CBSE Class 12 Biology Microbes In Human Welfare Worksheet Set D

 

Very Short Answer Questions

Question. Why are antibiotics always sold in combination with Lactobacillus? 
Answer. Antibiotics may kill even the useful bacteria present in the digestive tract. LAB is given, which will protect some microbes in the digestive tract and enhance the production and absorption of vitamin B12.

Question. Do you think microbes can also be used as source of energy? If yes, how? 
Answer. Yes, microbes can be used to produce energy indirectly. Methanogens (bacteria) like Methanobacterium are involved in the production of biogas which is used as source of energy.

Question. Give the scientific name of the source organism from which the first antibiotic was produced.
Answer. Penicillium notatum.

Question. In which food would you find lactic acid bacteria? Mention some of their useful applications.
Answer. The lactic acid bacteria (LAB) are found in curd. LAB convert the lactose sugar of milk into lactic acid. Lactic acid coagulates the milk protein called casein. It also increases the nutritional quality of curd as the curd contains vitamin B12 along with other vitamins. They also check the growth of other harmful microbes.

Question. Give examples to prove that microbes release gases during metabolism.
Answer. Puffed-up appearance of dough which is used for making ‘dosa’, ‘idli’ and bread is due to gas production. Methanogens (bacteria) in the biogas plant produce methane and carbon dioxide. Also large holes in the ‘Swiss cheese’ are due to production of a large amount of CO2 during its production.

Short Answer Questions

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. What does the Ganga Action Plan tend to achieve? 
Answer. Ganga Action Plan tends to save the major rivers from pollution like Ganga. Under these plans, a large number of sewage treatment plants were built so that only treated sewage is discharged in the rivers.

Question. How do biofertilisers enrich the fertility of the soil?
Answer. Biofertilisers are microorganisms which bring about nutrient enrichment of soil by enhancing the availability of nutrients to crops. They are of following types:
(i) Nitrogen fixing bacteria and cyanobacteria: They form symbiotic association with plants.
They get food and shelter from plants and on the other hand, plants get nitrogen fixed by these bacteria. For example, Rhizobium.
(ii) Mycorrhiza: It is an association between a fungus and roots of higher plants. It takes part in the solubilisation and absorption of nutrients from organic matter. Many members of the genus Glomus form mycorrhiza.
(iii) Manures: They are semi-decayed organic remains of various types—manure, green manure,compost and vermicompost.

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

Type of microbe	Name	Commercial product
Bacterium	a	Lactic acid
Fungus	b	Cyclosporin A
c	Monascus purpureus	Statins
Fungus	Penicillium notatum	d

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

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. Microbes can be used to decrease the use of chemical fertilisers and pesticides. Explain how this can be accomplished.
Answer. Microbes can be used both as fertilisers and pesticides called biofertilisers and biopesticides, respectively. Microbes are used as biofertilisers to enrich the soil nutrients, e.g., Rhizobium, Azotobacter, Azospirillum, etc., which can fix atmospheric nitrogen in the soil. Bacillus thuringiensis bacteria act as biopesticide to control the growth of insect pests. Trichoderma, fungal species,is an effective bicontrol agent of several plant pathogens. Baculoviruses used as biological control agents in genus Nucleopolyhedrovirus are excellent for species-specific, narrow spectrum insecticidal applications.

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. 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 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 a free-living and a symbiotic bacterium that serve as biofertiliser. Why are they so called? 
Answer. Azospirillium/Azotobacter and Rhizobium act as biofertilisers. They are so called because they enrich soil nutrients by nitrogen fixation.

Question. Why is Rhizobium categorised as a ‘symbiotic bacterium’? How does it act as a biofertiliser?
Answer. Rhizobium is present in the root nodules of leguminous plants. Theirs is a symbiotic relationship in which the bacterium obtains food and shelter from the plant and the plant gets fixed nitrogen in return. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient.

