One cell. Unicellular organisms are made up of only one cell that carries out all of the functions needed by the organism, while multicellular organisms use many different cells to function.
Hence the name, <u>single </u>celled organisms, or <u>uni</u>cellular organisms, (the prefix uni means one), single celled organisms only have <em>one cell. </em>
This single cell sustains life for the organism and carries out all the necessary processes.
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Usually, these types of organisms are extremely tiny and can't be seen without a microscope. For example, bacteria and amoebas are single celled organisms.
