Biology / Unit 11 Bio 2561 worked example, 60 to 90 seconds
The Darwin and Boysen-Jensen Phototropism Experiments, Worked
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The idea
This procedure traces how two classic experiments located phototropism's signal at the shoot tip and identified it as a diffusible chemical rather than a direct light response along the stem.
Where people slip
A single experiment alone cannot separate "detection happens at the tip" from "the tip alone can bend" — it takes the mica-barrier control specifically to show the signal must be a diffusible chemical rather than a structural or electrical connection.
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