CBSE Class 12 Biology Microbes in Human Welfare Assignment Set 02

Question: Microorganisms or microbes are found in
a) soil, air, water and inside the bodies of living organisms
b) thermal vents deep in soil
c) under snow and in highly acidic environments
d) All of the above

Answer: d

Question: The microscopic proteinaceous infectious agents are
a) viroids
b) prions
c) protozoans
d) bacteria

Answer: b

Question: The alcoholic beverages produced by the distillation of the fermented broth are
a) wine and beer
b) wine, whisky and brandy
c) whisky, brandy and rum
d) whisky, beer and brandy

Answer: c

Question: The starter or inoculum is added to the fresh milk in order to convert milk into curd and improves its nutritional quality by increasing
a) vitamin-B₁₂
b) protein
c) calcium
d) All of these

Answer: a

Question: Swiss cheese is formed by the bacterium
a) Aspergillus niger
b) Lactobacillus
c) Propionibacterium shemanii
d) Penicillium roqueforti

Answer: c

Question: Which of the following organisms is used in the production of beverages like wine, beer, whisky brandy or rum?
a) Clostridium butylicum
b) Aspergillus niger
c) Saccharomyces cerevisiae
d) Penicillium notatum

Answer: c

Question: Which gas is released during the process of fermentation that gives the puffy appearance to dough for making bread?
a) CO₂
b) CO
c) O₂
d) H₂

Answer: a

Question: Which one of the following antibiotics was extensively used to treat American soldiers wounded in World War-II?
a) Streptokinase
b) Penicillin
c) Statins
d) Neomycin

Answer: b

Question: Which one of these microbes is used in the commercial production of butyric acid?
a) Clostridium butylicum
b) Streptococcus butylicum
c) Trichoderma polysporum
d) Saccharomyces cerevisiae

Answer: a

Question: Which of the following bacteria convert milk into curd?
a) Propionibacterium shermanii
b) Saccharomyces cerevisiae
c) Lactobacillus
d) Thermophilic bacteria

Answer: c

Question: Choose the incorrect pair.
a) Lipases – Used in detergents for removing oil stains
b) Pectinases and proteases – Used in clarifying bottled juices
c) Statins – Competitively inhibit the enzyme responsible for cholesterol synthesis
d) None of the above

Answer: d

Question: Sewage contains large amounts of …A… and …B… . Here A and B refer to
a) A–inorganic matter, B–bacteria
b) A–organic matter, B–pathogenic microbes
c) A–organic matter, B–virus
d) A–inorganic matter, B–pathogenic microbes

Answer: b

Question: In the primary treatment of sewage, the soil and small pebbles are removed by
a) filtration
b) sedimentation
c) condensation
d) evaporation

Answer: b

Question: In the biological treatment of sewage, the masses of bacteria held together by fungal filament to form mesh-like structures called as
a) activated sludge
b) aerobic process
c) flocs
d) anaerobic sludge

Answer: c

Question: Antibiotics are used to treat diseases like
a) diphtheria, whooping cough
b) plague
c) leprosy
d) All of the above

Answer: d

Question: In the sewage treatment, bacterial flocs are allowed to sediment in a settling tank. This sediment is called as
a) activated sludge
b) primary sludge
c) anaerobic sludge
d) secondary sludge

Answer: a

Question: Which of the following is used as ‘clot buster’ for removing clots from blood vessels of patient who have undergone
myocardial infarction?
a) Ethanol
b) Statins
c) Cyclosporin-A
d) Streptokinase

Answer: d

Question: Microbes are used in
I. primary treatment of sewage.
II. secondary treatment of sewage.
III. anaerobic sludge digesters.
IV. production of biogas.
Choose the correct option.
a) I, II and III
b) I, III and IV
c) II, III and IV
d) All of the above

Answer: c

Question: Which of the following plans has been initiated by the Ministry of Environment and Forests to protect rivers from water pollution?
a) Ganga action plan
b) Yamuna action plan
c) Both (a) and (b)
d) None of the above

Answer: c

Question: Organic farming includes
a) use of fertilisers and pesticides of biological origin
b) IPM (Integrated Pest Management)
c) locally developed pest resistant varieties
d) All of the above

Answer: d

Question: Which of the following bacteria is present in the rumen of cattle?
a) Rhizobium
b) Azotobacter
c) Methanobacterium
d) Clostridium

Answer: c

Question: Gobar gas generation technology in India was developed by the collaboration of ...A... and ...B... . Here, A and B refer to
a) A–Rural Bank of India, B–Khadi and Village Industries Commission
b) A–Indian Agricultural Research Institute, B–Khadi and Village Industries Commission
c) A–National Bank for Agriculture and Development, B–Indian Agricultural Research Institute
d) A–National Bank for Agriculture and Development,

