An immunologist investigated the antimicrobial effectiveness of two essential oils, Tea Tree oil and Eucalyptus oil, against Staphylococcus aureus bacteria grown on nutrient agar in a Petri dish.
Filter paper discs soaked in each essential oil were placed on the agar surface. After incubating the plates at 25 ∘C25\text{ }^{\circ}\text{C}25 ∘C for 36 hours, circular zones of inhibition (clear areas where bacteria did not grow) were visible around the discs.
State the measurement the researcher must take in order to calculate the surface area of the zone of inhibition.
The researcher measured the diameter of the zone of inhibition for Tea Tree oil to be 34 mm. Calculate the area of this zone where bacterial growth was inhibited. Give your answer to 3 significant figures.
Describe how the researcher 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.