Unicellular organisms have a variety of functions depending upon the type of organism, but they generally need to synthesize all of the nutrients necessary for the cell to survive. The organism must carry out all of the life processes for the cell to function and reproduce itself, which sometimes occurs as frequently as every hour.
Many one-celled organisms are resistant to extreme temperatures. This means one-celled organisms are able to survive or remain dormant in extremely cold and hot temperatures. Other specialized functions depend on the type of unicellular organism. For instance, a protozoa, bacteria, unicellular algae or fungi may all have different specialized functions.
Cyanobacteria absorb light with a UV-absorbing pigment and use it to create a coat that allows them to survive extreme temperatures when exposed to rocky surfaces with high light exposure. Other bacteria produce spores that withstand freezing and boiling temperatures altogether. Usually, these one-celled organisms have a low water content and a protein coat. One-celled fungi, however, such as yeast and mold, have a different purpose. Yeast is often produced for making baked goods such as bread, and mold and other types of fungi function to decompose dead matter. Protozoa, which represent the one-cell organisms with animal-like behavior, control bacteria populations and decompose matter much like fungi.