plants response to the environment

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  • plant hormones and responding to the environment
    • auxins
      • promote cell elongation
      • inhibit growth of side shoots
        • apical dominance
          • the growing apical bud inhibits growth of lateral shoots
            • this is so that plant can maximise area exposed to sun
              • if apical bud broken off, side shoots begin to grow
          • if apical bud broken off, side shoots begin to grow
          • EVIDENCE: when medium containing auxin is placed on tip of plant with bud removed lateral bud growth stops
            • EVIDENCE: when auxin transoprt inhibitor applied above latteral bud but below apical bud, latteral buds grew
          • abcisic acid and auxins work together
            • SYNERGISTIC
          • cytokinins and auxin work against each other
            • ANTAGONISTIC
              • the fall of auxins in leaf absicion causes production of ethene which encourages absision
      • inhibit abscission
      • increases the stretchiness of cellulose cell wall by encouraging active transport of hydrogen ions into the cell
        • this means that pH is lower and is optimal for wall-loosening enzymes(expansins)
        • hydrogen ions disrupt hydrogen bonds in the cell wall while expansins break bonds within the cellulose
    • cytokinins
      • promote cell division
    • giberellins
      • promote seed germination
      • promotes growth of cells
    • ethene
      • promotes fruit ripening
    • abcisic acid
      • inhibits seed germination and growth
      • causes stomatal closure when water availiability is low
    • apical dominance
      • the growing apical bud inhibits growth of lateral shoots
        • this is so that plant can maximise area exposed to sun
        • EVIDENCE: when medium containing auxin is placed on tip of plant with bud removed lateral bud growth stops
          • EVIDENCE: when auxin transoprt inhibitor applied above latteral bud but below apical bud, latteral buds grew
        • abcisic acid and auxins work together
          • SYNERGISTIC
        • cytokinins and auxin work against each other
          • ANTAGONISTIC
            • the fall of auxins in leaf absicion causes production of ethene which encourages absision
      • shaded side of shoot elongates faster than illuminated side as auxins move towards the shadded side
        • auxins are broken down by enzymes further down the shoot

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