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14: Coordination and Response, Tropic responses, Positive phototropism:,…
14: Coordination and Response, Tropic responses
Tropism:
Tropisms are growth movements related to directional stimuli, e.g. a shoot will grow towards a source of light but away from the direction of gravity.
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Phototropism is a response in which a plant grows towards or away from the direction from which light is coming.
If the plant organ responds by growing towards the stimulus, the response is said to be ‘positive’.
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Advantages:
Positive phototropism:
By growing towards the source of light, a shoot brings its leaves into the best situation for photosynthesis.
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This lifts the leaves and flowers above the ground and helps the plant to compete for light and carbon dioxide.
Seed dispersal may be more effective from fruits on a long, vertical stem.
Positive gravitropism:
By growing towards gravity, roots penetrate the soil, which is their means of anchorage and their source of water and mineral salts.
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