CBSE Class 12 Biology Microbes in Human Welfare MCQs Set G

Question: Which of the following in sewage treatment removes suspended solids?
a) Secondary treatment
b) Primary treatment
c) Sludge treatment
d) Tertiary treatment
Answer: b

Question: 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

Question: Microbe used for biocontrol of pest butterfly caterpillars is
a) Saccharomyces cerevisiae
b) Bacillus thuringiensis
c) Streptococcus sp.
d) Trichoderma sp.
Answer: b

Question: In gobar gas, the maximum amount is that of
a) Butane
b) Methane
c) Propane
d) Carbon dioxide
Answer: b

Question: Which one of the following is a bacterial biofertiliser?
a) Anabaena
b) Nostoc
c) Rhizobium
d) Oscillatoria
Answer: c

Question: The puffed-up appearance of dough is due to fermentation by bacteria. Identify the gas liberated during the process.
a) Hydrogen sulphide
b) Methane
c) Ammonia
d) Carbon dioxide
Answer: d

Question: 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

Question: An organism used as a biofertiliser for raising soyabean crop is
a) Azotobacter
b) Azospirillum
c) Rhizobium
d) Nostoc
Answer: c

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

Question: Which of the following can be used as a biocontrol agent in the treatment of plant disease?
a) Lactobacillus
b) Trichoderma
c) Chlorella
d) Anabaena
Answer: b

Question: The domestic sewage in large cities
a) has a high BOD as it contains both aerobic and anaerobic bacteria
b) is processed by aerobic and then anaerobic bacteria in the secondary treatment in Sewage Treatment Plants (STPs)
c) when treated in STPs does not really require the aeration step as the sewage contains adequate oxygen
d) has very high amount of suspended solids and dissolved salts
Answer: b

Question: In biogas plant, the role of acidogenic bacteria is to
a) convert monomers to organic acids
b) convert monomers to complex polymers
c) transform acetic acid to biogas
d) digest fungi in the sludge
Answer: a

Question: Select the correct statement.
a) Acetobacter aceti produces citric acid
b) Saccharomyces cerevisiae is used as clot buster
c) Penicillium notatum restricts the growth of Staphylococci
d) Methanogens are found in aerobic conditions
Answer: c

Question: Viruses of the genus Nucleopolyhedrovirus are employed as
a) gobar gas producers
b) biological control agents
c) anaerobic sludge digesters
d) atmospheric nitrogen fixing agents
Answer: b

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

Assertion & Reasoning Based MCQs

Two statements are given-one labelled Assertion and the other labelled Reason.
Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(a) Both assertion and reason are true and reason is the correct explanation of assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of assertion.
(c) Assertion is true but reason is false.
(d) Assertion is false but reason is true.

Question: Assertion : Azotobacter fixes nitrogen in symbiotic form.
Reason : Rhizobium form root nodules in the roots of leguminous plants.
Answer: d

Question: Assertion : Whisky develops colour during the aging process.
Reason : Vodka is colourless.
Answer: b

Question: Assertion : Saccharomyces ellipsoidens is Brewer’s yeast.
Reason : Brewer’s yeast produces beer not wine.
Answer: d

Question: Assertion : Acetic acid is prepared by acetic acid bacteria.
Reason : Alcoholic fermentation and the conversion of alcohol to acetic acid are aerobic processes.
Answer: c

Question: Assertion : The alcoholic content of fortified wines are high.
Reason : The fermentation is stopped before all the sugars are being converted.
Answer: b

Statement Type Questions

Question: Which one of the following is not true about antibiotics?
a) First antibiotic was discovered by Alexander Flemming.
b) The term ‘antibiotic’ was coined by S. Waksman in 1942.
c) Some persons can be allergic to a particular antibiotic.
d) Each antibiotic is effective only against one particular kind of germ.
Answer: d

Question: What are the advantages of gobar gas over conventional utilization?
(i) It is most efficient source of energy.
(ii) It is used as good fertilizer.
(iii) It reduces the chances of spreading of pathogens.
a) (i) and (ii) only
b) (ii) and (iii) only
c) (i) and (iii) only
d) all of these
Answer: d

