Question

1. Describe the three domains into which living organisms can be divided, giving an example of a microbe that fits into each domain. What type of microbe is not included in the domain system and why?

Answer 1

Three domains

1. Archaea,

2. Bacteria,

3. Eukarya.

    Archaea, and Bacteria are all prokaryotic microorganisms, or single-celled organisms whose cells have no nucleus. Organisms with eukaryotic cells belong to the domain Eukarya. They include many large single-celled organisms and all known non-microscopic organisms.

Some examples of archaeal organisms are:

· methanogens – which produce the gas methane

· halophiles – which live in very salty water

· thermoacidophiles – which thrive in acidic high-temperature water

Some examples of bacteria include:

· Cyanobacteria – photosynthesizing bacteria that are related to the chloroplasts of eukaryotic plants and algae

· Spirochaetes – Gram-negative bacteria that include those causing syphilis and Lyme disease

· Actinobacteria – Gram-positive bacteria including Bifidobacterium animalis which is present in the human large intestine

Examples of Eukarya

Kingdom Fungi

· Saccharomycotina – includes true yeasts

· Basidiomycota – includes mushrooms

Microbes does not include viruses and prions, which are generally classified as non-living.

                        Viruses can replicate themselves only by infecting a host cell. They therefore cannot reproduce on their own. Prions are a recently discovered infectious agent. They are proteins that are folded and which can convert normally folded proteins to abnormally folded ones.