CBSE Class 12 Biology Microbes in Human Welfare Assignment Set A

ASSERTION REASON QUESTIONS

Directions  : Each of these questions contains an Assertion followed by Reason. Read them carefully and answer the question on the basis of following options. You have to select the one that best describes the two statements.
(a) If both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
(b) If both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion.
(c) If Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

Question. Assertion : Lichen is important for chemical industries.
Reason : Litmus and Orcein are formed from lichens.
Answer: A

Question. Assertion : Yeasts such as Saccharomyces cerevisiae are used in baking industry.
Reason : Carbon dioxide produced during fermentation causes bread dough to rise by thermal expansion.
Answer: A

Question. Assertion : Vitamins B2 is found in cereals, green vegetables, brewer's yeast, egg white, milk and liver.
Reason : It can be commercially produced by some yeasts.
Answer: B

Very Short Answer Questions

Question. Give an example of a rod-shaped virus. 
Answer. Tobacco mosaic virus.

Question. Write any two places where methanogens can be found. 
Answer. Anaerobic sludge (digester), rumen of cattle / ruminants / stomach of cattle / gut of cattle, marshy area, flooded rice field, biogas plant. 

Question. Why do we add an inoculum of curd to milk for curdling it ?
Answer. The inoculum contains Lactobacilli which curdles milk into curd with lactic acid. Lactobacillus converts lactose sugar of milk into lactic acid which causes coagulation and partial digestion of milk protein casein. As a result, milk gets changed into curd.

Question. How is lactic acid bacteria beneficial to us other than helping in curdling the milk ?
Answer. Lactic acid bacteria improves the nutritional quality by increasing Vitamin B12.

Question. What causes doughing of wheat flour? 
Answer. Production of CO₂ gas during yeast fermentation of bacteria.

Question. What would have happened if antibiotics were not discovered? 
Answer. If antibiotics were not discovered, bacterial diseases would not have been controllable. 

Question. How is the presence of cyanobacteria in the paddy fields beneficial to rice crop?
Answer. Cyanobacteria can fix atmospheric nitrogen. In paddy fields, the cyanobacteria act as an important biofertiliser. They also add organic matter to soil and increase its fertility.

Question. Mention the role of cyanobacteria as a biofertiliser. 
Answer. It is a biological organism that fixes atmospheric nitrogen.

Question. What are biofertilisers? Give two examples.
Answer. Biofertilisers are organisms that enrich the nutrients in the soil. e.g. Rhizobium, Azotobacter.

Question. Write the scientific name of the microbe used for fermenting malted cereals and fruit juices.
Answer. Saccharomyces cerevisiae.

Question. Why is distillation required for producing certain alcoholic drinks?
Answer. Distillation increases the alcohol content in alcoholic drinks.

Question. Why are drinks like Whisky and Rum more intoxicating than wine? 
Answer. This is because wine is produced without distillation whereas whisky and rum are produced by distillation of the fermented broth.

Short Answer Questions

Question. List the events that reduce the Biological Oxygen Demand (BOD) of a primary effluent during sewage treatment. 
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Explain the process of secondary treatment given to the primary effluent up to the point it shows significant change in the level of biological oxygen demand (BOD) in it. 
Answer. During secondary treatment of primary effluents, vigorous growth of useful aerobic microbes into flocs occur when it is agitated mechanically and air is pumped into it in a large aeration tank.These microbes while growing consume major part of the organic matter in the effluent. This significantly reduces BOD.

Question. Distinguish between the roles of flocs and anaerobic sludge digesters in sewage treatments.
Answer. Flocs are masses of bacteria associated with fungal filaments to form mesh-like structures. These
consume the major part of the organic matter in the effluent, significantly reducing the BOD.
The effluent is then passed into a settling tank where the flocs sediment. A part of this sediment (activated sludge) is pumped into anaerobic sludge digestors where anaerobic digestion of sludge takes place, producing biogas in the process.

