1. Protozoa are single celled, eukaryotic organisms that exhibit animal-like behaviour. 2. Viruses consists only of genetic material and a protein coat, and they are known to cause a wide variety of diseases such as AIDS. 3. Fungi have characteristics similar to plants, but they do not have root systems like plants do and they also do not rely on chlorophyll to photosynthesize. 4. Bacteria make up this category. 5. Rickettsiae is a genus of bacteria that are intracellular parasites.