IGCSE Biology Double Award Co-ordination and Response in Plants Notes

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  • Created on: 22-02-13 19:43
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CO-ORDINATION AND RESPONSE IN PLANTS
Plants respond to the world around them. Their responses are usually much slower
than animal responses as they do not have a nervous system. Some plants can respond
very quickly, such as the Venus fly trap.
Plants respond to stimuli. The two main stimuli are:
SUN ­ Phototropism
GRAVITY - Geotropism
Auxin is a plant hormone. It accumulates on
the shady side of the plant, causing the cells
to elongate and increase growth on that side.
This results in the plant bending towards
the sunlight. This is an example of positive
phototropism.
The hormone Auxin accumulates at the bottom of the stem and root.
Auxin stimulates growth in the shoot, making the cells elongate so that the stem
curves upwards. This is an example of negative geotropism.
Auxin slows the growth at the root so that the root curves downwards into the
ground. This is an example of positive geotropism.

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