🌸Chapter 8
Microbes in Human Welfare
(2 Marks)
Q1. Name the bacterium responsible
for the formation of curd from milk.
Answer:
Lactobacillus (or Lactic acid bacteria).
It converts milk sugar (lactose) into lactic acid, causing coagulation of milk
protein and formation of curd.
Q2. What causes the characteristic
holes in Swiss cheese?
Answer:
Propionibacterium shermanii produces CO₂ during fermentation, which
forms large holes in Swiss cheese.
Q3. Who discovered the first
antibiotic and what was it?
Answer:
Alexander Fleming discovered Penicillin in 1928 from the fungus Penicillium
notatum.
Q4. Name two bioactive molecules
produced by microbes and mention their uses.
Answer:
- Cyclosporin A: Immunosuppressive agent in
organ transplant.
- Statins: Lower blood cholesterol
levels.
Q5. What is the role of Lactobacillus
in our stomach?
Answer:
It improves digestion, checks the growth of harmful microbes, and enhances
nutritional value.
Q6. What is the function of yeast in
the bakery industry?
Answer:
Yeast (Saccharomyces cerevisiae) ferments sugars to produce CO₂, causing
the dough to rise and making bread soft and fluffy.
Q7. Name two bacteria used in
alcoholic fermentation.
Answer:
Saccharomyces cerevisiae (yeast) and Zymomonas mobilis.
Q8. What are antibiotics? Give one
example.
Answer:
Antibiotics are chemical substances produced by microbes that kill or inhibit
other microbes. Example: Penicillin.
Q9. Why are antibiotics ineffective
against viral diseases?
Answer:
Antibiotics act on bacterial cell structures like cell wall or protein
synthesis, which viruses lack.
Q10. Name two acids produced by
microbial activity used in industry.
Answer:
- Citric acid – Aspergillus
niger
- Acetic acid – Acetobacter
aceti
Q11. What is sewage?
Answer:
Sewage is wastewater containing organic and inorganic matter, microbes, and
harmful pathogens from households and industries.
Q12. Define BOD.
Answer:
Biochemical Oxygen Demand — the amount of oxygen required by microorganisms to
decompose organic matter in water.
Q13. What does a high BOD value
indicate?
Answer:
High BOD indicates high organic pollution and low water quality.
Q14. What is the purpose of primary
treatment of sewage?
Answer:
To remove large and small solid particles through sedimentation and filtration.
Q15. What is activated sludge?
Answer:
It is the aerated sewage water rich in microbial flocs (bacteria + fungi) used
for secondary sewage treatment.
Q16. What are microbial flocs?
Answer:
Aggregates of bacteria and fungal filaments that digest organic matter in
sewage during secondary treatment.
Q17. What are methanogens? Give one
example.
Answer:
Methanogens are anaerobic microbes that produce methane gas. Example: Methanobacterium.
Q18. Mention two uses of biogas.
Answer:
1.
Used
as a fuel for cooking and lighting.
2.
Used
to generate electricity in rural areas.
Q19. What is biogas mainly composed
of?
Answer:
Methane (CH₄) and Carbon dioxide (CO₂).
Q20. Which microbes are present in
the rumen of cattle? What is their function?
Answer:
Methanobacterium (methanogens) — they digest cellulose anaerobically and
produce methane.
Q21. What happens to the sludge left
after biogas production?
Answer:
It is used as nutrient-rich manure in agricultural fields.
Q22. Name two microbes used in
antibiotic production.
Answer:
Penicillium notatum (Penicillin) and Streptomyces griseus
(Streptomycin).
Q23. What are bioactive molecules?
Give one example.
Answer:
Biologically active compounds produced by microbes with medical use.
Example: Cyclosporin A (immunosuppressant).
Q24. What is the role of Trichoderma
polysporum?
Answer:
It produces Cyclosporin A, which suppresses the immune response in organ
transplantation.
Q25. Name the fungus used in the
production of citric acid.
Answer:
Aspergillus niger.
Q26. What is the scientific name of
baker’s yeast?
Answer:
Saccharomyces cerevisiae.
Q27. What are biofertilizers?
Answer:
Microorganisms that enrich the soil with nutrients by fixing nitrogen,
solubilizing phosphorus, etc. Example: Rhizobium.
Q28. Name one biofertilizer used for
rice crops.
Answer:
Azospirillum or Anabaena (present in Azolla).
Q29. Mention two biofertilizers used
in agriculture.
Answer:
Rhizobium and Azospirillum.
Q30. Name the organism used as a
biofertilizer for leguminous crops.
Answer:
Rhizobium.
Q31. What is the role of Anabaena
in rice fields?
Answer:
Anabaena, a cyanobacterium, fixes atmospheric nitrogen and increases
soil fertility.
Q32. What is the use of Monascus
purpureus in industry?
Answer:
It produces statins that lower blood cholesterol levels.
Q33. Name one fungus used as a
biocontrol agent.
Answer:
Trichoderma — used against plant pathogens.
Q34. How do biofertilizers benefit
farmers economically?
Answer:
They reduce the use of chemical fertilizers and improve soil fertility
naturally.
Q35. What is biocontrol?
Answer:
The use of living organisms to control pests and plant diseases.
Q36. Give one example of a
biocontrol agent used against insect pests.
Answer:
Bacillus thuringiensis (Bt) — produces a toxin harmful to insect larvae.
Q37. Name one example of a fungus
used as a biocontrol agent in agriculture.
Answer:
Trichoderma — protects roots from fungal infections.
Q38. Why is Bacillus
thuringiensis used in organic farming?
Answer:
It is a natural insecticide that kills pests without harming beneficial insects
or the environment.
Q39. What are probiotics?
Answer:
Live beneficial microbes that improve intestinal health, e.g., Lactobacillus.
Q40. Name two microbial products
used in food industries.
Answer:
- Lactic acid (from Lactobacillus)
- Citric acid (from Aspergillus
niger)
Q41. What is meant by secondary
sewage treatment?
Answer:
Biological treatment of sewage using aerobic microbes to decompose organic
matter.
Q42. What are the end products of
anaerobic digestion in biogas plants?
Answer:
Methane (CH₄), CO₂, and water.
Q43. What is the use of Acetobacter
aceti?
Answer:
It converts alcohol into acetic acid (vinegar) in industries.
Q44. What is meant by floc formation
in sewage treatment?
Answer:
Bacteria and fungi form aggregates (flocs) to digest organic matter during secondary
treatment.
Q45. Which type of bacteria is used
in nitrogen fixation in legume roots?
Answer:
Rhizobium.
Q46. Why are cyanobacteria called
“blue-green algae”?
Answer:
They are photosynthetic prokaryotes containing chlorophyll a and
phycobilins, giving them a blue-green color.
Q47. Give two examples of
cyanobacteria used as biofertilizers.
Answer:
Anabaena and Nostoc.
Q48. Mention one advantage of using
biofertilizers over chemical fertilizers.
Answer:
Biofertilizers are eco-friendly and improve soil structure without pollution.
Q49. What is the full form of BOD?
What does it indicate?
Answer:
Biochemical Oxygen Demand — it indicates the level of organic pollution in
water.
Q50. Name two microbes involved in
sewage treatment.
Answer:
Nitrosomonas and Nitrobacter (nitrifying bacteria).
