Important Questions for CBSE Class 12 Biology Microbes in Household Products, Industrial Products and in Sewage Treatment

Microbes in Human Welfare Important Questions for CBSE Class 12 Biology Microbes in Household Products, Industrial Products and in Sewage Treatment

1. Microbes are the major components of biological systems on the earth. They are present everywhere, i.e. in soil, water, air, inside our bodies and those of other animals and plants. They can also be found deep inside the geysers (thermal vents), deep in soil, under the layer of snow and in highly acidic environments.

Microbes are so minute that they cannot be seen by naked eyes.
Various types of microbes are Protozoa, bacteria, fungi, virus, viroids and prions.

2. Microbes in household products The common products obtained by the use of microbes are curd, dough, toddy, cheese, etc.
(i) Curd is formed by adding bacteria such as Lactobacillus and others, commonly called as Lactic Acid Bacteria (LAB) in milk.

A small amount of curd is added to the fresh milk as starter, which contain millions of LAB.
LAB at suitable temperature multiply and convert milk into curd, which also improves nutritional quality by increasing vitamin-B₁₂.
During growth, LAB produce acids that coagulate and partially digest the milk proteins.
LAB also checks disease causing microbes in the stomach.

(ii) Dough is formed by fermentation caused by bacteria.

Dough used to make bread, is fermented using baker’s yeast (Saccharomyces cerevisiae).
Carbon dioxide released during the process of fermentation gives the fluffy appearance to dough.
Dough is also used to make foods like idli, dosa, in addition to different types of breads.

(iii) Toddy is a traditional drink of Southern India. It is made by fermentation of sap from palm trees by bacteria. A number of other drinks and food are also made by fermentation.
(iv) Cheese is made by partial degradation of milk using different microbes.
(a) Swiss cheese is made by a bacterium Propionibacterium shermanii. The large holes in this cheese are due to production of a large amount of C0₂ by the bacterium.
(b) Roquefort cheese is made by ripening with the fungi, Penicillium roqueforti to obtain a specific flavour.
(v) Microbes are also used to ferment fish, soybean and bamboo shoots to make food.

3. Microbes in industrial products have immense importance. The main industrial products obtained from microbes are fermented beverages, antibiotics, organic acids, alcohol, enzymes and bioactive molecules, etc. Production of these products on industrial scale needs growing microbes in very large vessels called fermentors.
(i) Fermented beverages are wine, beer, whisky, brandy and rum.

These are obtained by fermenting malted cereals and fruit juices with Saccharomyces cerevisiae or brewer’s yeast to produce ethanol.
Variety of alcoholic drink depend on the type of raw material used and the type of processing.
Wine and beer are produced without distillation.
Whisky, brandy and rum are produced by the distillation of the fermented broth.

(ii) Antibiotics (anti – against and bio – life) are chemical substances, which are produced by some microbes and can kill or retard the growth of other (disease causing) microbes.

Penicillin was the first antibiotic discovered by Alexander Fleming.
Fleming discovered penicillin, while working on Staphylococcus 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. He named it penicillin after the mould Penicillium notatum.
Ernst Chain and Howard Florey discovered full potential of this antibiotic.
Penicillin was extensively used during World War II. Fleming, Chain and Florey were awarded Nobel Prize in 1945 for this discovery.
Antibiotics are used to cure deadly diseases such as plague, whooping cough, diphtheria and leprosy.

(iii) Organic acids are produced by the microbial metabolic action. Important ones are:

Citric acid – Aspergillus niger (fungi)
Acetic acid – Acetobacter aceti (bacteria)
Butyric acid – Clostridium butylicum (bacteria)
Lactic acid – Lactobacillus (bacteria)

(iv) Ethanol is produced by yeast (Saccharomyces cerevisiae) on commercial scale.
(v) Enzymes used in various fields are also produced by microbes as given below:

Lipase used in detergent formulations and helps in removing oily stains from the laundry.
Pectinase and protease used for clarifying bottled juices.
Streptokinase produced by Streptococcus and modified by genetic engineering is used as a ‘Clot buster’ for removing clots from blood vessels of patients, who have undergone myocardial infarction leading to heart attack.

(vi) Bioactive molecules produced by microbes are:

Cyclosporin-A produced by Trichodermapolysporum (fungus). It is used as immunosuppressive agent in organ-transplant patients.
Statins produced by Monascus purpureus (yeast), is used as blood cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible for the synthesis of cholesterol.

4. Microbes in sewage treatment play major role:

(i) Sewage is the municipal wastewater containing mainly human excreta. It contains large quantity of organic matter and pathogenic microbes. Therefore, before discharging into natural bodies, sewage needs to be made less polluting.

