December 27, 2012

What is a Protist?

Hi, I’m Emerald Robinson, and in this “What Is” video, we’re going to discuss a group of organisms called protists.

Protists are organisms that have a nucleus and other membrane-bound organelles. Most are one celled, and they are classified as plant, animal, or fungus like, meaning they have things in common with these organisms, but they’re not quite the same thing. This is because they’re relatively simple, and don’t have tissues and organs.

If you think this definition sounds a little confusing, that’s with good reason. Biologists use the protist group as sort of a garbage can: If a form of life doesn’t meet the criteria for being a plant, animal, or fungus, and it has a nucleus, it’s classified as a protist. Still, there are a few characteristics that most protists share.

Because protists have a defined nucleus, they belong to the domain “Eukarya,” and are called “eukaryotes.”  Protists were probably the very first eukaryotes: according to what’s called “endosymbiotic theory,” the first protists formed when cells that did not have a nucleus engulfed smaller cells. Over many years, these smaller cells evolved into the larger cells’ nucleus and other organelles.

Most protists live in water or very wet environments, and most are able to move. Some swim via whip-like projections called flagella, some glide using hair-like extensions called cilia, and some pull themselves along using pseudopods, “false feet” made of cytoplasm.

Some protists are free-living, and some are parasites. Some make their own food, and some get nutrition by hunting food, or by simply absorbing it from their environment. Protists can reproduce via sperm and egg, or by binary fission, splitting into two genetically identical cells. Protists may be simple forms of life, but they are certainly one of the most diverse!

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