Once again, Kathy ran her fingers through her hair and then touched surfaces that people touch often, such as door knobs, refrigerator door handles, phones, and the computer keyboard. She ran a third cotton swab over her hand, under her fingernails, and between her fingers. Then she rubbed it in a zigzag pattern over the third petri dish. She covered the dish and disposed of the swab. She labeled this petri dish “unwashed #2.” Kathy applied hand sanitizer to her hands, following the directions on the bottle. She rubbed her hands together until the sanitizer evaporated. She rubbed a new cotton swab on her hand, making sure to get under her nails and between her fingers, and then rubbed it in a zigzag pattern over the fourth petri dish. She covered the dish and disposed of the swab. She labeled the petri dish “sanitizer.” She stored these petri dishes at room temperature.

The photographs show these petri dishes after 24 and 48 hours. Write down your observations.

four petri dishes: at 24 hours unwashed #2 shows a large amount of growth, sanitizer shows only one dot of growth, at 48 hours unwashed #2 is nearly covered with growth while sanitizer shows only a very small amount of growth