Answer: b

Question: B–Khadi and Village Industries Commission 24. Bacillus thuringiensis is used as
a) biofungicide
b) biopesticide
c) biocontrol agent
d) bioweapon

Answer: c

Question: Cultivation of Bt cotton has been much in the news. The prefix Bt means
a) ‘Barium-treated’ cotton seeds
b) ‘Bigger thread’ variety of cotton with better tensile strength
c) produced by ‘biotechnology’ using restriction enzymes and ligases
d) carrying an endotoxin gene from Bacillus thuringiensis

Answer: d

Question: Trichoderma species, free-living fungi, are present in root ecosystems are potentially useful as
a) biopesticides
b) biofertilisers
c) methanogens
d) vectors for genetic engineering

Answer: a

Question: The BOD test measures the rate of uptake of oxygen by microbes in water bodies. The greater BOD of sample water,indicates that
a) it is highly polluted
b) it is not polluted
c) it is moderately polluted
d) pollution level cannot be determined

Answer: a

Question: Baculoviruses (Nucleopolyhedrovirus) do not show
a) host specificity
b) narrow spectrum applications
c) effects on non-target insects
d) utility in IPM programme

Answer: c

Question: A biocontrol agent to be a part of an integrated pest management should be
a) species-specific and symbiotic
b) free-living and broad spectrum
c) narrow spectrum and symbiotic
d) species-specific and inactive on non-target organisms

Answer: d

Question: Which of the following are the part or example of symbiotic mutualistic association?
a) Rhizobium
b) Mycorrhiza
c) Both (a) and (b)
d) Oscillatoria

Answer: c

Question: Which of the following bacteria convert milk into curd?
a) Propionibacterium shermanii
b) Saccharomyces cerevisiae
c) Lactobacillus
d) Thermophilic bacteria

Answer: c

Question: The most flammable gaseous component of biogas is
a) methane, CO₂, H₂ and H₂S
b) methane
c) CO₂, H₂ and H₂S
d) CO, methane and N₂

Answer: b

Question: Which of the following is common to Azospirillum, Anabaena, Nostoc and Oscillatoria?
a) N2-fixer microbes
b) Prokaryotic organism
c) Both (a) and (b)
d) Eukaryotic organism

Answer: c

Question: Select the group of organisms that are used as biofertilisers in organic farming.
a) Clostridium, Beijerinckia, Glomus and Anabaena
b) Trichoderma, Baculovirus and B. thuringiensis
c) Nostoc, Azolla pinnata and Tobacco mosaic virus
d) Penicillium, Streptococcus and Aspergillus

Answer: a

Ques. Conversion of milk to curd improves its nutritional value by increasing the amount of
(a) vitamin D
(b) vitamin A
(c) vitamin B12
(d) vitamin E.

Answer: C

Ques. Dough kept overnight in warm weather becomes soft and spongy because of
(a) absorption of carbon dioxide from atmosphere
(b) fermentation
(c) cohesion
(d) osmosis.

Answer: B

Ques. During the formation of bread it becomes porous due to release of CO2 by the action of
(a) yeast
(b) bacteria
(c) virus
(d) protozoans.

Answer: A

Ques. In cheese manufacture, the microorganisms are important for
(a) the ripening only
(b) the souring of milk only
(c) the development of resistance to spoilage only
(d) both the souring and the ripening processes.

Answer: D

Ques. Match the following columns and select the correct option.
       Column-I                                         Column-II
(A) Clostridium butylicum                (i) Cyclosporin-A
(B) Trichoderma polysporum           (ii) Butyric acid
(C) Monascus purpureus                 (iii) Citric acid
(D) Aspergillus niger                     (iv) Blood cholesterol lowering agent
     (A) (B) (C) (D)
(a) (iii) (iv) (ii) (i)
(b) (ii) (i) (iv) (iii)
(c) (i) (ii) (iv) (iii)
(d) (iv) (iii) (ii) (i) 

Answer: B

Ques. Which of the following is a commercial blood cholesterol lowering agent?
(a) Lipases
(b) Cyclosporin A
(c) Statin
(d) Streptokinase

Answer: C

Ques. Match the following organisms with the products they produce.
(A) Lactobacillus (i) Cheese
(B) Saccharomyces (ii) Curd cerevisiae
(C) Aspergillus niger (iii) Citric acid
(D) Acetobacter aceti (iv) Bread
(v) Acetic acid
Select the correct option.
     (A) (B) (C) (D)
(a) (ii)  (i)  (iii)  (v)
(b) (ii) (iv) (v)  (iii)
(c) (ii) (iv) (iii)  (v)
(d) (iii) (iv) (v)  (i) 

Answer: C

Ques. Which of the following is correctly matched for the product produced by them?
(a) Methanobacterium : Lactic acid
(b) Penicillium notatum : Acetic acid
(c) Sacchromyces cerevisiae : Ethanol
(d) Acetobacter aceti : Antibiotics 

