NCERT MOST IMPORTANT QUESTIONS CLASS – 12 | BIOLOGY IMPORTANT QUESTIONS | CHAPTER – 10 | MICROBES IN HUMAN WELFARE| EDUGROWN |

In This Post we are  providing Chapter- 10 MICROBES IN HUMAN WELFARE NCERT MOST IMPORTANT QUESTIONS for Class 12 BIOLOGY which will be beneficial for students. These solutions are updated according to 2021-22 syllabus. These MCQS  can be really helpful in the preparation of Board exams and will provide you with a brief knowledge of the chapter

NCERT MOST IMPORTANT QUESTIONS ON MICROBES IN HUMAN WELFARE

Question 1.

Name the toxin produced by B. Thuringiensis.
Answer:
∝-exotoxin, β-exotoxin, γ-exotoxin, and louse factor

(ii) Nitrogen fixers are available on a commercial basis in the market? Also, name the beneficial crop and microbes used in the following table.

Product	Microbe used	Beneficial crop
1. NitraginTM	(A)	Soybean
2. Rhizocote	Rhizobium	(B)
3. Nodosit	Rhizobium	(C)

Answer:
A. Rhizobium B. Legume C. Legume

(iii) Expand BOD and COD
Answer:
BOD- Biological Oxygen Demand COD- Chemical Oxygen Demand

Question 2.
By a flow chart showing the stages in anaerobic digestion during the production of biogas.
Answer:

Stages in Anaerobic Digestion during biogas formation

Question 3.
Given below is a list of six microorganisms. State their usefulness to humans.
(i) Nucleopolyhedrovirus
(ii) Saccharomyces cerevisiae
(iii) Monascus Purpureus
(iv) Trichoderma polypore
(v) Penicillium Notatum
(vi) Propionibacterium shamanic.
Answer:

Name of Micro-organisms	Uses
(i) Nucleopolyhedrovirus	Used in biocontrol of insects
(ii) Saccharomyces cerevisiae	Bread making, Ethanol making
(iii) Monascus Purpureus	Produces Statin used as blood cholesterol-lowering agent
(iv) Trichoderma polypore	Preparation of cyclosporin having antifungal, anti-inflammatory, immuno-suppressive properties
(v) Penicillium Notatum	Production of antibiotic, Penicillin
(vi) Propionibacterium shamanic	Preparation of large-holed swiss cheese.

Question 4.
Explain the different steps involved in the secondary treatment of sewage. (CBSE Sample paper 2018—19)
Or
Secondary treatment of sewage is also called biological treatment. Justify this statement and explain the process. (CBSE 2018)
Answer:

1. Secondary treatment of sewage is a biological process that employs the heterotrophic bacteria naturally present in the sewage.
2. The effluent from the primary treatment is passed into large aeration tanks, where it is constantly agitated and the air is pumped into it.
3. This allows the rapid growth of aerobic microbes into ‘floes’ which consume the organic matter of the sewage and reduce the biological oxygen demand (BOD). The greater is the BOD of wastewater, the more is its polluting potential.
4. When the BOD of sewage is reduced significantly, the effluent is passed into a settling tank, where the ‘floes’ are allowed to sediment forming the activated sludge.
5. A small part of the activated sludge is pumped back into the aeration tanks.
6. The remaining major part of the sludge is pumped into anaerobic sludge digesters, where the anaerobic bacteria digest the bacteria and fungi in the sludge-producing methane, hydrogen sulfide, and carbon dioxide,
   i. e. biogas. This is why secondary treatment of sewage is also called biological treatment.
7. The effluent after secondary treatment is released into water-bodies like streams or rivers.

