An agricultural scientist investigates the antimicrobial properties of two plant extracts, garlic (Allium sativum) extract and ginger (Zingiber officinale) extract, against the plant pathogen Pseudomonas syringae.
They place paper discs soaked in the extracts, alongside a control disc soaked in sterile water, onto an agar plate inoculated with the bacteria. After incubating the plate at 25 ∘C25\ ^\circ\text{C}25 ∘C for 24 hours, circular zones of inhibition (where no bacteria grow) are observed around some of the discs.
What physical dimension of the circular zone of inhibition must be measured to calculate its surface area?
If the measured diameter of the zone of inhibition for the garlic extract is 3.4 cm3.4\text{ cm}3.4 cm, calculate the area of this zone. Give your answer to 2 significant figures. (Use π=3.1416\pi = 3.1416π=3.1416).
State how the scientist could confirm that the results of this investigation are repeatable.