Answer: C

Ques. Match column I with column II and select the correct option using the codes given below.
     Column I                   Column II
A. Citric acid               (i) Trichoderma
B. Cyclosporin A         (ii) Clostridium
C. Statins                  (iii) Aspergillus
D. Butyric acid           (iv) Monascus
(a) A-(iii), B-(i), C-(ii), D-(iv)
(b) A-(iii), B-(i), C-(iv), D-(ii)
(c) A-(i), B-(iv), C-(ii), D-(iii)
(d) A-(iii), B-(iv), C-(i), D-(ii) 

Answer: B

Ques. Which of the following is wrongly matched in the given table?
    Microbe                                   Product                          Application
(a) Streptococcus                     Streptokinase          Removal of clot from blood vessel
(b) Clostridium butylicum          Lipase                     Removal of oil stains
(c) Trichoderma polysporum      Cyclosporin A           Immunosuppressive drug
(d) Monascus purpureus            Statins                   Lowering of blood cholesterol

Answer: B

Ques. Match the following list of microbes and their importance.
      Column I                                               Column II
A. Saccharomyces cerevisiae            (i) Production of immuno- suppressive agent
B. Monascus purpureus                    (ii) Ripening of Swiss cheese
C. Trichoderma polysporum              (iii) Commercial production of ethanol
D. Propionibacterium shermanii         (iv) Production of blood-cholesterol lowering agents
(a) A-(iv), B-(ii), C-(i), D-(iii)
(b) A-(iii), B-(i), C-(iv), D-(ii)
(c) A-(iii), B-(iv), C-(i), D-(ii)
(d) A-(iv), B-(iii), C-(ii),D-(i)  

Answer: C

Ques. A good producer of citric acid is
(a) Clostridium
(b) Saccharomyces
(c) Aspergillus
(d) Pseudomonas.

Answer: C

Ques. Monascus purpureus is a yeast used commercially in the production of
(a) ethanol
(b) streptokinase for removing clots from the blood vessels
(c) citric acid
(d) blood cholesterol lowering statins. 

Answer: D

Ques. A patient brought to a hospital with myocardial infarction is normally immediately given
(a) penicillin
(b) streptokinase
(c) cyclosporin-A
(d) statins. 

Answer: B

Ques. Read the following four statements (A-D).
(A) Colostrum is recommended for the new born because it is rich in antigens.
(B) Chikungunya is caused by a Gram negative bacterium.
(C) Tissue culture has proved useful in obtaining virus-free plants.
(D) Beer is manufactured by distillation of fermented grape juice.
How many of the above statements are wrong?
(a) Two (b) Three
(c) Four (d) One

Answer: B

Ques. The most common substrate used in distilleries for the production of ethanol is
(a) corn meal
(b) soya meal
(c) ground gram
(d) molasses. 

Answer: D

Ques. Ethanol is commercially produced through a particular species of
(a) Saccharomyces
(b) Clostridium
(c) Trichoderma
(d) Aspergillus. 

Answer: A

Ques. Continuous addition of sugars in ‘fed batch’ fermentation is done to
(a) produce methane
(b) obtain antibiotics
(c) purify enzymes
(d) degrade sewage.

Answer: C

Ques. Read the following statement having two blanks (A and B).
A drug used for A patients is obtained from a species of the organism B . The one correct option for the two blanks is
         A                                    B
(a) heart                          Penicillium
(b) organ-transplant         Trichoderma
(c) swine flu                     Monascus
(d) AIDS                        Pseudomonas.

Answer: B

Ques. Which one of the following is a wrong matching of a microbe and its industrial product, while the remaining three are correct?
(a) Yeast – Statins
(b) Acetobacter aceti – Acetic acid
(c) Clostridium butylicum – Lactic acid
(d) Aspergillus niger – Citric acid 

Answer: C

Ques. Which one of the following pairs is wrongly matched?
(a) Alcohol - Nitrogenase
(b) Fruit juice - Pectinase
(c) Textile - Amylase
(d) Detergents - Lipase 

Answer: A

Case-based MCQs

I. Read the following text and answer any four questions on the basis of the same :
Ecological Indicators :
The presence of dragonflies can reveal changes in the water ecosystems more quickly than studying other animals or plants. In fact, from the nymph to the adult stage, the dragonfly has a significant, positive ecological impact. Dragonfly eggs are laid and hatched in or near water, so their lives show impact both on water and land ecosystems. Once hatched, dragonfly nymphs can breathe in the air or underwater which enables them to eat mosquito
larvae, other aquatic insects and worms, and even small aquatic vertebrates like tadpoles and small fish. Adult dragonflies capture and eat adult mosquitoes. Community wide mosquito control programs that spray insecticides to kill adult mosquitoes also kill dragonflies.

