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Class 8, Science, Chapter-2, Lecture-2, Microbes (Notes)

Habitat of micro-organisms:

  • They can survive under all climatic conditions, ranging from ice cold temperatures to hot springs and deserts to marshy lands.
  • Some microbes grow on other organisms while others exist freely.
  • They are also found inside the bodies of other animals and humans.
  • Amoeba can live alone while fungi and bacteria inhabit in colonies.

Based on their behaviour, miroorganisms can be divided into two categories:

  • Friendly Microorganisms
  • Harmful Microorganisms

Friendly Microorganisms

  1. Lactobacillus is used for preparation of curd.
  2. They are used in the baking industry.
  3. They are used in the commercial preparation of pickles and many dairy products.
  4. They are used in industrial production of alcohol, wine and acetic acid.
    • Yeast converts the natural sugars present in grains (like barley, wheat, rice or crushed fruit juices) into alcohol.
    • Wine is produced by the process of fermentation.
    • The process of converting sugar into alcohol is called fermentation.
  5. Microorganisms are used in the preparation of medicines called antibiotics.
  6. Penicillin produce by Penicillium is used in the preparation of vaccines.
  7. Microorganisms present in the soil help in increasing the soil fertility. 
    Bacteria act as decomposers to clean up organic waste by decomposing them into usable substances.
  8. Bacteria present in the soil fix the nitrogen to the plants.
  9. Bacteria help in the tanning process of leather industries.
  10. Bacteria can also help in the digestion of sewage.
  11. Fungi like mushrooms are used as food.
  12. Algae release lot of oxygen into water as a by-product of photosynthesis. This is the source of dissolved oxygen for aquatic organisms.

Cleansing the Environment

Microorganisms act to keep the soil nutrients intact. Some microbes decompose dead organic wastes of plants and animals into simpler substances.

Example: Anaerobic bacteria degrade the animal dung into biogas and the leftover slurry can be used as manure.

Fermentation: 

The breakdown of large organic molecules into smaller ones by enzymes in the absence of air is called fermentation.

  • Alcohol is obtained from sugar by fermentation with yeast.
  • Yeast contains enzymes zymase and invertase.

Antibiotics: 

Medicines which are prepared using some microorganisms to kill or stop the growth of disease-causing microbes are termed as antibiotics. 
Example: Streptomycin, tetracycline and erythromycin are antibiotics made from fungi and bacteria.

Antibodies: 

When a disease carrying microbe enters a human body, the body produces antibodies to fight the invader. 
It is a characteristic feature of the body to remember how to fight the microbe if it enters the body again.

Immunisation: 

The process of developing disease-fighting capability in a living body is called immunisation.

Vaccines: 

Inactivated or weakened form of bacteria or virus which is injected into the body to simulate an actual infection is termed as vaccine.

  • ‘Dead' or ‘weakened’ microbes do not sicken a person.
  • vaccines stimulate an immune response by the body that will fight off that type of illness.