Cambridge Secondary (7-9). Stage 7. MCE Science. Workbook - Unit 5: Food Chains and Food Webs - Question 2

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.

Rank the Petri dishes according to the number of microorganisms growing in each Petri dish. Exclude the control Petri dish. Use ranks 1 (least growth), 2, 3 and 4 (most growth).