Long Answer Questions

Question. (a) Why are the fruit juices bought from market clearer as compared to those made at home?
(b) Name the bioactive molecules produced by Trichoderma polysporum and Monascus purpureus. 
Answer. (a) The fruit juices bought from market are clearer because they have been clarified by pectinases and proteases.
(b) Trichoderma polysporum: Cyclosporin A Monascus purpureus: Statins

Question. (a) Name the category of microbes occurring naturally in sewage and making it less polluted during the treatment.
(b) Explain the different steps involved in the secondary treatment of sewage. 
Answer. (a) Aerobic microbes
(b) Secondary treatment or biological treatment
• Primary effluent is passed into large aeration tanks with constant mechanical agitation and air supply.
• Useful aerobic microbes grow rapidly and form flocs.
• Flocs are masses of bacteria associated with fungal filaments to form mesh-like structures.
• The growing microbes consume organic matter and thus reduce the biochemical oxygen demand (BOD).
• When BOD of sewage has reduced, the effluent is passed into settling tank.
• Here, the bacterial flocs settle and the sediment is called activated sludge.
• A small part of the sludge is used as an inoculum in the aeration tank and the remaining part is passed into large tanks called anaerobic sludge digesters.
• In the digesters, heterotrophic microbes anaerobically digest bacteria and fungi in sludge producing mixture of gases such as methane, hydrogen sulphide (H2S) and CO2, which form the biogas.
• Effluent is now released into rivers and streams.

Question. Explain the function of “anaerobic sludge digester” in a sewage treatment plant.
Answer. Anaerobic sludge digester has anaerobic bacteria that digests the aerobic bacteria and fungi present in the sludge. During the digestion these bacteria produce mixture of gases such as methane, H2S and CO2 (biogas).

Question. Explain the different steps involved during primary treatment phase of sewage. 
Answer. Primary treatment or physical treatment
• It is the physical removal of large and small particles from sewage.
• First, the floating debris is removed by sequential filtration by passing through wire mesh screens.
• Then, the grit (soil and small pebbles) are removed by sedimentation in settling tanks. The sediment is called primary sludge and the supernatant is the effluent.
• The effluent is taken for secondary treatment.

Question. (i) List the components of biogas.
(ii) What makes methanogens suitable for biogas production?
Answer. (i) Biogas is a mixture of inflammable gases like methane, carbon dioxide and hydrogen.
(ii) Methanogens grow anaerobically and help in breakdown of cellulosic material to produce large amount of methane, carbon dioxide and hydrogen and so it is suitable for biogas production.

Question. How can sewage be used to generate biogas? Explain.
Answer. When biochemical oxygen demand (BOD) of sewage is reduced, effluent is passed into a settling tank for bacterial flocs to settle down. The sediment is called activated sludge. Activated sludge is pumped into anaerobic sludge digesters. In the digesters, heterotrophic microbes anaerobically digest bacteria and fungi in the sludge producing a mixture of gases which form the biogas.

Question. Why do we add an inoculum of curd to milk for curdling it? 
Answer. The starter or inoculum used in preparation of milk products actually contains millions of lactic acid bacteria. Curd is prepared by inoculating cream and skimmed milk with Lactobacillus acidophilus at a temperature of about 40° C or less. Lactobacillus converts lactose sugar of milk into lactic acid which causes coagulation and partial digestion of milk protein casein, and 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 is beneficial to us in the following ways other than helping in curdling of milk: (i) Increases nutritional quality of curd by increasing vitamin B12 content.
(ii) Checks the growth of disease-causing microbes in the gut.

Question. Name the nutrient that gets enhanced while curdling of milk by Lactobacillus.
Answer. The curdling of milk by Lactobacillus changed milk into curd and its nutritional quality is enhanced due to increase in vitamin B12 content.

Question. Name the gas released and the process responsible for puffng up of the bread dough when Saccharomyces cerevisiae is added to it.
Answer. When Saccharomyces cerevisiae (baker’s yeast) is added to dough it causes its fermentation and releases CO₂ gas which is responsible for puffed up appearance of dough.

Question. Name the bacterium responsible for the large holes seen in “Swiss Cheese”. What are these holes due to?
Answer. Bacterium responsible for large holes in swiss cheese is Propionibacterium sharmanii. Large holes in swiss cheese are due to CO2 gas produced by these bacteria.

Question. During the production of curd, a small amount of curd is added as a starter to the fresh milk at a suitable temperature. Explain the changes the milk undergoes when it sets into curd.
Answer.  For the production of curd, a small amount of curd is added to fresh milk at suitable temperature. Curd contains millions of lactic acid bacteria (LAB). These bacteria grow in milk and convert the lactose sugar of milk in lactic acid. Lactic acid coagulates and partially digests milk protein casein. This causes curdling of milk and it changes to curd, which also improves its nutritional quality by increasing vitamin B₁₂ content. 