(ii) Sewage treatment is carried out in Sewage Treatment Plants (STPs) in following

steps:
A. Primary treatment of sewage is:

This step involves physical removal of large and small particles from sewage through filtration and sedimentation.
Floating debris is removed by sequential filtration by passing through wire mesh screens.
After this, the grit (soil and small pebbles) is removed by sedimentation in settling tanks. The sediment is called primary sludge and the supernatant forms the primary effluent.
The effluent is taken for secondary treatment.

B. Secondary treatment (biological treatment) of sewage is done on primary effluent.

Primary effluent is passed into large aeration tanks with constant mechanical agitation and air supply.
This allows vigorous growth of useful aerobic microbes into floes (masses of bacteria associated with fungal filaments to form mesh-like structures).
These microbes consume major part of organic matter in the effluent, while growing. This reduces the Biochemical Oxygen Demand (BOD) of the effluent.
When BOD of sewage gets reduced, it is passed into settling tank.
The bacterial floes settle in tank and the sediment is called activated sludge.
A small amount of activated sludge is pumped back into the aeration tank to serve as inoculum.
The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters.
In sludge digesters, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge. During this process, bacteria produce a mixture of gases, such as methane, hydrogen sulphide and the carbon dioxide, which form biogas (can be used as source of energy).
The effluent from secondary treatment is generally released into natural water bodies.

(iii) Biochemical Oxygen Demand (BOD) refers to the amount of the oxygen that would be consumed if all the organic matter in one litre of water is oxidised by bacteria.

BOD measures the rate of uptake of oxygen by the microbes in a sample of water. Indirectly, it measures the organic matter present in the water.
More BOD of waste water indicates more polluting potential.

(iv) Due to the increasing urbanisation, sewage is being produced in larger quantities. So, the untreated sewage is often discharged directly into rivers leading to their pollution and increase in water borne diseases.

(v) The Ministry of Environment and Forests has initiated Ganga Action Plan and Yamuna Action Plan to save the major rivers of our country from pollution.
Under these plans, it is proposed to build a large number of sewage treatment plants so that only treated sewage can be discharged in the rivers.

Previous Years Examination Questions

1 Mark Questions
1. Give the scientific name of the source organism from which the first antibiotic was produced. [Foreign 2014]
Ans. The scientific name of organism, i.e. mould from which first antibiotic was produced is Penici Ilium notatum.

2. Which of the following is the baker’s yeast used in fermentation? Saccharum barberi, Saccharomyces cerevisiae and Sonalika. [All India 2011,2009,2012]
Ans.Saccharomyces cerevisiae is the baker’s yeast used in fermentation.

3. Write the scientific name of the microbe used for fermenting malted cereals and fruit juices.[Delhi 2011]
Ans. Saccharomyces cerevisiae also, commonly called brewer’s yeast is the microbe used for fermenting malted cereals and fruit juices.11]

4. Mention the information that the health workers derive by measuring BOD of a waterbody. [All India 2010]
Ans. Higher the BOD of water body, more is its polluting potential and vice-versa. BOD indicates the presence of organic matter in the water.

5. Why is sewage water treated until the BOD is reduced? Give a reason. [Delhi 2010c]
Ans. The greater the BOD of sewage water, more is its polluting potential. So, the sewage water is treated, till its BOD is reduced to reduce the organic matter present in it.

6. Milk starts to coagulate when Lactic Acid Bacteria (LAB) is added to warm milk as a starter. Mention any other two benefits LAB provides.[All India 2009]
Ans. Two benefits of LAB:
(i) They improve the nutrient quality of curd by increasing the vitamin-B12 content.
(ii) LAB also check the growth of disease causing microbes in the stomach.

7. BOD of two samples of water A and B were 120 mg/L and 400 mg/L,Which sample is more polluted?
[Foreign 2009]
Ans. Sample B(BOD 400 mg/L) is more polluted as higher the BOD, more is the polluting potential

8. Given below are a few impurities in urban wastewater. Select two colloidal impurities : ammonia, faecal matter, silt, bacteria, calcium. [All India 2009c]
Ans. Faecal matter and silt are the colloidal impurities in urban wastewater.

2 Marks Questions
9.Name two groups of organisms which constitute ‘floes’. Write their influence on the level of BOD during biological treatment of sewage. [Delhi 2014c]
Ans. The groups of organisms that constitute mesh like structures called ‘floes’ are bacteria and fungi.
These bacterial masses associated with fungal filaments called floes, consume the major part of organic matter present in effluent, thereby reducing the BOD of the waste significantly during biological or secondary treatment of sewage.