Question: Baculoviruses are excellent candidates for
a) species-specific narrow spectrum pesticidal applications.
b) species-specific broad spectrum pesticidal applications.
c) species-specific narrow spectrum insecticidal applications.
d) species-specific broad spectrum insecticidal applications.
Answer: c

Question: Which of the following statements is not true for stirred tank fermentation?
a) Buffer needed to control pH.
b) Batch and feed possible.
c) Control dissolved oxygen.
d) Easy in process sampling.
Answer: c

Question: Benefits of mycorrhizae are
(i) resistance to root-borne pathogens.
(ii) tolerance of salinity and absorption of phosphorus.
(iii) tolerance to drought.
(iv) overall increase in the plant growth and development.
a) (i) and (ii)
b) (ii) and (iii)
c) (iii) and (iv)
d) all of these
Answer: d

Question: Which one of the following is the most important role of microorganism for the well-being of humans?
a) Sewage treatment
b) Production of methane
c) Biological control of plant disease
d) Conversion of milk to curd
Answer: c

Critical Thinking Questions

Question: Cheese and yogurt are products of
a) Pasteurisation
b) Fermentation
c) Dehydration
d) Distillation
Answer: b

Question: Biogas can be a good substitute for
a) Fuel wood
b) Petroleum and oil
c) Coal
d) Charcoal
Answer: a

Question: Microbes are a diverse group which includes
I. Bacteria
II. Mosses
III. Protozoans
IV. Fungi
a) I, III, IV
b) I, IV
c) I, II
d) III, IV
Answer: a

Question: 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 centre 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
Answer: b

Question: Some industrial products are given below which are synthesized from microbes
I. Antibiotics
II. Fermented beverages
III. Enzymes and chemicals
IV. Bioactive molecules
Choose the correct option.
a) I, III, IV
b) I, II, III, IV
c) I, III
d) I, II, III
Answer: b

Question: The following bacteria help in nitrogen fixation from atmosphere
I. Azotobacter
II. Rhizobium
III. Azospirillum
IV. Lactobacillus
Identify the correct bacteria.
a) I, III, IV
b) I, II, III, IV
c) II, III, IV
d) I, II, III
Answer: d

Question: Bacillus thuringiensis (Bt) strains have been used as
a) Biofertilizers
b) Biometallurgical techniques
c) Biomineralization processes
d) Bioinsecticidal plants
Answer: d

Question: Which of the following is common to Azospirillum, Azotobacter, Anabaena, Nostoc and Oscillatoria?
a) Prokaryotes
b) Nitrogen-fixers
c) Both (a) and (b)
d) Eukaryotes
Answer: c

Question: Crystals of Bt-toxin produced by some bacteria do not kill the bacteria themselves because
a) Bacteria are resistant to the toxin
b) Toxin is inactive
c) Toxin is immature
d) Bacteria enclose toxins in a special sac
Answer: a

Question: Read the following statement.
“A drug used for ———— (A) ———— patients is obtained from a species of the organism ———— (B) — ———.” Identify A and B.

        A                                 B
(a) Heart                          Penicillium
(b) Organ-transplant       Trichoderma
(c) Swine flu                    Monascus
(d) AIDS                          Pseudomonas
Answer: b

Matching Type Questions

Question: 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

Question: Which one of the following is wrongly matched?
(a) Yeast – Ethanol
(b) Streptomyces – Antibiotics
(c) Lactobacillus – Beer
(d) Methanogens – Gobar gas
Answer: c

Question: Match the items of column-I with column-II and choose correct answer.

Column-I                             Column-II
A. Lady bird                   I. Methanobacterium
B. Mycorrhiza                II. Trichoderma
C. Biological control     III. Aphids
D. Biogas                     IV. Glomus

(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
Answer: b

Question: The given table contains type of microbe (Column I), Scientific name (Column II) and commercial product (Column III). Some names are replaced by A, B, C and D. Identify the correct names.