Question. Name the enzyme produced by Streptococcus and its action (after being modified).
Answer. Streptokinase (Tissue Plasminogen Activator or TPA) is an enzyme obtained from cultures of some haemolytic bacterium Steptococcus which is modified genetically to function as clot buster. It has fibrinolytic effect hence, it helps in clearing blood clots inside the blood vessels through dissolution of intravascular fibrin.

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

Question. Which one of the following is the baker’s yeast used in fermentation? Saccharum barberi, Saccharomyces cerevisiae, Sonalika. 
Answer. Yeast or Saccharomyces cerevisiae is used for fermenting malted cereals and fruit juices.

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) LAB (Lactic acid bacteria)- Curd
(b) Saccharomyces cerevisiae - Bread
(c) Propionibacterium - Swiss cheese sharmanii
(d) Aspergillus niger - Citric acid

Question. Bottled fruit juices are clearer as compared to those made at home. Explain. 
Answer. The fruit juices sold in market or botted juices are treated with pectinases and proteases which makes them clearer than those made at home.

Question. Name the source of cyclosporin-A. How does this bioactive molecule function in our body?
Answer. Cyclosporin A is an eleven membered cyclic oligopeptide obtained through fermentive activity of fungus Trichoderma polysporum. It has antifungal, anti-inflammatory and immunosuppressive proper- ties. It inhibits activation of T cells and therefore prevents rejection reactions in organ transplantation.

Question. Why are some molecules called bioactive molecules? Give two examples of such molecules. 
Answer. Bioactive compounds are those compounds that have an effect on living organisms tissues or cells. Bioactive compounds are found in both plant and animal products or can be synthetically produced. Two examples of bioactive compounds are cyclosporin A and statins.

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 is obtained from fungus Trichoderma polysporum whereas statin is obtained from yeast Monascus purpureus.
Cyclosporin A has immunosuppressive properties. It inhibits activation of T cells and therefore prevents rejection of transplants. Statin inhibits cholesterol synthesis and is therefore used in lowering blood cholesterol.
 

Question. Identify A, B, C and D in the table given below :

Microorganism	Product	Biological Activity	Medical Ailment/ Procedure
A	Streptokinase	C l o t - buster	B
Trichoderma polysporum	C	D	Transplant surgery

Answer. A - Streptococcus
B - Clears blood clots inside blood vessels
C - Cyclosporin A
D - Immunosuppressive

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

Type of Microbe	Name	Commercial Product
Fungus	a	Penicillin
Bacterium	Acetobacter aceti	b
c	Aspergillus niger	citric acid
Yeast	d	ethanol

Answer. a - Penicillium notatum
b - Acetic acid c - Fungus
d - Saccharomyces cerevisiae
 

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

Type of Microbe	Name	Commercial Product
Bacterium	a	Lactic acid
Fungus	b	Cyclosporin A
c	Monascus purpureus	Statins
Fungus	Penicillium notatum	d

Answer. a - Lactobacillus acidophilus or Streptococcus lactis
b - Trichoderma ploysporum
c - Fungus
d - Penicillin

Question. List two advantages that a mycorrhizal association provides to the plant.
Answer. Mycorrhiza is a mutually beneficial or symbiotic association of a fungus with root of a higher plant.The two advantages that a mycorrhizal association provides to the plant is as follows:
(i) This association provides phosphorous to the plant. The fungal symbiont of mycorrlizal association absorbs phosphorus from soil and passes it to the plant.
(ii) This association also provides other benefits such as resistance to root borne pathogens, tolerance to salinity and drought and an overall increase in plant growth and development.

Question. Why is Rhizobium categorised as a ‘symbiotic bacterium’? How does it act as a biofertiliser?
Answer. Rhizobium is a soil bacterium which either lives freely in soil or lives in symbiotic association with roots of leguminous plants. The bacterium forms nodules or roots of leguminous plants where it lie in groups. When it occurs freely in soil, it cannot fix nitrogen. Nitrogen fixing ability develops only when it is present inside root nodules. Hence, Rhizobium is categorised as symbiotic bacterium. It acts as a biofertiliser as it helps plants in obtaining their nitrogen nutrition.

