In this kind of tropism, biological entities like plants can respond to light stimuli. The response can be negative or positive based on the fact whether the organism moves or grows towards the light source or away from it. The shoots of plants demonstrate positive tropism as they grow towards the light to increase photosynthesis yield and rate.
The light triggers a plant hormone auxin that bends growing shoots in direction of light by promoting localized cell elongation. Light also influences the growth of root so it is correctly oriented towards the soil. Red light is responsible for positive phototropism in roots while white or blue light results in negative phototropism.
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