Type of Microbe       Scientific Name                 Commercial Product
Bacterium                  A                                  Clot buster enzyme
B                            Aspergillus niger               Citric acid
Fungus                  Trichoderma polysporum     C
Bacterium                D                                    Butyric acid

(a) A – Streptococcus, B – Fungus, C – Cyclosporin-A, D – Clostridium butylicum
(b) A – Clostridium butylicum, B – Streptococcus, C – Fungus, D – Cyclosporin-A
(c) A – Cyclosporin-A, B – Clostridium butylicum C – Streptococcus, D – Fungus
(d) A – Fungus, B – Cyclosporin-A, C – Clostridium butylicum, D – Streptococcus
Answer: a

Question: Find out the pairs which are correctly matched.

     Column-I                               Column-II
A. Cyanobacteria                     I. Biopesticides
B. Mycorrhiza                         II. Solubilization of phosphate
C. Bacillus thuringiensis          III. Cry protein
D. Single cell protein              IV. Rhizobia
(a) A and II
(b) C and III
(c) C and IV
(d) A and III
Answer: b

Question: Match column-I with column-II and choose the correct option

Column-I                   Column-II
A. Statins                   I. Yeast
B. Ethanol                 II. Blood-cholesterol lowering agent
C. Dung                   III. Insect-resistant plant
D. Bt-cotton             IV. Biogas

(a) A – II; B – I; C – IV; D – III
(b) A – III; B – IV; C – I; D – II
(c) A – I; B – II; C – III; D – IV
(d) A – IV; B – II; C – I; D – III
Answer: a

Very Short Answer Type Questions

Question: Name the group of organisms and the substrate they act on to produce biogas.
Answer : Methanogenic bacteria or methanogens are the group of anaerobic microbes which digest organic mass as well as aerobic microbes of the sludge to produce a mixture of gases containing methane, H₂S and CO₂ called biogas.

Question: What is the economic value of Spirulina?
Answer : Spirulina is single cell protein (SCP), which is rich in high quality protein and is used for consumption as human food and animal feed. 

Question: Name the enzyme produced by Streptococcus bacterium. Explain its importance in medical sciences.
Answer : Streptokinase is produced by bacterium Streptococcus.
Streptokinase is modified by genetic engineering which is further used as a ‘clot bluster’ for removing clots from the blood vessels of the patients who have undergone myocardial infarction leading to heart attack.

Short Answer Type Questions

Question: (a) Give the metabolic pathway involved in the puffing up of idli dough.
(b) Name the two different categories of microbes naturally occurring in sewage water.
Explain their role in cleaning sewage water into usable water.
Answer : (a) The metabolic pathway involved in the puffing up of idli dough is fermentation in which incomplete oxidation of glucose is achieved under anaerobic conditions by sets of reactions that produces CO₂. Carbon dioxide produced during fermentation causes puffing up of idli dough.
(b) Aerobic heterotrophs like bacteria and fungi occur in sewage water. They are natural decomposers and digest a lot of organic matter present in the polluted water thereby releasing minerals and reducing organic waste. Hence, they play an important role in cleaning water and making it fit for various domestic uses.

Question: Name the bacterium responsible for the large holes seen in “Swiss Cheese”. What are these holes due to?
Answer : Bacterium responsible for large holes in Swiss cheese is Propionibacterium shermanii. Large holes in Swiss cheese are due to CO₂ gas produced by these bacteria.

Question: State one reason for adding blue-green algae to the agricultural soil.
Answer : A number of free living and symbiotic blue green algae or cyanobacteria have the property of nitrogen fixation and are photosynthetic. Therefore, they add organic matter as well as extra nitrogen to the soil. Hence, blue green algae serve as biofertilisers and are added to agricultural fields such as cotton, maize, jowar, rice, etc.

Question: What makes the Nucleopolyhedrovirus a desirable biological control agent?
Answer : Nucleopolyhedrovirus a genus of baculoviruses are useful in controlling many insects and other arthropods. They are species specific narrow spectrum bioinsecticides with no side effects on plants, mammals, birds, fish and non-target insects. Therefore, they serve as an important component of integrated pest management programme in dealing with ecological sensitive areas. These properties are useful in organic farming.

