Q42 - Extracellular vs Intracellular Resistance Enzymes Shape Selection Pressure

Theoretical B Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Sir Alexander Fleming (1881-1955) discovered antibiotics, but humanity’s biggest killers are now mostly resistant to them. In one pathogen, antibiotics are degraded either by intracellular enzymes, or by enzymes released into the surrounding environment. A strain susceptible to antibiotics was labelled red, and a resistant strain was labelled yellow. Equal amounts of susceptible and resistant bacteria were mixed and seeded as a dense lawn on plates. These were treated with drug A or B at different concentrations, and grown for a period of time. The colour of the remaining cells was photographed.

Figure 1 for Q42: Extracellular vs Intracellular Resistance Enzymes Shape Selection Pressure

Using the information and data, determine which of the statements are true or which are false.

A. This species of bacteria expresses the target of Drug B.

B. When there is no drug, the plates will become increasingly yellow, and less red, with time.

C. Resistance to Drug A involves an extracellular enzyme.

D. Plasmids carrying genes for antibiotic resistance are more likely to spread when resistance uses extracellular enzymes, than when it uses intracellular enzymes.

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Question reproduced from IBO 2017, Theoretical Exam B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Official answer key & worked solutions