Biology and Human Welfare

8 practice questions on Biology and Human Welfare for NSEB, with answers

Shishya's practice questions, written with AI. Each answer was checked by an automated second pass, not by a person.

1. 1.Cyclosporin A, an immunosuppressant drug used to prevent organ transplant rejection, is produced by which microorganism?

   • (A)Streptococcus pyogenes
   • (B)Trichoderma polysporum
   • (C)Penicillium notatum
   • (D)Rhizobium leguminosarum
   Show the answer and solution

   Answer: (B) Trichoderma polysporum

   Solution: Cyclosporin A is produced by the fungus Trichoderma polysporum and is widely used as an immunosuppressive agent in organ transplantation to prevent rejection by suppressing T-cell activity.

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2. 2.Cyclosporin A, an immunosuppressant used in organ transplantation, is produced by which microorganism?

   • (A)Streptococcus species
   • (B)Trichoderma polysporum
   • (C)Penicillium notatum
   • (D)Bacillus thuringiensis
   Show the answer and solution

   Answer: (B) Trichoderma polysporum

   Solution: Cyclosporin A is produced by the fungus Trichoderma polysporum and is widely used to prevent organ transplant rejection.

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3. 3.A patient receives a primary vaccination against a pathogen at time T₀. After 3 weeks, antibody levels peak and then decline. Six months later, the patient receives a booster dose. Which statement best describes the immune response following the booster?

   • (A)Antibody levels rise slowly and remain lower than after the primary dose
   • (B)Antibody levels rise rapidly to a higher peak and persist longer than after the primary dose
   • (C)Only cell-mediated immunity is activated without antibody production
   • (D)The response is identical in magnitude and timing to the primary response
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   Answer: (B) Antibody levels rise rapidly to a higher peak and persist longer than after the primary dose

   Solution: The booster triggers a secondary (anamnestic) immune response characterized by memory B-cells, resulting in faster antibody production, higher peak levels, and longer persistence compared to the primary response.

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4. 4.Bacillus thuringiensis (Bt) toxin genes have been successfully incorporated into cotton plants to provide resistance against lepidopteran pests. The toxin becomes active and binds to receptors in the insect gut because:

   • (A)The alkaline pH of insect gut converts the protoxin to active form
   • (B)Plant enzymes pre-activate the toxin before insect ingestion
   • (C)The acidic pH of insect stomach denatures the toxin into active form
   • (D)Insect saliva contains specific activating proteases
   Show the answer and solution

   Answer: (A) The alkaline pH of insect gut converts the protoxin to active form

   Solution: Bt toxin is produced as an inactive protoxin. The alkaline pH environment in the lepidopteran insect midgut activates the toxin by proteolytic cleavage, allowing it to bind to gut epithelial receptors.

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5. 5.Antibiotics are widely used to treat bacterial infections, but their misuse has led to the emergence of antibiotic-resistant bacteria. Which of the following mechanisms is NOT a common way bacteria develop antibiotic resistance?

   • (A)Production of enzymes that degrade or modify the antibiotic
   • (B)Alteration of the antibiotic target site through mutation
   • (C)Increased uptake of the antibiotic into the bacterial cell
   • (D)Efflux pumps that actively remove antibiotics from the cell
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   Answer: (C) Increased uptake of the antibiotic into the bacterial cell

   Solution: Bacteria develop resistance by degrading antibiotics, altering target sites, or pumping antibiotics out. Increased uptake would make antibiotics MORE effective, not lead to resistance. Resistance mechanisms reduce antibiotic effectiveness.

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6. 6.A dairy farm uses Lactobacillus acidophilus to produce probiotic yogurt. Which of the following mechanisms BEST explains the health benefit of consuming this product?

   • (A)The bacteria produce antibiotics that kill harmful gut pathogens
   • (B)The bacteria compete for nutrients and adhesion sites, preventing colonization by pathogenic microbes
   • (C)The bacteria directly destroy intestinal parasites through enzyme secretion
   • (D)The bacteria stimulate red blood cell production in the bone marrow
   Show the answer and solution

   Answer: (B) The bacteria compete for nutrients and adhesion sites, preventing colonization by pathogenic microbes

   Solution: Probiotic bacteria like Lactobacillus compete with harmful microbes for nutrients and binding sites in the gut, thereby preventing pathogenic colonization through competitive exclusion.

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7. 7.Bt cotton is genetically modified to be resistant to certain insect pests. The gene responsible for this resistance is derived from:

   • (A)Agrobacterium tumefaciens
   • (B)Bacillus thuringiensis
   • (C)Rhizobium leguminosarum
   • (D)Escherichia coli
   Show the answer and solution

   Answer: (B) Bacillus thuringiensis

   Solution: Bt cotton contains the Cry gene from Bacillus thuringiensis, which produces a protein toxic to certain lepidopteran insects, providing resistance to bollworms.

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8. 8.Bacillus thuringiensis (Bt) produces crystal proteins toxic to certain insect larvae. Genes encoding these Cry proteins have been introduced into cotton plants to confer insect resistance. Which statement correctly describes the mechanism of Bt toxin action?

   • (A)Bt toxin inhibits photosynthesis in the plant, making it unpalatable to insects
   • (B)The crystal protein is activated in the alkaline insect gut and creates pores in midgut epithelial cells
   • (C)Bt toxin acts as a systemic pesticide transported through the plant's phloem
   • (D)The protein binds to insect neurotransmitter receptors, causing paralysis
   Show the answer and solution

   Answer: (B) The crystal protein is activated in the alkaline insect gut and creates pores in midgut epithelial cells

   Solution: Bt Cry proteins are inactive protoxins that become activated in the alkaline pH of insect midgut, then bind to receptors and form pores in epithelial cells, leading to cell lysis and insect death.

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