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Reason: Herd immunity requires ~85-95% of a population to have antibodies. However, individual variation in immune response (age, genetics, prior health) means the vaccine is not 100% effective for everyone. Non-compliance in healthy individuals indirectly kills the immunocompromised. Therefore, the biggest threat is not the virus’s mutation rate, but the human failure to act as one biological unit.
She read the stem: A 45-year-old male, Mr. Chan, has a fasting blood glucose of 13.2 mmol/L. Explain the negative feedback mechanism that is failing in his body. (6 marks)
Then, for the bonus, she wrote: Real-world implication: Overuse of antibiotics in livestock farming accelerates the evolution of multi-drug resistant pathogens like MRSA, leading to untreatable infections in humans. biology mock paper dse
Megan hesitated. The official definition was the maintenance of a constant internal environment.
“Pens down. Pencils up for MC questions,” the invigilator, Dr. Yip, said, his voice flat as a petri dish. “You have one hour and thirty minutes. Begin.” Reason: Herd immunity requires ~85-95% of a population
“In a long-term study, a population of bacteria was exposed to a sub-lethal dose of an antibiotic. After 50 generations, the minimum inhibitory concentration (MIC) had increased 1000x. Using the theory of natural selection, explain how this occurred. (8 marks) Bonus: Provide a real-world implication beyond the lab.”
But then, the killer.
Megan flew through Section A. Enzyme inhibition? Competitive. Kidney dialysis? Diffusion and osmosis. She felt the familiar click of facts locking into place. Question after question, she drew the nephron, labelled the loop of Henle, and calculated the water potential of a potato cell.
