🌸Chapter 8
Microbes in Human Welfare
(3 Marks)
1. What are antibiotics? Give two
examples.
Answer:
Antibiotics are chemical substances produced by some microbes that kill or
inhibit the growth of other microbes.
- They are used to treat
bacterial infections.
- Examples:
- Penicillin (from Penicillium notatum)
- Streptomycin (from Streptomyces griseus)
2. Explain the role of Lactobacillus
in the production of curd.
Answer:
- Lactobacillus bacteria convert lactose (milk
sugar) into lactic acid.
- The lactic acid causes
coagulation and partial digestion of milk protein casein, forming curd.
- It improves nutritional quality
and increases vitamin B12 content.
3. Mention the role of microbes in
sewage treatment.
Answer:
Microbes are used in sewage treatment plants to decompose organic matter.
- Primary treatment: Removes large particles.
- Secondary treatment: Aerobic microbes form
activated sludge that digests organic matter.
- Anaerobic digesters: Anaerobic bacteria produce
biogas.
4. What are bioreactors?
Answer:
- Bioreactors are large vessels
in which raw materials are biologically converted into specific products
such as enzymes, vaccines, and antibiotics.
- They provide optimal growth
conditions — temperature, pH, nutrients, and oxygen.
- Used in large-scale industrial
production.
5. Name two industrially important
enzymes and the microbes producing them.
Answer:
1.
Amylase – produced by Aspergillus
and Bacillus species (used in detergents).
2.
Lipase – produced by Candida lipolytica
(used in food and dairy industries).
6. What is fermentation? Give
examples.
Answer:
- Fermentation is the process of
converting sugar into alcohol or acids using microorganisms under
anaerobic conditions.
- Examples:
- Saccharomyces cerevisiae (yeast) converts sugar to
ethanol.
- Used in brewing, baking, and
wine-making industries.
7. How is cheese made using
microbes?
Answer:
- Lactobacillus and Streptococcus are
used to curdle milk and form cheese.
- In ripening:
- Penicillium roqueforti → gives flavour to blue
cheese.
- Propionibacterium sharmanii → forms holes in Swiss cheese
by CO₂ production.
8. Describe the role of microbes in
sewage treatment.
Answer:
- Sewage water contains organic
matter and microbes.
- Primary treatment: Removes large debris.
- Secondary (biological)
treatment:
Aerobic microbes oxidize organic matter into CO₂ and water; sludge formed
is digested anaerobically to produce biogas.
9. What are methanogens? Give
examples and functions.
Answer:
- Methanogens are anaerobic
archaebacteria that produce methane.
- Example: Methanobacterium.
- Found in rumen of cattle and
sewage treatment plants.
- They help in biogas production
and digestion of cellulose.
10. What are biofertilizers? Give
examples.
Answer:
Biofertilizers are microorganisms that enrich soil fertility by fixing
nitrogen, solubilizing phosphorus, or decomposing organic matter.
Examples:
- Rhizobium – fixes nitrogen in legume
roots.
- Azospirillum, Azotobacter –
free-living nitrogen fixers.
- Cyanobacteria – Anabaena, Nostoc
(in rice fields).
11. Explain the role of Rhizobium
in agriculture.
Answer:
- Rhizobium forms symbiotic association
with legume roots (root nodules).
- It fixes atmospheric nitrogen
into ammonia, enriching soil nitrogen content.
- Increases crop yield naturally,
reducing chemical fertilizer use.
12. What is biological nitrogen
fixation? Give examples.
Answer:
Conversion of atmospheric nitrogen (N₂) into ammonia (NH₃) by microbes.
Examples:
- Symbiotic: Rhizobium
(legumes)
- Free-living: Azotobacter,
Anabaena
13. What is biogas? Name its major
components.
Answer:
- Biogas is a mixture of gases
produced by anaerobic breakdown of organic matter by microbes.
- Main components:
- Methane (CH₄) – 50–70%
- CO₂ – 30–40%
- H₂, N₂, H₂S – traces
14. Name the microbes used in biogas
production.
