NCERT Exemplar Microbes in Human Welfare - Biology Class 12 - NEET PDF

MULTIPLE CHOICE QUESTIONS

Q.1. The vitamin whose content increases following the conversion of milk into curd by lactic acid bacteria is:
(a) Vitamin C
(b) Vitamin D
(c) Vitamin B₁₂
(d) Vitamin E
Ans. (c)
Solution. The content of vitamin B₁₂ increases when milk is converted into curd by lactic acid bacteria (LAB). LAB synthesise certain B-group vitamins during fermentation, increasing the nutritive value of curd.

Q.2. Wastewater treatment generates a large quantity of sludge, which can be treated by:
(a) Anaerobic digesters
(b) Floc
(c) Chemicals
(d) Oxidation pond
Ans. (a)
Solution. The sludge produced from wastewater treatment is commonly treated in anaerobic sludge digesters, where anaerobic microbes decompose organic matter producing biogas.

Q.3. Methanogenic bacteria are not found in:
(a) Rumen of cattle
(b) Gobar gas plant
(c) Bottom of water-logged paddy fields
(d) Activated sludge
Ans. (d)
Solution. Methanogenic bacteria (methanogens) are obligate anaerobes found in anaerobic habitats such as the rumen of cattle, gobar gas plants and water-logged paddy fields. They are not typical inhabitants of activated sludge that is aerated (option d).

Q.4. Match the following list of bacteria and their commercially important products:

Choose the correct match:
(a) A-ii, B-iii, C-iv, D-i
(b) A-ii, B-iv, C-iii, D-i
(c) A-iv, B-iii, C-ii, D-i
(d) A-iv, B-i, C-iii, D-ii
Ans. (c)
Solution.

Q.5. Match the following list of bioactive substances and their roles:

Choose the correct match:
(a) A-ii, B-iii, C-i, D-iv
(b) A-iv, B-ii, C-i, D-iii
(c) A-iv, B-i, C-ii, D-iii
(d) A-iii, B-iv, C-ii, D-i
Ans. (d)
Solution.

Q.6. The primary treatment of waste water involves the removal of:
(a) Dissolved impurities
(b) Stable particles
(c) Toxic substances
(d) Harmful bacteria.
Ans. (b)
Solution. Primary treatment is mainly physical and focuses on removal of suspended and settleable particles from sewage. The common steps are:

• Removal of floating debris by screens and grit chambers (sequential filtration).
• Removal of heavier grit (soil, pebbles) and settleable solids by sedimentation.

Q.7. BOD of waste water is estimated by measuring the amount of:
(a) Total organic matter
(b) Biodegradable organic matter
(c) Oxygen evolution
(d) Oxygen consumption
Ans. (d)
Solution. BOD (Biochemical Oxygen Demand) is estimated by measuring the oxygen consumption by microorganisms as they oxidise organic matter in a water sample.

Q.8. Which one of the following alcoholic drinks is produced without distillation?
(a) Wine
(b) Whisky
(c) Rum
(d) Brandy
Ans. (a)
Solution. Wine and beer are produced by fermentation only and are not distilled. Whisky, rum and brandy are distilled spirits produced by distillation following fermentation.

Q.9. The technology of biogas production from cow dung was developed in India largely due to the efforts of:
(a) Gas Authority of India
(b) Oil and Natural Gas Commission
(c) Indian Agricultural Research Institute and Khadi & Village Industries Commission
(d) Indian Oil Corporation
Ans. (c)
Solution. Development and promotion of biogas (from cattle dung) in India were largely due to efforts by the Indian Agricultural Research Institute (IARI) and the Khadi & Village Industries Commission (KVIC).

Q.10. The free-living fungus Trichoderma can be used for:
(a) killing insects
(b) biological control of plant diseases
(c) controlling butterfly caterpillars
(d) producing antibiotics
Ans. (b)
Solution. The free-living fungus Trichoderma is used as a biological control agent against many soil-borne plant pathogens by antagonism and competition.

