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Merighi Pietro What is a Geotropism? A geotropism is the growthof living plants in response to gravity. It is given by the downward of the plant roots What is a Phototropism? It is the directional growth in which the direction of the growth is determined by the direction of the light source. In other words it is the growth and response to a light stimulus. Plant Auxins As with animals , plants also use a variety of hormones to control their growth and development. A family of hormones called auxins are commonly found in plants, and promote (and sometimes inhibit) growth. What are Auxins? Auxins are produced in the meristems (tissue that grows) of plants Auxins are responsibile in promoting cell elongation, a process that is required before differentiation of a cell. It is able to this by promoting the intake of water, increasing the elasticity of the cell to cope with the increase of water taken in by the cell. (One of the most common auxins is indole acetic acid.) Phototropism in Auxins. Auxins also play a part in phototropism, an occurance thay involves plants bending or moving away from light. The shoot tip is responsible for directional movement by the plant in response to sunlight, as this is the area where auxins can be found. Sunlight eradicates auxin, meaning that the part of the shoot tip of the plant which is reaciving direct sunlight wil have the least amount of auxin The extra auxin present on the shaded side promotes more cell division and elongation, causing the plant to bend towards the sunlight after this lop-sided growth. Geotropism in Auxins. Geotropism is a similar occurance to the phototropism where the plant exihibits directional growth in response to gravity. The shoot tip illustrates negative geotropism (grows against force of gravity) while the root tip exhibits positive geotropism (grows in the same direction as gravity). Questions….. What is a geotropism and a phototopism? What are Auxins?