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Chapter: 12th Zoology : Chapter 9 : Microbes in Human Welfare

Microbes in Human Welfare: Questions and Answers (Evaluation)

Zoology : Microbes in Human Welfare : Book Back Questions Answers: Choose the Correct Answers, Short Answers, brief Answers, Important Questions and Answers



1. Which of the following microorganism is used for production of citric acid in industries?

a) Lactobacillus bulgaris

b) Penicillium citrinum

c) Aspergillus niger

d) Rhizopus nigricans

Answer: c) Aspergillus niger


2. Which of the following pair is correctly matched for the product produced by them?

a) Acetobacter aceti - Antibiotics

b) Methanobacterium - Lactic acid

c) Penicilium notatum - Acetic acid

d) Saccharomyces cerevisiae - Ethanol

Answer: d) Saccharomyces cerevisiae - Ethanol


3. The most common substrate used in distilleries for the production of ethanol is_________

a) Soyameal

b) Groundgram

c) Molasses

d) Corn meal

Answer: c) Molasses


4. Cry toxins obtained from Bacillus thuringiensis are effective against for______

a) Mosquitoes

b) Flies

c) Nematodes

d) Bollworms

Answer: d) Bollworms


5. Cyclosporin – A is an immunosuppressive drug produced from _______

a) Aspergillus niger

b) Manascus purpureus

c) Penicillium notatum

d) Trichoderma polysporum

Answer: d) Trichoderma polysporum


6. Which of the following bacteria is used extensively as a bio-pesticide?

a) Bacillus thurigiensis

b) Bacillus subtilis

c) Lactobacillus acidophilus

d) Streptococcus lactis

Answer: a) Bacillus thurigiensis


7. Which of the following is not involved in nitrogen fixation?

a) Pseudomonas

b) Azotobacter

c) Anabaena

d) Nostac

Answer: a) Pseudomonas


8. CO2 is not released during

a) Alcoholic fermentation

b) Lactate fermentation

c) Aerobic respiration in animals

d) Aerobic respiration in plants

Answer: b) Lactate fermentation


9. The purpose of biological treatment of waste water is to _______

a) Reduce BOD

b) Increase BOD

c) Reduce sedimentation

d) Increase sedimentation

Answer: a) Reduce BOD


10. The gases produced in anaerobic sludge digesters are

a) Methane, oxygen and hydrogen sulphide.

b) Hydrogen sulphide, methane and sulphur dioxide.

c) Hydrogen sulphide, nitrogen and methane.

d) Methane, hydrogen sulphide and CO2.

Answer: d) Methane, hydrogensulphide and CO2


11. How is milk converted into curd? Explain the process of curd formation.

a) It is prepared by the action of LAB (Lactic Acid Bacteria)

b) It grows in milk and digesting the milk protein casein and converts it into curd.

Process of curd formation :

1. A small amount of curd added to fresh milk as starter or inoculum

2. It contains millions of Lactobacilli

3. Under suitable temperature ie 40 ° C

4. They partially digest the milk proteins casein

5. Curd is more nutritious than milk as it contains a number of organic acids and vitamins (Vit-B12)


12. Give any two bioactive molecules produced by microbes and state their uses.

1. Streptokinase 2. Cyclosporin A

1. Streptokinase :

Produced by the bacterium streptococcus and genetically engineered streptococci.

It is used as "clot buster" for removing clots from the blood vessels of patients who have undergone myocardial infraction.

2. Cyclosporin :

It is produced from the fungus Trichoderma polysporium

It is used as an immuno suppressant in organ transplantation.

It is also used for its antiinflammatory anti - fungal and anti - parasitic properties.


13. What is biological oxygen demand?

BOD refers to the amount of the oxygen that would be consumed, if all the organic matter in one litre of water were oxidized by bacteria.

The greater the BOD of the waste water more is its polluting potential.


14. Explain the role of cry-genes in genetically modified crops.

Bacillus thuringiensis is a soil dwelling bacteria.

It is an example of mircobial bio control agents that can be introduced in order to control butterfly caterpillars.

It is used as a biopesticide

It contains a toxin called cry toxin.

Scientists have introduced this toxin producing genes into plants and have raised genetically engineered insect resistant plants. eg:- Bt - Cotton

During sporulation Bacillus thuringiensis produces crystal proteins called Delta - end otoxin which is encoded by "cry genes'.