Q.11. What would happen if oxygen availability to activated sludge flocs is reduced?
(a) It will slow down the rate of degradation of organic matter
(b) The center of flocs will become anoxic, which would cause death of bacteria and eventually breakage of flocs.
(c) Flocs would increase in size as anaerobic bacteria would grow around flocs.
(d) Protozoa would grow in large numbers.
Ans. (b)
Solution. If oxygen supply to activated sludge flocs is reduced, the inner parts become anoxic, causing death of aerobic bacteria and eventual disintegration (breakage) of the flocs.

Q.12. Mycorrhiza does not help the host plant in:
(a) Enhancing its phosphorus uptake capacity
(b) Increasing its tolerance to drought
(c) Enhancing its resistance to root pathogens
(d) Increasing its resistance to insects.
Ans. (d)
Solution. Mycorrhiza (symbiotic association of fungal hyphae with plant roots) help plants by improving phosphorus uptake, increasing tolerance to drought and enhancing resistance to some root pathogens. They do not generally increase resistance to insect herbivores (option d).

Q.13. Which one of the following is not a nitrogen-fixing organism?
(a) Anabaena
(b) Nostoc
(c) Azotobacter
(d) Pseudomonas
Ans. (d)
Solution. Anabaena and Nostoc are cyanobacteria capable of nitrogen fixation; Azotobacter is a free-living nitrogen fixer. Pseudomonas species are generally not nitrogen-fixing.

Q.14. Big holes in Swiss cheese are made by a:
(a) A machine
(b) A bacterium that produces methane gas
(c) A bacterium producing a large amount of carbon dioxide
(d) A fungus that releases a lot of gases during its metabolic activities
Ans. (c)
Solution. Large holes (eyes) in Swiss cheese are due to production of large amounts of CO₂ by bacteria such as Propionibacterium shermanii during fermentation.

Q.15. The residue left after methane production from cattle dung is:
(a) Burnt
(b) Burried in land fills
(c) Used as manure
(d)Used in civil construction.
Ans. (c)
Solution.

• Gobar (cattle dung) is rich in organic matter and microbes; it can be used for biogas (methane) generation.
• The residue (digested slurry) remaining after methane production is nutrient-rich and is commonly used as manure.

Q.16. Methanogens do not produce:
(a) Oxygen
(b) Methane
(c) Hydrogen sulfide
(d) Carbon dioxide.
Ans. (a)
Solution.  Methanogens are obligate anaerobes involved in biogas production. They produce methane along with carbon dioxide and hydrogen sulphide but never produce oxygen.

Q.17. Activated sludge should have the ability to settle quickly so that it can:
(a) Be rapidly pumped back from sedimentation tank to aeration tank
(b) Absorb pathogenic bacteria present in waste water while sinking to the bottom of the settling tank
(c) Be discarded and anaerobically digested
(d) Absorb colloidal organic matter
Ans. (a)
Solution. Fast settling of activated sludge allows a portion to be rapidly returned from the sedimentation tank to the aeration tank as inoculum, maintaining effective biological treatment (option a).

Q.18. Match the items in Column 'A' and Column 'B' and choose correct answer.

The correct answer is:
(a) A-ii, B-iv, C-iii, D-i
(b) A-iii, B-iv, C-ii, D-i
(c) A-iv, B-i, C-ii, D-iii
(d) A-iii, B-ii, C-i, D-iv
Ans. (b)
Solution.

VERY SHORT ANSWER TYPE QUESTIONS

Q.1. Why does 'Swiss cheese' have big holes?
Ans. The large holes in Swiss cheese are due to the production of a large amount of CO₂ by the bacterium Propionibacterium shermanii, which forms gas bubbles in the cheese during fermentation.

Q.2. What are fermentors?
Ans. In industry, microbes are grown in very large vessels called fermentors (or bioreactors). Fermentors provide controlled conditions-sterility, aeration, temperature, pH and nutrient supply-for large-scale microbial growth and product formation (e.g., beverages, antibiotics, enzymes).

