Antibiotic sensitivity tests may be used to select the most suitable antibiotics for treating bacterial disease. A researcher performed an antibiotic sensitivity test on two pathogenic bacteria, X and Y. Two Petri dishes of agar were prepared, and a culture of each bacterium was spread across the agar surface. Filter paper discs soaked with antibiotics were then placed on the agar in each dish. The Petri dishes were incubated at $25^{\circ}\text{C}$ for two days. The outcomes for the test with three antibiotics, P, Q and R, are shown in Fig. 4.1.
(a(i))[1]
State the antibiotic that is most effective against bacterium X and the antibiotic that is most effective against bacterium Y.
(a(ii))[2]
Suggest a reason for why bacterium Y showed a different sensitivity to each of the three antibiotics.
(b)[3]
Explain how the use of vaccines in controlling infectious diseases is different from the use of antibiotics.
Worked solution & mark scheme
This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “X = R and Y = P” …