Microbes in Human Welfare

What to remember

• Lactic acid bacteria (Lactobacillus) turn milk into curd and increase its vitamin B12 content; Saccharomyces cerevisiae (baker's and brewer's yeast) makes dough rise and produces ethanol.
• Antibiotics, organic acids, enzymes and bioactive molecules (streptokinase, cyclosporin A, statins) are obtained from microbes, each from a specific named organism.
• Sewage is treated in two stages: primary (physical removal of solids) and secondary (biological, using flocs in aeration tanks to reduce BOD); the sludge digested without air gives biogas, rich in methane.
• Microbes also act as biocontrol agents (Bacillus thuringiensis, Trichoderma, baculoviruses) and as biofertilisers (Rhizobium, Azotobacter, Azospirillum, Glomus, cyanobacteria).

Microbes in household products

Microbes such as bacteria, fungi and protozoa are present everywhere. Many are useful in daily life.

Curd: Lactic acid bacteria (LAB) such as Lactobacillus are added to milk as a small amount of curd, called the inoculum or starter. At suitable temperature the bacteria multiply and convert milk to curd. They produce lactic acid, which coagulates and partially digests the milk proteins. LAB also improve the nutritional quality of milk by increasing vitamin B12. In our stomach, LAB check disease-causing microbes.

Dough: The dough used for making foods such as dosa and idli is also fermented by bacteria. The puffed-up appearance of dough is due to the production of CO₂ gas. Bread dough is fermented by baker's yeast, Saccharomyces cerevisiae, which also produces CO₂ and makes the dough rise.

Other fermented foods: Toddy, a traditional drink in some parts of southern India, is made by fermenting sap from palms. Microbes are also used to ferment fish, soybean and bamboo shoots to make foods.

Cheese: Cheese is one of the oldest foods that use microbes. Different microbes give different cheeses their own flavour, texture and taste. The large holes in Swiss cheese are due to the production of a large amount of CO₂ by a bacterium named Propionibacterium sharmanii. The Roquefort cheese is ripened by growing a specific fungus on it, which gives it a particular flavour.

Microbes in industrial products

Production on an industrial scale needs growing microbes in very large vessels called fermentors.

Fermented beverages: The yeast Saccharomyces cerevisiae, commonly called brewer's yeast, is used for fermenting malted cereals and fruit juices to produce ethanol. Depending on the raw material and the type of processing, different alcoholic drinks are produced. Wine and beer are produced without distillation. Whisky, brandy and rum are produced by distillation of the fermented broth.

Antibiotics: Antibiotics are chemical substances produced by some microbes that can kill or retard the growth of other (disease-causing) microbes. The word means "against life". Penicillin was the first antibiotic to be discovered, by Alexander Fleming. While working on Staphylococcus bacteria, he observed a mould growing in one of his unwashed culture plates around which Staphylococci could not grow. He found out that it was due to a chemical produced by the mould, which he named penicillin, after the mould Penicillium notatum. Its full potential as an effective antibiotic was established much later by Ernest Chain and Howard Florey. This discovery was honoured by a Nobel Prize in 1945 to all three. Penicillin was extensively used to treat wounded soldiers in World War II. Since then many other antibiotics have been discovered and used to treat diseases such as plague, whooping cough, diphtheria and leprosy.

Chemicals, enzymes and other bioactive molecules: Microbes are used to produce organic acids, alcohols and enzymes.

Enzymes: Lipases are used in detergent formulations and help to remove oily stains from laundry. Pectinases and proteases are used to make bottled juices clearer. Streptokinase, produced by the bacterium Streptococcus and modified by genetic engineering, is used as a clot buster; it removes clots from the blood vessels of patients who have suffered a myocardial infarction (heart attack).

Bioactive molecules: Cyclosporin A, produced by the fungus Trichoderma polysporum, is used as an immunosuppressive agent in organ-transplant patients. Statins, produced by the yeast Monascus purpureus, act as blood-cholesterol lowering agents. They work by competitively inhibiting the enzyme responsible for the synthesis of cholesterol.

Microbes in sewage treatment

Sewage is the municipal waste water. It contains large amounts of organic matter and microbes, many of which are pathogenic. It cannot be discharged directly into natural water bodies like rivers and streams. It is treated in sewage treatment plants (STPs) so that it is made less polluting. Treatment is done by heterotrophic microbes naturally present in the sewage, in two stages.

