Contributor: Meghan Vestal. Lesson ID: 11530

The ocean is the biggest body of water in the world, but it contains some of the tiniest creatures, drifting around in their own little world! Watch them live, and create trading cards to honor them!


Earth Science

learning style
personality style
Grade Level
Middle School (6-8)
Lesson Type
Dig Deeper

Lesson Plan - Get It!

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  • What are the smallest living organisms that inhabit the ocean?

Whatever they are, they live in the water but many can't swim!

The smallest living organism in the ocean is plankton, which is any living organism that drifts in a body of water.

The name plankton is derived from a Greek word that means wanderer. This term is suitable because plankton spend their lives wandering, or drifting, through the ocean.

Plankton are called drifters because they are unable to swim against the ocean's currents. Some types of plankton are able to swim vertically, but none are able to swim horizontally against the ocean's currents.

Some plankton are as small as bacteria, and other plankton are as large as jellyfish. Some marine animals start their life as plankton, but lose this title once they are able to swim on their own.

There are three types of plankton:

  • Animal-like plankton are called zooplankton. You can remember this because animals are kept in a zoo.
  • Plant-like plankton are called phytoplankton.
  • Finally, bacteria-like plankton are called bacterioplankton.

Each type of plankton plays a role as either a producer, consumer, or decomposer in the ocean ecosystem

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There are many different types of zooplankton. Examples of zooplankton include copepods, krill, crustaceans, protozoans, and daphnia. Jellyfish are also considered zooplankton because they can swim vertically, but not horizontally.

Zooplankton are consumers, meaning they feed on other organisms. Most zooplankton feed on other types of plankton.

To learn more about the many types of zooplankton, read Zooplankton (Biology Dictionary).

Phytoplankton are algae.

Phytoplankton are producers, meaning they produce their own food through the process of photosynthesis.

  • Do you remember what element plants produce and release into the atmosphere after they go through the process of photosynthesis?

Tell your teacher or parent.

Plants release oxygen into the air as they complete the process of photosynthesis. This is important because humans and animals need oxygen to breathe. Phytoplankton carries out the majority of photosynthesis that takes place on Earth, contributing around 50% of the oxygen that is in the atmosphere.

  • Since phytoplankton have to perform photosynthesis to survive, where do you think most phytoplankton are found?

Tell your teacher or parent.

Most phytoplankton are found near the surface of the ocean because sunlight is needed to perform photosynthesis. Phytoplankton cannot survive in the deep sea because sunlight cannot reach these depths, and the phytoplankton will starve to death.

Bacterioplankton consists of bacteria and archaea that live in the ocean.

Bacterioplankton are decomposers. They feed off dead organisms, recycling nutrients back into the ocean.

Plankton comes in all shapes and sizes!

  • Did you know hundreds of plankton can exist in a single drop of water?

Move on to the Got It? section to learn more about the different species of plankton.

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