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iGCSE Edexcel Biology

Plants respond to stimuli.
Tropisms are directional responses to their environment.
Phototropisms are responses to light.
Geotropisms are responses to gravity.
Roots and stems have geotropic responses, roots positive
(towards gravity), stems negative (away).
Stems have positive phototrophic responses (towards light).
Their responses are much slower than…

Page 2

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iGCSE Edexcel Biology


Gravity acts downwards on the plant.
Even if a seedling is placed on its side the root tips will always
grow downwards.
Auxin levels may be a part of this response however as of yet
not much is known about it.


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