Class XII – Microbes in Human Welfare – PYQs

Ans. Generally, Lactic Acid Bacteria (LAB) are found in milk and its products.

Some useful applications of LAB are

• LAB play very beneficial role in checking disease causing microbes in our stomach.
• They also improve nutritional quality by increasing vitamin-B12 content of the curd.

Ans. Some Indian traditional food made of wheat, rice and Bengal gram are

Wheat–Bhature and nan

Rice–Idli and dosa

Bengal gram–Dhokla and khandvi

Ans. The three household products along with the names of the microorganisms producing them are as given below

Items                           Microorganisms

(i) Curd –                    Lactobacillus

(ii) Bread –                  Saccharomyces cerevisiae

(iii) Swiss cheese –     Propionibacterium shermanii

Ans. Microbes play major role in controlling diseases by harmful bacteria as they are used in preparing medicines. The most important medicines for which microbes are used, are antibiotics. These are chemical compounds produced by some microbes, which are used to kill or to subside the growth of other diseases causing microbes. Streptomycin, tetracycline and penicillin are some of the commonly used antibiotics. Antibiotics have significantly contributed towards the welfare of the human society.

Ans. Bioactive molecules are produced from microbes that are useful to other living organisms in modifying their metabolism, e.g. streptokinase, cyclosporin-A, statins, etc.

6. Find out the name of microbes from which cyclosporin-A and statins are obtained.

Ans. (i) Cyclosporin-A is obtained from the fungus, Trichoderma polysporum.

(ii) Statins is obtained from yeast, Monascus purpureus.

Ans. Sewage is the municipal wastewater collected from city or town homes that contain toilet, bathroom and kitchen waste. It contains large amounts of organic matter and many pathogenic microbes which are harmful to humans as they can cause diseases like cholera, typhoid, polio, etc.

Ans. During secondary treatment, the primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it which allows vigorous growth of useful aerobic microbes into flocs, i.e. masses of bacterial cells in association with fungal filaments, forming mesh-like structure. As they grow, the microbes consume a major part of the organic matter in the effluent, which significantly reduces BOD.

Ans. In sewage treatment, flocs consume major part of the organic matter, converting it into microbial biomass and releasing lot of minerals. It reduces the BOD of sewage. While in anaerobic sludge digesters, many anaerobic bacteria are present, which digest the organic mass as well as aerobic microbes. During this digestion, methane, CO₂, etc., are produced.

Ans. Differences between primary and secondary sewage treatment are as follows

Ans. Two different categories of microbes naturally occurring in sewage water are aerobic and anaerobic microbes.

(i) Role of aerobic microbes in cleaning water Aerobic microbes grow excessively in the aeration tank and consumes a major part of the organic matter. It helps in reducing the BOD of the effluent.

(ii) Role of anaerobic microbes in cleaning water In the settling tank, anaerobic microbes digest the aerobic bacteria and fungi and produce gases like CH₄, CO₂, H₂S, etc. It makes the water less polluted to be released in the water bodies.

Ans. Yes, microbes can be used as a source of energy, e.g. methanogens like Methanobacterium are used to produce biogas, which is a source of energy.

Ans. Bacteria which grow anaerobically on cellulosic material, produce large amounts of methane along with CO2 and H2 are called methanogens (one of the common bacterium is Methanobacterium).

Methanogens are found in anaerobic sludge and in rumen of cattle. These methanogens are grown in slurry which comprises of cattle dung, they act upon it by breaking it down and release gases like methane and CO₂. Hence, methanogens help to generate biogas.

Ans. A genus of baculoviruses is Nucleopolyhedrovirus. They are considered good biological control agents because of their species-specific and narrow spectrum insecticidal applications. They do not have any negative impact on plants, mammals, birds, fish or even on non-target insects.

Thus, making them useful in overall integrated pest management programme.

(i) Nucleopolyhedrovirus – Nucleopolyhedrovirus is widely used biopesticide in crop fields.

(ii) Saccharomyces cerevisiae – Saccharomyces cerevisiae commonly called brewer’s yeast, is used for fermenting malted cereals and fruit juices to ethanol.

(iii) Monascus purpureus – Statins are produced by yeast, Monascus purpureus. These have been commercialised as blood cholesterol lowering agents.

(iv) Trichoderma polysporum – Cyclosporin-A is produced by the fungus, Trichoderma polysporum and it is used as an immunosuppressive agent in case of organ transplants.

(v) Penicillium notatum – Penicillium notatum is used for the production of penicillin.

(vi) Propionibacterium shermanii – Propionibacterium shermanii is used to produce Swiss cheese.

Ans. Organic farmers do not recommend eradication of insect-pests as without them, the beneficial predatory and parasitic insects which depend upon pests as food or hosts would not be able to survive.

Ans. The organic farmers control pests by the use of insect pest’s resistant varieties. The two examples are

(a) The Pusa Gaurav variety of Brassica is resistant to aphids.

(b) Pusa Sawani variety of okra is resistant to shoot and fruit borer.

