Biology 9700 · AS & A Level · Natural and artificial selection
Natural and artificial selection — practice question
The bacterium that causes disease, Pseudomonas aeruginosa, can sometimes be present as a ‘biofilm’. A biofilm is a bacterial layer growing on a surface and attached to another surface. Antibiotics have difficulty controlling such biofilms. A mutant strain of P. aeruginosa has been identified that forms biofilms indistinguishable from those made by the wild-type bacteria. Even so, the mutant strain is different from the wild-type in how resistant it is to antibiotic A. Antibiotic A is in the antibiotic group called anti-pseudomonal penicillins.
(a(i))[3]
Describe the way penicillin acts on bacteria.
(a(ii))[2]
Explain why penicillin does not affect viruses.
(b)[4]
With reference to Fig. 2.1, describe how the numbers of wild-type and mutant bacteria change on culture media with antibiotic A and without antibiotic A.
(c(i))[2]
Explain how a mutation of a gene coding for an enzyme may lead to an enzyme with reduced activity.
(c(ii))[2]
Explain the different effects of antibiotic A, shown in Fig. 2.1, on the wild-type and mutant strains of bacteria.
(d)[3]
Explain the part played by natural selection in the evolution of antibiotic resistance in bacteria.
Worked solution & mark scheme
This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Penicillin inhibits the enzyme peptidase” …