What is Plankton? - Definition, Types & Facts

What is Plankton? - Definition, Types & Facts
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  • 0:00 What Is Plankton?
  • 1:09 Phytoplankton
  • 2:57 Zooplankton
  • 4:38 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

Plankton is a diverse community of organisms that spend part or all of their existence drifting freely in aquatic environments. In this lesson, learn more about these creatures and take a quiz at the end.

What is Plankton?

Have you ever visited an aquarium? If so, you've observed many different forms of marine life. Wildly colorful fish, playful sea otters and perhaps sea turtles caught your eye. Maybe your favorites were the sea lions or sharks. But did you see any plankton? You may be raising an eyebrow at this, imagining tiny organisms too small to even notice. However, if you saw the jellyfish exhibit, then you have seen plankton.

The term plankton comes from the Greek derivative planktos, meaning wandering. Organisms in this group spend either part or all of their life in a drifting state, with no ability to swim against a current. Most have little or no ability to swim at all. Though some are larger, most planktonic creatures are microscopic and make up the bottom of the food chain in aquatic environments.

Plankton can be divided into two categories: phytoplankton are those organisms that are plant-like, and zooplankton are organisms that are animal-like. Interestingly enough, many planktonic species are neither plant nor animal but are creatures that belong to the kingdom Protista.


Let's take a look at the group known as phytoplankton. Most of these organisms are very tiny microscopic creatures. They are plant-like in that they contain chlorophyll, a molecule that makes them able to undergo photosynthesis. This makes them a crucial component in the marine food web. Phytoplankton drift near the water's surface, producing their own food and thus, providing meals for countless other aquatic dwellers.

Let's zoom in on more types phytoplankton that can be found drifting in aquatic habitats. One type is known as blue-green algae. Don't be fooled by the name, as this is not actually algae. Otherwise known as cyanobacteria, blue-green algae is a form of bacteria and is highly toxic. A diatom is a single-celled form of algae with an outer shell comprised of silica. You may know silica as the main component in glass. Found in differing shapes, some diatoms look more like Christmas ornaments than anything we could imagine as algae. And when diatoms die, their shells drift to the ocean floor to help make up sediment that will be later transformed.

Coccolithophores are single-celled algae with shells comprised of limestone. Seen under a scanning electron microscope, these tiny organisms look like perfect spheres decorated with round scales. Interestingly enough, when these little guys die, their shells also sink to the floor of the ocean. Over time they will be transformed into a common household substance: chalk.

Dinoflagellates have no interesting glass or limestone coating. However, they have been gifted by being creatures with the ability to move. They get their name from two tail-like flagella that they whip around, creating a tiny bit of movement. If you've ever been floating on a raft and tried to propel yourself with a pool noodle, then you understand their form of motility.

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