NEET Microbes in Human Welfare Previous Year Questions with Solutions

Streptokinase is an enzyme produced by the bacterium Streptococcus and modified by genetic engineering to improve its clinical efficacy and reduce allergic adverse reactions.

• • Engineered for intravenous thrombolytic therapy.

In the bloodstream, streptokinase binds to human plasminogen, activating it into active plasmin. Plasmin is a proteolytic enzyme that cleaves insoluble fibrin meshes holding intravascular thrombi together, dissolving the clot and reperfusing ischemic myocardium.

• • Used clinically within the first few hours following acute myocardial infarction.

Penicillin is an antibiotic that inhibits bacterial peptidoglycan transpeptidation. Cyclosporin A is an immunosuppressive cyclic peptide from the fungus Trichoderma polysporum. Statins (from yeast Monascus purpureus) competitively inhibit HMG-CoA reductase to lower blood cholesterol.

• • Matches official NTA final answer key Option A / (1).

Saccharomyces cerevisiae ferments malted cereals and fruit juices into ethanol and carbon dioxide:

• • Natural yeast fermentation ceases when alcohol concentration reaches ~13% due to ethanol toxicity.

Fermented products are processed in two ways to achieve different alcohol concentrations:

• • Wine and Beer: Filtered and bottled without distillation, maintaining lower alcohol percentages (3–6% in beer, 9–12% in wine).
• • Whisky, Brandy, and Rum: Distilled to concentrate alcohol content to 40% or higher.
• • Therefore, Beer is the correct non-distilled alcoholic beverage, matching Option (3).

Streptokinase is a bacterial protein secreted by various strains of hemolytic Streptococcus bacteria and modified through recombinant DNA technology:

• • It complexes with plasminogen to activate plasmin, which enzymatic breaks down fibrin networks holding blood clots together.

Examine medical utility described in NCERT:

• • Administered intravenously to restore blood perfusion to ischemic cardiac tissue.
• • Used explicitly for "removing clots from blood vessels", matching Option (4).

Microorganisms utilized daily in home kitchens and traditional dairy/culinary fermentations:

• • B. *Lactobacillus* and other Lactic Acid Bacteria (LAB): Convert milk into curd by producing acids that coagulate and partially digest milk proteins, enriching nutritional value with vitamin B₁₂.
• • D. *Saccharomyces cerevisiae* (Baker's yeast): Ferments dough used for making bread, releasing $\text{CO}_2$ to give puffed-up appearance.
• • E. *Propionibacterium sharmanii*: Bacterium used in the ripening of Swiss cheese; generates large amounts of $\text{CO}_2$ creating characteristic large holes.
• • Thus, B, D, and E are classical household microbes.

Microorganisms cultured in massive fermentors for commercial chemicals and pharmaceuticals:

• • A. *Aspergillus niger*: A filamentous fungus used for the commercial, industrial-scale aerobic fermentation of citric acid.
• • C. *Trichoderma polysporum*: An ascomycete fungus used in industrial biotechnology to biosynthesize Cyclosporin A, a vital bioactive peptide used as an immunosuppressive agent in organ-transplant patients.
• • Neither *Aspergillus niger* nor *Trichoderma polysporum* is utilized in domestic household food preparation.

The microbes NOT involved in the preparation of household products are A and C only, corresponding to Option (2).

Clostridium butylicum is a bacterium that ferments substrates to produce butyric acid (A -> III). Saccharomyces cerevisiae (Brewer’s yeast) ferments malted cereals and fruit juices to produce ethanol (B -> I).

Trichoderma polysporum (fungus) produces Cyclosporin-A, an immunosuppressive agent used in organ-transplant patients (C -> IV). Streptococcus produces streptokinase, modified by genetic engineering and used as a "clot buster" to remove clots from blood vessels of patients suffering from myocardial infarction (D -> II).

The unique valid combination is A-III, B-I, C-IV, D-II, corresponding to Option (1).

Microbes are utilized commercially for the aerobic and anaerobic fermentation of organic acids: - (a) *Aspergillus niger*: A filamentous ascomycete fungus; primary industrial producer of Citric Acid (used as an acidifier and preservative in food/beverages). - (b) *Acetobacter aceti*: An obligate aerobic bacterium; oxidizes ethanol into Acetic Acid (vinegar). - (c) *Clostridium butylicum*: An obligate anaerobic endospore-forming bacterium; ferments carbohydrates to produce Butyric Acid. - (d) *Lactobacillus*: Lactic acid bacteria (LAB); converts lactose/glucose into Lactic Acid.

The combined match is (a)-(iii), (b)-(i), (c)-(iv), (d)-(ii). This corresponds precisely to Option (1).

Municipal wastewater undergoes sequential stages of purification: 1. Primary Treatment: Physical removal of large and small particles via sequential filtration (floating debris) and sedimentation (settled solids form primary sludge). 2. Aeration Tank (Secondary Treatment): Effluent from primary settling is vigorously agitated in aeration tanks where aerobic microbes form flocs (masses of bacteria associated with fungal filaments), dramatically consuming dissolved organic matter and slashing the Biochemical Oxygen Demand (BOD). 3. Settling Tank & Activated Sludge: Once BOD is sharply lowered, the effluent flows into a settling tank where the microbial flocs settle under gravity to form activated sludge. 4. Anaerobic Digestion: A minor aliquot of activated sludge is recycled back into the aeration tank as inoculum. The major bulk of activated sludge is pumped into large anaerobic sludge digesters.

In the anaerobic digester, obligate and facultative anaerobic bacteria (including methanogens like *Methanobacterium*) digest the bacterial and fungal biomass of the activated sludge. This anaerobic decomposition generates a flammable gas mixture (biogas consisting predominantly of methane, carbon dioxide, and hydrogen sulphide).

Clostridium butylicum is a bacterium that produces butyric acid (organic acid) industrially. Thus, (a) matches (ii).

Trichoderma polysporum is a fungus that produces Cyclosporin A, an important bioactive molecule used as an immunosuppressive agent in organ-transplant patients. Thus, (b) matches (i).

Monascus purpureus is a yeast that produces statins, which act as competitive inhibitors of HMG-CoA reductase to lower blood cholesterol levels. Thus, (c) matches (iv).

Aspergillus niger is a fungus that produces citric acid industrially. Thus, (d) matches (iii).