Answer:
- Methanogens like Methanobacterium, Methanococcus.
- Found in cattle dung and sewage
sludge.
- They decompose organic matter
anaerobically to release methane.
15. Explain the three stages of
biogas plant operation.
Answer:
1.
Input
chamber: Cow dung
+ water slurry is fed.
2.
Digester
tank: Anaerobic
microbes break down organic matter → methane, CO₂.
3.
Outlet
chamber: Digested
slurry is removed → used as manure.
16. What are bio-control agents?
Give examples.
Answer:
Bio-control agents are living organisms used to control pests and diseases
naturally.
Examples:
- Trichoderma – fungi that kills plant
pathogens.
- Bacillus thuringiensis – insecticidal bacteria used
against caterpillars.
17. Explain how Bacillus
thuringiensis acts as a bio-pesticide.
Answer:
- B. thuringiensis produces Cry protein
(toxin).
- When insects ingest it, toxin
binds to gut lining → cell lysis → insect death.
- Used in Bt cotton and sprays
for pest control.
18. How does Trichoderma act
as a bio-control agent?
Answer:
- Trichoderma fungi live in root ecosystems.
- They produce antifungal
compounds and enzymes that kill plant pathogens.
- They are environmentally safe
and prevent soil-borne diseases.
19. What are biofertilizers and
biopesticides? Differentiate.
|
Biofertilizers |
Biopesticides |
|
Microbes that enhance soil fertility. |
Microbes that control pests/diseases. |
|
Example: Rhizobium, Anabaena |
Example: Bacillus thuringiensis |
20. Explain the role of microbes in
household products.
Answer:
1.
Lactobacillus – curd, cheese, yogurt.
2.
Saccharomyces
cerevisiae – bread,
beer, wine.
3.
Aspergillus
oryzae – soy
sauce, vinegar.
21. What is the function of yeast in
baking?
Answer:
- Saccharomyces cerevisiae ferments sugars to produce CO₂
and ethanol.
- CO₂ causes dough to rise,
making bread soft and spongy.
22. Name the microorganisms used in
the following industrial products:
(a) Alcohol
(b) Citric acid
(c) Penicillin
Answer:
(a) Saccharomyces cerevisiae
(b) Aspergillus niger
(c) Penicillium notatum
23. Write short notes on microbial
enzymes.
Answer:
Microbes secrete enzymes used in industries:
- Lipases – detergents.
- Pectinases – fruit juice clarification.
- Amylases – starch breakdown in textiles
and foods.
24. What is the role of microbes in
retting of jute?
Answer:
- Anaerobic bacteria like Clostridium
species help in retting.
- They decompose pectins binding
fibers to stem → fibers separate easily.
25. Define antibiotics. How are they
produced?
Answer:
- Antibiotics are chemical
substances that destroy/inhibit other microbes.
- Produced by fungi and bacteria
under controlled fermentation.
- Example: Penicillin from
Penicillium notatum.
26. Explain briefly the discovery of
Penicillin.
Answer:
- Discovered by Alexander Fleming
(1928) from Penicillium notatum.
- Later, Chain and Florey
purified it for large-scale production.
- It was the first true
antibiotic.
27. What is the difference between
primary and secondary sewage treatment?
|
Primary |
Secondary |
|
Physical process |
Biological process |
|
Removes large solids |
Uses microbes to digest organic matter |
|
Sedimentation tanks |
Aeration tanks with microbes |
28. Describe the process of
secondary sewage treatment.
Answer:
- Aeration tank: Air pumped to
promote growth of aerobic microbes.
- Microbes consume organic matter
forming activated sludge.
- Sludge settled and part reused
as inoculum.
- Clear effluent released into
rivers.
29. Why is it dangerous to release
untreated sewage into water bodies?
Answer:
- Untreated sewage contains
organic matter and pathogens.
- Causes oxygen depletion → kills
aquatic life.
- Leads to eutrophication and
spread of water-borne diseases.
30. What are activated sludge and
its use?
Answer:
- Thick microbial mass formed during
secondary sewage treatment.
- Part reused as inoculum; rest
digested anaerobically to produce biogas.
