hard · Enhanced ACT science
A biologist grew identical algae cultures under a red lamp and under a blue lamp, keeping the measured light intensity equal, and found more growth under blue light. She concluded that algae grow best in blue light. A colleague noted that the blue lamp was newer and ran a few degrees warmer than the red lamp throughout the trial.
Which additional trial would best determine whether light color, rather than temperature, caused the difference in growth?
- Grow algae under green light using the older, cooler lamp
- Grow both cultures with each lamp held at the same temperature
- Repeat the blue-light trial using a denser starting culture
- Grow algae in complete darkness to establish a baseline growth rate
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