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

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

Tube 2 (BTB + Dark, 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 contains BTB and is exposed to light but has no plant, so any color change would be due to light alone. If the BTB stays the same, you know light by itself doesn't alter the indicator — the plant (photosynthesis/respiration) must be causing any color changes seen in the other tubes.