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Pre AP Biology -EVO 2.2 Selective Mechanisms- FRQ Exam Style Questions -New Syllabus

Pre AP Biology -EVO 2.2 Selective Mechanisms- FRQ Exam Style Questions – New Syllabus 2025-2026

Pre AP Biology -EVO 2.2 Selective Mechanisms- FRQ Exam Style Questions – Pre AP Biology – per latest Pre AP Biology Syllabus.

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Question

A patient consumed dirty water and developed the bacterium Escherichia coli (E.coli). The diagram shows the effects of the antibiotics, streptomycin and Penicillin on this bacterium.
Using the diagram, justify whether the patient should take Penicillin or streptomycin.

Most-appropriate topic codes (Pre-AP Biology):

• TOPIC: ECO 2.2 – Population Growth: Use data to explain the growth of a population.
• TOPIC: EVO 2.2 – Selective Mechanisms: Describe how selective pressures in the environment can affect an organism’s fitness.
▶️ Answer/Explanation
Detailed solution

The patient should take streptomycin.

Justification:

  • Observation: In the diagram, there is a clear area labeled “Zone of no growth” around the disc marked S (streptomycin). In contrast, colonies of E. coli are growing right up to the edge of the disc marked P (Penicillin).
  • Reasoning: The “Zone of no growth” (zone of inhibition) indicates that streptomycin has effectively killed or inhibited the reproduction of the bacteria in that area. The absence of such a zone around the Penicillin disc indicates that the E. coli bacteria are resistant to Penicillin and it is ineffective.
  • Conclusion: Since streptomycin is effective at stopping the bacterial growth while Penicillin is not, streptomycin is the correct treatment choice.
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