Question 5.
Microbes can be used to decrease the use of chemical fertilizers. Explain how this can be accomplished. (CBSE Delhi 2019)
Answer:

1. Rhizobium bacteria present in the root nodules of leguminous plants (pea family) forms a symbiotic association and fixes atmospheric nitrogen into organic forms as nitrates/nitrites which are used by the plant as nutrient.
2. Free-living bacteria in the soil Azospirillum and Azotobacter can fix atmospheric nitrogen thus enriching the nitrogen content of the soil.
3. Many members of the genus Glomus (Fungi) form mycorrhizal symbiotic associations with higher plants. In these, the fungal symbiont absorbs phosphorus from soil and passes it to the plant.

Question 6.
Organic farmers prefer biological control of diseases and pests to the use of chemicals for the same purpose. Justify.
Answer:
Chemical methods often kill both useful and harmful living beings indiscriminately. The organic farmer holds the view that the eradication of the creatures that are often described as pests is not only possible but also undesirable, for without them the beneficial predatory and parasitic insects which depend upon them as food or hosts would not be able to survive. Thus, the use of biocontrol measures will greatly reduce our dependence on toxic chemicals and pesticides.

(ii) Give an example of a bacterium, a fungus, and an insect that are used as biocontrol agents. (CBSE 2018)
Answer:
Insects = Ladybird and Dragonflies. Bacteria = Bacillus thuringiensis. Fungus = Trichoderma

Question 7.
The three microbes are listed below. Name the product produced by each one of them and mention their use.
(i) Aspergillus niger
(ii) Trichoderma polypore
(iii) Monascus Purpureus (CBSE Delhi 2018C)
Or
(i) A patient had suffered myocardial infarction and clots were found in his blood vessels. Name a ‘clot buster’ that can be used to dissolve clots and the microorganism from which it is obtained.
(ii) A woman had just undergone a kidney transplant. A bioactive molecular drug is administered to oppose kidney rejection by the body. What is the bioactive molecule? Name the microbe from which this is extracted.
(iii) What do doctors prescribe to lower the blood cholesterol level in patients with high blood cholesterol? Name the source organism from which this drug can be obtained.
Answer:
(i) Aspergillus niger produces citric acid. Citric acid is used as a flavoring agent and as a food preservative.
(ii) Trichoderma Polysporum produces a bioactive molecule cyclosporin A. It is used as an immunosuppressive agent in organ transplant patients.
(iii) Monascus Purpureus produces statins. Statins are capable of competitive inhibition of enzymes required for cholesterol synthesis. Hence, it is used as blood cholesterol-lowering agents.
Or
(i) Streptokinase-‘Clot buster’ can be used to dissolve clots. It is obtained from the bacteria Streptococcus.
(ii) The bioactive molecule is Cyclosporin A which is used as an immunosuppressive agent in organ transplantation. It is produced by the fungus Trichoderma Polysporum.
(iii) Doctors prescribe Statins to lower blood cholesterol. It is obtained from the fungus Monascus Purpureus.

Question 8.
Baculoviruses are good examples of biocontrol agents. Justify giving reasons. (CBSE Delhi 2018C)
Answer:
Baculoviruses kill insects and other arthropods, hence they are used as biocontrol agents especially Nucleopolyhedrovirus.

Reasons for their use:

• These viruses are species-specific and have narrow spectrum insecticidal applications.
• They do not harm non-target organisms like other harmless insects, birds, animals, etc.
• It is very useful in integrated pest management programs or treatment of ecologically sensitive areas.

Question 20.
Describe the primary and secondary treatment of domestic sewage before it is released for reuse. (CBSE, 2014)
Answer:
Treatment of domestic sewage. The municipal wastewaters are treated in Effluent Treatment Plant (ETP) prior to disposal in water bodies.

It consists of 3 steps: primary, secondary, and tertiary.
1. Primary treatment. It includes physical processes, such as sedimentation, floatation, shredding (fragmenting and filtering). These processes remove most of the large debris.