Question. Mention the importance of Lactic acid bacteria to humans other than setting milk into curd.
Answer. Lactic acid bacteria increase vitamin B12 absorption and also checks disease-causing microbes.

Question. Explain the different steps involved during primary treatment phase of sewage.
Answer. Physical removal of particles (large and small), by filtration and sedimentation, forming primary sludge / sedimented solids, forming effluent (supernatant) for secondary treatment.

Question. Explain the function of ‘‘anaerobic sludge digester’’ in a sewage treatment plant.
Answer. In an aerobic sludge digester, the anaerobic bacteria the methanogen, digest the flocs of bacteria and fungi in activated sludge and produce methane
along with H₂S and CO₂ i.e., biogas which is a source of energy as it is inflammable. 

Question. How do mycorrhiza help the plants to grow better? 
Answer. Mycorrhiza refers to symbiotic association between the fungus and the root of higher plants. These fungi in these associations absorb water, phosphorus, nitrogen, potassium, calcium from soil and pass it to the plant. The fungus brings about the solubilization of organic matter of soil humus, release of inorganic nutrients absorption and their transfer to roots. The genus Glomus forms a mycorrhizal association with plants.

Question. Your advice is sought to improve the nitrogen content of the soil to be used for cultivation of a non-leguminous terrestrial crop.
(a) Recommend two microbes that can enrich the soil with nitrogen.
(b) Why do leguminous crops not require such enrichment of the soil? 
Answer. (a) Azospirillum/ Azotobacter/ Anabaena/ Nostoc / Oscillatoria /Frankia (Any two correct names of microbes).
(If cyanobacteria mentioned=½, but if along with cyanobacteria-Anabaena / Nostoc / Oscillatoria mentioned then no mark on cyanobacteria).
(b) They can fix atmospheric nitrogen, due to presence of Rhizobium/N2 fixing bacteria in their root nodules

Question. List the events that reduce the biological oxygen demand (BOD) of a primary effluent during sewage treatment.
Answer. Effluent from the primary settling tank passed into aeration tank, agitated mechanically and air is pumped into it, vigorous growth of aerobic microbes into flocs, microbes consume major part of the organic matter in effluent.

Question. Name a free-living symbiotic bacterium that serve as bio-fertilizer. Why are they so called?
Answer. Azospirillum/Azotobacter, Rhizobium.
They enrich soil nutrient/nitrogen fixation.

Question. Name the microbes that help the production of the following products commercially :
(i) Statins
(ii) Citric acid
(iii) Penicillin
(iv) Butyric acid 
Answer. (i) Monascus purpureus
(ii) Aspergillus niger
(iii) Penicillium notatum
(iv) Clostridium butylicum 

Question. What is the pathogenic property of baculovirus, used as a biological agents ?
Name the genus of these organisms.
Answer. Attack insects and other arthropods.
Nucleopolyhedrovirus.

Question. Mention a product of human welfare obtained with the help of each one of the following microbes:
(a) LAB                                                  (b) Saccharomyces cerevisiae
(c) Propionibacterium sharmanii        (d) Aspergillus niger 
Answer. (a) Convert milk to curd (b) Bread/alcoholic drinks
(c) Swiss cheese (d) Citric acid

Question.Name the bacterium responsible for the large holes seen in “Swiss Cheese”. What are these holes due to? 
Answer. Propionibacterium sharmanii.
The holes are because of production of large amount of CO₂.

Question. Write the binomials of two fungi and mention the products/bioactive molecules they help to produce. 
Answer. 

Question. How do mycorrhizae help the plants to grow better? 
Answer. Mycorrhizae absorb phosphorus, provide resistance to root-borne pathogens and enhance the tolerance of the plants towards salinity and drought.

Question. Describe the main ideas behind the biological control of pests and diseases.
Answer. Biological control means life against life. It is a natural and ecofriendly concept. It employs natural organisms to control the population of pathogens and pests in an ecosystem. Classical examples are Trichoderma which is antagonist against many soil-borne plant pathogens. Similarly, Penicillium inhibits the growth of Staphylococcus and therefore has been successfully used in the production of penicillin antibiotic to control many human bacterial pathogens.Ladybirds used to control aphids and dragonflies used to control mosquitoes.

