Exercises

1. Bacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes with the help of a microscope, which sample would you carry and why?

• I would carry a sample of curd.
• Why: Curd contains millions of Lactic Acid Bacteria (LAB), such as Lactobacillus, which can be easily observed under a microscope. It is a safe and readily available concentrated source of live bacteria.

2. Give examples to prove that microbes release gases during metabolism.

• Dough: The puffed-up appearance of dough for idli and dosa is due to CO2 produced by bacteria during fermentation.
• Bread: Baker’s yeast ferments dough, releasing CO2, which makes the bread soft and spongy.
• Swiss Cheese: Large holes in this cheese are caused by the production of large amounts of CO2 by the bacterium Propionibacterium sharmanii.
• Biogas: Methanogens produce methane, CO2, and H2 while decomposing organic matter in anaerobic conditions.

3. In which food would you find lactic acid bacteria? Mention some of their useful applications.

• Found in curd and milk.
• Applications:
  1. Convert milk into curd.
  2. Improve nutritional quality by increasing Vitamin B12.
  3. In the human stomach, LAB check the growth of disease-causing microbes.

4. Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.

• Wheat: Bread, Bhatura.
• Rice & Bengal Gram: Idli, Dosa, Dhokla.

5. In which way have microbes played a major role in controlling diseases caused by harmful bacteria?

• By the production of antibiotics. Microbes like fungi (Penicillium) and bacteria produce chemical substances that kill or inhibit the growth of pathogenic bacteria. Antibiotics have successfully controlled diseases like plague, diphtheria, and leprosy.

6. Name any two species of fungus, which are used in the production of the antibiotics.

1. Penicillium notatum
2. Penicillium chrysogenum

7. What is sewage? In which way can sewage be harmful to us?

• Sewage is municipal wastewater containing human excreta, organic matter, and pathogenic microbes.
• Harmful effects: If discharged directly into water bodies, it causes water pollution, depletion of dissolved oxygen (high BOD), and the spread of water-borne diseases like cholera and typhoid.

8. What is the key difference between primary and secondary sewage treatment?

• Primary Treatment: A physical process involving filtration and sedimentation to remove large and small particles.
• Secondary Treatment: A biological process involving aerobic and anaerobic microbes to consume organic matter and reduce the BOD of the effluent.

9. Do you think microbes can also be used as source of energy? If yes, how?

• Yes. Microbes like methanogens (Methanobacterium) decompose organic waste (like cattle dung) anaerobically to produce Biogas (predominantly methane). Biogas is inflammable and used for cooking and lighting.

10. Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.

• Biocontrol Agents: Using natural predators like Ladybirds (for aphids) and microbes like Bacillus thuringiensis (Bt) to control pests without toxic chemicals.
• Biofertilisers: Using nitrogen-fixing bacteria (Rhizobium, Azotobacter) and cyanobacteria (Nostoc) to enrich soil nutrients naturally. Mycorrhiza (fungal association) helps plants absorb phosphorus.

11. BOD test results: A (20mg/L), B (8mg/L), C (400mg/L). Which sample is most polluted? Assign correct labels.

• Most polluted: Sample C (highest BOD).
• Labels:
  • A (20mg/L): Secondary effluent (BOD reduced but still present).
  • B (8mg/L): River water (relatively clean).
  • C (400mg/L): Untreated sewage (highest organic load).

12. Find the names of microbes for:

• Cyclosporin A: Trichoderma polysporum (fungus).
• Statins: Monascus purpureus (yeast).

13. Role of microbes in:

• (a) Single Cell Protein (SCP): Microbes like Spirulina or Methylophilus methylotrophus are used as a protein-rich food supplement for humans and animals.
• (b) Soil: Microbes decompose organic matter into humus and fix atmospheric nitrogen, maintaining soil fertility.

14. Arrange in decreasing order of importance: Biogas, Citric acid, Penicillin, Curd.

• (Subjective, but a logical sequence:)
  1. Penicillin: Crucial for saving millions of lives from bacterial infections.
  2. Biogas: Sustainable energy source for rural development.
  3. Curd: Daily nutritional source and gut health.
  4. Citric acid: Industrial chemical used in food preservation.

15. How do biofertilisers enrich the fertility of the soil?

• By fixing atmospheric nitrogen into organic forms (Rhizobium, Cyanobacteria).
• By increasing the availability of phosphorus to plants (Mycorrhiza).
• By adding organic matter (humus) to the soil (Cyanobacteria).
• By producing growth-promoting substances and providing resistance to root pathogens.