A student investigated the antibacterial effectiveness of two disinfectants, Brand X and Brand Y, against E.coliE. coliE.coli bacteria grown on agar in a Petri dish.
Filter paper discs soaked in each disinfectant were placed on the agar. After incubation at 20 ∘C20\text{ }^\circ\text{C}20 ∘C for 48 hours, circular zones of inhibition (clear areas with no bacterial growth) appeared around the discs.
What measurement must the student take in order to calculate the surface area of the zone of inhibition?
The student measures the diameter of the zone of inhibition for Brand X to be 28 mm28\text{ mm}28 mm. Calculate the area of this zone where no bacteria are growing. Give your answer to 3 significant figures.
Describe how the student could check if these experimental results are repeatable.
163 exam-style questions on AQA GCSE Biology 1.1 Cell structure, covering 1.1.1 Eukaryotes and prokaryotes, 1.1.2 Animal and plant cells, 1.1.3 Cell specialisation, 1.1.4 Cell differentiation, 1.1.5 Microscopy, and 1.1.6 Culturing microorganisms. Each one has a worked solution and a mark scheme showing where the marks go.