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.

Exam points

Explain that random mutation or plasmid-borne genetic variation can confer antibiotic resistance in a bacterial population.
Trace selection: antibiotic exposure kills susceptible bacteria, while resistant variants survive, reproduce and increase in frequency.
Use resistance graphs or multi-antibiotic data to compare strains and evaluate how overuse or incomplete courses promote multi-resistant populations.

[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 $\left(5,10,20,40,80,160 \mu \mathrm{gml}^{-1}\right)$ .

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 $25^{\circ} \mathrm{C}$ and the resulting plates are shown.

(a)

State the strain with the least resistance to antibiotic.

[ 1 ]

(b)

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

[ 2 ]

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

Question (a)

Question (b)