Immunity Disease and Organismal Responses Practice Questions | A-Level Biology

Immunity Disease and Organismal Responses

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A Gram positive bacterium causing a systemic infection is treated with an antibiotic that inhibits transpeptidase activity involved in peptidoglycan cross linking. After several days, symptoms initially improve, then relapse. Culture reveals the same species, now resistant. Which explanation is most consistent with evolutionary selection rather than induced change?

Select one option.

Rare pre existing resistant variants survived, then expanded once susceptible cells were removed
The antibiotic triggered directed mutations in genes for cell wall synthesis
The host immune system neutralised the antibiotic, allowing bacterial recovery
Resistance arose because all bacteria converted to a wall free form under drug pressure
Resistance developed because antibiotics directly increase plasmid replication rate in all cells

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