This pump a lot of carbon dioxide out

This lesson defines protist and photosynthetic protists and gives examples of some relevant species. We’ll also discuss mixotrophs and explains how they obtain nutrients in both plant-like and animal-like ways.

What Is a Protist?

Most things are categorized by what they have or what they are like. But sometimes there are leftovers – like that stuff in your junk drawer in the kitchen. Biologically speaking, protists are similar to this sort of miscellaneous category.A protist is a eukaryotic organism (meaning it has a membrane-bound nucleus) that is usually unicellular, and cannot be classified as belonging to either the plant, animal, fungus, or bacteria kingdoms.

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I know it sounds weird that an organism would be defined by what it isn’t, but protists are misfits: some of them are more like plants, and others more like animals or fungi.

Photosynthetic Protists

Now that we know what a protist is (or at least what it isn’t) let’s add on the other part of this lesson – photosynthesis. Because we know that photosynthesis is a process that plants use, we can define photosynthetic protists as ‘plant-like’ protists that get their nutrients by converting sunlight into energy using photosynthesis.Some examples of exclusively photosynthetic protists include some phytoplankton and unicellular algae.


The word ‘phytoplankton’ comes from the Greek ‘phyto-‘ meaning plant and ‘-plankton’ meaning ‘wanderer’. Combine the two and you get plant-like things that wander, or drift, in the ocean.

For example, diatoms are a branch of phytoplankton that can’t swim against a current, they just drift around. They make a silica-based shell and make for a beautiful array of unique organisms when seen under the microscope.

the bioluminescence from mixotrophic dinoflagellates lights up a wave

Mixotrophic protists are all able to do both autotrophic and heterotrophic processes. By having both chloroplasts to synthesize nutrients and the ability to move to catch prey, you can think of them as plant/animal hybrid organisms.

Cool, huh?

Lesson Summary

A protist is a typically unicellular eukaryotic organism (has a membrane-bound nucleus) that cannot be classified as plant, animal, fungus, or bacteria. Photosynthetic protists may either be strictly autotrophic, meaning that they exclusively create their own nutrients from the sun like diatoms, or mixotrophic, meaning they use photosynthesis and phagocytosis (a type of heterotrophic prey acquisition) to obtain nutrients. Mixotrophic protists like dinoflagellates have flagellum, or a tail-like appendage, that enables them to move and consume smaller protists and bacteria.


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