plant responses

• How would a plant respond to a lack of H20 (4)

  • root hair cell detects low H20 so releases ABA
  • ABA binds to gaurd cell receptors
  • K+ ions move out , water follows by osmosis down water potential gradient
  • gaurd cells become flaccid and stomata close
• how would a plant undergo abscission in autumn (4)

  • phytochromes detect falling light levels
  • decreases auxin production and increases ethene production
  • ethene activates digestive cellulase in abcission zone to digest cell wall in seperation layer
  • vascular bundles are sealed
• where are the food stores in dicot and monocot seeds (2)

  cotyledons and the endosperm
• how do gibberellins and ABA germinate seeds (in depth) (4)

  • switch on genes for amylases and proteases
  • ABA acts as an antagonist to gibberellins
  • the relative levels of both hormones determine weather a seed will germinate
• What effect do auxins (IAA) have on the apical shoot (4)

  • promote growth of apical shoot by diffusing from the tip of the meristem downwards , binding to receptor sites causing ph of cell walls to drop and become flexible , water enters so the vacuol expands , enzymes destroy auxins and cell wall becomes rigid again
• what effect do high auxin concentrations have on shoots (3)

  • suppress growth of lateral shoots
  • resulting in apical dominance
• what effect do auxin concentrations have on roots (2)

  • low auxin concentrations promote root growth
  • high auxin concentrations inhibit root growth
• what effect do gibberellins have on plant growth (1)

  • increase the length of internodes (the distance between leaves on a stem)
• define antagonism 


  the balance of two substances having opposing effects determining the response of the plant
• define synergism 


  different hormones working together to give a greater response
• how would a plant prevent freezing (2)

  • sap in the vacuole contains solutes which lower the freezing point
  • ABA stimulates production of polysaccharides and proteins which act as antifreeze
• define pheromone 


  a chemical made by an organism which affects the social behaviour of other members of the same species
• what are the commercial use of plant hormones

  • control ripening
  • rooting powders
  • really high concentrations of auxins as hormonal weed killers
  • production of seedless fruit (auxins)
  • cytokinins used to prevent ripening
• how would a plant respond to overcrowding from other plants

  • climbing plants will show positive thigmotropism
  • grow roots towards water and minerals
  • auxins will show positive phototropism
  • plant will bend towards light