GCSE Edexcel Biology Investigating antibiotics & antiseptics: Streptococcus pyogenes is a bact

Question

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 onto 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 after 24 hours of incubation.

antiseptic 1                       antiseptic 2
   bacterial growth                  zone of inhibition
   filter disc of antiseptic

**Figure 3**

(i) Calculate the area of the zone of inhibition for antiseptic 2.

Give the answer to 3 significant figures.

(π = 3.14)

zone of inhibition for antiseptic 2 = ................................. mm²

(ii) Explain which antiseptic is the most effective.

(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.

(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.

Streptococcus pyogenes is a bacterium that causes communicable infections - Edexcel - GCSE Biology - Question 2 - 2016 - Paper 1

Worked Solution & Example Answer:Streptococcus pyogenes is a bacterium that causes communicable infections - Edexcel - GCSE Biology - Question 2 - 2016 - Paper 1

Calculate the area of the zone of inhibition for antiseptic 2.

Explain which antiseptic is the most effective.

Give a reason why the plates were incubated at 37°C.

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