10. Why is ‘starter’ added to set the milk into curd? Explain. [All India 2014c]
Ans. When a small amount of curd as starter is added to fresh milk, millions of Lactic Acid Bacteria (LAB) present in the starter grow in milk and convert it to curd. During this process, acids are produced by LAB that coagulate and partially digest the milk proteins (casein). LAB increases vitamin-B₁₂content along with other vitamins in the curd

11. Name the bacterium responsible for the large holes seen in swiss cheese. What are these holes due to?
[All India 2013, Delhi 2008C]
Ans. Swiss cheese is produced by the bacterium Propionibacterium shermanii. The large holes in swiss cheese are due to the large amount of C0₂ production

12. Name the source of streptokinase. How does this bioactive molecule function in our body. [Delhi 2012]
or
Name the enzyme produced by Streptococcus bacterium. Explain its importance in medical sciences.
[All India 2011]
Ans. Streptokinase enzyme is produced by the bacterium Streptococcus. It is modified by genetic engineering and is used as a clot buster for removing clots from the blood vessels of patients who have suffered from myocardial infarction.

13. Mention the importance of lactic acid bacteria to humans other than setting milk into curd.[Delhi 2012]
Ans. (i)Lactic Acid Bacteria (LAB) are used to produce an acid called lactic acid that is an important industrial product. It is also used in beverages, meat products, confectionary, dairy products, etc.
(ii) It also checks disease causing microbes in stomach.

14. Name the source of cyclosporin-A. How does this bioactive molecule function in our body? [All India 2012]
Ans. Cyclosporin-A is produced by the fungus Trichoderma polysporum. It is used as an immunosuppressive agent in organ-transplant patients.

15. Name the source of statin and state its action on the human body. [Foreign 2012]
or
Give the scientific name of the microbes from which cyclosporin-A and statin are obtained. Write one medical use of each one of these drugs. [Foreign 2011]
Ans. Statin is produced by yeast Monascus purpureus. It is used as blood cholesterol lowering agent.
It acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol.
or
Cyclosporin-A is produced by the fungus Trichoderma polysporum. It is used as an immunosuppressive agent in organ-transplant patients.
Statin is produced by yeast Monascus purpureus. It is used as blood cholesterol lowering agent.
It acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol.

16. Why are some molecules called bioactive molecules? Give two examples of such molecules. [All India 2011]
Ans. Bioactive molecules are produced from living organisms and are useful in other living organisms. Examples are streptokinase, cyclosporin-A, statins.

17. How does addition of a small amount of curd to fresh milk help formation of curd? Mention a nutritional quality that gets added to the curd. [Delhi 2010]
or
Explain the change fresh milk undergoes when a small amount of curd as starter is added to it and kept at suitable temperature. [Delhi 2009c]
Ans. When a small amount of curd as starter is added to fresh milk, millions of Lactic Acid Bacteria (LAB) present in the starter grow in milk and convert it to curd. During this process, acids are produced by LAB that coagulate and partially digest the milk proteins (casein). LAB increases vitamin-B₁₂content along with other vitamins in the curd

18. During the secondary treatment of the primary effluent. How does the significant decrease in BOD occur? [Delhi 2009]
Ans. During the secondary treatment, the aeration allows vigorous growth of useful aerobic microbes into floes (masses of bacterial cells in association with fungalfilaments forming mesh-like structures). As they grow, the microbes consume a major part of the organic matter in the effluent, so BOD is significantly reduced.

19. Identify A, B, C and D in table given below: [All India 2009C]

Ans.A- Streptococcus
B- Cyclosporin-A
C- Immunosuppressive agent
D-Myocardial infarction

20. Name the blank spaces A, B, C and D in the table given below:
[Delhi 2008]

Ans.A- Penicillium notatum B- Acetic acid
C- Fungus
D- Saccharomyces cerevisiae

21. Name the blank spaces A, B, C and D given in following table:[All India 2008]

Ans.A- Lactobacillus
B- Trichoderma polysporum
C- Yeast
D-Penicillin

22. Name the blank spaces A, B, C and D given in the following table:
[All India 2008]

Ans. A- Streptococcus
B- Fungus
C- Cyclosporin-A
D- Clostridium butylicum

23.Name the blank spaces A, B, C and D from the table given below:
[All India 2008]

Ans.A- Trichoderma polysporum
B- Immunosuppressive agent
C- Yeast
D- Blood cholesterol lowering agent

24. State the use of following enzymes/acids produced by the microbes
(i)lipase (ii) lactic acid
(iii) streptokinase (iv) pectinase [Foreign 2008]
Ans. The use of following products formed by microbes are:
(i) Lipase is used in detergent preparation and in removal of oil stains from clothes.
(ii) Lactic acid produced by Lactobacillus converts milk into curd.
(iii) Streptokinase is used as a ‘clot buster’ for removing blood clots from blood vessels in patients of myocardial rction.
(iv) Pactinase is used to clear (bottled) fruit juices.