31. What is the role of microbes in
biogas production?
Answer:
- Anaerobic bacteria
(methanogens) digest organic matter → methane.
- Converts waste into fuel and
manure.
- Useful for rural energy
generation.
32. Why is biogas called ‘gobar
gas’?
Answer:
Because it is produced from cow dung (gobar) mixed with water in biogas plants
using methanogenic microbes.
33. List any three advantages of
biogas plants.
Answer:
1.
Provides
clean and renewable energy.
2.
Produces
nutrient-rich manure.
3.
Reduces
pollution and waste accumulation.
34. What are cyanobacteria and their
agricultural importance?
Answer:
- Blue-green algae (e.g., Anabaena,
Nostoc).
- Fix atmospheric nitrogen in
rice fields.
- Increase soil fertility
naturally.
35. What is the use of Anabaena
in Azolla association?
Answer:
- Anabaena lives symbiotically in water
fern Azolla.
- Fixes nitrogen in paddy fields,
enriching soil and reducing fertilizer need.
36. Name the organisms used in
organic farming.
Answer:
- Rhizobium, Azospirillum, Azotobacter,
Anabaena, Trichoderma, Bacillus thuringiensis.
37. Why is organic farming
beneficial?
Answer:
- Uses natural biofertilizers and
biopesticides.
- Improves soil fertility,
prevents pollution.
- Environmentally safe and
sustainable.
38. How do microbes help in
composting?
Answer:
- Bacteria and fungi decompose
organic waste into humus-rich compost.
- Converts biodegradable waste
into manure, improving soil quality.
39. Name any three diseases caused
by bacteria which are controlled by antibiotics.
Answer:
1.
Tuberculosis
– Mycobacterium tuberculosis
2.
Typhoid
– Salmonella typhi
3.
Cholera
– Vibrio cholerae
Controlled by antibiotics like tetracycline, penicillin.
40. What are probiotics? Give
examples.
Answer:
- Probiotics are beneficial
microbes consumed in food.
- Improve gut health and
immunity.
- Example: Lactobacillus
acidophilus in curd, yogurt.
41. Why are antibiotics ineffective
against viral infections?
Answer:
Because viruses lack cell walls and metabolic machinery.
Antibiotics target bacterial cell functions, not viruses.
42. What is the function of Streptococcus
in dairy industry?
Answer:
- Used in production of curd,
butter, and cheese.
- Converts lactose → lactic acid
→ curdling of milk.
43. Define the term “bio-control.”
Answer:
Biological control is the use of natural organisms (predators, parasites,
pathogens) to control harmful pests and diseases.
44. How are microbes used in vinegar
production?
Answer:
- Acetobacter aceti oxidizes ethanol → acetic
acid.
- Used in vinegar and acetic acid
industries.
45. Name microbes used in beverage
industries.
Answer:
- Saccharomyces cerevisiae – beer, wine, whiskey.
- Ferments sugar into alcohol and
CO₂.
46. Explain the role of microbes in
antibiotic resistance.
Answer:
- Overuse/misuse of antibiotics
causes bacteria to evolve resistance genes.
- Resistant strains survive and
multiply (e.g., MRSA).
47. Mention three useful
applications of fungi.
Answer:
1.
Penicillium → antibiotic.
2.
Aspergillus
niger → citric
acid.
3.
Trichoderma → bio-control agent.
48. Differentiate between
biofertilizer and chemical fertilizer.
|
Biofertilizer |
Chemical Fertilizer |
|
Contains living microbes |
Contains inorganic salts |
|
Eco-friendly |
Causes pollution |
|
Long-term soil fertility |
Depletes soil quality |
49. Give examples of microbes used
in organic agriculture.
Answer:
- Rhizobium, Azospirillum, Anabaena,
Trichoderma, Bacillus thuringiensis.
50. What are single-cell proteins
(SCP)? Give examples.
Answer:
- SCP are microbial cells used as
protein-rich food.
- Example: Spirulina, Methylophilus
methylotrophus.
- Rich in proteins, vitamins, and
minerals.