2. Secondary treatment. It is a biological method. Activated sludge method. Sewage, after primary treatment, is pumped into aeration tanks or oxidation ponds. Here, it is mixed with air and sludge containing algae and bacteria. Bacteria consume organic matter. The process results in the release of C02 and the formation of sludge or biosolid. Algae produce oxygen for the bacteria. The water, which is now almost clear of organic matter, is chlorinated to kill microorganisms.

3. Tertiary treatment. It involves. removal of nitrates and phosphates. The water, after the above treatment, is then released. It can be reused.

Question 9.
Explain biological control of pests and plant pathogens with examples.
Answer:
The very familiar beetle with red and black markings the Ladybird, and Dragonflies are useful to get rid of aphids and mosquitoes, respectively.

Role of Bacillus Thuringinesis:
Bt Coming to microbial biocontrol agents that can be introduced in order to control butterfly caterpillars is the bacteria Bacillus thuringiensis (often written as Bt). These are available in sachets of dried spores which are mixed with water and sprayed onto vulnerable plants such as Brassica and fruit trees, where these are eaten by the insect larvae. In the gut of the larvae, the toxin is released and the larvae get killed.

The bacterial disease will kill the caterpillars, but leave other insects unharmed. Because of the development of the methods of genetic engineering in the last decade or so, scientists have introduced B. thuringiensis toxin genes into plants. Such plants are resistant to attack by insect pests. Bt-cotton is one such example which is being cultivated in some states of our country.

Biological control of plant pathogens: A biological control developed for use in the treatment of plant disease is the fungus Trichoderma. Trichoderma sp. are free-living fungi that are very common in soil and root ecosystems. They are effective biocontrol agents of several plant pathogens.

Baculoviruses are pathogens that attack insects and other arthropods. The majority of baculoviruses used as biological control agents are in the genus Nucleopolyhedrovirus. These viruses are excellent candidates for species-specific, narrow spectrum insecticidal applications.

They have been shown to have no negative impacts on plants, mammals, birds, fish, or even on non-target insects. This is especially desirable when beneficial insects are being conserved to aid in an overall IPM (integrated pest management) program, or when an ecologically sensitive area is being treated.

Question 22.
How do biofertilizers enrich the soil?
Answer:
Biofertilizers play a vital role to solve the problems of soil fertility and soil productivity.

1. Anabaena azollae, a cyanobacterium, lives in symbiotic association with the free-floating water fern, Azolla. The symbiotic system Azolla-Anabaena complex is known to contribute 40-60 mg N ha-1 per rice crop. In addition to this, cyanobacteria add organic matter, secretes growth-promoting substances like auxins and vitamins, mobilizes insoluble phosphate, and thus improves the physical and chemical nature of the soil.
2. Rhizobium Leguminoserum and Azospirillum fix atmospheric nitrogen as nitrates and nitrites.
3. Mycorrhizae formed by an association of bacteria and roots of higher plants increase soil fertility.

Question 10.
Discuss the role of Microbes as Biofertilizers. (CBSE Delhi 2011, 2015, 2019)
Answer:
Role of microbes as biofertilizers:
Bacteria, cyanobacteria, and fungi (mycorrhiza) are the three groups of organisms used as biofertilizers.
1. Bacteria:
(a) Symbiotic bacteria Rhizobium.
(b) Free-living bacteria Azospirillum and Azotobacter.
(c) They fix the atmospheric nitrogen and enrich soil nutrients.

2.  Cyanobacteria, e.g. Anabaena, Nostoc, Aulosira, Oscillatoria, etc.
(a) They function as biofertilizers by fixing atmospheric nitrogen and
(b) Increasing the organic matter of the soil through their photosynthetic activity.

3. Fungi/mycorrhizae:
(a) Fungi form a symbiotic association with roots of higher plants (mycorrhizae), e.g. Glomus.
(b) The fungus absorbs phosphorus and passes it on to the plant.
(c) Other benefits of mycorrhizae are :

• resistance to root-borne pathogens.
• tolerance to salinity.
• tolerance to drought.
• the overall increase in the plant growth and development