Plant response

• What is the effect of Gibberellins ?


  stimulate the production of digestive enzymes ton release glucose from food stores. This can be used to create energy for seedling growth
• Describe the mechanisms of cell elongation ?


  1. Auxin released by meristem binds to receptors on cell surface membranes
  2. H+ pumped into cell to lower pH, this increases cell wall flexibility
  3. Cell absorbs H2O and expands cell wall.
  4. Cell wall becomes rigid as auxins are broken down due to cells maturing
• what is apical dominance ?


  Auxins promote apical growth in the shoots but inhibits lateral growth. Resulting in a christmas tree shape
• Gibberellins = stimulate seed germination and stem elongation
• What is a benefit of a taller plant ?

  better ability ot compete for light for photosynthesis
• Name abiotic stresses to plants ?


  Water availability, temperature, winds, light availability
• Name 2 benefits of abscission.

  Less light available, lower rate of photosynthesis, leaves no longer energy efficient

  Leaves on the floor can help insulate the roots
• Describe the mechanisms of abscission ?

  Light receptors detect falling levels and a decrease auxin production occurs

  This results in increased ethene concentration in leaf

  Ethene activates genes in cells in abscission zones to produce digestive enzymes

  Enzymes digest the cell wall in the seperation zone and vascular bundles are later sealed after leaves have dropped off
• Outline the process of stomata closing due to poor water availability ?


  1. lack of water in detected in the root hair cells and ABA is produced and transported up the plant towards the leaves
  2. ABA binds to receptors on guard cells causing conformational changes opening the ion channels
  3. this allows for diffusion of ions out of the cells lowing the surroundings water potential
  4. Resulting in diffusion of water via osmosis out of the guard cells
  5. This causes the guard cells to become flaccid and close
• Name physical defences to herbivores ?


  Thorns, spikes and hairy leaves
• Tannins = bitter tasting chemical toxic to insects
• Alkaloids = bitter tasting chemicals poisonous to animals by affecting their metabolisms
• examples of alkaloids ?


  caffeine, cocaine, morphine and nicotine
• Terpenoids = chemical toxic to insects and fungi
• Example of terpenoid ?


  citronella
• Pheromones = affect social behaviours of other members of the same species
• Volatile organic compounds = affect social behaviours of others members of different species
• What chemical is able to attract predators of the pest insect ?

  volatile organic compounds
• What plant folds in response to touch ?

  mimosa pudica
• tropism = plants response to a stimuli
• phototropism = plants response towards light
• What is the effect of auxins in the shoot ?


  Promote growth
• What is the effect of auxins in the roots ?


  they inhibit growth
• Describe phototropism ?

  Unilateral light causes auxins to move laterally in shoot tip to shaded side

  Higher auxin concentration on shaded side results in faster growth

  This causes the shoot to bend towards the light
• What is the benefit of phototropism in shoots?


  ensures maximum light uptake for maximum rate of photosynthesis
• Geotropism = plant response to gravity
• Describe geotropism in the roots ?

  This inhibits growth so the top side grows faster

  Resulting in the roots be

  Auxins lie on bottom side of leaf due to gravity Auxins lie on bottom side of leaf due to gravity

  This results in root growth downwards
• what does auxins inhibit ?


  fruit ripening

  abscission
• What does ethene promote ?


  fruit ripening

  abscission
• synergism = working together
• antagonistic = opposing each other
• Commercial uses of auxin ?

  Produce seedless fruit

  Stimulate root growth

  Selective Weedkillers

  Prevent abscission
• commercial use of ethene ?


  Ripen fruit

  Promote fruit drop in cherries and walnuts
• Commercial use of gibberellins ?


  Promote growth

  Fruit retention

  Increase sucrose yield

  stimulate germination