Question: Distinguish between the roles of flocs and anaerobic sludge digesters in sewage treatments.
Answer : Aerobic bacteria and fungi constitute ‘flocs’. Flocs are masses of aerobic bacteria held together by slime and fungal filaments to form mesh like structures. These microbes digest a lot of organic matter converting it into microbial biomass and releasing a lot of minerals. This reduces biochemical oxygen demand or BOD.
In anaerobic sludge digesters, aerobic microbes present in the sludge get killed. Anaerobic microbes digest the organic mass as well as aerobic microbes of the sludge. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas which can be used as source of energy as it is inflammable. The spent sludge of anaerobic sludge digester can be used as manure or part of compost.

Question: Define the term biofertilizers? How does each of the following serve as a biofertilizer?
(i) Rhizobium (ii) Ectomycorrhiza
Answer : Biofertilizers are microorganisms which bring about nutrient enrichment of soil by enhancing the availability of nutrients like nitrogen (N) and phosphorus (P) to crops.
The microorganisms which act as biofertilizers are bacteria, cyanobacteria (blue green algae) and mycorrhizal fungi.
(i) Rhizobium is one of the most important symbiotic nitrogen fixing bacteria. It forms nodules on the roots of legume plants. They develop the ability to fix nitrogen only when they are present inside the root nodules. In the nodule cells, bacteria (bacteroids) lie in groups surrounded by membrane of the host which is lined by a pink-red pigment called leghaemoglobin. Leghaemoglobin in root nodules rapidly combines with oxygen and protects the enzyme nitrogenase by any inhibitory effect of oxygen.
(ii) In ectotrophic mycorrhiza, the fungal mycelium completely encloses the feeder rootlets forming sheath or mantle. The mantle of fungal hyphae increases the absorptive surface of roots and hence serve better intake of nutrients such as nitrogen, phosphorus, calcium and potassium from the surrounding soil. The major functions which ectomycorrhiza perform are (a) absorption of water, (b) solubilisation of complex organic molecules into simple inorganic nutrients, their absorption and transfer to the roots, and (c) protection of plants from attack of disease-inciting pathogens by secreting antimicrobial substances. Ectomycorrhizae are known to occur in Pinus, Quercus, Betula, Eucalyptus, peach, etc.

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 : Among the given microbes, the ones which are in great demand for organic farming are: Mycorrhiza, Anabaena and Rhizobium. Mycorrhiza is a mutually beneficial or symbiotic association of a fungus with the roots of a higher plant.
Mycorrhizal roots show a sparse or dense wooly growth of fungal hyphae on their surface. Plants having mycorrhizal associations show resistance to root-borne pathogens.
Anabaena is free living and symbiotic nitrogen fixing cyanobacteria. Cyanobacteria are photosynthetic and have the property of nitrogen fixation. They add organic matter as well as extra nitrogen to the soil. Cyanobacteria are an extremely low cost biofertilisers. Rhizobium is symbiotic nitrogen fixing bacteria. They form a mutually beneficial association with the plants. The bacteria obtain food and shelter from plants. In return, they give a part of their fixed nitrogen to the plants, thus enhancing the availability of nutrient to crops. It forms nodules on the roots of legume plants. They develop the ability to fix nitrogen only when they are present inside the root nodules.

Question: How has the fungus, Trichoderma polysporum proved to be very essential to organ transplant patients?
Answer : Trichoderma polysporum produces a bioactive molecule known as cyclosporin–A which has antifungal, antiinflammatory and immunosuppressive properties. It inhibits activation of T-cells and therefore, prevents rejection reactions in organ transplantation.

