Unicellular organism

Tiny Living Wonders

Unicellular organisms are very small living things that are made of just one cell. They are different from animals and plants, which are made of many cells. Scientists think these tiny creatures might be the oldest form of life on Earth.

These little organisms live almost everywhere — in water, soil, and even inside other living things. Some are called prokaryotic and others are eukaryotic. Most prokaryotic organisms are bacteria and archaea. Some eukaryotic organisms, like protozoa, algae, and fungi, can also be made of just one cell.

Even though some prokaryotic organisms live together in groups called colonies, each cell must do everything by itself to stay alive. This is different from animals and plants, where many cells work together. Some interesting tiny creatures, like Dictyostelium discoideum, can change how they live.

Big Single Cells

Most unicellular organisms are so tiny you need a microscope to see them. But a few are big enough to see without help! For example, Brefeldia maxima, a type of slime mold, can be as thick as a finger. Another big one is Valonia ventricosa, a green alga, that can be the size of a small ball. These big single cells show just how amazing tiny life can be!