When the insects ingest the toxin crystals their alkaline digestive tract denatures the insoluble crystals making them soluble.

The 'crytoxin' then gets inserted into the gut cell membrance and paralyzes the digestive tract.

The insect then stops eating and starves to death.

This toxin can kill certain insects of the order Lepidoptera, Diptera, Coleoptera and Hymenoptera.


15. Write the key features of organic farming.

Key features of organic farming :-

Protecting soil quality using organic materials and encouraging biological activity.

Indirect provision of crop nutrients using soil micro organisms.

Nitrogen fixation in soil using legumes.

Weed and pest control based on methods like crop rotation, biological diversity, natural predators, organic manures and suitable chemical, thermal and biological intervention.


16. Justify the role of microbes as a bio-fertilizer.

Bio fertilizers are living micro organism that enrich the nutrient quality of the soil.

They increase physico - chemical properties of soil such as structure, water holding capacity, and PH by providing several nutrients, and sufficient organic matter.

The main sources of biofertilizers are bacteria fungi and cyano bacteria.

Rhizobium is a classical example for symbiotic Nitrogen fixing bacteria that infects the root nodules of leguminous plants and fixes atmospheric nitrogen into organic forms.

A symbiotic association between a fungus and the roots of the plant called mycorrhiza absorbs the phosphorous from soil and transfers to the plant. e.g. Genus Glomus form mycorrhiza

Plants with such association also show other benefits such as resistance to root born pathogens, tolerence, to salinity, drought, enhances plant growth and developments.

Cyanobacteria or blue green algae can fix molecular nitrogen.e.g.:- oscillatoria, Nostoc, Anabaena, Tolypothrix.

They secrete growth promoting substances like indole - 3 -acetic acid, indole - 3 - butyric acid naphthalene acetic acid, amino acids, proteins, vitamins, which promotes plant growth and production.

Thus biofertilizers are used in organic farming methods which involves cultivation of plants and rearing of animals in natural ways, avoiding synthetic substances.


17. Write short notes on the following.

a) Brewer's yeast b) Ideonella sakaiensis c) Microbial fuel cells

a) Brewer's yeast:

Saccharomyees cerevisiae used for bread making and commonly called brewer's yeast

It is used for fermenting malted cereals and fruit juices to produce various alcoholic beverages.

Wine and beer are produced without distillation.

Whisky, brandy and rum are obtained by fermentation and distillation.

b) Ideonella sakaiensis

It is currently tried for recycling of PET plastics.

These bacteria use PETase and MHETase enzymes to break down PET plastic into terephthalic acid and ethylene glycol.

c) Microbial fuel cells

It is a bio - electrochemical system that drives an electric current by using bacteria.

If mimicks bacterial interaction found in nature.

Bacterial respiration involves redox  reaction in which electrons are being moved around.

MFC consists of an anode and a cathode separated by a proton exchange membrane.

Microbes at the anode oxidize the organic fuel.

It generates protons which pass through the membrane to the cathode.

Electrons pass through the anode to the external circuit to generate current.


18. List the advantages of biogas plants in rural areas.

Biogas can be produced from raw materials such as agricultural wastes, manure, municipal water, plant material, sewage, food waste etc.

Cattle dung is available in large quantities in rural areas where cattle are used for a variety of purposes.

The organic materials are converted into gas and organic fertilizer under microbial reactions.

It is a renewable natural gas.

It provides reliable, clean and cheap energy.

It has high calorific value.

Creating a bio gas system for a rural home is much simple.

This system produces methane gas which flows through a PVC pipe to the home where we can turn it on when we need to use it.

It also produces manure that is free of pathogens which farmers can use as fertilizer.

People need not collect large amounts of fire wood and the emission of smoke from burning fire wood is also reduced.

A bio gas system can replace approximately the related 4 tons of annual green house gas emission according to world wild life fund.

Using the biogas resource materials available in our daily life when used as a fuel source reduces the amount of methane released into the atmosphere.

Thus turning the waste into biogas could solve both the energy problem and the sanitation problem.

Once people do have biogas systems in their homes they can live healthier and comfortable while also reducing their impacts on the environment.,

So Biogas plants are more often built in rural areas. 