Question. The approach to biological control includes :
(A) Import and release of an insect pest to a new area to provide hosts for natural enemies.
(B) Import and release of natural enemies from the native home of an alien insect pest that has invaded a new area.
(C) Preservation of natural enemies (predators & parasites) that are already established in an area.
(D) Use of insecticides to reduce alien insect pests to establish new equilibrium position.
Answer : C

Question. Assertion (A) : Releasing dragonflies in areas where there is an outbreak of malarial diseases can be an environment friendly method of
control.
Reason (R) : Dragonflies are dominant species and will not allow mosquitoes to reproduce.
(A) Both assertion and reason are true, and the reason is the correct explanation of the assertion.
(B ) Both assertion and reason are true, but the reason is not the correct explanation of the assertion.
(C) Assertion is true but reason is false.
(D) Assertion is false but reason is true.
Answer : B

Question. Two diseases less likely to occur in a region with plenty of dragonflies are_____
(A) Yellow fever and amoebic dysentery
(B) Malaria and Yellow fever
(C) Anthrax and typhoid
(D) Cholera and typhoid
Answer : B

Question. The most effective stages in the life cycle of dragonfly that eradicates mosquitoes are.
(A) Larvae and adult
(B) Caterpillar and adult
(C) Nymph and adult
(D) Pupa and adult
Answer : C

Question. Dragonflies indicate positive ecological impact as :
(A) The presence of dragonflies indicates polluted water.
(B) Dragonfly nymphs selectively eat mosquito larvae.
(C) They help to decrease the probability of diseases spread by vectors.
(D) Dragonfly do not cause any harm to beneficial species.
Answer : C

Question. Identify a, b, c, d, e and f in the table given below:

Answer : (a) Statins
(b) Blood cholesterol lowering agent
(c) Penicillium notatum
(d) Penicillin
(e) Trichoderma polysporum
(f) Immunosuppressant

Question. State the medicinal value and the bioactive molecules produced by Streptococcus, Monascus and Trichoderma.
Answer :  

Question. (a) Why are the fruit juices bought from market clearer as compared to those made at home?
(b) Name the bioactive molecules produced by Trichoderma polysporum and Monascus purpureus. 
Answer : (a) The fruit juices bought from market are clearer because they have been clarified by pectinases and proteases.
(b) Trichoderma polysporum: Cyclosporin A
Monascus purpureus: Statins

Question. Explain the function of “anaerobic sludge digester” in a sewage treatment plant.
Answer : Anaerobic sludge digester has anaerobic bacteria that digests the aerobic bacteria and fungi present in the sludge. During the digestion these bacteria produce mixture of gases such as methane, H₂S and CO₂ (biogas).

Question. Describe how do ‘flocs’ and ‘activated sludge’ help in sewage treatment. 
Answer : Flocs are masses of aerobic bacteria associated with fungal filaments to form mesh like structures.
These aerobic microbes consume the major part of the organic matter in the effluent. This significantly reduces Biological oxygen demand (BOD) of the effluent.
A small part of the activated sludge is used as inoculum and pumped back to aeration tank. The remaining major part of the sludge is pumped into anaerobic sludge digesters where microbes or bacteria grow anaerobically to produce CH₄ or H2S or CO₂ or biogas.

Question. (i) List the components of biogas.
(ii) What makes methanogens suitable for biogas production? 
Answer : (i) Biogas is a mixture of inflammable gases like methane, carbon dioxide and hydrogen.
(ii) Methanogens grow anaerobically and help in breakdown of cellulosic material to produce large amount of methane, carbon dioxide and hydrogen and so it is suitable for biogas production.

Question. How can sewage be used to generate biogas? Explain. 
Answer : When biochemical oxygen demand (BOD) of sewage is reduced, effluent is passed into a settling tank for bacterial flocs to settle down. The sediment is called activated sludge. Activated sludge is pumped into anaerobic sludge digesters. In the digesters, heterotrophic microbes anaerobically digest bacteria and fungi in the sludge producing a mixture of gases which form the biogas.

Question. Secondary treatment of the sewage is also called Biological treatment. Justify this statement and explain the process. 
Answer : Secondary treatment of sewage involves biological organism such as aerobic and anaerobic microbes or bacteria and fungi to digest or consume organic waste. Therefore, it is also called biological treatment.

Question. (a) How is activated sludge produced during sewage treatment?
(b) Explain how this sludge is used in biogas production.
Answer : (a) Once the BOD of sewage or waste water is reduced significantly, the effluent is passed into a settling tank where the bacterial flocs undergo sedimentation and the sediment is thus called activated sludge.
(b) A small part of the activated sludge is pumped back into the aeration tank to serve as the inoculum. The remaining major part of the activated sludge is pumped into large tanks called anaerobic sludge digesters. The anaerobic bacteria digest the bacteria and fungi in the sludge and produce mixture of gases like methane, hydrogen sulphide and CO2 which constitute biogas.

