Biology Lecture Notes: Bacteria and Kingdom Protista

Biology Study Notes

Bacteria

  • Definition and Characteristics: Bacteria are single-celled organisms lacking a nucleus. They can be pathogens, causing various diseases in humans, crops, farm animals, and pets.

  • Common Diseases Caused by Bacteria:
      - Cholera
      - Typhoid
      - Tetanus
      - Citrus canker

  • Reproduction:
      - Main Method: Bacteria primarily reproduce through a process known as fission, as illustrated in Figure 2.3.
      - Alternative Methods:
        - Under unfavorable conditions, bacteria can produce spores.
        - They also have a primitive form of sexual reproduction that involves DNA transfer between individual bacteria.

  • Mycoplasma:
      - Description: Mycoplasma are unique organisms that completely lack a cell wall.
      - Size and Survival: They are the smallest living cells known and can survive without oxygen.
      - Pathogenicity: Many species of Mycoplasma are pathogenic, affecting animals and plants.

Kingdom Protista

  • Overview: Protista encompasses all single-celled eukaryotic organisms, but the boundaries of the kingdom are not well-defined. Definitions may vary:
      - A protistan could be categorized as a plant by some biologists.

  • Members Included:
      - Chrysophytes
      - Dinoflagellates
      - Euglenoids
      - Slime moulds
      - Protozoans

  • Habitat and Features:
      - Members of Protista are primarily aquatic.
      - This kingdom serves as a link between plants, animals, and fungi.
      - As eukaryotes, protists possess a well-defined nucleus and various membrane-bound organelles.
      - Some protists have flagella or cilia, which aid in movement.

  • Reproduction: Protists can reproduce both asexually and sexually, involving processes such as cell fusion and zygote formation.

Chrysophytes

  • Definition: This group consists of diatoms and golden algae (desmids).

  • Habitat: Found in both freshwater and marine environments.

  • Physical Characteristics:
      - They are microscopic and drift in water currents, classified as plankton.
      - Most species are photosynthetic.
      - In diatoms, the cell wall is composed of two thin, overlapping shells that fit together like a soap box.
      - The cell walls are embedded with silica, making them indestructible.

  • Geological Impact:
      - Diatoms have contributed to 'diatomaceous earth', a significant accumulation of their cell wall deposits over billions of years.
      - This gritty substance is utilized in various industries for purposes such as polishing and oil/syrup filtration.

  • Ecological Role: Diatoms are considered the primary producers in ocean ecosystems, playing a crucial role in the marine food web.