IGCSE Biology - Co-ordination and Response in Plants

In IGCSE biology curriculum, 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. Usually in IGCSE biology, this is an example of positive phototropism.

There are 3 key ideas of geotropism in IGCSE biology, they are:

• 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.

End of this topic!

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