Primary treatment: These are physical steps that remove small and large particles from the sewage through filtration and sedimentation. First, floating debris is removed by sequential filtration. Then the grit (soil and small pebbles) is removed by sedimentation. All solids that settle form the primary sludge, and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.

Secondary treatment (biological treatment): The primary effluent is passed into large aeration tanks, where it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into flocs. Flocs are masses of bacteria associated with fungal filaments to form mesh-like structures. While growing, these microbes consume the major part of the organic matter in the effluent. This significantly reduces the biochemical oxygen demand (BOD) of the effluent.

BOD is the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria. The BOD test measures the organic matter in water. The greater the BOD of waste water, the more is its polluting potential.

Once the BOD of the sewage is reduced significantly, the effluent is passed into a settling tank, where the bacterial flocs are allowed to sediment. This sediment is called activated sludge. 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 sludge is pumped into large tanks called anaerobic sludge digesters. In these tanks, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge. During this digestion, bacteria produce a mixture of gases such as methane, hydrogen sulphide and carbon dioxide. These gases form biogas and can be used as a source of energy.

The effluent from the secondary treatment plant is generally released into natural water bodies such as rivers and streams. To protect major rivers from pollution, the Ministry of Environment and Forests has initiated the Ganga Action Plan and the Yamuna Action Plan. These plans set up sewage treatment plants.

Microbes in production of biogas

Biogas is a mixture of gases (mainly methane) produced by the microbial activity, which can be used as fuel. Certain bacteria, which grow anaerobically on cellulosic material, produce large amounts of methane along with CO₂ and H₂. These bacteria are collectively called methanogens, and one such common bacterium is Methanobacterium. These bacteria are commonly found in the anaerobic sludge during sewage treatment. They are also present in the rumen (a part of the stomach) of cattle, where a lot of cellulosic material is present in the food, and they help in the breakdown of cellulose. Thus, the excreta (dung) of cattle, called gobar, is rich in these bacteria. Dung is used for the generation of biogas, commonly called gobar gas.

Biogas plant: The plant has a concrete tank about 10 to 15 feet deep, in which bio-wastes are collected and a slurry of dung is fed. A floating cover is placed over the slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity. The biogas plant has an outlet, which is connected to a pipe to supply biogas to nearby houses. The spent slurry is removed through another outlet and may be used as fertiliser. The technology of biogas production was developed in India mainly due to the efforts of the Indian Agricultural Research Institute (IARI) and the Khadi and Village Industries Commission (KVIC).

Microbes as biocontrol agents

Biological control means the use of biological methods for controlling plant diseases and pests. A holistic approach in which chemicals are reduced is the aim of integrated pest management (IPM).

• Ladybird beetles are used to control aphids, and dragonflies are used to get rid of mosquitoes.
• Bacillus thuringiensis (Bt): Dried spores of this bacterium are available in sachets, mixed with water and sprayed onto vulnerable plants such as brassicas and fruit trees. The bacterial spores are eaten by the insect larvae, in whose gut the toxin is released and the larvae are killed. The toxin is not harmful to other organisms. Bt-cotton plants carry the toxin gene.
• Trichoderma: free-living fungi that are very common in the root ecosystems. They are effective biocontrol agents of several plant pathogens.
• Baculoviruses: pathogens that attack insects and other arthropods. The genus Nucleopolyhedrovirus is the most used. These viruses are species-specific, with narrow spectrum insecticidal applications. They have no negative impacts on plants, mammals, birds, fish or even on non-target insects. This is desirable when beneficial insects are being conserved to aid in an overall IPM programme.

Microbes as biofertilisers

Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria. They help to reduce the use of chemical fertilisers, which are costly and cause pollution.

Mycorrhiza is a symbiotic association of fungus with plants. Plants with mycorrhiza show resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in plant growth and development. In paddy fields, cyanobacteria are important biofertilisers. They also add organic matter to the soil and increase its fertility. Use of biofertilisers is a part of organic farming.

