Lecture notes Microbiology 1 domains of life

Chapter 2
Domains of life




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, Domains of life
 The three major subdivisions of all organisms/life
 They are:
 Bacteria,

 Archaea, and

 Eukarya.




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, Domains of Life
Bacteria (Procaryotes)
 Organisms are small (1-2 µm), unicellular/single-celled.
 They are prokaryotic organisms/prokaryotes: meaning they do not
have a nucleus and lack complex organelles.
 Has a cell wall, a plasma membrane and a cytoplasm.
 DNA/bacterial chromosome located in cytoplasm.
 Reproduce by cellular fission/binary fission (produces genetically
identical copies of original cell).
 Mode to acquire nutrition: Autotrophic – using simple
substances in environment to produce complex compounds.
Example: Photosynthetic bacteria uses energy from sun (light
energy) and carbon dioxide (CO2) to synthesize food.

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, Domains of Life
Archaea (Procaryotes)
 Small, unicellular organisms.

 Organisms are prokaryotes/prokaryotic: lack a nucleus and

organelles.
 Reproduce by means of binary fission.

 Major mode to acquire nutrition: Some species are
autotrophs: utilise inorganic chemical [ammonia (NH3)] and
CO₂ as carbon source to synthesize their own food.

• Scientists believe/think that archaea were among the earliest
organisms on Earth because of their unique adaptations.


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