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•  Microorganisms are metabolically diverse

Microorganisms may be differentiated according to their diverse morphological and metabolic characteristics:

  • Microorganisms may differ in their cellular organisation – e.g. prokaryotes versus eukaryotes
  • Microorganisms may exhibit different nutritional requirements – e.g. autotrophic versus heterotrophic
  • Their method of respiration may vary according to type – e.g. aerobic versus anaerobic respiration
  • They may have different structural characteristics – e.g. shape or cell wall composition

Modes of Nutrition

Microorganisms can be categorised according to their mode of nutrition:

  • Photoautotrophs use light energy to synthesise organic molecules (e.g. cyanobacteria)
  • Chemoautrophs use energy from chemical oxidation to synthesise organic molecules (e.g. nitrogen-fixating bacteria)
  • Heterotrophs obtain organic nutrients via feeding (e.g. amoeba)
  • Saprotrophs release digestive enzymes onto non-living organic matter and absorb the products (e.g. fungi)

Nutritional Patterns in Microorganisms

microorganism nutrition

Methods of Respiration

Microorganisms can also be categorised according to their mechanism of respiration:

  • Obligate anaerobes respire anaerobically and can only grow in the absence of oxygen
  • Aerotolerant anaerobes respire anaerobically but can grow in the presence of oxygen
  • Facultative anaerobes can respire anaerobically or aerobically depending on oxygen availability
  • Obligate aerobes only respire aerobically and cannot survive in the absence of oxygen

Respiration Patterns in Microorganisms

microorganism respiration