Plant hormones

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  • Plant hormones
    • Auxin
      • Is a plant hormone that controls growth near the tip of shoots and roots
      • It controls the growth of a plant in response to light (phototropism), gravity (gravitropism or geotropism) and moisture
      • If the tip of a shoot is removed no auxin is available and the shoot may stop growing
    • Shoot grows towards light (phototropism)
      • This then makes the cells grown faster on the shaded side the the shoot growns towards the light
        • When a shoot tip is exposed to light, more auxin accumulates on the side that's in the shade than the side in the light
    • Shoot grow away from gravity (gravitropism)
      • When a shoot is growing sideways gravity produces an unequal distribution of the auxin in the tip, with more auxin on the lower side
        • This causes the lower side to grow faster bending the shoot upwards
    • Roots grow towards gravity (gravitropism)
      • But in a root the extra auxin inhibits growth, this means the cells on the top elongate faster and the root bends downwards
        • A root growing sideways will also have more auxin on its lower side
    • Root grow towards moisture
      • An uneven amount of moisture either side of a root produces more auxin on the side with more moisture
        • This inhibits growth on that side, causing the root to bend in that direction towards the moisture
    • Agriculture
      • Most weeds in crop fields have broad leaves unlike grass, selective weedkillers are made of plant growth hormones, they disruty the weeds and kill them but leave the crops untouched
      • Plant cuttings wont always grow in soil, if you add rooting power which contains the plant hormone auxin they'll produce roots rapidly and starts growing new plants, this helps growers produce lots of clones of a really good plant quicjly


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