B1 H - Sample set 1 Q2 Answers
2) Streptococcus pyogenes is a bacterium that causes communicable infections. (a) Scientists tested the ability of two antiseptics to kill Streptococcus pyogenes bacteria. They spread Streptococcus pyogenes bacteria on two agar jelly plates and placed a small disc of filter paper containing antiseptic in the centre of each dish. Figure 3 shows the results of the test after 24 hours of incubation.
(i) Calculate the area of the zone of inhibition for antiseptic 2.
Give the answer to 3 significant figures.
(π = 3.14) (3)
Give the answer to 3 significant figures.
(π = 3.14) (3)
zone of inhibition for antiseptic 2 = .............................................................. mm2
(ii) Explain which antiseptic is the most effective. (2)
(iii) After the bacteria were spread on the plates, both plates were incubated for 24 hours at 37°C. Give a reason why the plates were incubated at 37°C. (1)
(b) The wire loop used to spread bacteria on an agar plate was heated in a Bunsen burner flame before being used. Explain why this aseptic precaution was used. (2)
(Total for Question 2 = 8 marks)
Answers
