular to multicellular types and can be found in a variety of aquatic or wet environments. Some species are marine and include a lot of seaweed, while others are found in fresh water or in damp, shady places. Several types have formed a symbiotic relationship with certain fungi, in the form of lichens.

The chromista are an extremely varied group of plant-like protists. They include the huge kelp seaweeds that can form great forests on the ocean floor, as well as the diatoms, which are microscopic, single-celled organisms that encase themselves in silica coatings, often with very intricate and beautiful structures. Diatoms occur in fresh water, and in the sea, where they are an important part of the phytoplankton that forms the base of the marine food chain.

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Fungus-Like Forms

These consist of various types of slime mold; however, although they resemble fungi in their outward appearance, and were once classified as such, they are in fact completely unrelated. They consist of mobile, single celled organisms that move around in colonies, feeding on microorganisms, such as bacteria. The cells can merge together at a certain stage, sometimes forming what is, in effect, one huge cell with many nuclei. They can reproduce by forming structures containing spores, which are released to form new slime molds when they land in a favorable environment. Slime molds can be found on soil, tree bark, and decaying organic matter, such as rotting wood.

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