RESPONDING TO THE ENVIRONMENT

Module 4: Responding to the environment. A2 Biology.

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WHY PLANTS RESPOND TO THE ENVIRONMENT

tropism is a directional growth response in which the direction of the response is determined  by the direction of external stimulus.

Tropisms include:
 - Phototropism - shoots grow towards light, enables photosynthesis
 - Geotropism - roots grow towards pull of gravity
 - Chemotropism - on a flower, pollen tubes grow down the style, attracted by chemicals, towards where fertilisation takes place
 - Thigmotropism - shoots of climbing plants wind around objects and gain support

Hormones coordinate plant responses to environmental stimuli. When hormones reach their target cells, they bind to specific complementary receptors on the plasma membrane. Allows hormones to acts upon only the correct tissues. Hormones moves around the plant by active transport, diffusion and mass flow in the xylem/phloem. Different hormones have different effects.

Auxins promote cell elongation; cytokinins promote cell division; gibberellins promote seed germination; abscisic acid inhibits seed germination/growth; ethene promotes fruit ripening.

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Comments

Amy

useful stuff, though my teacher says it's best not to call plant hormones hormones, Plant Growth Substances are more accurate, because hormones imply that they have to move around to get to a destination but in plants this isn't necessarily the case.

I think, not 100% sure on that though :)

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