Class 12 Microbes in Human Welfare Mock Test (CBSE)

Topics in Microbes in Human Welfare

• Microbes in household products
• Microbes in industrial products
• Microbes in sewage treatment
• Microbes in production of biogas
• Microbes as biocontrol agents
• Microbes as biofertilisers

Microbes in Human Welfare practice questions with answers

1. Q1Multiple choice·1 mark
   During sewage treatment, 'flocs' are formed in the aeration tanks. These consist of:

   1. (a)Masses of bacteria associated with fungal filaments to form mesh-like structures
   2. (b)Anaerobic sludge digested by methanogenic bacteria
   3. (c)Pathogenic bacteria floating on the surface of primary effluent
   4. (d)Sedimented mineral particles separated during primary treatment
   Show answer and step marks

   1. Correct option: (a) Masses of bacteria associated with fungal filaments to form mesh-like structures+1

   Answer: (a)
2. Q2Multiple choice·1 mark
   Which of the following bioactive molecules is used as an immunosuppressive agent in organ-transplant patients and is produced by the fungus Trichoderma polysporum?

   1. (a)Statins
   2. (b)Cyclosporin A
   3. (c)Streptokinase
   4. (d)Citric acid
   Show answer and step marks

   1. Correct option: (b) Cyclosporin A+1

   Answer: (b)
3. Q3Short answer·2 marks
   Explain how mycorrhiza acts as a biofertiliser. State any two specific benefits it provides to the host plant.
   Show answer and step marks

   1. Mycorrhiza is a symbiotic association between a fungus (e.g. Glomus) and the roots of higher plants; the fungal hyphae absorb nutrients from the soil for the plant, so it acts as a natural biofertiliser.+1
   2. First benefit, any one of: absorbs phosphorus from the soil and passes it to the plant; gives resistance to root-borne pathogens; gives tolerance to salinity; gives tolerance to drought; increases overall plant growth and development; or any other valid benefit.+0.5
   3. Second benefit, a different one from the same list.+0.5

   Answer: Mycorrhiza is a symbiotic association of a fungus (e.g. Glomus) with plant roots in which the fungus absorbs nutrients from the soil for the plant. Any two benefits of: absorbs phosphorus and passes it to the plant; resistance to root-borne pathogens; tolerance to salinity; tolerance to drought; better overall plant growth.
4. Q4Short answer·3 marks
   Name the source organism and one commercial application for each of the following industrial products: (a) Citric acid (b) Statins (c) Streptokinase
   Show answer and step marks

   1. (a) Citric acid source: the fungus Aspergillus niger.+0.5
   2. (a) Citric acid use, any one of: acidulant and flavouring agent in foods and soft drinks; preservative in foods such as jams and pickles; or any other valid use.+0.5
   3. (b) Statins source: the fungus Monascus purpureus (called a yeast in NCERT).+0.5
   4. (b) Statins use: blood-cholesterol lowering agents (they competitively inhibit the enzyme of cholesterol synthesis).+0.5
   5. (c) Streptokinase source: the bacterium Streptococcus.+0.5
   6. (c) Streptokinase use: a 'clot buster' that dissolves clots in the blood vessels of patients who have had a myocardial infarction (heart attack).+0.5

   Answer: (a) Citric acid: Aspergillus niger; used as an acidulant/flavouring agent and preservative in foods. (b) Statins: Monascus purpureus; used to lower blood cholesterol. (c) Streptokinase: Streptococcus; used as a clot buster to remove blood clots in heart-attack patients.
5. Q5Short answer·3 marks
   Name the bacterium used in the conversion of milk into curd and explain two beneficial changes it brings about in the milk. Also, name the microbe used for fermenting dough in the preparation of bread and the gas released during this process.
   Show answer and step marks

   1. Bacterium used to convert milk into curd: Lactic Acid Bacteria (LAB), e.g. Lactobacillus.+1
   2. First beneficial change, any one of: acids produced by LAB coagulate the milk proteins (casein), setting the milk into curd; LAB partially digest the milk proteins, making curd easier to digest; LAB increase the vitamin $B_{12}$ content, improving nutritional quality; or any other valid beneficial change.+0.5
   3. Second beneficial change, a different one from the same list.+0.5
   4. Microbe used to ferment bread dough: baker's yeast, Saccharomyces cerevisiae.+0.5
   5. Gas released: carbon dioxide ($\text{CO}_2$), which makes the dough puff up.+0.5

   Answer: Lactic acid bacteria (LAB), e.g. Lactobacillus. Any two changes of: their acids coagulate milk proteins, setting the milk into curd; they partially digest milk proteins, making curd easier to digest; they increase vitamin $B_{12}$, improving nutritional quality. Bread dough: baker's yeast (Saccharomyces cerevisiae), releasing carbon dioxide ($\text{CO}_2$).
6. Q6Short answer·3 marks
   A farmer sprays a formulation of *Bacillus thuringiensis* on a cotton field to control bollworm caterpillars. Farm workers who handle the same formulation are not harmed. Explain why the spray kills the caterpillars but does not affect the workers.
   Show answer and step marks

   1. The formulation contains spores and crystals of an inactive protoxin protein, which the caterpillar ingests while feeding on the sprayed leaves.+1
   2. The alkaline pH of the caterpillar's midgut dissolves the crystals and activates the protoxin into an active toxin, which binds to specific receptors on the midgut epithelium and creates pores that lead to the death of the larva.+1
   3. The human stomach is acidic and human gut cells lack these specific receptors, so the protoxin is not activated and the toxin has no effect on the workers.+1

   Answer: The protoxin crystals are activated only in the alkaline midgut of the target insect larva, where the toxin binds to specific midgut receptors and kills it; the acidic human stomach does not activate the protoxin and human cells lack these receptors, so the workers are not harmed.

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