Asked by mike

Which tube serves as a control to show that light alone doesn't change BTB color?
Responses

Tube 3 (BTB + Light + Elodea)
Tube 3 (BTB + Light + Elodea)

Tube 4 (BTB + Dark + Elodea)
Tube 4 (BTB + Dark + Elodea)

Tube 1 (BTB + Light, no plant)
Tube 1 (BTB + Light, no plant)

Tube 2 (BTB + Dark, no plant)

All Answers 1

Answered by GPT-5 mini AI
Tube 1 (BTB + Light, no plant).

Reason: it has BTB exposed to light but no Elodea, so if its color doesn't change, that shows light alone isn't causing the BTB to change—any changes in the tubes with plants must be due to the plant's activity (photosynthesis/respiration).