Question. Cow dung and water is mixed and this slurry is fed into the biogas plant for digestion by microbes. The person performing the process shares that there is no need to provide inoculum for it, why? What is the role of microbes at the source? Under which condition will they be most active and effective? 
Answer : There is no need to provide inoculum for it because the bacteria, methanogens are present in cow dung. The role of these microbes is breakdown of cellulose. These are most active in an anaerobic condition.

Question. Name the genus to which baculoviruses belong. Describe their role in the integrated pest management programmes. 
Answer : Baculovirus belongs to the genus Nucleopolyhedrovirus. Baculoviruses are pathogens that attack insects and other arthopods. These viruses are very useful for species-specific, narrow spectrum insecticidal applications. Also, as they show no negative impacts on plants, mammals, birds, fish or even on non-target insects, they are beneficial in integrated pest management (IPM) programme in which beneficial insects are conserved.

Question. Given below is a list of six microorganisms. State their usefulness to humAnswer :
(a) Nucleopolyhedrovirus   (b) Saccharomyces cerevisiae
(c) Monascus purpureus    (d) Trichoderma polysporum
(e) Penicillium notatum     (f ) Propionibacterium sharmanii
Answer : (a) Nucleopolyhedrovirus: Used as bio-control agents.
(b) Saccharomyces cerevisiae: Used in bread making and in brewing industry.
(c) Monascus purpureus: Cholesterol lowering agent.
(d) Trichoderma polysporum: Produces Cyclosporin-A, used as immunosuppressive agent.
(e) Penicillium notatum: Produces antibiotic penicillin.
(f) Propionibacterium sharmanii: Produces large amount of CO₂ in Swiss cheese.

Question. Choose any three microbes, from the following which are suited for organic farming, which is in great demand these days for various reasons. Mention one application of each one chosen.Mycorrhiza; Monascus; Anabaena; Rhizobium; Methanobacterium; Trichoderma.
Answer :
Mycorrhiza: (Fungal symbiont of the association) Absorbs phosphorus from soil.
Anabaena: Fix atmospheric nitrogen and adds organic matter to the soil.
Rhizobium: Fix atmospheric nitrogen (in leguminous plants).
Methanobacterium: They digest cellulosic material and their product/spent slurry can be used as a fertiliser.
Trichoderma: Biocontrol agent for several plant pathogens. (Any three)

Question. What are the harmful effects of chemical pesticides?
Answer : The harmful effects of chemical pesticides are:
(i) They pollute the soil and water.
(ii) They kill many useful organisms in the soil.
(iii) They enter the food chain and cause disease at various trophic levels (Biological magnification).
(iv) They affect the salinity of the soil.

Question. What are the advantages of using biofertilisers in agriculture?
Answer : Following are the advantages of using biofertilisers in agriculture:
(i) Biofertilisers do not cause any pollution.
(ii) These are cheap and economical.
(iii) Some of them act as biopesticides also.
(iv) In ill-irrigated conditions few biofertilisers can enhance the crop yield.
(v) They improve soil structure and function.
(vi) They make available vitamins and other growth promoting biochemicals.

Question. An organic farmer relies on natural predation for controlling plant pests and diseases. Justify giving reasons why this is considered to be a holistic approach. 
Answer : Besides acting as ‘conduits’ for energy transfer across trophic levels, predators are used in biological control of plant pests. This ability of the predator is based on its regulating the prey population.
The natural predators reduce interspecific competition and does not harm the crop plants. For example, in an area the invasive cactus can be brought under control by cactus-feeding predator (a moth).
Using natural predation, the ecosystem is kept stable without harming any of the trophic levels.

Question. Identify ‘a’, ‘b’, ‘c’, ‘d’, ‘e’ and ‘f’ in the table given below:

Answer : (a) Bioactive molecule used to remove blood clot
(b) Trichoderma polysporum
(c) Immunosuppressant
(d) Statin
(e) Blood cholesterol lowering agent
(f) Lactic acid

Question. Complete the given table.

Answer : (i) Citric acid
(ii) Saccharomyces cerevisiae
(iii) Trichoderma polysporum
(iv) Acetobacter aceti
(v) Statin
(vi) Streptokinase

Question. “Microbes play a dual role when used for sewage treatment as they not only help to retrieve usable water but also generate fuel”. Explain. 
Answer : l Microbes naturally present in the sewage are employed in the secondary treatment of the sewage.
- The effluent from the primary treatment is passed into large aeration tanks.
- This allows the rapid growth of aerobic microbes into flocs which consume the organic matter of the sewage and reduces the BOD.
- Then the effluent is passed into a settling tank, where the flocs are allowed to sediment forming the activated sludge.
- Major parts of this activated sludge is pumped into anaerobic sludge digesters, where the anaerobic bacteria digest microbes in the activated sludge.
- During this digestion bacteria produce a mixture of gases like methane, hydrogen sulphide and carbon dioxide, which form the biogas and can be used as a source of energy. The effluent is generally released into rivers and streams.