Question. How do mycorrhizae act as biofertilisers?
Explain. Name a genus of fungi that forms a mycorrhizal association with plants. 
Answer. Mycorrhiza is a mutually beneficial or symbiotic association of a fungus with the root of a higher plant. The most common fungal partners of mycorrhiza are Glomus species. Mycorrhizal roots show a sparse or dense wooly growth of fungal hyphae on their surface.
They perform several functions for the plant— (i) Absorption of water, (ii) Solubilisation of organic matter of the soil humus, release of inorganic nutrients, absorption and their transfer to root. (iii) Direct absorption of minerals from the soil over a large area and handing over the same to the root. Plants with ectomycorrhiza are known to absorb
2–3 times more of nitrogen, phosphorus, potassium and calcium. (iv) The fungus secretes antimicrobial substances which protect the young roots from attack of pathogens.

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 chosen.Mycorrhiza; Monascus; Anabaena; Rhizobium;
Methanobacterium; Trichoderma. 
Answer. Among the given microbes, the ones which are in great demand for organic farming are: Mycorrhiza, Anabaena and Rhizobium.
Mycorrhiza is a mutually beneficial or symbiotic association of a fungus with the roots of a higher plant. Mycorrhizal roots show a sparse or dense wooly growth of fungal hyphae on their surface. Plants having mycorrhizal associations show resistance to root-borne pathogens.
Anabaena is free living and symbiotic nitrogen fixing cyanobacteria. Cyanobacteria are photosynthetic and have the property of nitrogen fixation. They add organic matter as well as extra nitrogen to the soil. Cyanobacteria are an extremely low cost biofertilisers.
Rhizobium is symbiotic nitrogen fixing bacteria. They form a mutually beneficial association with the plants. The bacteria obtain food and shelter from plants. In return, they give a part of their fixed nitrogen to the plants, thus enhancing the availability of nutrient to crops. It forms nodules on the roots of legume plants. They develop the ability to fix nitrogen only when they are present inside the root nodules.

Question. (a) Why do farmers prefer biofertilisers to chemical fertilisers these days? Explain.
(b) How do Anabaena and mycorrhiza act as biofertilisers?
Answer. (a) Chemical fertilisers cause pollution of water bodies as well as ground water, besides getting stored in crop plants. Therefore, farmers are pressing for switch over to organic farming which includes the use of manures biofertilisers, biopesticides. Biofertilisers are microorganisms which bring about nutrient enrichment of soil by enhancing the availability of nutrients to crops. The microorganisms which act as biofertilisers are bacteria, cyanobacteria (blue green algae) and mycorrhizal fungi. Bacteria and cynobacteria have the property of nitrogen fixation while mycorrhizal fungi preferentially withdraw minerals from organic matter for the plant with which they are associated. Phosphate is also solubilised by some bacteria and by some fungi that form association with plant roots
(b) Anabaena is a free living nitrogen fixing cyanobacterium. Therefore, it adds organic matter as well as extra nitrogen to agricultural field. Cyanobacteria are an extremely low cost biofertilisers. 

Question. What are biofertilisers? Describe their role in agriculture. Why are they preferred to chemical fertilisers?
Answer. Biofertilisers are microorganisms which bring about nutrient enrichment of soil by enhancing the availability of nutrients like nitrogen (N) and phosphorus (P) to crops. Biofertilisers includes– nitrogen fixing bacteria, nitrogen fixing cyanobacteria and mycorrhiza. Azotobacter occurring in fields of cotton, maize, jowar and rice, not only increases yield but also saves nitrogen fertiliser upto 10–25 kg/ha.
A number of free living cyanobacteria or blue-green algae have the property of nitrogen fixation, e.g., Anabaena, Nostoc, Oscillatoria, Aulosira, Tolypothrix, Cylindrospermum, Stigonema. Cyanobacteria are extremely low cost biofertilizers.
The most important of the symbiotic nitrogen fixing bacteria is Rhizobium. It forms nodules on the roots of legume plants. There are about a dozen species of Rhizobium which form association with different legume roots, e.g., R. leguminosarum, R. lupini, R. trifolii, R. meliloti, R. phaseoli.
Nitrogen fixing cyanobacteria (blue–green algae) form symbiotic association with several plants, e.g., cycad roots, lichens, liverworts, Azolla (fern). Azolla–Anabaena association is of great importance to agriculture. Azolla pinnata is a free floating fresh water fern which multiplies rapidly, doubling every 5–7 days. The fern can coexist with rice plants because it does not interfere with their growth. In some South-East Asian countries, especially China, the rice fields are regularly provided with Azolla. 

Please click on below link to download CBSE Class 12 Biology Microbes In Human Welfare Worksheet Set D