Question. How do mycorrhizal fungi help the plants harbouring them? 
Answer. The mycorrhizal fungi absorb phosphorus from the soil and transfer them to the host cells. They also impart resistance to host plants against root pathogens. They also help plants to tolerate salinity and drought.

Question. Name the blank spaces a, b, c and d given in the following table:

Answer.
(a) Lactobacillus
(b) Trichoderma polysporum
(c) Fungus
(d) Penicillin

Question. Name a bioactive molecule, its source organism and the purpose for which it is given to organ transplant patients.
Answer. Cyclosporin A is a bioactive molecules given to organ transplant patients. It is obtained from a fungus Trichoderma polysporum. It is used as an immunosuppressive agent.

Question. (a) Patients who have undergone myocardial infarction are given clot buster. Mention the clot buster administered and its microbial source.
(b) A person recuperating from illness is advised to have curd regularly. Why?
Answer. (a) Streptokinase is the clot buster and its microbial source is Streptococcus.
(b) Curd contains Lactic Acid Bacteria, which play beneficial role in checking disease-causing microbes. It is also a source of vitamin B12.

Question. What is a broad spectrum antibiotic? Name one such antibiotic. 
Answer. A broad spectrum antibiotic is one which can inhibit the growth of both gram positive and gram negative bacteria. For example, tetracycline, which is obtained from Streptomyces aureofaciens.

Question. How was penicillin discovered? 
Answer. Penicillin was an accidental discovery. Sir Alexander Fleming observed that in unwanted culture plates of Staphylococcus a mould of Penicillium was growing This mould inhibited the growth of Staphylococcus around it. Later the antibiotic penicillin was isolated from this fungus.

Question. Name the source of streptokinase. How does this bioactive molecule function in our body?
Answer. Source: Streptococcus.
Streptokinase is a clot buster, i.e., it removes clot from the blood vessels of patients who had a heart attack.

Question. Name the enzyme produced by Streptococcus bacterium. Explain its importance in medical sciences.
Answer. Streptococcus bacterium produces streptokinase.
It is used for removing clots from the blood vessels in a patient suffering from myocardial infarction/or in a heart patient.

Question. (a) A patient who had an organ transplant was given cyclosporin A. Mention the microbial source and state the reason for administration of this bioactive molecule.
(b) Bottled fruit juices bought from the market are clearer as compared to those made at home.
Give reason.
Answer. (a) Source: Trichoderma polysporum
Reason: It is an Immunosuppressive agent.
(b) Bottled fruit juices are clarified by pectinases and proteases which makes them clearer.

Question. Describe how biogas is generated from activated sludge. List the components of biogas.
Answer. The activated sludge is pumped into large tanks called anaerobic sludge digesters. Here, bacteria which grow anaerobically digest the bacteria and the fungi in the sludge. During this digestion,bacteria produce a mixture of gases which form biogas. Biogas is made up of methane, hydrogen sulphide and carbon dioxide.

Question. What are methanogens? Name the animals they are present in and the role they play there.
Answer. Methanogens are bacteria which grow anaerobically on cellulosic material.
They are present in the rumen of cattles.
These bacteria are responsible for the breakdown of cellulose, thus help in nutrition of animal.

Question. What is the chemical nature of biogas? Name an organism which is known to be employed in biogas. 
Answer. The biogas contains methane, CO₂ and H₂. Methanobacterium, a type of methanogen is employed for biogas production.

Question. What is BOD? What does it mean if a water sample has more BOD?
Answer. BOD stands for biochemical oxygen demand which represents the amount of dissolved oxygen that would be consumed if all the organic matter in one litre of water were oxidised by microorganisms. More BOD value means the water sample is polluted by organic matter.

