Why do pine cones open and close?
For grown-ups: the science
A pine cone uses its flaps, which change shape with water, to protect its seeds and then send them flying.
The scales of a pine cone move based on humidity. The tissue in each scale absorbs water and shrinks unevenly, so it closes when damp and opens when dry. This isn't caused by living cells actively moving—it's a passive bending from the tissue's structure. This helps seeds spread easily in dry weather and keeps them from getting wet or scattering poorly in damp conditions.
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Transcript
Do you think a pine cone's little flaps close up on a rainy day?
On a sunny day, a pine cone's flaps spread wide open. This lets the tiny seeds inside catch the wind and fly away.
When rain falls, the flaps soak up water and curl back inward. This keeps the seeds safe and dry so they don't get too heavy.
As it dries out, one side of each flap shrinks more than the other. That difference makes the flaps slowly open back up again.
So a pine cone closes up when it's wet, and opens up when it's dry. That way, the wind can carry its seeds far away.