NEET traps

• 1. Streptokinase comes from the bacterium Streptococcus; cyclosporin A comes from the fungus Trichoderma polysporum; statins come from the yeast Monascus purpureus.
• 2. Citric acid is made by the fungus Aspergillus niger; acetic acid by the bacterium Acetobacter aceti; butyric acid by Clostridium butylicum.
• 3. Wine and beer are not distilled; whisky, brandy and rum are distilled.
• 4. Large holes in Swiss cheese are due to CO₂ from Propionibacterium sharmanii; Roquefort cheese is ripened by a fungus.
• 5. Primary sewage treatment is physical; secondary treatment is biological.
• 6. Activated sludge is the sediment of flocs; part of it is returned to the aeration tank as inoculum.
• 7. High BOD means more organic matter and more pollution, not less.
• 8. Rhizobium is symbiotic; Azotobacter and Azospirillum are free-living nitrogen fixers.
• 9. Glomus (mycorrhiza) helps phosphorus absorption; it is a fungus, not a nitrogen-fixing bacterium.
• 10. Bt toxin kills insect larvae that eat the spores; baculoviruses are species-specific.

One-liners

• 1. Lactobacillus converts milk to curd and increases vitamin B12.
• 2. CO₂ makes dough puffed up.
• 3. Saccharomyces cerevisiae is brewer's and baker's yeast.
• 4. Penicillin was discovered by Alexander Fleming from Penicillium notatum.
• 5. Chain and Florey established penicillin as an effective antibiotic.
• 6. Lipases are used in detergents to remove oily stains.
• 7. Pectinases and proteases clarify bottled juices.
• 8. Streptokinase is a clot buster.
• 9. Cyclosporin A is an immunosuppressive agent.
• 10. Statins lower blood cholesterol.
• 11. Flocs are masses of bacteria with fungal filaments.
• 12. Anaerobic sludge digesters produce biogas.
• 13. Methanobacterium is a methanogen found in the rumen of cattle.
• 14. Ladybirds control aphids and dragonflies control mosquitoes.
• 15. Anabaena, Nostoc and Oscillatoria are nitrogen-fixing cyanobacteria.

Practice questions

1. Which vitamin content of milk is increased when lactic acid bacteria convert it to curd?

   1. Vitamin A
   2. Vitamin B12
   3. Vitamin C
   4. Vitamin K
   Answer

   B. Vitamin B12

   LAB improve the nutritional quality of milk by increasing vitamin B12.

2. The large holes in Swiss cheese are due to

   1. citric acid made by Aspergillus niger
   2. ethanol made by Saccharomyces
   3. CO₂ produced by Propionibacterium sharmanii
   4. lactic acid made by Lactobacillus
   Answer

   C. CO₂ produced by Propionibacterium sharmanii

   A large amount of CO₂ produced by Propionibacterium sharmanii makes the holes.

3. Citric acid is commercially produced by

   1. Aspergillus niger
   2. Acetobacter aceti
   3. Clostridium butylicum
   4. Lactobacillus
   Answer

   A. Aspergillus niger

   Citric acid is obtained from the fungus Aspergillus niger.

4. Cyclosporin A, an immunosuppressive agent, is obtained from

   1. Streptococcus
   2. Penicillium notatum
   3. Monascus purpureus
   4. Trichoderma polysporum
   Answer

   D. Trichoderma polysporum

   Cyclosporin A is produced by the fungus Trichoderma polysporum.

5. Blood-cholesterol lowering statins are produced by the yeast

   1. Monascus purpureus
   2. Aspergillus niger
   3. Saccharomyces cerevisiae
   4. Trichoderma polysporum
   Answer

   A. Monascus purpureus

   Statins come from Monascus purpureus.

6. Which of the following is used as a clot buster in patients with a heart attack?

   1. Pectinase
   2. Lipase
   3. Cyclosporin A
   4. Streptokinase
   Answer

   D. Streptokinase

   Streptokinase removes clots from blood vessels.

7. Which of the following alcoholic drinks is produced by distillation of the fermented broth?

   1. Wine
   2. Beer
   3. Rum
   4. Toddy
   Answer

   C. Rum

   Whisky, brandy and rum are distilled; wine and beer are not.

8. Biochemical oxygen demand (BOD) is the

   1. amount of oxygen released by algae in water
   2. amount of oxygen consumed if all the organic matter in one litre of water were oxidised by bacteria
   3. amount of CO₂ released by one litre of sewage
   4. number of bacteria in one litre of sewage
   Answer

   B. amount of oxygen consumed if all the organic matter in one litre of water were oxidised by bacteria

   BOD measures the organic matter in water as oxygen demand.