Q.3. Name a microbe used for statin production. How do statins lower blood cholesterol level?
Ans. Monascus purpureus. Statins produced by microbes such as Monascus purpureus lower blood cholesterol by competitive inhibition of the key enzyme in cholesterol biosynthesis (HMG-CoA reductase), thereby reducing endogenous cholesterol synthesis.

Q.4. Why do we prefer to call secondary waste water treatment as biological treatment?
Ans. Secondary treatment uses living organisms-mainly aerobic bacteria, fungi and protozoa-to degrade organic pollutants in sewage; therefore it is called biological treatment.

Q.5. What for Nucleopolyhydro viruses are being used now a days?
Ans. Nucleopolyhedroviruses (NPVs) are used as biocontrol agents against insect pests. They are specific insect pathogens employed in integrated pest management.

Q.6. How has the discovery of antibiotics helped mankind in the field of medicine?
Ans. The discovery of antibiotics made bacterial infections controllable and treatable, greatly reducing mortality and morbidity from infectious diseases.

Q.7. Why is distillation required for producing certain alcoholic drinks?
Ans. Distillation is used to concentrate alcohol (ethanol) produced by fermentation, increasing alcohol content to produce spirits such as whisky, rum and brandy.

Q.8. Write the most important characteristic that Aspergillus niger, Clostridium butylicum, and Lactobacillus share.
Ans. They are all acid producers: Aspergillus niger produces citric acid, Clostridium butylicum produces butyric acid, and Lactobacillus produces lactic acid.

Q.9. What would happen if our intestine harbours microbial flora exactly similar to that found in the rumen of cattle?
Ans. If human intestines harboured rumen-type microbes, we would be able to digest cellulose from plant cell walls, since rumen flora specialise in cellulolytic fermentation.

Q.10. Give any two microbes that are useful in biotechnology.
Ans. Escherichia coli and Saccharomyces cerevisiae.

Q.11. What is the source organism for ECORI, restriction endonuclease?
Ans. Escherichia coli RY 13.

Q.12. Name any genetically modified crop.
Ans.  Bt cotton.

Q.13. Why are blue green algae not popular as biofertilisers?
Ans. Blue-green algae (cyanobacteria) such as Anabaena and Nostoc are actually useful biofertilisers. They fix atmospheric nitrogen and enrich soil fertility, especially in paddy fields.

Q.14. Which species of Penicillium produces Roquefort cheese?
Ans. Penicillium roqueforti.

Q.15. Name the states involved in Ganga action plan.
Ans. Uttarakhand, Uttar Pradesh, Bihar and West Bengal

Q.16. Name any two industrially important enzymes.
Ans. Lipase, Amylase.

Q.17. Name an immune immunosuppressive  agent?
Ans. Cyclosporin A.

Q.18. Give an example of a rod shaped virus.
Ans. Tobacco mosaic virus (TMV).

Q.19. What is the group of bacteria found in both the rumen of cattle and sludge of sewage treatment?
Ans. Methanogens.

Q.20. Name a microbe used for the production of Swiss cheese.
Ans. Propionibacterium shermanii.

SHORT ANSWER TYPE QUESTIONS

Q.1. Why are flocs important in biological treatment of waste water?
Ans. In secondary (biological) treatment, the primary effluent is aerated in large tanks so that aerobic microbes grow vigorously and form flocs-masses of bacteria and fungal filaments forming a mesh. These flocs:

• Consume most of the organic matter in the effluent, reducing BOD.
• Aggregate and later settle as activated sludge in sedimentation tanks, allowing separation of biomass from treated water.

Q.2. How has the bacterium Bacillus thuringiensis helped us in controlling caterpillars of insect pests?
Ans. Bacillus thuringiensis (Bt) produces crystalline protein endotoxins that, when ingested by insect larvae, are activated in the gut and disrupt the gut lining, killing the larvae. Bt toxins are widely used as bioinsecticides and in Bt-transgenic crops.

Q.3. How do mycorrhizal fungi help the plants harbouring them?
Ans. Mycorrhizae increase the effective root surface area via fungal hyphae, enhancing absorption of phosphorus and other nutrients, improving drought tolerance, and often increasing resistance to certain root pathogens.

