- Bacteria = single celled prokaryotic organism.
- Eukaryote = organism that possess a cell nucleus and other organelles.
- Fungi = eukaryotic organisms that absorb their food from other living or dead organisms.
- Parasite = an organism that grows, feeds, and is sheltered on or in a different organism while contributing nothing to the survival of its host organism.
- Prokaryote = organisms that lack a cell nucleus (= karyon), or any other membrane-bound organelles.
- Protozoa = A single-cell organism that can only divide within a host organism.
- Rickettsiae = non-motile, Gram-negative, non-spore forming, highly pleomorphic bacteria (it is an obligate intracellular parasite as it reproduction depends on being inside a eukaryotic cell).
- Spirochaetes = spiral-shaped gram negative bacteria
- Virus = ultramicroscopic, metabolically inert infectious agent that replicates within the cells of living hosts – composed of RNA or DNA core, protein coat +/- surrounding envelope.