Ans. The use of resistant variety is safer to control the pests as it does not involve chemical pesticides which are used in conventional method of controlling pests. Thus, it is environmental friendly method and reduce soil pollution.

Ans. Microbes can be used to decrease the use of chemical fertilisers and pesticides as

(i) Microbes play an important role in organic farming, which reduce the use of chemical fertilisers and pesticides, etc.

(ii) They act as biofertilisers which help in increasing the fertility of the soil. They also help in improving plant growth by supplying plant nutrients. Many species of bacteria and cyanobacteria help in fixing the nitrogen in the soil.

(iii) Many biological agents like ladybird and Bacillus thuringiensis, etc., are useful in eradicating pests.

Ans. The main sources of biofertilisers are bacteria, fungi and cyanobacteria. They help in enriching the fertility of the soil in many ways

(i) Rhizobium that forms nodules on the roots of leguminous plants (a symbiotic association) fixes atmospheric nitrogen into organic forms, which is used by the plant as nutrient.

(ii) Azospirillum and Azotobacter fix atmospheric nitrogen, while living freely and enriching the nitrogen content of the soil.

(iii) Many members of the genus–Glomus (fungi) form symbiotic associations with plant known as mycorrhiza that

(a) absorb phosphorus from soil and pass it to the plant.

(b) help the plants to develop resistance to root-borne pathogens.

(iv) Cyanobacteria autotrophic microbes, e.g. Anabaena, Nostoc, Oscillatoria can fix atmospheric nitrogen in aquatic and terrestrial environment and also add organic matter to the soil and increase its fertility.

Ans. Rhizobium lives in the root nodules of leguminous plants and fixes the atmospheric nitrogen in the soil as nitrogenous compounds that can be utilised by the plants as nutrients. Since, both are mutually benefitted, it is called symbiotic bacterium. Hence, Rhizobium acts as a biofertiliser.

Ans. The two microorganisms belonging to two different kingdoms that are commonly used as biofertiliser are

1. Fungi

Many members of genus–Glomus form mycorrhiza. Plants with mycorrhizal association show benefits such as

(i) Resistance to root-borne pathogens.

(ii) Tolerance to salinity and drought.

(iii) Increase in plant growth and development.

2. Bacteria

Nitrogen-fixing bacteria fix atmospheric nitrogen into organic form, which is used by the plant as nutrient, e.g. Rhizobium is a symbiotic bacterium that lives in the root nodules of legumes and fixes atmospheric nitrogen into organic compounds. Azotobacter and Azospirillum are free-living bacteria, which absorb free nitrogen from the soil, air and convert it into salts of nitrogen compounds.

Ans. The three microbes that can be chosen for organic farming are

(i) Rhizobium: The nodules on the roots of leguminous plants are formed by the symbiotic association of Rhizobium bacteria. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plants as nutrient.

(ii) Mycorrhiza: Fungi form symbiotic association with plants called mycorrhiza. The fungal symbiont absorbs phosphorus from soil and passes it to the plant. Such plant shows resistance to root-borne pathogens, tolerance to salinity and drought and overall increase in plant growth and development.

(iii) Anabaena: It is a cyanobacteria that is used as a biofertiliser. It fixes atmospheric nitrogen.

Ans. The sewage treatment is essential before being released into water bodies as it leads to water pollution and as a consequence increased incidence of waterborne diseases.

This treatment is carried out in two stages

Primary Treatment:

It is also known as physical treatment because it basically involves physical removal of small and large, floating and suspended solids from sewage through filtration and sedimentation. Initially, floating debris is removed by sequential filtration.

Then, the grit (soil and small pebbles) are removed by sedimentation in settling tanks. Aluminium or iron sulphate is added in certain places for flocculation.

All solids that settle form the primary sludge. It traps lots of microbes and debris. The supernatant forms the effluent. This effluent is then taken from the primary settling tank for secondary treatment.

Secondary Treatment

This treatment is also known as biological treatment because it involves the use of microbes or microbiota for the treatment of sewage.

• The effluent from primary treatment is passed into large aeration tanks, where it is constantly, mechanically agitated and air is pumped into it which helps in the growth of useful aerobic microbes into flocs. While growing, these microbes consume major part of the organic matter converting it into microbial biomass and releasing lot of minerals. This significantly reduces the Biochemical Oxygen Demand (BOD). The sewage water is treated till the BOD is reduced.
• The sewage water is treated till the BOD is reduced. n When the BOD of effluent is reduced significantly, it is then 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 then pumped back into the aeration tank to serve as the inoculum.
• The remaining part of the sludge is pumped back into large tanks called anaerobic sludge digesters, in which other anaerobic bacteria (methanogens) are also present.

They digest the organic mass as well as aerobic microbes (bacteria and fungi of the sludge). During the digestion, mixture of gases like methane (CH₄), hydrogen sulphide (H₂S), carbon dioxide (CO₂), etc., are produced.

• These gases form biogas that is used as a source of energy because it is inflammable. The effluent from secondary treatment plant is released into natural water bodies like rivers and streams.

Ans. Hetrotrophic microbes are naturally occurring in sewage which make it less polluted during sewage treatment.