HSA 2009 Biology Item 13
- CID
- CIDebf56b8b15e7111f28626e5d7ecabe26
- itemNum
- 13
- initialLetter
- A
- itemType
- SR
- itemAnswerKey
- 3
- itemMaxScorePoints
- 1
- origNum
- 18
Students tested two cleansers for their effectiveness against bacteria. In their experiment, each cleanser was used on two different household surfaces. The students took samples from each surface before and after using each cleanser. Then they transferred each sample to a culture medium. The students counted the number of bacterial colonies that grew on each culture medium. The results of their test are shown in the table below.
Which of these would be the best control for their experiment?
- Use only Cleanser 1 on both sinks and counters.
- Use Cleanser 1 on the sinks and Cleanser 2 on the counters.
- Test the number of bacteria on the counters and sinks after scrubbing without using cleansers.
- Test the number of bacteria on the counters and sinks without scrubbing with cleansers.