9. Flocs formed during secondary sewage treatment are

   1. masses of bacteria associated with fungal filaments
   2. masses of algae and protozoa only
   3. grit and small pebbles
   4. settled solids of primary treatment
   Answer

   A. masses of bacteria associated with fungal filaments

   Flocs are mesh-like masses of bacteria with fungal filaments.

10. Which of the following is a methanogen used in biogas production?

    1. Lactobacillus
    2. Rhizobium
    3. Azotobacter
    4. Methanobacterium
    Answer

    D. Methanobacterium

    Methanobacterium grows anaerobically and produces methane.

11. The technology of biogas production was developed in India mainly through the efforts of

    1. ISRO and BARC
    2. CSIR and DRDO
    3. IARI and KVIC
    4. NACO and ICMR
    Answer

    C. IARI and KVIC

    IARI and KVIC developed biogas technology in India.

12. The toxin of Bacillus thuringiensis, when used as a biocontrol agent, kills

    1. nitrogen-fixing bacteria
    2. insect larvae that eat the spores
    3. fungal pathogens of roots
    4. aphids by contact
    Answer

    B. insect larvae that eat the spores

    Larvae eat the spores and the toxin is released in their gut.

13. The fungus that forms mycorrhiza and helps in the absorption of phosphorus is

    1. Oscillatoria
    2. Glomus
    3. Trichoderma
    4. Rhizobium
    Answer

    B. Glomus

    Glomus forms mycorrhiza that absorbs phosphorus from the soil.

14. Which pair consists of free-living nitrogen-fixing bacteria?

    1. Rhizobium and Anabaena
    2. Rhizobium and Glomus
    3. Azotobacter and Azospirillum
    4. Glomus and Nostoc
    Answer

    C. Azotobacter and Azospirillum

    Azotobacter and Azospirillum are free-living bacteria that fix nitrogen.

15. The antibiotic penicillin is named after the mould

    1. Penicillium notatum
    2. Penicillium chrysogenum
    3. Staphylococcus aureus
    4. Aspergillus niger
    Answer

    A. Penicillium notatum

    Fleming named penicillin after Penicillium notatum.

16. In detergent formulations, which enzymes are used to remove oily stains?

    1. Streptokinase
    2. Proteases
    3. Pectinases
    4. Lipases
    Answer

    D. Lipases

    Lipases break down oils and help remove oily stains.

17. Given below are two statements: Statement I: Lactobacillus converts milk to curd. Statement II: Conversion of milk to curd decreases its vitamin B12 content.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    LAB increase vitamin B12, so Statement II is incorrect.

18. Given below are two statements: Statement I: Wine and beer are produced by distillation. Statement II: Whisky, brandy and rum are produced by distillation.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    Wine and beer are produced without distillation.

19. Given below are two statements: Statement I: Penicillin was discovered by Alexander Fleming. Statement II: Ernest Chain and Howard Florey established its full potential as an antibiotic.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    A. Both Statement I and Statement II are correct

    Both are correct.

20. Given below are two statements: Statement I: Statins increase the level of blood cholesterol. Statement II: Cyclosporin A is used as a clot buster.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    B. Both Statement I and Statement II are incorrect

    Statins lower cholesterol, and cyclosporin A is an immunosuppressant.

21. Given below are two statements: Statement I: Primary sewage treatment involves physical removal of particles. Statement II: Primary sewage treatment is a biological process that uses flocs.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Flocs are used in the secondary (biological) treatment.

22. Which of the following statements are correct? 1. Flocs are masses of bacteria associated with fungal filaments. 2. Activated sludge is the sediment of bacterial flocs. 3. Anaerobic sludge digesters need vigorous aeration.

    1. 2 and 3 only
    2. 1 and 3 only
    3. 3 only
    4. 1 and 2 only
    Answer

    D. 1 and 2 only

    Sludge digesters work without air, so only 1 and 2 are correct.

23. Given below are two statements: Statement I: Methanogens are present in the rumen of cattle. Statement II: Cattle dung is rich in methanogens.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    A. Both Statement I and Statement II are correct

    Methanogens in the rumen help break down cellulose, so dung contains them.

