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🦠 Single-Celled Organisms

Meet the tiny living things that carry out every part of life inside just one cell.

lessons

~15 min

to learn

🔬 Science

subject

Teens

level

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What you’ll learn

One Cell, One LifeUnderstand what a single-celled (unicellular) organism is and why it needs a microscope to be seen.A unicellular organism is a living thing made of just one cell, which must move, feed, grow, and reproduce all by itself. These organisms are so tiny that a microscope is needed to see them, yet they live almost everywhere around and inside us.
Meet the MicrobesDescribe how the amoeba, bacteria, and euglena each move, feed, and differ from one another.The amoeba moves and grabs food using pseudopods (false feet) and has a nucleus. Bacteria are much tinier and have no nucleus, making them prokaryotes, and they can be helpful or harmful. The euglena swims with a flagellum and also photosynthesizes with chloroplasts, so it is both animal-like and plant-like.
Comparing the CellsCompare amoeba, bacteria, and euglena by how they move, whether they have a nucleus, and whether they make their own food.Comparing the three shows that the amoeba moves with pseudopods and has a nucleus, bacteria have no nucleus, and the euglena stands out by both swimming and making its own food. Many microbes, especially bacteria, are helpful rather than harmful.

Questions this course answers

What does it mean if an organism is unicellular?

Unicellular means one-celled, so the organism's entire body is a single cell that does every job.

Why do single-celled organisms need a microscope to be seen?

A single cell is tiny, so single-celled organisms are far too small for our eyes to see without a microscope.

How does an amoeba move and catch its food?

An amoeba pushes out pseudopods (false feet) to creep along and to wrap around and engulf its food.

What makes bacteria different from an amoeba or a euglena?

Bacteria have no nucleus, which places them in the prokaryote group, unlike the amoeba and euglena which both have a nucleus.

Why is the euglena described as part animal-like and part plant-like?

The euglena swims using a flagellum like an animal, but also photosynthesizes with chloroplasts like a plant.

Which of the three organisms can make its own food using sunlight?

Only the euglena carries chloroplasts, so it is the one that can photosynthesize and make its own food.

Grounded in trusted sources

Britannica Kids
BBC Bitesize
Britannica
National Geographic Kids

Every Wunder lesson is built from real, reputable sources — never invented.

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