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Biology 2nd Baccalaureate

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12.1. Microbiology


The microbiology is the science in charge of the study and analysis of microorganisms, living things small not visible to the human eye, also known as microbes. Microbes are those organisms that are only visible through the microscope: prokaryotic and simple eukaryotic organisms.

They can be made up of a single cell (unicellular), or of small cell aggregates formed by cells without cell differentiation.

They can be eukaryotic (such as fungi and protoctists) and prokaryotes (such as bacteria).

However, traditional microbiology has dealt especially with the pathogenic microorganisms of bacteria, viruses, and fungi, leaving the other microorganisms for other branches of biology to study.

In addition to bacteria and fungi, there are acellular forms, without a life of their own, capable of altering the functioning of the organisms they infect. They are virusesviroids and prions.

In this topic we will not deal with bacteria because we already studied them when we saw the prokaryote.

Classification of microorganisms

Microorganisms are made up of a heterogeneous set of microscopic organisms, which can be acellular and cellular beings, prokaryotes and eukaryotes:

  • Acellular microorganisms:
  • Cellular microorganisms.
    • Prokaryotes.
      • Archaeobacteria (Domain Archaea). Adapted to living in environments with extreme characteristics of temperature, pH ... For example, the halophilic bacteria of the Dead Sea.
      • Eubacteria (Bacteria Domain):
        • Bacteria. They can be autotrophic beings (photo or chemosynthetic) or heterotrophs (saprophytes, symbionts or parasites). Example, SalmonellaEscherichia coli, ... They can be aerobic or anaerobic (like Clostridium).
        • Cyanobacteria. They carry out oxygenic photosynthesis. By endosymbiosis, they are the origin of chloroplasts. For example, Anabaena, which lives in symbiosis in the Azolla water fern.
    • Eukaryotes (Domino Eukaria):
      • Protozoa:
      • Mushrooms:
        • Yeasts: Unicellular. They are divided by budding. For example, Saccharomyces cerevisiae, useful in making bread, beer and wine.
        • MoldsMulticellular filamentous fungi. For example, Penicillium.
      • Algae:
        • Green algae. Unicellular, photosynthetic, green in color. For example, Volvox.
        • Red algae. Unicellular and multicellular, with reddish pigmentation. For example, Bangia.
        • Diatoms. Unicellular, they constitute phytoplankton, they have a silica cell wall. 
        • Dinoflagellates. Almost always unicellular, with flagella.


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.