19. When does antibiotic resistance develop?

Antibiotic resistance occurs when bacteria develop the ability to defeat the during designed to kill or inhibit their growth.

Now a days, it is one of the most acute threat to public health.

It may be due to misuse and overuse of antibiotics also due to poor infection prevention control.

Antibiotics prescribed by a certified health professional alone should be used.

Narrow spectrum antibiotics are preferred over broad spectrum antibiotics.

They accurately target specific pathogens and are less likely to cause resistance.

When the bacteria become resistant antibiotics cannot fight against them and the bacteria multiply.

"Superbug" is a term used to describe strains of bacteria that are resistant to the majority of antibiotics commonly used today.


20. What is the key difference between primary and secondary sewage treatment?

Primary treatment

1. It is a physical process involves removal of solid particles of organic and in organic materials from sewage

2. Removal of larger solid wastes by filtration and sedimentation

3. BOD is not reduced in this step

4. Filters and Grit chambers are used to separate solid particles

5. No biogases are produced.

6. It takes a shorter period to finish.

Secondary treatment

1. It involves microbiological degradation of organic matter in the primary efficient.

2. Biological treatment through microbes

Involves growth of useful aerobic microbes and anaerobic bacteria to decompose the smaller particles already dissolved.

3. BOD is reduced by "flocs"

4. Aeration tanks and anaerobic sludge digester are used to treat the sewage.

5. During the digestion of bacteria and fungi in the sludge gases like methane, hydrogen sulphide and CO2 are produced which can be used as biogas.

6. It takes much longer as organic microbes consume the waste.


Extra One mark Questions and Answers


1. When domestic sewage mixes with river water

a) Small animals like rat will die after drinking river water

b) The increased microbial activity releases micronutrients such as iron.

c) The increased microbial activity uses up dissolved oxygen.

d) The river water is still suitable for drinking as impurities are only about 0.1 per cent


2. Select the correct statement from the following.

a) Biogas is produced by the activity of aerobic bacteria on animal waste.

b) Methanobacterium is an aerobic bacterium found in rumen of cattle.

c) Biogas, commonly called gober gas, is pure methane.

d) Activated sludge-sediment in settlement tank of sewage treatment plant is a right source of aerobic bacteria.


3. Read the following four statements (A to D):

A) Colostrums is recommended for the new born because it is rich in antigen.

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) Three

b) Four

c) One

d) Two


4. Which of the following are likely to be present in deep sea water?

a) Archaebacteria

b) Eubacteria

c) Blue – green algae

d) Saprophytic fungi


5. During sewage treatment, biogas are produced which includes

a) Methane, hydrogen sulphide, carbon dioxide

b) Methane, oxygen, hydrogen sulphide

c) Hydrogen sulphide, methane, sulphur dioxide

d) Hydrogen sulphide, nitrogen, methane


6. What gases are produced in anaerobic sludge digesters?

a) Methane and CO2 only

b) Methane, hydrogen sulphide and CO2

c) Methane, hydrogen sulphide and O2

d) Hydrogen sulphide and CO2

e) Consumption of organic matter in the water is higher by the microbes


7. Match the following list of microbes and their importance:

a)Saccharomyces cerevisiae (i)Production of immunosuppressive agents

b)Monasus 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) (iv) (iii) (ii) (i)

b) (iv) (ii) (i) (iii)

c) (iii) (i) (iv) (ii)

d) (iii) (iv) (i) (ii)


8. Which of the following is wrongly matched in the given table?

(a) Microbe: Trichoderma polysporum, Product: Cyclosporin A , Application: Immunosuppressive drug

(b) Microbe:Monascus purpureus, Product: Statins, Application:  Lowering of blood cholesterol

(c) Microbe:Streptococcus, Product: Sterptockinase , Application: Removal of clot from blood vessel

(d) Microbe: Clostridium, Product: butylicum Lipase , Application: Removal of oil stains


9.  Match Column – I with Column – II and select the correct options using the codes given 9.below:

Column I :

A.Citric acid

B.Cyclosporin A


D.Butyric acid

Column II :

1. Trichoderma

2. Clostridium

3. Aspergillus

4. Monoscus

a) A:3, B:1, C:4, D:2

b) A:1, B:4, C:2, D:3

c) A:3, B:4, C:1, D:2

d) A:3, B:1, C:2, D:4

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