1.1 Cell structure

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Question 13
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A student investigated the effectiveness of three different antibiotics, labeled X, Y, and Z, against a specific species of bacteria growing on an agar plate. After incubation at 25∘C25^\circ\text{C}25∘C for 48 hours, the results were observed.

A Petri dish containing nutrient agar seeded with a bacterium. Three paper discs containing different antibiotics, labeled X, Y, and Z, are placed on the agar. Around X, there is a very large clear circular zone (zone of inhibition). Around Y, there is a medium-sized clear circular zone. Around Z, there is a very small clear circular zone. The rest of the agar plate is shaded grey to represent bacterial growth.

a.

Describe two aseptic techniques the student should have used when preparing and setting up the agar plate.

[2]
b.

Which antibiotic is the most effective? Give a reason for your answer.

[1]
c.

Calculate the area where no bacteria were growing for antibiotic X. The diameter of the zone of inhibition for antibiotic X is measured to be 2.4 cm. Use π=3.14\pi = 3.14π=3.14. Give the unit.

[5]
d.

Suggest one way the student could improve this investigation.

[1]

1.1 Cell structure Questions

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