24. Given below are two statements: Statement I: Ladybirds are used to control mosquitoes. Statement II: Dragonflies are used to control aphids.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    B. Both Statement I and Statement II are incorrect

    Ladybirds control aphids and dragonflies control mosquitoes.

25. Given below are two statements: Statement I: Rhizobium is a free-living nitrogen-fixing bacterium. Statement II: Azospirillum is a free-living nitrogen-fixing bacterium in soil.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    Rhizobium is symbiotic with roots of legumes.

26. Which of the following statements are correct? 1. Glomus forms mycorrhiza. 2. Mycorrhiza helps plants absorb phosphorus from soil. 3. Anabaena is a fungus.

    1. 1 and 3 only
    2. 2 and 3 only
    3. 1 and 2 only
    4. 1, 2 and 3
    Answer

    C. 1 and 2 only

    Anabaena is a cyanobacterium, so only 1 and 2 are correct.

27. Assertion (A): The dough used for idli and dosa becomes puffed up. Reason (R): Bacteria in the dough produce CO₂ gas.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    A. Both A and R are true and R is the correct explanation of A

    CO₂ released by the fermenting microbes puffs up the dough.

28. Assertion (A): Streptokinase is used as a clot buster. Reason (R): Streptokinase is produced by the fungus Trichoderma polysporum.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    C. A is true but R is false

    Streptokinase comes from the bacterium Streptococcus.

29. Assertion (A): Rhizobium is a free-living nitrogen fixer in soil. Reason (R): Rhizobium fixes atmospheric nitrogen in association with the roots of leguminous plants.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    D. A is false but R is true

    Rhizobium is symbiotic with legume roots, not free-living; the reason is true.

30. Assertion (A): Bacillus thuringiensis spores are sprayed on brassicas to kill larvae. Reason (R): Baculoviruses are species-specific insect pathogens.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    B. Both A and R are true but R is not the correct explanation of A

    Both are true, but the second does not explain the first.

31. Assertion (A): BOD of the effluent falls in the aeration tank. Reason (R): Aerobic microbes in flocs consume the organic matter of the effluent.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    A. Both A and R are true and R is the correct explanation of A

    Consumption of organic matter by the microbes lowers BOD.

32. Match List I with List II. List I: a. Aspergillus niger b. Acetobacter aceti c. Clostridium butylicum d. Lactobacillus List II: i. Butyric acid ii. Acetic acid iii. Citric acid iv. Lactic acid

    1. a-iii, b-ii, c-i, d-iv
    2. a-iii, b-i, c-ii, d-iv
    3. a-iii, b-ii, c-iv, d-i
    4. a-ii, b-iii, c-i, d-iv
    Answer

    A. a-iii, b-ii, c-i, d-iv

    Aspergillus: citric acid; Acetobacter: acetic acid; Clostridium: butyric acid; Lactobacillus: lactic acid.

33. Match List I with List II. List I: a. Cyclosporin A b. Streptokinase c. Statins d. Curd List II: i. Monascus purpureus ii. Trichoderma polysporum iii. Streptococcus iv. Lactobacillus

    1. a-i, b-iii, c-ii, d-iv
    2. a-iii, b-ii, c-i, d-iv
    3. a-ii, b-iii, c-iv, d-i
    4. a-ii, b-iii, c-i, d-iv
    Answer

    D. a-ii, b-iii, c-i, d-iv

    Cyclosporin A: Trichoderma polysporum; streptokinase: Streptococcus; statins: Monascus purpureus; curd: Lactobacillus.

34. Match List I with List II. List I: a. Rhizobium b. Azotobacter c. Glomus d. Nostoc List II: i. Mycorrhiza ii. Cyanobacterium iii. Symbiotic with legumes iv. Free-living soil bacterium

    1. a-iv, b-iii, c-i, d-ii
    2. a-iii, b-iv, c-ii, d-i
    3. a-iii, b-iv, c-i, d-ii
    4. a-iii, b-i, c-iv, d-ii
    Answer

    C. a-iii, b-iv, c-i, d-ii

    Rhizobium is symbiotic with legumes; Azotobacter is free-living; Glomus forms mycorrhiza; Nostoc is a cyanobacterium.

