|Life on Earth
Temporal range: Late Hadean - Recent
|These Escherichia coli cells provide an example of a prokaryotic microorganism|
|(unranked):||Life on Earth (Gaeabionta)|
|Domains and Kingdoms|
Some organisms are made up of millions of cells. They are called multicellular organisms. Some examples are dogs, trees, and humans. Most multicellular organisms can be seen without using a microscope.
Some organisms are so small that they cannot be seen with the naked eye. You need a microscope to see them. They are called microorganisms. Organisms can be made up of just one cell. They are called unicellular organisms or single celled organisms. Examples include bacteria, amoeba and protozoa such as the paramecium.