Biology 9700 · AS & A Level · Principles of genetic technology
Principles of genetic technology — practice question
The disc diffusion method can be used to determine how sensitive bacteria are to antibiotics. First, a bacterial inoculum is spread over agar culture plates, then filter paper discs soaked with antibiotic are placed on the agar surface. The plates are incubated. The bacteria form a ‘lawn’ across the agar, but a circular clear area (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 kinds of filter paper disc: 1 - no antibiotic (control); 2 - penicillin V, a natural penicillin; 3 - carboxypenicillin, a synthetic penicillin. The appearance of the incubated plates is shown in Fig. 3.1.
(a)[3]
With reference to Fig. 3.1, explain the effect of penicillin V on bacterium A.
(b(i))[2]
With reference to Fig. 3.1 and Fig. 3.2, describe how the outer layers of bacterium B differ from those of bacterium A.
(b(ii))[2]
With reference to Fig. 3.1 and Fig. 3.2, explain the different effects of penicillin V on bacterium A and B.
(b(iii))[2]
Suggest how the synthetic penicillin, carboxypenicillin, is able to affect the growth of bacterium B.
(c)[3]
Distinguish between batch culture and continuous culture of microorganisms.
(d)[3]
Explain why batch culture rather than continuous culture is used in 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 inhibits enzyme” …