Chapter 2 : Microorganisms

Topics covered in this snack-sized chapter:



Microorganisms arrow_upward


  • An organism is a living thing that ingests and breaks down food for energy and nutrients, excretes undigested food as waste and is capable of reproduction.
  • A microorganism is simply a very, very small organism that cannot be seen with the naked eye.
  • Microorganisms are studied extensively in the subject of microbiology.
  • A microorganism can have one cell or a cluster of cells, and can only be seen by using a microscope.
  • Microorganisms are organized into six fields of study:
    • Bacteriology
    • Virology
    • Mycology
    • Phycology
    • Protozoology
    • Parasitology

    Bacteriology arrow_upward


  • Bacteriology is the study of bacteria.
  • This subdivision of microbiology involves the identification, classification, and characterization of bacterial species.
  • A person who studies bacteriology is a bacteriologist.

    • Virology arrow_upward


  • Virology is the study of viruses and virus-like agents.
  • The study includes:
    • Their structure,
    • Classification and evolution,
    • Their ways to infect and exploit cells for virus reproduction,
    • The diseases they cause,
    • The techniques to isolate and culture them,
    • Their use in research and therapy.
  • Virology is often considered a part of either microbiology or medicine.

    • Mycology arrow_upward


  • Mycology is the branch of biology concerned with the study of fungi.
  • The study includes:
    • Their genetic and biochemical properties,
    • Their taxonomy,
    • Their uses to humans, including as a source for tinder, medicinal uses (e.g., penicillin), food (e.g., beer, wine, cheese, edible mushrooms) and entheogens,
    • Their dangers, such as poisoning or infection.

    Phycology arrow_upward


  • Phycology is the scientific study of algae.
  • Phycology is a branch of life science and often is regarded as a sub discipline of botany.

    • Protozoology arrow_upward


  • Protozoology is the study of protozoan, the "animal-like" protists.
  • Studies the origins, behavior, diseases, genetics, and life processes of animals and wildlife.

    • Parasitology arrow_upward


  • Parasitology is the study of parasites, their hosts, and the relationship between them.
  • As a biological discipline, the scope of parasitology is not determined by the organism or environment in question, but by their way of life.

    • Classification of Microorganisms arrow_upward


  • There are three distinct domains of organisms in nature:
    • Bacteria
    • Eukarya
    • Archaea

    The Bacteria (Eubacteria) arrow_upward


  • The Bacteria possess the following characteristics:
    • Bacteria are prokaryotic cells.
    • Like the Eukarya, they have membranes composed of unbranched fatty acid chains attached to glycerol by ester linkages.

    • The cell walls of Bacteria, unlike the Archaea and the Eukarya, contain peptidoglycan.
    • Bacteria are sensitive to traditional antibacterial antibiotics but are resistant to most antibiotics that affect Eukarya.
    • Bacteria contain rRNA that is unique to the Bacteria as indicated by the presence of molecular regions distinctly different from the rRNA of Archaea and Eukarya.

    The Eukarya (Eukaryotes) arrow_upward


  • The Eukarya possess the following characteristics:
    • Eukarya have eukaryotic cells.
    • Like Bacteria, they have membranes composed of unbranched fatty acid chains attached to glycerol by ester linkages.
    • Not all Eukarya possess cells with a cell wall, but for those Eukarya having a cell wall, that wall contains no peptidoglycan.
    • Eukarya are resistant to traditional antibacterial antibiotics but are sensitive to most antibiotics that affect eukaryotic cells.
    • Eukarya contain rRNA that is unique to Eukarya as indicated by the presence of molecular regions distinctly different from the rRNA of Archaea and Bacteria.
  • The Eukarya are subdivided into the following kingdoms:

    • Protista Kingdom

  • Protista are simple, predominately unicellular eukaryotic organisms.
  • Examples:
    • Slime molds
    • Euglenoids
    • Algae
    • Protozoans

    Fungi Kingdom

  • Fungi are unicellular or multicellular organisms with eukaryotic cell types.
  • The cells have cell walls but are not organized into tissues.
  • They do not carry out photosynthesis. Instead, they obtain nutrients through absorption.
  • Examples:
    • Sac fungi
    • Club fungi
    • Yeasts
    • Molds

    Plantae Kingdom

  • Plants are multicellular organisms composed of eukaryotic cells.
  • The cells are organized into tissues and have cell walls.
  • They obtain nutrients by photosynthesis and absorption.
  • Examples:
    • Mosses
    • Ferns
    • Conifers
    • Flowering plants

    Animalia Kingdom

  • Animals are multicellular organisms composed of eukaryotic cells.
  • The cells are organized into tissues and lack cell walls.
  • They do not carry out photosynthesis and obtain nutrients primarily by ingestion.
  • Examples:
    • Sponges
    • Worms
    • Insects
    • Vertebrates

    The Archaea (Archaebacteria) arrow_upward


  • The Archaea possess the following characteristics:
    • Archaea are prokaryotic cells.
    • Unlike Bacteria and Eukarya, the Archaea have membranes composed of branched hydrocarbon chains (many also containing rings within the hydrocarbon chains) attached to glycerol by ether linkages.
    • The cell walls of Archaea contain no peptidoglycan.
    • Archaea are not sensitive to some antibiotics that affect Bacteria, but are sensitive to some antibiotics that affect Eukarya.
    • Archaea contain rRNA that is unique to the Archaea as indicated by the presence of molecular regions distinctly different from the rRNA of Bacteria and Eukarya.


    Thank You from Kimavi arrow_upward


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