Microorganisms - Friend and Foe: Class 8, Chapter 2 (Study Notes)

What are Microbes?

  • Microbes or microorganisms are tiny organisms so small that we cannot see them with an unaided eye.
  • Some microorganisms can be seen with a magnifying glass (e.g., fungus that grows on bread).
  • Some can only be seen with a microscope (e.g., bacteria and protozoa).
  • Microorganisms were first observed by Anton Van Leeuwenhoek.

Omnipresence of Microorganisms

  • Microbes can survive in all kinds of environments: icy cold climates to hot springs, deserts to marshy lands (any temperature and humidity levels).
  • Some microbes live independently; others exist as parasites inside the bodies of other organisms (including animals and humans).
  • The field of study of microorganisms is called MICROBIOLOGY.

Four major types of microorganisms

  • Bacteria
  • Fungi
  • Protozoa
  • Algae
    • Examples include: Chalmydomonas, Bread Mould, Amoeba, Paramecium, Plasmodium (which causes malaria), Spirogyra
  • Note: The slide lists these major groups with representative examples under each.

Bacteria

  • Bacteria are single-celled microorganisms.
  • They have a rigid definite cell wall.
  • Bacteria can be seen under a light microscope when magnified from about to
    • Magnification commonly used: 100×100\times to 1000×1000\times.
  • Shapes include various forms such as cocci (spherical), bacilli (rod-shaped), spirilla (spiral-shaped).

Shape of the Bacteria

  • Examples:
    • Comma-shaped: Vibrio cholerae
    • Spherical (Cocci): Streptococcus
    • Rod-shaped (Bacillus): Salmonella
    • Spiral-shaped: Borrelia

Fungi

  • Fungi are a group of eukaryotic organisms.
  • Most fungi are multicellular; yeast is a single-celled fungus.
  • Fungi lack chlorophyll.
  • They can live as parasites (deriving nutrition from host organisms; e.g., Puccinia which causes wheat leaf rust) or as saprotrophs (growing on organic matter such as bread mould).
  • Examples mentioned: Bread mould, Puccinia candida.

Algae

  • Algae are simple plant-like organisms, usually aquatic.
  • They have a cell wall and contain chlorophyll and can perform photosynthesis to make their own food.
  • They can be unicellular or multicellular.
  • Common examples: diatoms, Chlamydomonas, Spirogyra, and seaweed (seaweeds).

Protozoa

  • Protozoa are unicellular organisms.
  • Some protozoa live independently; others as parasites.
  • Parasitic protozoans can cause diseases in plants, domestic animals, and humans.
  • Examples: Amoeba, Plasmodium, Paramecium.

Viruses

  • Viruses are microscopic organisms but differ from other microbes because they reproduce only inside the cells of a host organism (which can be a plant, animal, or bacterium).
  • Outside the host, viruses do not show any activity and can crystallize and be stored like non-living things.
  • Viruses are much smaller than bacteria and come in a wide variety of shapes and sizes.
  • They can be seen through powerful microscopes called electron microscopes.

Types of Viruses

  • A notable example mentioned: COVID-19 virus.
  • General takeaway: viruses require a host cell to replicate and vary in shape/size.

Recap

  • What are microbes?
  • Microbial diseases
  • Where do microorganisms live?
  • Types of microbes
  • Bacteria, Fungi, Algae, Protozoa, and Virus

Quick Evaluation

1) _ are small organisms that cannot be seen with naked eyes.

  • Answer: Microbes
    2) Microbes are present everywhere, therefore they are called _.
  • Answer: omnipresent
    3) The four types of microorganisms are ___.
  • Answer: Bacteria, Fungi, Algae, Protozoa, and Virus
    4) Paramecium and amoeba are examples of___.
  • Answer: Protozoa
    5) Algae are green due to the presence of _.
  • Answer: Chlorophyll

Home work questions

  • 1. What are microorganisms or microbes?
  • 2. Name the types of microorganisms.
  • 3. Name two multicellular Microorganisms.
  • 4. Why are viruses different from other microbes?

YouTube Links for session 1

  • https://www.youtube.com/watch?v=B1CFVuQVG2U
  • https://www.youtube.com/watch?v=VVuYGkk_18s
  • https://www.youtube.com/watch?v=0TdQeTMOxec
  • https://www.youtube.com/watch?v=sK6Us18yEAE&list=PLmdFyQYShrjcxsrAR9keci-INX8bvrvl&index=5

Note on concepts and connections

  • Microbiology as a field: links to discovery by Leeuwenhoek and the development of microscopy in studying life at microscopic scales.
  • Ecological breadth: microbes inhabit extreme environments, illustrating adaptation and the breadth of life.
  • Practical implications: understanding pathogens (viruses, bacteria, protozoa, fungi) informs health, agriculture (e.g., Puccinia on wheat), and industry (yeast in fermentation).
  • Distinctions between living and non-living states for viruses, highlighting the dependency on host cells for replication and metabolism.
  • Ethical/philosophical angle: the boundary between living and non-living can be explored through viruses’ replication requirements and the role of microbiology in public health.