Why does a potted plant on a windowsill bend and grow toward the light?
Light causes auxin to move to the shaded side of the shoot tip.
Light causes auxin to move to the shaded side of the shoot tip. Auxin promotes cell elongation, so the cells on the shaded side grow longer than those on the lit side. Uneven growth bends the shoot toward the light — a response called phototropism. The plant isn't 'reaching' consciously; it's simply that auxin-driven elongation is greater on the darker side.
Key point
Auxin accumulates on the shaded side and elongates those cells, bending the shoot toward light (phototropism).
Common mistake
thinking the plant actively senses and moves toward light like an animal.
Memory tip
auxin piles up in shade → that side grows more → the shoot bends to the light.
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