Q.4. Why are cyanobacteria considered useful in paddy fields?
Ans. Cyanobacteria (blue-green algae) are autotrophic and some species fix atmospheric nitrogen (e.g., Anabaena, Nostoc, Oscillatoria). In paddy fields they act as biofertilisers, adding nitrogen and organic matter to the soil and improving fertility.

Q.5. How was penicillin discovered?
Ans. Penicillin was discovered accidentally by Sir Alexander Fleming, who observed that a mould (Penicillium) growing on an unwashed Staphylococcus culture plate inhibited the bacteria. The antibacterial compound, penicillin, was later isolated from this mould.

Q.6. Name the scientists who were credited for showing the role of Penicillin as an antibiotic?
Ans. The therapeutic potential of penicillin was established by Ernst Chain and Howard Florey. Fleming, Chain and Florey were awarded the Nobel Prize in Physiology or Medicine, 1945, for the discovery and development of penicillin. Penicillin was extensively used to treat infected soldiers in World War II.

Q.7. How do bioactive molecules of fungal origin help in restoring good health of humans?
Ans. Examples include:

• Cyclosporin A (from fungi such as Trichoderma polysporum): an immunosuppressive agent used to prevent graft rejection in organ transplants.
• Statins (some produced by Monascus purpureus): lower blood cholesterol by inhibiting cholesterol-synthesising enzymes.

Q.8. What roles do enzymes play in detergents that we use for washing clothes? Are these enzymes produced from some unique microorganisms?
Ans. Enzymes such as lipases and proteases are added to detergent formulations to break down oily stains and proteinaceous dirt. Many of these enzymes are produced by microbes; for example, lipases are produced by fungi such as Candida lipolytica and by various bacterial strains.

Q.9. What is the chemical nature of biogas. Name an organism which is involved in biogas production?
Ans. Biogas is a mixture of mainly methane (CH4), carbon dioxide (CO2) and traces of hydrogen and hydrogen sulfide. Methanogenic archaea such as Methanobacterium species are involved in methane production during anaerobic digestion.

Q.10. How do microbes reduce the environmental degradation caused by chemicals?
Ans. Certain microbes (sometimes called bioremediators) can degrade toxic compounds. For example, Pseudomonas strains with plasmid-encoded pathways (sometimes referred to colloquially as a "Chakravarthy Bug") can metabolise hydrocarbons and help clean oil spills by biodegradation.

Q.11. What is a broad spectrum antibiotic? Name one such antibiotic.
Ans. A broad-spectrum antibiotic inhibits the growth of both Gram-positive and Gram-negative bacteria. An example is tetracycline (or others such as chloramphenicol).

Q.12. What are viruses parasitising bacteria called? Draw a well labelled diagram of the same.
Ans. Viruses that parasitise bacteria are called bacteriophages.

Q.13. Which bacterium has been used as a clot buster? What is its mode of action.
Ans. Streptokinase, produced by Streptococcus (and now often produced recombinantly), is used as a clot buster. It activates plasminogen to plasmin, an enzyme that digests fibrin clots, helping to remove blood clots after myocardial infarction.

Q.14. What are biofertilisers? Give two examples.
Ans. Biofertilisers are preparations containing living microorganisms that enhance the nutrient status of the soil by fixing atmospheric nitrogen, solubilising phosphorus, or decomposing organic matter. Examples include Azotobacter (free-living nitrogen fixer) and cyanobacteria such as Anabaena (symbiotic nitrogen fixer in paddy fields).

