Plant Responses

• What is a stimulus?


  Anything that causes a response in an organism.
• What is a tropism?

  The growth response of a plant to a stimulus.
• When does a positive tropism occur?

  When a plant grows toward the stimulus.
• When does a negative tropism occur?

  When a plant grows away from the stimulus.
• What is phototropism?


  The growth response of a plant to light.
• What is geotropism?


  The growth response of a plant to gravity.
• What is thigmotropism?


  The growth response of a plant to touch.
• What is hydrotropism? 


  The growth response of a plant to water.
• What is chemotropism?


  The growth response of a plant to chemicals.
• What is a growth regulator?

  A chemical that controls the growth of a plant.
• Where are growth regulators produced?

  Meristematic tissue.
• How and where are growth regulators transported.


  They're transported by diffusion in the phloem.
• Name 2 growth promoters.

  Auxins and giberellins.
• What is IAA?


  A type of auxin.
• Where (in meristematic tisse) are auxins produced??

  In shoot tips and root tips.
• Giive 4 functions of auxins.

  Causes root growth, causes tissue culturing, causes phototropism, and causes geotropism.
• What is apical dominance?

  Auxins produced in the apical meristem pass down the stem and inhibit side branches from growing.
• What is the benefit of apical dominance?

  Allows the plant to grow tall.
• What is the importance of IAA in controlling phototropism?

  Causes the cell to bend towards the light as IAA diffuses down the shaded side of the plant.
• Name a growth inhibitor.

  Ethene.
• What is the function of ethene?

  Causes fruits to ripen and causes ageing in plants.
• What is ethene's commercial use?

  Ethene is commercially used to ripen bananas.
• What stress regulator is prouced in plants?

  Abscisic acid.
• What effect does abscisic acid have on seeds?

  Causes dormancy.
• What are rooting powders?


  A commercially used powder contaning an artificially produced growth regulator.
• What is gibberellin's commercial function?

  Increase the size of a fruit.
• Give 2 examples of anatomical plant protective features.

  Thorns prevent animals from eating plants, and waxy cuticles on leaves prevent water loss.
• Give 2 examples of chemical plant protective features.

  Many plants form heat-shock proteins in response to excessive heat, and produce stress proteins when attacked by microorganisms.
• Why do plants form heat-shock proteins?


  Plants form heat-shock proteins to prevent their enzymes from becoming denatured during periods of excessive heat. (above 40ºc)
• What does denatured mean?

  The active site has been destroyed.