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Plants11 - causes the plant to bend in the opposite...

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Plants: Essential Processes Plant Hormones A hormone is a chemical that affects the ways in which an organism functions; it is produced in one part of the plant (or animal) body but affects many other parts of the body as well. Hormones work by coming in contact with target cells, causing the organism to respond in various ways to the chemical signal. In plants, hormones usually work by influencing cell differentiation, elongation, and division. They also affect the timing of reproduction and germination. These hormones are divided int o five categories: auxins, cytokinins, gibberellins, inhibitors (or abscisic acid), and ethylene. Auxins The primary function of the auxin hormones is to elongate plant cells in the stem. For instance, auxins are the hormones responsible for phototropism, the growth of a plant toward the light. Phototropism results from the rapid elongation of cells on the dark side of the plant, which
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Unformatted text preview: causes the plant to bend in the opposite direction. The acid growth hypothesis explains this occurrence by speculating that auxins trigger proton pumps in cell membranes, lowering the pH in the cell wall to such an extent that the hydrogen bonds holding its cellulose fibers together break apart. These broken bonds give the cell wall greater flex ibility and expandability, so that more water can enter the cell by diffusion, causing the cell itself to elongate. Auxins are also responsible for adventitious root development, secondary growth in the vascular cambium, inhibition of lateral branching, and fruit development. In fact, seedless fruits can be artificially created by applying synthetic auxin to plants; this causes fruit to develop even though fertilization (and thus seed formation) has not occurred....
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