Question. Name the two different categories of microbes naturally occurring in sewage water. Explain their role in cleaning sewage water into usable water. 
Answer. Aerobic and anaerobic bacteria or fungi exist in sewage water.
After the primary treatment of water, aerobic bacteria are added in aeration tanks. Growth of these bacteria reduces BOD as they consume organic matter. Anaerobic bacteria are added in anaerobic sludge digesters, where these digest the sludge and form biogas, etc.

Question. List the events that lead to biogas production from waste water whose BOD has been reduced significantly.
Answer. The effluent is passed into a settling tank where the bacterial ‘flocs’ are allowed to sediment. This is called activated sludge. The sludge is pumped into anaerobic sludge digesters where they are anaerobically digested. During this digestion, bacteria produce biogas.

Question. Why are some molecules called bioactive molecules? Give two examples of such molecules.
Answer. Some molecules are called bioactive molecules, because microbes like bacteria or fungi are used in their production.
e.g., Citric acid produced by Aspergillus niger Butyric acid produced by Clostridium butylicumEthanol produced by Saccharomyces cerevisiae Streptokinase produced by Streptococcus (Any two)

Question. Give the binomials of two types of yeast and the commercial bioactive products they help to produce. 
Answer. 

Question. Name the source of statin and state its action on the human body.
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Name a microbe used for statin production. How do statin lower blood cholesterol level?
Answer. Statin is produced by the yeast Monascus purpureus. It acts as a blood-cholesterol lowering agent, by competitively inhibiting the enzyme responsible for synthesis of cholesterol.

Question. 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. 
Answer. Cyclosporin A that is used as an immuno-suppressive agent during organ transplantation in patients is produced by the fungus Trichoderma polysporum. Statins produced by yeast Monascus purpureus have been commercialised as blood cholesterol lowering agents.

Question. Name the source of cyclosporin-A. How does this bioactive molecule function in our body?
Answer. Trichoderma polysporum.
It acts as an immuno-suppresant and is used in organ transplant patient.

Long Answer Type Questions

Question. Describe the process of secondary treatment given to municipal waste water (sewage) before it can be released into fresh water bodies. Mention another benefit provided by this process.
Answer. Process of secondary treatment :
Passing of primary effluent into large aeration tank which is constantly agitated mechanically & air is pumped into it that allows vigorous growth of useful aerobic microbes into flocs.
                                                           ↓
Microbes consume major part of organic matter in effluent which significantly reduces BOD.
                                                          ↓
Now effluent is passed into settling tank where flocs are allowed to settle/ sediment called activated sludge.
                                                          ↓                                                          
Digestion of activated sludge by anaerobic microbes and effluents from secondary treatment can be released into river/ stream.
                                                          ↓
Resulted in production of Bio gas (CH₄, H₂S and CO₂) which can be used as source of energy.

Question. Describe the process of waste-water treatment under the following heads 
(i) Primary treatment.
(ii) Secondary treatment.
Answer. Sewage treatment involves the following phases :
(i) Primary Treatment : In this, physical particles like debris and soil, sand, silt etc., are removed by :
(a) sequential filtration (b) sedimentation.
The substances that settle down forms primary sludge and the effluent is primary effluent.
(ii) Secondary Treatment : Biological treatment in which primary effluent is passed to large aeration tanks and is constantly agitated and supplied with air/O₂. This causes the vigorous growth of flocs or association of useful aerobic bacteria and fungal filaments into a mesh-like structure. In this process, the microbes use up reduce the BOD (Biological Oxygen Demand).
Once the BOD is sufficiently reduced, it is allowed to pass to a settling tank where flocs are allowed to settle down. 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. 

Question. Choose any three microbes, from the following which are suited for organic farming which is in great demand these days
for various reasons. Mention one application of each one choosen. Mycorrhiza; Monascus; Anabaena; Rhizobium; Methanobacterium; Trichoderma. 
Answer. Mycorrhiza : Fungal symbiont of the association/ absorb phosphorus from soil.
Anabaena : Fix atmospheric nitrogen / Adds organic matter to the soil.
Rhizobium : It is a symbiotic root nodule bacterium which fixes atmospheric nitrogen (in leguminous plants) in organic form which is used by plant as nutrient.
Methanobacterium : They digest cellulosic material and the product / spent slurry can be used as fertilizer.
Trichoderma : Biocontrol agent for several plant pathogens.