Question: (a) What are the properties of an antibiotic?
(b) Explain the scientific reason for growing Azolla pinnata in the rice field.
Answer : (a) Antibiotics are chemical substances produced by some microbes which in small concentration can kill or retard the growth of harmful microbes without adversely affecting the host. Broad spectrum antibiotic can kill or destroy a number of pathogens that belong to different groups with different structures and wall compositions. Specific antibiotics are effective only against one type of pathogen.
Good antibiotics should be harmless to host with no side effects. They should be harmless to beneficial microorganism of alimentary canal and should be effective against all strains of pathogen. They should also be quick in action.
(b) Azolla pinnata supplies nitrogen, increases physicochemical properties of soils such as soil structure, texture, water holding capacity, cation exchange capacity and pH by providing several nutrients and sufficient organic matter. So, Azolla pinnata grows in rice field to increase productivity.

Question: Why biogas is more suitable and advantageous in rural areas?
Answer : Biogas is more suitable and advantageous in rural areas as :
(i) It provides both energy and manure.
(ii) Biogas has wider applications than the direct burning of organic wastes.
(iii) The energy value of biogas is lower than that of organic matter but due to more efficient handling, the net energy output is roughly equal to the output in direct burning of organic wastes.
(iv) It minimises the chances of spread of faecal pathogens.
(v) The fertiliser value of the manure produced in biogas plants is similar to that of manure formed directly from organic wastes.
(vi) Biogas use does not add to pollution.

Long Answer Type Questions

Question: Prior to sowing rice, a legume crop was cultivated and ploughed back in the field, why? Explain.
Answer : Prior to sowing rice, a leguminous crop was cultivated and ploughed back in the field. The root nodules of leguminous plants contain Rhizobium bacteria. Rhizobium is one of the most important source of biofertilizer. It forms an efficient symbiotic relationship with leguminous plants and can fix upto 100 – 500 kg nitrogen per hectare of land. The fixed nitrogen is used up by the leguminous plants. However, a sizeable amount of fixed nitrogen is left behind in the soil in the form of residue which can be utilized by the succeeding crop.

Question: What are biofertilisers? Describe their role in agriculture. Why are they preferred over chemical fertilisers?
Answer : Biofertilisers are microorganisms which bring about nutrient enrichment of soil by enhancing the availability of nutrients like nitrogen (N) and phosphorus (P) to crops. 
Biofertilisers includes–nitrogen fixing bacteria, nitrogen fixing cyanobacteria and mycorrhiza. Azotobacter occurring in fields of cotton, maize, jowar and rice, not only increases yield but also saves nitrogen fertiliser upto 10–25 kg/ha.
A number of free living cyanobacteria or blue-green algae have the property of nitrogen fixation, e.g., Anabaena, Nostoc, Oscillatoria, Tolypothrix. Cyanobacteria are extremely low cost biofertilizers.
The most important of the symbiotic nitrogen fixing bacteria is Rhizobium. It forms nodules on the roots of legume plants. There are about a dozen species of Rhizobium which form association with different legume roots, e.g., R.leguminosarum, R. lupini, R. trifolii, R. meliloti, R. phaseoli. Nitrogen fixing cyanobacteria (blue–green algae) form symbiotic association with several plants, e.g., cycad roots, lichens, liverworts, Azolla (fern). Azolla–Anabaena association is of great importance to agriculture. Azolla pinnata is a free floating fresh water fern which multiplies rapidly, doubling every 5–7 days. The fern can coexist with rice plants because it does not interfere with their growth. In some South-East Asian countries, especially China, the rice fields are regularly provided with Azolla.
Chemical fertilisers cause pollution of water bodies as well as ground water, besides getting stored in crop plants. Therefore, farmers are pressing for switch over to organic farming which includes the use of manures biofertilisers, biopesticides.
Biofertilisers are microorganisms which bring about nutrient enrichment of soil by enhancing the availability of nutrients to crops. The microorganisms which act as biofertilisers are bacteria, cyanobacteria (blue green algae) and mycorrhizal fungi. Bacteria and cyanobacteria have the property of nitrogen fixation while mycorrhizal fungi preferentially withdraw minerals from organic matter for the plant with which they are associated. Phosphate is also solubilised by some bacteria and by some fungi that form association with plant roots.