25. How has fungus Trichoderma polysporum proved to be very essential to organ transplant patients? [Delhi 2008C]
Ans.This fungus produces a bioactive molecule, called cyclosporin-A, which is used as an immunosuppressive agent in organ transplant patients.

3 Marks Questions
26. Identify A, B, C, D, E and F in the table given below: [Foreign 2014]

Ans.The codes are identified as
A- Clot buster in patents who underwent myocardial infarction.
B- Trichoderma polysporum
C- Immunosuppressive agent in organ transplantation
D- Statins
E – Blood cholesterol lowering agents
F – Lactic acid

27. Name the two different categories of microbes naturally occurring in sewage water. Explain their role in cleaning sewage water into usable water. [Delhi 2012]
Ans. Bacteria and fungi are the two categories of naturally occurring microbes in sewage. The bacteria along with the fungal mycelia form the floes. These floes are utilised during the secondary treatment of sewage. The primary effluent after separation of the grit and debris is taken to the secondary treatment.
Here, the effluent is passed to an aeration tank, where it is constantly agitated and air is pumped into it. This leads to vigorous growth of bacteria and floe formation. The bacteria in these floes consume organic matter, thus decreasing the BOD of the sewage.

28. Explain the different steps involved in sewage treatment before it can be released into natural water bodies. [Foreign 2011]
Ans.Sewage treatment includes following steps:
(i) Primary Treatment

It is a physical process of removal of small and large particles through filtration and sedimentation.
The first step is to remove the floating objects (like polythene bags) by letting the sewage to pass through wire mesh screens of sequential smaller pore sizes.
Sewage is then passed into the grit chamber, where grit is sedimented.
Sewage is then allowed to pass into the settling tank, where the suspended materials settle down to form primary sludge.
Effluent is then taken for the secondary treatment.
(ii)Secondary Treatment
It is a biological process in which bacteria naturally occurring in sewage are used.
Effluent obtained from the primary treatment is passed into large aeration tank. Here, it is constantly agitated and air is pumped into it.
Due to this, rapid growth of aerobic bacteria occur into floes. These consume the organic matter of the sewage and reduce the BOD.
Effluent is passed into settling tank, where the floes are allowed to settle forming the activated sludge.
A small amount of activated sludge is pumped back into aeration tank as inoculum.
The remaining major part of the activated sludge is pumped into anaerobic sludge digesters, where the anaerobic bacteria digest the organic matter and produce methane, hydrogen sulphide and carbon dioxide.
Effluent is then allowed to pass into the water body.

29. Identify A, B, C, D, E and F in the table given below:
—————————-29—————————
Ans.A-Statins, B-They are used as blood cholesterol lowering agent, C-Penicillium notatum, D-Penicillin, E-Trichoderma polysporum, F-Used as an immunosuppressive agent in organ transplant patients.

30. Mention the product and its use produced by each of the microbes listed below:

Streptococcus
Lactobacillus
Saccharomyces cerevisiae [All India 20101]

Ans.(i) Streptococcus Product is streptokinase. It is used as a clot-buster for removing the clots from the blood vessels of patients suffering from myocardial infarction.
(ii) Lactobacillus Product is lactic acid. It is used to convert milk into curd and improves nutrient quality of curd by enriching it with vitamin-B12.
(iii) Saccharomyces cerevisiae Product is ethanol and also used for bread making and beverages.31. Describe how biogas is obtained from the activated sludge?
[Foreign 2010]
Ans. Biogas formation from activated sludge:
(i) A small part of activated sludge is pumped into the aeration tank to serve as inoculum. It grows into floes and consume organic matter to reduce BOD.
(ii) The remaining major part of sludge is pumped into large tanks called anaerobic sludge digesters.
(iii) Here, anaerobic bacteria digest the organic material of the sludge.
(iv) During this digestion, the bacteria produces a mixture of gases like carbon dioxide, methane and hydrogen sulphide which form the biogas.

