Cambridge Secondary (7-9). Stage 7. MCE Science. Workbook - Unit 5: Food Chains and Food Webs - Question 9

Five nutrient-agar Petri dishes are labelled 1 Control (not opened), 2 Inside of mouth, 3 Unwashed fingertip, 4 Clean fingertip and 5 A chosen surface. Observe through the closed lids; do not reopen growing cultures. Your teacher handles safe disposal.

Suggest and explain one other way in which you would change this investigation to find out how effective different cleaning methods are.