OCR Biology Plant Growth

    A 'tropism' is a growth response to a stimulus. Plants grow towards sources of water and light, which they need to

                                           survive and grow.

Auxin is a plant hormone in the stem tips and roots, which controls the direction of growth. Plant hormones are used in weedkillers, rooting powders and to

control fruit ripening.

Plants have developed responses called tropisms to help mak sure they grow towards souces of light and water.

There are two main types of tropisms;

positive tropisms - the plant grows towards stimulus,

negative tropisms - the plant grows away from the stimulus.

Phototropism is a tropism where the stimulus is light (plant grows upwards).

Geotropism is a tropism where the stimulus is gravity (plant roots grow downwards).