32. (i) How does activated sludge get produced during sewage treatment?
(ii) Explain how this sludge is used in biogas production? [All India 2009]
Ans.(i) (a) The primary effluent is passed into large aeration tanks. Due to the constant agitation floes formation occur, which are masses of bacteria associated with fungal hyphae.
(b) These microbes consumes sufficient quantity of organic matter and there by reduce BOD.
(c) Once, the BOD of sewage water gets reduced significantly, the effluent is passed into a settling tank, where the bacterial floes undergo sedimentation and the sediment is called activated sludge.
(ii) Biogas formation from activated sludge:
(i) A small part of activated sludge is pumped into the aeration tank to serve as inoculum. It grows into floes and consume organic matter to reduce BOD.
(ii) The remaining major part of sludge is pumped into large tanks called anaerobic sludge digesters.
(iii) Here, anaerobic bacteria digest the organic material of the sludge.
(iv) During this digestion, the bacteria produces a mixture of gases like carbon dioxide, methane and hydrogen sulphide which form the biogas.

33. How are floes produced in the secondary treatment plant of the sewage? Explain their role. [All India 2009C]
Ans. The effluent obtained from primary treatment is passed into large aeration tanks, where it is constantly agitated and air is pumped into it. This allows rapid growth of aerobic microbes into floes.

Floes consume organic matter of the sewage and reduce the Biochemical Oxygen Demand (BOD). When BOD of sewage is reduced, the effluent is passed into a settling tank, where the floes are allowed to form the activated sludge.

34. (i)Expand BOD.
(ii) At a particular segment of a river near a sugar factory, the BOD is much higher than the normal level. What is it indicative of? What will happen to the living organism in this part of the river?
(iii) Under what conditions will the BOD be lowered in the river? How will it affect the aquatic life? [HOTS; Foreign 2008]
Ans. (i) Biochemical Oxygen Demand.
(ii) The higher BOD indicates high organic matter in river. Microbes involved in the biodegradation of organic matter in water body consume a lot of oxygen.
Due to this, a sharp decline occur in the amount of dissolved oxygen. This leads to killing of fish and othe microorganisms in that part of river.
(iii) BOD of water body decreases when the amount of organic matter decreases. Thus, microbes do not need oxygen for its decomposition.
Due to the decreased BOD, aquatic life will start flourishing.

5 Marks Questions
35. Explain the process of sewage water treatment before it can be discharged into natural water bodies. Why is this treatment essential? [All India 2014]
Ans. The process of sewage water treatment before being discharged into natural water bodies.
Sewage treatment includes following steps:
(i) Primary Treatment

It is a physical process of removal of small and large particles through filtration and sedimentation.
The first step is to remove the floating objects (like polythene bags) by letting the sewage to pass through wire mesh screens of sequential smaller pore sizes.
Sewage is then passed into the grit chamber, where grit is sedimented.
Sewage is then allowed to pass into the settling tank, where the suspended materials settle down to form primary sludge.
Effluent is then taken for the secondary treatment.
(ii)Secondary Treatment
It is a biological process in which bacteria naturally occurring in sewage are used.
Effluent obtained from the primary treatment is passed into large aeration tank. Here, it is constantly agitated and air is pumped into it.
Due to this, rapid growth of aerobic bacteria occur into floes. These consume the organic matter of the sewage and reduce the BOD.
Effluent is passed into settling tank, where the floes are allowed to settle forming the activated sludge.
A small amount of activated sludge is pumped back into aeration tank as inoculum.
The remaining major part of the activated sludge is pumped into anaerobic sludge digesters, where the anaerobic bacteria digest the organic matter and produce methane, hydrogen sulphide and carbon dioxide.
Effluent is then allowed to pass into the water body
This sewage treatment is essential before being released into water bodies as it leads to water pollution and as a consequence increase in water borne diseases.

36. (i) Name the category of microbes naturally occurring in sewage and making it less polluted during the treatment.
(ii) Explain the different steps involved in the secondary treatment of sewage. [Foreign 2014]
Ans. (i) The category of microbes naturally occurring in sewage and making it less polluted are bacteria and fungi, wherein masses of bacteria gets associated with filaments of fungi to form mesh like structure called floes.
(ii) The different steps involved in secondary or biological treatment of sewage.
Secondary Treatment

It is a biological process in which bacteria naturally occurring in sewage are used.
Effluent obtained from the primary treatment is passed into large aeration tank. Here, it is constantly agitated and air is pumped into it.
Due to this, rapid growth of aerobic bacteria occur into floes. These consume the organic matter of the sewage and reduce the BOD.
Effluent is passed into settling tank, where the floes are allowed to settle forming the activated sludge.
A small amount of activated sludge is pumped back into aeration tank as inoculum.
The remaining major part of the activated sludge is pumped into anaerobic sludge digesters, where the anaerobic bacteria digest the organic matter and produce methane, hydrogen sulphide and carbon dioxide.
Effluent is then allowed to pass into the water body

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