Question. Why should biological control of pests and pathogens be preferred to the conventional use of chemical pesticides? Explain how the following microbes act as biocontrol agents:
(a) Bacillus thuringiensis
(b) Nucleopolyhedrovirus
Answer : Biological control of pests and pathogens is preferred because:
(i) The chemicals cause pollution of water bodies as well as ground water, besides getting stored in the plants.
(ii) The chemicals are toxic thus extremely harmful to human beings and other animals.
(a) Bacillus thuringiensis: Bacillus thuringiensis is available in sachets as dried spores, which are mixed with water and sprayed onto vulnerable plants. When they are eaten by
the insect larvae, the toxin is released in the gut where it becomes active and kills the larvae.
B. thuringiensis toxin genes when introduced into plant, develop resistance to attack by insect pests. Specific Bt toxin genes obtained from B. thuringiensis are used in several crop
plants which make them resistant to insect pest.
(b) Nucleopolyhedrovirus: These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications. This is especially desirable when beneficial insects are being conserved to aid in an overall integrated pest management (IPM) programme.

Question. Explain the significant role of the genus Nucleopolyhedrovirus in an ecological sensitive area.
Answer : Baculoviruses are pathogens that attack insects and other arthropods. Baculoviruses of genus Nucleopolyhedrovirus are used as biological control agents. They are excellent candidates for species-specific, narrow spectrum insecticidal applications. They do not show negative impact on plants, mammals, birds, non-target insects. Therefore, they are used as biological control agents. Importance in organic farming: It is desirable when beneficial insects are being conserved to aid in an overall Integrated Pest Management (IPM) programme. In organic farming, it is used to conserve beneficial insects and kills harmful ones.

POINTS TO REMEMBER

Activated Sludge Process : Aerobic sewage treatment process using aerobic micro-organisms present in sewage sludge to break down organic matter in sewage.

Biofertilisers : Microorganisms which produce fertilisers and enrich the soil e.g., Bacteria, cyanobacteria and fungi.

Bioactive Molecules : Molecules produced for commercial use from microbes and used for various purposes e.g., Trichoderma polysporum (fungus) is used to obtain immunosuppressive agent cyclosporin A.

Biochemical Oxygen Demand (BOD) : Total amount of oxygen consumed by bacteria for oxidation of organic matter present in one litre of water.

Baculovirus : Pathogens that attack insects and other arthropods. They are used to kill harmful pests and arthropods e.g., Nucleopolyhedrovirus.

Biocontrol Agents : Use of biological methods for controlling plant diseases and pests

Effluent : The product of primary treatment of sewage which is passed into large aeration tanks for secondary treatment.

Fermentation : The process by which microorganisms turn organic materials such as glucose into products like alcohol.

Fermentors : A very large vessel used in industry where microbes are grown on an industrial scale.

Flocs : During secondary treatment of effluent, excessive growth of aerobic bacteria and fungi form a mass of mesh like structure called flocs.

Immunosuppressive Agent : Chemical substances which suppress the immunity against organ transplant.

Lactic Acid Bacteria (LAB) : Bacteria growing in milk and convert it into curd e.g., Lactobacillus.

Question 1. How does a small amount of curd added to fresh milk convert it into curd? Mention a nutritional quality that get added to the curd.
Answer: A small amount of curd contains millions of lactic acid bacteria (LAB) such as Lactobacillus. When added to fresh milk at a suitable temperature, these bacteria multiply and convert lactose sugar present in the milk into lactic acid. The lactic acid coagulates and partially digests the milk protein (casein), converting milk into curd.
The nutritional quality of milk is improved by the addition of curd as it increases the amount of Vitamin \(\text{B}_{12}\).
In simple words: Bacteria in curd feed on milk sugar to produce lactic acid, turning milk solid and boosting Vitamin \(\text{B}_{12}\).

Exam Tip: Always mention the specific bacterium (Lactobacillus/LAB) and the specific vitamin (\(\text{B}_{12}\)) to secure full marks.

Question 2. Why is secondary treatment of water in sewage treatment plant called biological treatment?
Answer: Secondary treatment of sewage is called biological treatment because it relies heavily on native, heterotrophic aerobic and anaerobic microorganisms (such as bacteria and fungal filaments in flocs) to naturally consume, break down, and digest the organic matter and pollutants present in the waste water.
In simple words: It uses living microbes instead of chemicals to clean the water.

Exam Tip: Contrast primary treatment (physical process involving filtration and sedimentation) with secondary treatment (biological process involving microbes) when asked.

