Virus

A virus is an infectious microbe consisting of a segment of nucleic acid (either DNA or RNA) surrounded by a protein coat. A virus cannot replicate alone; instead, it must infect cells and use components of the host cell to make copies of itself. 

Bacteria

Bacteria are microscopic, single-celled organisms that exist in every environment, both inside and outside other organisms. Some bacteria are harmful, but most serve a useful purpose. They support many forms of life, both plant and animal, and they are used in industrial and medicinal processes. 

Protists

A protist is any eukaryotic organism that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor, the exclusion of other eukaryotes means that protists do not form a natural group, or clade 

Fungi

 A type of eukaryotic organism belonging to the kingdom Fungi, alongside plants, animals, protozoa, and monera. Fungi are incredibly diverse, with commonly encountered forms including yeast, molds, truffles, and mushrooms.