Biology 9700 · AS & A Level · Genetic technology applied to medicine
Genetic technology applied to medicine — practice question
The disc diffusion method can be used to assess how sensitive bacteria are to antibiotics. First, an inoculum of the bacteria is spread over agar culture plates, and then filter paper discs soaked with antibiotic are placed on the agar surface. After incubation, the bacteria form a continuous ‘lawn’ over the agar, but a circular clear region, called the zone of inhibition, is seen around any disc where bacterial growth has been prevented.
Two bacterial species, A and B, were cultured on separate plates with three different filter paper discs:
1 - no antibiotic (control)
2 - penicillin V, a natural penicillin
3 - carboxypenicillin, a synthetic penicillin.
The incubated plates are shown in Fig. 3.1.
(a)[3]
Using Fig. 3.1 as a reference, explain what penicillin V does to bacterium A.
(b(i))[2]
Using Fig. 3.1 and Fig. 3.2, describe the ways in which the outer layers of bacterium B are different from those of bacterium A.
(b(ii))[2]
Using Fig. 3.1 and Fig. 3.2, explain why penicillin V has different effects on bacterium A and bacterium B.
(b(iii))[2]
Suggest how the synthetic penicillin, carboxypenicillin, is able to influence the growth of bacterium B.
(c)[3]
Distinguish between batch culture and continuous culture of microorganisms.
(d)[3]
Explain why batch culture is used instead of continuous culture for the production of penicillin.
Worked solution & mark scheme
This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Penicillin blocks an enzyme” …