Question. (a) Write the scientific name of methanogen bacteria. Where are these bacteria generally found? Explain their role in biogas production.
(b) Name the components of biogas.
Answer. (a) The scientific name of methanogens :
Methanobacterium.
Methanobacterium is found in the anaerobic sludge and rumen of cattle (for cellulose digestion). A lot of cellulosic material present in the food of cattle is also present in the rumen. In the rumen, these bacteria help in the breakdown of cellulose and play an important role in the
nutrition of cattle. Thus, the excreta (dung) of cattle, commonly called Gobar, is rich in these bacteria. Dung can be used for the generation of biogas commonly called gobar gas.
(b) Biogas contains methane (CH4), CO₂ and H₂.

Question. Name the two different categories of aerobic microbes naturally occurring in sewage water. Explain their role in cleaning sewage water into usable water. 
Answer. Microbes are tiny structures that are not visible to the naked eye, they are microscopic in nature. Some microbes are beneficial but some are fatal
for life. Human health and the environment are mainly affected by the direct disposal of industrial and human effluents into natural resources without any  treatment. Sewage contains a huge amount of toxic organic matters. The two categories of aerobic microbes present in sewage are bacteria and fungi. Aerobic microbes grow excessively in the aeration tank and it consumes a major part of the organic matter. It helps in reducing the BOD of the effluent.
Microorganisms that are natural to the wastewater environment play a vital role in the wastewater treatment process. Bacteria and fungi feed on organic material in wastewater & break it down.
Bacteria clump together, or floc, forming masses that settle and separate from the waste water. This settled mass is called sludge.

Question. (a) How does Bacillus thuringiensis act as a biocontrol agent for protecting Brassica and fruit trees? Explain.
(b) List the components of biogas.
(c) What makes methanogens a suitable source for biogas production?
Answer. (a) Bacterium Bacillus thuringiensis (Bt) are available in sachets as dried spores, mixed with water and sprayed onto vulnerable plants, these are eaten up by the insect larvae, the toxins are released in the gut and larvae gets killed.
(b) Methane, H₂S, CO₂ , H₂.
(c) Methanogens grow anaerobically, on cellulosic material, produce large amount of methane, along with CO₂ and H₂.

Question. Explain Microbe as Biocontrol agents.
Answer. Biocontrol means the use of biological methods for controlling plant diseases and pests. To meet
the increasing demand for food for the growing population the use of insecticides and pesticides has increased tremendously. But their ill effects and the
chemicals which get released from these pesticides and insecticides are very harmful too. They are
polluting the soil, water, fruit and vegetables. So many biological methods were developed to overcome their ill-effect.
(i) Biological control of pests and diseases : In this method, natural predation methods are used rather than the use of chemicals. Example :
(a) Ladybird, a beetle with red and black markings, is used in controlling aphids.
(b) Dragonflies, are used to get rid of mosquitoes.
(c) Gambusia fishes are used to kill the larvae of mosquitoes.
(d) Bacillus thuringiensis (Bt) is a microbial agent, which is used to control butterfly caterpillars.
(e) Transgenic plants are used in agriculture which are resistant to attack by insect pests.
e.g., BT cotton.
(f) Trichoderma species are free living fungi, they are effective against several plant pathogens.
(g) Baculoviruses are pathogens that attack insects and other arthropods.
(h) Biopesticides are used to destroy the weeds as well as the insect pests. They are of two types bioherbicides and bioinsecticides.
• Bioherbicides : It involves the biological control of weeds by some living organisms e.g.,
Weed Control by Opuntia, Cactoblastis cactorum
• Bioinsecticides : They are living organisms or their products, which are used to kill or repel specific insect. e.g., Nicotine from tobacco, Azadirachtin from neem leave are natural insecticide.