CHAPTER 5: The Microbial World


  • Prokaryotes
  • Bacteria
  • Heterotrophic Bacteria

    Autotrophic Bacteria



  • Unicellular Algae

  • Diatoms


    Other Unicellular Algae

  • Protozoans: The Animal-like Protists

  • Foraminiferans



  • Fungi


    Boxed Readings:


    Chapter Summary

    Chapter 5 emphasizes the importance of microorganisms in the marine environment, highlighted by recent discoveries.

    Two boxed essays, one on symbiotic bacteria and another on the use of new technology to search for microbial life in the ocean cover exciting, new information.

    Four groups of marine organisms are discussed:

    (1) Prokaryotes (bacteria and archaea)

    (2) Eukaryotic, unicellular algae (diatoms, dinoflagellates, and other groups)

    (3) Protozoans

    (4) Fungi


    Answers to Critical Thinking Questions

    1. Scientists use the particular structure of nucleic acids and other chemical differences to separate the archaea from the bacteria. Can you think of other characteristics that could be used to separate not only these two kingdoms but also between them and members of the kingdom Protista.

    Morphological features, most especially the structure of cell components, could be used. The Protista have organelles, whereas Archaea and Bacteria do not.

    2. An autotrophic protist, such as a diatom or a dinoflagellate, can evolve into a heterotrophic protist (and therefore a protozoan) simply by losing its chloroplasts. Under what conditions could such a situation take place?

    One possibility is a decrease (or absence) in light intensity, as in the case of the hypothetical protist sinking to deeper water. Another possibility is the protist becoming a parasite of a larger organism, a situation that is actually the case of some diatoms and dinoflagellates. It may also be hypothesized by students that the absence of a particular nutrient needed to synthesize chlorophyll or any other participant in the process of photosynthesis may induce the development of a heterotrophic lifestyle.