Microbes
Microorganisms – Organisms and acellular biological entities too small to be seen clearly by the unaided eye.
Cellular microbes are found in plants and animals.
Prokaryotic cells lack a nucleus unlike eukaryotic cells.
Eukaryotic cells have membrane enclosed nuclei and are more complex and larger than prokaryotes.

Organisms are divided into five kingdoms:
Monera – Prokaryotes are places in this kindgom
Protista
Fungi
Animalia
Plantae
*This classification system is no longer accepted by microbiologists.*

Based on comparisons of ribosomal RNA genes, microorganisms are divided into 3 categories:
1. Bacteria (True bacteria)
2. Archaea (Archaeobacteria)
3. Eukarya (Eukaryotes)

Bacteria – single celled organisms containing cell walls with the structural molecule peptidogylcan. Exhibits typical prokaryotic structure (no nucleus). Cyanobacteria (blue-green algae) produces a significant amount of oxygen through oxygenic photosynthesis.
Role – Some bacteria can cause disease but mostly plays as a cycling element in the biosphere, breaking down dead plant/animal material, and producing vitamins.
Archaea – has distinctive rRNA sequences, lacks peptidoglycan in cell walls, and has unique membrane lipids. Found in extreme environments including those with high temperatures and high salt concentrations.
Role – not yet established.
Eukarya – microorganisms in this domain are classified as protists and fungi, also animals and plants are placed in this domain.
Protists – unicellular but larger than most bacteria and archaea. Divided into subcategories: protozoa, algae, slime molds, and water molds.
Algae – photosynthetic. Make up 75% of the planet’s oxygen together with cyanobacteria.
Protozoa – unicellular, animal-like protists that are motile. “Hunters and Grazers”
Obtain nutrients by ingesting organic matter and other microbes. Found in many different inhabitants, and normally in the intestinal tracts of animals where they aid in digestion of cellulose for example.
Slime Molds – protists that behave like protozoa in one stage of their cycle but fungi in the others.
Water Molds – protists that grow on the surface of freshwater and moist soil. They feed off of decaying vegetations and produces devastating plant infections.
Fungi – microorganisms that range from unicellular to multicellular.
Yeast – unicellular
Molds and mushrooms – multicellular organisms that form thin structures called hyphae.
Hyphae – absorbs nutrients from their environments.
Fungi play an important role in making bread rise, producing antibiotics and decomposing dead organisms.
Viruses – acellular entities that must invade a host cell in order to replicate itself. Composed of proteins and nucleic acids and are the smallest of all microbes.
Role – causes a range of diseases and some cancers.
Viroids and Virusoids – infectious agents only composed of RNA. Viroids causes