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IB Biology HL C3.2.14 Antibiotic Resistance Evolution Questions

Explore how mutation and plasmid variation, antibiotic selection and overuse produce multi-resistant bacterial strains in IB Biology HL C3.2.14.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam points

  • Explain how random mutations or plasmids can introduce heritable antibiotic resistance into a bacterial population.
  • Explain how antibiotic use selects resistant variants: susceptible bacteria die while resistant bacteria survive, reproduce and become more common.
  • Interpret resistance data by comparing strains and identifying resistance to multiple antibiotics.

IB Biology HL C3.2.14 Antibiotic Resistance Evolution Questions question 1

[Maximum number: 3]

Different strains of the bacterium Enterobacter cloacae were grown on a plate and identified according to their place on the plate (for example, the first strain top left is A1). They were then transferred to Petri dishes containing agar with varying concentrations of antibiotic (5,10,20,40,80,160μgml−1)\left(5,10,20,40,80,160 \mu \mathrm{gml}^{-1}\right).

Figure for Question IB Biology HL C3.2.14 Antibiotic Resistance Evolution Questions question 1 — IB Biology HL

The Petri dishes were left for 24 hours in an incubator at 25∘C25^{\circ} \mathrm{C} and the resulting plates are shown.

Figure for Question IB Biology HL C3.2.14 Antibiotic Resistance Evolution Questions question 1 — IB Biology HL

Question (a)

(a)

State the strain with the least resistance to antibiotic.

[ 1 ]

Question (b)

(b)

Suggest reasons for the presence of strains such as B2 in all of the plates.

[ 2 ]
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