Question 3. An antibiotic called 'Wonder Drug' was used to treat the wounded soldiers of America during World War-II. Name the drug and the scientist who discovered it.
Answer: The wonder drug is Penicillin, and it was discovered by Alexander Fleming.
In simple words: Penicillin was the first major antibiotic discovered by Alexander Fleming and saved countless soldiers.

Exam Tip: Do not confuse Alexander Fleming (discoverer of Penicillin) with Ernst Chain and Howard Florey (who established its full potential as an effective antibiotic).

Question 4. You have observed that fruit juice in bottles bought from the market are clearer as compared to those made at home. Give reason.
Answer: Bottled fruit juices available in the market are clarified by the commercial addition of microbial enzymes, specifically pectinases and proteases, which break down plant cell wall pectins and proteins making the juice clear.
In simple words: Market juices are treated with specific enzymes (pectinases and proteases) to remove cloudiness.

Exam Tip: Memorize both enzyme names (pectinases and proteases) as they are frequently asked in one-mark questions.

Question 5. Alexander Fleming discovered 'Penicillin', but its full potential as an effective antibiotic was established by other scientists. Name the two scientists.
Answer: The two scientists were Ernst Chain and Howard Florey.
In simple words: Ernst Chain and Howard Florey proved how useful Penicillin is as a medicine.

Exam Tip: This is a direct factual question; ensure spellings of Ernst Chain and Howard Florey are correct.

Question 6. Name the plant whose sap is used in making 'Toddy'. Mention the process involved in it.
Answer: The plant whose sap is used is the palm tree (or coconut palm). The process involved is fermentation by natural yeasts.
In simple words: Toddy is made by fermenting palm sap using natural yeast.

Exam Tip: State both the plant source (palm tree) and the biochemical process (fermentation) clearly.

Question 7. Name two alcoholic drinks produced in each of the following ways. (i) by distillation and (ii) without distillation.
Answer:
(i) By distillation: Whisky, Brandy, and Rum (any two).
(ii) Without distillation: Wine and Beer.
In simple words: Drinks like whisky are distilled to increase alcohol content, while beer and wine are fermented without distillation.

Exam Tip: Remember that fermented beverages like wine and beer are produced without distillation because yeast is poisoned at higher alcohol concentrations, whereas distilled drinks have higher alcohol content.

Question 8. Lactic Acid Bacteria (LAB) is commonly used in the conversion of milk into curd. Mention any two other functions of LAB that are useful to humans.
Answer: Two other useful functions of LAB are:
1. They play a beneficial role in our stomach and intestines by checking the growth of harmful disease-causing microbes.
2. They synthesize and increase the nutritional value of food by producing Vitamin \(\text{B}_{12}\).
In simple words: LAB protects our gut from bad germs and adds important vitamins to our food.

Exam Tip: Keep the points distinct: one related to human health/digestion in the gut, and one related to nutrition/vitamins.

Question 9. How do mycorrhizae function as biofertilisers? Explain with example.
Answer: Mycorrhizae are symbiotic associations between fungi and the roots of higher plants (e.g., members of the genus Glomus). As biofertilisers, the fungal symbiont absorbs water and essential minerals like phosphorus from the soil and supplies them to the plant root. In return, the plant provides the fungus with food. Additionally, these associations confer resistance to root-borne pathogens, tolerance to salinity and drought, and overall an increase in plant growth.
In simple words: Fungi in the soil team up with plant roots to absorb water and phosphorus better.

Exam Tip: Always mention the fungal genus Glomus and highlight the absorption of phosphorus to score full marks.

Question 10. Cyanobacteria (Nostoc, Anabaena) are used as biofertilisers in certain crop fields. Name such one crop. Also, mention the names of two other microorganisms which perform the same function.
Answer: Crop: Paddy (Rice crop).
Two other microorganisms performing the same nitrogen-fixing biofertiliser function: Rhizobium and Azotobacter.
In simple words: Rice fields use cyanobacteria to fix nitrogen, just like Rhizobium and Azotobacter do for other crops.

Exam Tip: Cyanobacteria are autotrophic microbes widely used in aquatic-based crop systems like paddy fields.

Question 11. Which Ministry of Govt. of India had initiated Ganga Action Plan and Yamuna Action Plan? What are the objectives of these plans?
Answer: The Ministry of Environment and Forests, Government of India, initiated the Ganga Action Plan and Yamuna Action Plan.
Objectives: The primary objective is to save these major rivers from severe pollution by building a large number of sewage treatment plants (STPs) to ensure that only treated sewage water is discharged into the rivers.
In simple words: The government started these plans to clean major rivers by building sewage treatment plants so dirty water is not dumped directly into them.

Exam Tip: Mention the exact name of the ministry and the key strategy (building sewage treatment plants) to get full credit.

Question 12. Fill in the blanks spaces a, b, c, d, e, and f, given in the following table:
 

Answer:
(a) To kill disease-causing bacteria / Antibiotic
(b) Lactobacillus
(c) Remove clots from blood vessels
(d) Cyclosporin A
(e) Beverage / Medicines
(f) Propionibacterium sharmanii
In simple words: This table links microbes to the useful commercial products and medical applications they provide.

