Biology / Unit 11 Bio 2555 short lesson, about 20 seconds
Gravitropism
Captions available
The idea
Gravitropism orients growth to gravity: shoots show negative gravitropism, growing upward, while roots show positive gravitropism, growing downward, both mediated by settling starch-filled amyloplasts.
In practice
A plant laid on its side redirects shoot growth upward within hours as amyloplasts settle to the new lower cell wall.
Where people slip
"Positive" and "negative" describe direction relative to gravity's pull, not a value judgment about usefulness.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Builds on
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