[问答题]
n a classroom investigation
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8w -+mir z tqybj3zj71to the effects of herbal remedies on bacterial infections, studen
mzri-jz y78tj 1w3q+bts selected a range of herbal teas, marketed as possessing “Immune System Boosting” properties. Teas each contained one main ingredient, in addition to other secondary ingredients, present in lower concentrations.
A concentrated solution of each tea was prepared and a 0.2 g mass of cotton wool was soaked in each.
A petri dish was prepared using nutrient agar gel and inoculated with a strain of Staphylococcus aureus. The masses of cotton wool were each placed on the petri dish, which was then incubated at 20
o
C for 5 days, after which the zone of inhibition for each mass of cotton wool was measured.
The experiment was repeated 3 times, a mean and standard deviation was calculated.
1.(1)State the dependent variable in this investigation.
(2)Identify one control variable from the methodology.
2.(1)Based on the results, suggest which ingredient is most effective at inhibiting the growth of bacteria. Give a reason for your answer.
(2)State the TWO brands of tea whose results are unlikely to show statistically significant differences. Give a reason for your answer.
3.Calculate the size of the inhibition zone for EterniTea as a percentage of the size of that for ResisTea.
4.Outline the techniques which should be employed in order to reduce risk when working with bacterial cultures.
5.(1)Identify a limitation of the methodology in allowing a valid comparison of each tea brand.
(2)State how the size of the error bars could be reduced.
