Bacteria, Virus, Prion, Protists,

Bacteria: A bacteria's complex structure is made up of a cell wall, thin cell membrane surrounding hte ctoplasm. It contains chromosomes that contains DNA needed to make copies of itself.

Virus: A virus' size is much smaller than a bacteria. Its structure is much simple. These infectious particles are made up of a protein coat and a core of either RNA or DNA and sometimes a membranous envelope. They can only reproduce inside the cells of a host.

Prion: A prion is an infectious protein that needs a host to survive. It can cause tissue damage and cell damage.  It can exist in multiple forms compared to viruses.

Protist: Protists are a group of eukaryotic microorganisms. They live in any environment that contains water. Many are photosynethic and are primary producers in the ecosystem. Some protists reproduce sexually while others reproduce asexually.