35. Match List I with List II. List I: a. Ladybird b. Dragonfly c. Bacillus thuringiensis d. Nucleopolyhedrovirus List II: i. Feeds on aphids ii. Feeds on mosquitoes iii. Toxin sprayed on brassicas iv. Species-specific insect pathogen

    1. a-iii, b-ii, c-i, d-iv
    2. a-i, b-ii, c-iii, d-iv
    3. a-i, b-ii, c-iv, d-iii
    4. a-ii, b-i, c-iii, d-iv
    Answer

    B. a-i, b-ii, c-iii, d-iv

    Ladybird: aphids; dragonfly: mosquitoes; Bt: sprayed toxin; baculovirus: species-specific pathogen.

36. Match List I with List II. List I: a. Primary treatment b. Secondary treatment c. Activated sludge d. Anaerobic sludge digester List II: i. Sediment of flocs ii. Biogas production iii. Physical removal of particles iv. Aeration tank with flocs

    1. a-iii, b-iv, c-i, d-ii
    2. a-i, b-iv, c-iii, d-ii
    3. a-iii, b-iv, c-ii, d-i
    4. a-iv, b-iii, c-i, d-ii
    Answer

    A. a-iii, b-iv, c-i, d-ii

    Primary: physical; secondary: aeration with flocs; activated sludge: sediment of flocs; digester: biogas.

37. Match List I with List II. List I: a. Alexander Fleming b. Saccharomyces cerevisiae c. Propionibacterium sharmanii d. Methanobacterium List II: i. Swiss cheese ii. Methanogen iii. Discovery of penicillin iv. Brewer's yeast

    1. a-iv, b-iii, c-i, d-ii
    2. a-iii, b-iv, c-i, d-ii
    3. a-iii, b-iv, c-ii, d-i
    4. a-iii, b-i, c-iv, d-ii
    Answer

    B. a-iii, b-iv, c-i, d-ii

    Fleming: penicillin; S. cerevisiae: brewer's yeast; P. sharmanii: Swiss cheese; Methanobacterium: methanogen.

38. A person wants to make curd at home from warm milk. What should be added to the milk?

    1. A little sugar
    2. Baker's yeast
    3. A small amount of curd as inoculum
    4. A small amount of vinegar
    Answer

    C. A small amount of curd as inoculum

    Curd contains Lactobacillus, which multiplies in warm milk and forms curd.

39. A farmer wants a cheap biofertiliser to add nitrogen to a flooded paddy field. Which organism is most suitable?

    1. Rhizobium
    2. Glomus
    3. Methanobacterium
    4. Anabaena
    Answer

    D. Anabaena

    Anabaena is a nitrogen-fixing cyanobacterium useful in paddy fields.

40. A manufacturer wants to make bottled fruit juice clearer. Which enzymes should be used?

    1. Lipases and streptokinase
    2. Statins and lipases
    3. Cyclosporin and pectinases
    4. Pectinases and proteases
    Answer

    D. Pectinases and proteases

    Pectinases and proteases clarify bottled juices.

41. A baker finds that bread dough does not rise. Which microbe, if added, would correct this?

    1. Saccharomyces cerevisiae
    2. Lactobacillus
    3. Methanobacterium
    4. Propionibacterium sharmanii
    Answer

    A. Saccharomyces cerevisiae

    Baker's yeast produces CO₂ that makes the dough rise.

42. A farmer wishes to protect a brassica crop from caterpillars without using chemical insecticides. What can be sprayed?

    1. Azotobacter cells
    2. Glomus spores
    3. Bacillus thuringiensis spores
    4. Trichoderma spores
    Answer

    C. Bacillus thuringiensis spores

    Bt spores are eaten by larvae, in whose gut the toxin kills them.

43. Gas collects under the floating cover of a gobar gas plant. Which gas is the main component?

    1. Oxygen
    2. Methane
    3. Hydrogen sulphide
    4. Nitrogen
    Answer

    B. Methane

    Methanogens produce mainly methane along with CO₂ and H₂.

44. A plant growing in poor soil shows better phosphorus uptake and tolerance to salinity and drought. Which partner is most likely associated with its roots?

    1. Azospirillum
    2. Glomus
    3. Rhizobium
    4. Nostoc
    Answer

    B. Glomus

    Glomus forms mycorrhiza, which gives these benefits.