Exam Tip: Questions from this table are standard board exam favourites. Memorize microbe names and their exact products.

Question 13. What is biochemical oxygen demand (BOD) test? At what stage of Sewage treatment this test is performed? 
BOD level of three samples of water labelled as A, B and C are 30 mg/L, 10 mg/L and 500 mg/L respectively. Which sample of water is most polluted?
Answer: Biochemical Oxygen Demand (BOD) refers to the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidized by bacteria. It is a measure of the organic matter present in water.
Stage of test: It is measured to test water pollution levels and assess the efficiency of secondary (biological) treatment in sewage treatment plants.
Most polluted sample: Sample C (500 mg/L) is the most polluted because higher BOD indicates a higher amount of organic waste, requiring more oxygen for decomposition.
In simple words: BOD measures how much oxygen bacteria need to clean waste in water. Higher BOD means dirtier water, so sample C is the most polluted.

Exam Tip: Remember: Higher BOD = Higher organic pollution = Lower dissolved oxygen in water bodies.

Question 14. Given below is the Flow chart of Sewage treatment. Fill in the blank spaces marked 'a' to 'f'. 
[Sewage treatment is done in step, subjected to filtration and sedimentation, called...(a)......] → [Supernatant is shifted to separate tanks and air is pumped mechanically, called...(b)......] → [Microbes grow into masses, called...(c)......] → [There is reduction in...(d)......] → [Bacterial flocs are allowed to settle, the sedimentation is called...(e)......] → [After Secondary treatment, the water is released into...(f)......]
Answer:
(a) Primary treatment
(b) Aeration
(c) Flocs
(d) Biochemical Oxygen Demand (BOD)
(e) Activated sludge
(f) Water bodies like river streams
In simple words: This flow chart tracks sewage from primary cleaning to biological aeration, settling, and release into rivers.

Exam Tip: Trace the chronological steps of wastewater treatment: Primary filtration → Aeration tank → Floc formation → BOD reduction → Activated sludge settling → Discharge into rivers.

Question 15. What are biofertilisers? A farmer is advised to add a culture of bacterium in the soil before sowing the crop. Name the bacterium in the culture. How is this bacterium useful to the crop?
Answer: Biofertilisers are organisms (microbes) that enrich the nutrient quality of the soil.
Name of bacterium: Rhizobium (or Azotobacter / Azospirillum for free-living forms).
Usefulness: These bacteria fix atmospheric nitrogen into organic forms (such as nitrates and ammonia) which are readily used by plants as vital nutrients, reducing the need for chemical fertilizers.
In simple words: Biofertilisers are friendly soil microbes that pull nitrogen from the air and feed it to plants.

Exam Tip: Emphasize atmospheric nitrogen fixation into plant-available nutrients.

Question 16. What are statins? Name the microorganism that produces this substance. How is it medically important?
Answer: Statins are blood-cholesterol-lowering agents.
Microorganism: Yeast named Monascus purpureus.
Medical importance: They act by competitively inhibiting the enzyme responsible for the synthesis of cholesterol, thus lowering blood cholesterol levels and helping prevent heart attacks and cardiovascular disorders in patients.
In simple words: Statins are medicines produced by yeast that block cholesterol production in the body.

Exam Tip: Clearly link the fungus Monascus purpureus with its commercial product (statin) and its precise mechanism (competitive inhibition of cholesterol-synthesizing enzymes).

Question 17. How does primary sludge differ from activated sludge? What type of changes in the sludge are carried out in anaerobic sludge digester? Give the composition of biogas produced in the sewage treatment plant.
Answer:
Difference: Primary sludge consists of all the solid debris, soil, and small pebbles that settle down in the settling tank during primary sewage treatment. In contrast, activated sludge is the sediment of bacterial 'flocs' (masses of aerobic bacteria and fungal filaments) that settle down in the settling tank during secondary (biological) treatment.
Changes in anaerobic sludge digester: A small part of activated sludge is pumped back into the aeration tank as inoculum, while the remaining major part is passed into large anaerobic sludge digesters. In this tank, anaerobic bacteria digest the bacteria and fungi (biomass) present in the sludge, producing a mixture of gases known as biogas.
Composition of biogas: Biogas is a mixture of Methane (\(\text{CH}_4\)), Hydrogen (\(\text{H}_2\)), and Carbon dioxide (\(\text{CO}_2\)).
In simple words: Primary sludge is raw settled dirt, while activated sludge is living microbial flocs. Anaerobic digesters break down this sludge to release useful biogas.

Exam Tip: Structure your answer clearly in three parts: (1) comparison of sludges, (2) role of anaerobic digester, and (3) exact chemical composition of biogas.