LONG ANSWER QUESTIONS

Q.1. Why is aerobic degradation more important than anaerobic degradation for the treatment of large volumes of waste waters rich in organic matter. Discuss.
Ans. The secondary (biological) treatment of wastewater usually employs aerobic degradation for the following reasons:

• Aerobic microbes oxidise organic pollutants rapidly and efficiently, significantly reducing the BOD of sewage. BOD is the amount of oxygen that would be consumed if all organic matter in one litre of water were oxidised biologically; high BOD indicates greater polluting potential.
• In aeration tanks, continuous mechanical agitation and aeration support vigorous growth of aerobic bacteria and fungi, which form flocs that consume organic matter.
• After aerobic degradation, the effluent passes to settling tanks where the flocs settle as activated sludge. A portion of this sludge is returned to aeration tanks to maintain active biomass; the excess sludge is sent to anaerobic digesters.
• Aerobic treatment is generally faster and reduces odour and the concentration of soluble organic compounds more effectively than anaerobic treatment for large volumes of municipal wastewater.

In subsequent anaerobic sludge digestion of excess activated sludge, anaerobic microbes break down biomass and produce combustible gases (methane, CO₂, H₂S), which can be recovered as biogas.

Q.2. (a) Discuss about the major programs that the Ministry of Environment and Forests, Government of India, has initiated for saving major Indian rivers from pollution.
(b) Ganga has recently been declared the national river. Discuss the implication with respect to pollution of this river.
Ans. 

(a) To reduce river pollution from untreated sewage and industrial effluents, the Ministry of Environment and Forests initiated programmes such as the Ganga Action Plan and the Yamuna Action Plan. These programmes aim to construct and upgrade sewage treatment plants, control industrial discharges and implement solid-waste management so that only treated sewage is discharged into rivers.

(b) The Ganga is a river of immense geographical, cultural and economic importance, supplying water to a large portion of the population. Numerous initiatives have been attempted to clean the river; however, many efforts did not achieve expected outcomes. After 2014, the Government launched the Namami Gange project to intensify cleaning efforts and river conservation. Significant funds have been allocated and spent (for example, several thousand crores up to 2016) to build sewage treatment infrastructure, promote riverfront development and engage in pollution control. Declaring the Ganga as a national river emphasises its priority in conservation policies and mobilises administrative action and funding to control pollution and restore its ecological health.

Q.3. Draw a diagrammatic sketch of biogas plant, and label its various components given below: Gas Holder, Sludge Chamber, Digester, Dung+water chamber.
Ans.

Q.4. Describe the main ideas behind the biological control of pests and diseases.
Ans. Biological control (biocontrol) is the use of living organisms to reduce the population of pests or pathogens. Key ideas are:

• Use of antagonistic microbes (e.g., Trichoderma) to suppress soil-borne pathogens through competition, antibiosis and parasitism.
• Use of natural predators or parasitoids (e.g., ladybirds preying on aphids) to control pest populations.
• Deployment of microbial insecticides (e.g., Bacillus thuringiensis, nucleopolyhedroviruses) that are specific to target pests and safe for non-targets and environment.
• Biocontrol is an eco-friendly alternative to chemical pesticides and fits well in integrated pest management (IPM) systems.

Q.5. (a) What would happen if a large volume of untreated sewage is discharged into a river?
(b) In what way anaerobic sludge digestion is important in sewage treatments?
Ans.

(a) Discharging large volumes of untreated sewage into a river increases organic load and BOD, depletes dissolved oxygen, harms aquatic life, causes eutrophication and increases incidence of water-borne diseases among human populations dependent on the river.

(b) Excess activated sludge from secondary treatment is pumped into anaerobic sludge digesters, where anaerobic bacteria decompose organic matter in the sludge. This process stabilises the sludge, reduces pathogen load, and produces biogas (methane, CO₂, H₂S) that can be harnessed as an energy source. The digested residue is often used as manure.

Q.6. Which type of food would have lactic acid bacteria. Discuss their useful application.
Ans.  Curd (yoghurt) contains lactic acid bacteria (LAB). LAB ferment lactose in milk to produce lactic acid which:

• Coagulates and partially digests milk proteins, improving digestibility.
• Acts as a preservative by lowering pH and inhibiting pathogens.
• Enhances nutritional quality (e.g., increases some B-vitamin content such as vitamin B₁₂).
• Contributes beneficial microbes to the gut, helping to check disease-causing organisms.