Protozoa thrive in damp environments. As a result, polluted water is regularly used to spread intestinal illnesses and the diseases they induce, such as amebiasis and giardiasis. Protozoa are parasites in some cases. This implies they must survive by living on or in another organism (such as an animal or plant). They use their own enzymes to digest food because they don't have any digestive organs like stomachs or intestines. Protista is a large group of single-celled organisms that does not include fungi or plants. It includes bacteria, archaea, and unicellular eukaryotes such as algae and moss. Although not technically multicellular organisms, colonies of protists can form through cell division and association. For example, if you put red blood cells into liquid nitrogen, they will die but the protozoans that live in your gut will be able to survive this process since they are not dependent on being alive for reproduction. Protists are defined as single-celled organisms that are not plants or animals. However, this term is also used to describe certain groups of multi-cellular organisms that lack tissues specific to plants or animals. For example, slime molds are called protists because they are composed of only one type of cell without tissues or organs. But humans are multi-cellular organisms that contain many different types of cells in our bodies; thus we are not covered by the definition of "protoctist".