Class 12 Biology – Microbes in Human Welfare Notes

Class 12 Biology – Microbes in Human Welfare Notes

Microbes in Human Welfare – Short Notes

1. Introduction to Microbes

  • Microbes (microorganisms) are microscopic organisms such as bacteria, fungi, protozoa, viruses, and algae.
  • They are found in soil, water, air, and inside living organisms.
  • Though some cause diseases, many microbes are beneficial to humans.

2. Microbes in Household Products

A. Curd Formation

  • Lactic acid bacteria (LAB) convert milk into curd.
  • LAB produces lactic acid, which coagulates milk proteins.
  • Improves nutritional quality (Vitamin B12).

B. Fermented Foods

  • Idli, dosa, bread → fermentation by microbes.
  • Yeast (Saccharomyces) is used in baking and brewing.

C. Alcoholic Beverages

  • Yeast converts sugar into alcohol (ethanol) and CO₂.
  • Used in production of wine, beer, whisky.

3. Microbes in Industrial Products

A. Antibiotics

  • Chemical substances produced by microbes to kill or inhibit other microbes.
  • Example: Penicillin (from Penicillium fungus).
  • Used to treat bacterial infections.

B. Organic Acids

  • Citric acid → Aspergillus niger
  • Acetic acid → Acetobacter
  • Lactic acid → Lactobacillus

C. Enzymes

  • Used in detergents, food processing, and pharmaceuticals.
  • Example: Lipases, proteases, amylases.

D. Bioactive Molecules

  • Cyclosporin A → Used as immunosuppressant.
  • Statins → Lower blood cholesterol.

4. Microbes in Sewage Treatment

  • Sewage contains organic waste.
  • Microbes break down organic matter.
  • Treatment stages:
    1. Primary treatment – Physical removal of solids.
    2. Secondary treatment – Microbial decomposition.
  • Produces biogas (methane).

5. Microbes in Biogas Production

  • Biogas mainly contains methane.
  • Produced by methanogenic bacteria.
  • Used as fuel.
  • Slurry left behind is used as manure.

6. Microbes as Biocontrol Agents

  • Used to control pests naturally.
  • Example: Bacillus thuringiensis (Bt) kills insect larvae.
  • Reduces use of chemical pesticides.

7. Microbes as Biofertilizers

  • Improve soil fertility naturally.
  • Examples:
    • Rhizobium – Fixes nitrogen in legume roots.
    • Azotobacter – Free-living nitrogen fixer.
    • Cyanobacteria – Improve soil nitrogen content.

Microbes in Human Welfare | MCQs

1. Microbes in Household Products

  1. Curd formation from milk is due to:
    a) Yeast
    b) Lactic acid bacteria
    c) Virus
    d) Fungi
    Answer: b) Lactic acid bacteria
  2. During curd formation, milk protein is coagulated by:
    a) Alcohol
    b) Carbon dioxide
    c) Lactic acid
    d) Methane
    Answer: c) Lactic acid
  3. Bread making involves fermentation by:
    a) Lactobacillus
    b) Rhizobium
    c) Saccharomyces (yeast)
    d) Penicillium
    Answer: c) Saccharomyces (yeast)
  4. Yeast produces which two main products during fermentation?
    a) Oxygen and water
    b) Alcohol and CO₂
    c) Lactic acid and oxygen
    d) Methane and hydrogen
    Answer: b) Alcohol and CO₂

2. Microbes in Industrial Products

  1. The first discovered antibiotic was:
    a) Streptomycin
    b) Tetracycline
    c) Penicillin
    d) Erythromycin
    Answer: c) Penicillin
  2. Penicillin is obtained from:
    a) Bacteria
    b) Virus
    c) Fungus
    d) Algae
    Answer: c) Fungus
  3. Citric acid is produced by:
    a) Lactobacillus
    b) Aspergillus niger
    c) Rhizobium
    d) Methanobacterium
    Answer: b) Aspergillus niger
  4. Cyclosporin A is used as:
    a) Antibiotic
    b) Immunosuppressant
    c) Fertilizer
    d) Enzyme
    Answer: b) Immunosuppressant
  5. Statins are used to:
    a) Kill bacteria
    b) Increase immunity
    c) Lower blood cholesterol
    d) Improve digestion
    Answer: c) Lower blood cholesterol

3. Microbes in Sewage Treatment

  1. Primary treatment of sewage mainly involves:
    a) Chemical treatment
    b) Physical removal of solids
    c) Bacterial digestion
    d) Methane production
    Answer: b) Physical removal of solids
  2. Secondary treatment of sewage involves:
    a) Filtration only
    b) Microbial decomposition
    c) Chemical sterilization
    d) Boiling
    Answer: b) Microbial decomposition
  3. The gas produced during sewage treatment is mainly:
    a) Oxygen
    b) Carbon dioxide
    c) Methane
    d) Nitrogen
    Answer: c) Methane

4. Biogas Production

  1. Biogas mainly contains:
    a) Carbon dioxide
    b) Methane
    c) Oxygen
    d) Hydrogen
    Answer: b) Methane
  2. Biogas is produced by:
    a) Yeast
    b) Methanogenic bacteria
    c) Viruses
    d) Fungi
    Answer: b) Methanogenic bacteria
  3. The slurry left after biogas production is used as:
    a) Fuel
    b) Manure
    c) Antibiotic
    d) Acid
    Answer: b) Manure

5. Microbes as Biocontrol Agents

  1. Bacillus thuringiensis (Bt) is used to:
    a) Increase milk production
    b) Control insect pests
    c) Produce alcohol
    d) Treat diseases
    Answer: b) Control insect pests
  2. Biocontrol agents reduce the use of:
    a) Biofertilizers
    b) Chemical pesticides
    c) Enzymes
    d) Antibiotics
    Answer: b) Chemical pesticides

6. Microbes as Biofertilizers

  1. Rhizobium helps in:
    a) Photosynthesis
    b) Nitrogen fixation
    c) Alcohol production
    d) Sewage treatment
    Answer: b) Nitrogen fixation
  2. Cyanobacteria are important because they:
    a) Cause disease
    b) Fix nitrogen in soil
    c) Produce alcohol
    d) Produce antibiotics
    Answer: b) Fix nitrogen in soil
  3. Azotobacter is a:
    a) Fungal biofertilizer
    b) Free-living nitrogen-fixing bacterium
    c) Virus
    d) Protozoa
    Answer: b) Free-living nitrogen-fixing bacterium