Plant Responses

• How do FLOWERING PLANTS increase their chances of survival?

  By responding to changes in their environment
• give examples of plants responding to changes?

  1. Sense direction of light- grow towards it to maximise light absorption for photosynthesis
  2. Sense gravity- so their roots & shoots grow in the right direction
  3. climbing plants have a sense of touch, so can find things to climb up and reach the sunlight
• What is a tropism?

  A the response of a plant to a directional stimulus
• what is a directional stimulus?


  a stimulus coming from a particular direction
• How do plants response to stimuli?

  by regulating their growth
• what is a positive tropism?

  growth towards the stimulus
• what is a negative tropism?

  growth away from the stimulus
• What is phototropism?


  The growth of a plant in response to light
• Shoots are...?


  Positively phototropic and grow towards light
• Roots are...?


  Negatively phototropic and grow away from light
• What is Gravitropism?


  the growth of a plant in response to gravity
• How do shoots respond to gravity?

  Negatively gravitropic , grow upwards
• How do roots respond to gravity?

  Positively gravitropic, grow downwards
• Responses are brought about by what?

  Growth factors
• How do plants respond to directional stimuli?

  Using specific growth factors
• What are growth factors?

  Hormone-like chemicals that speed up or slow down plant growth
• Where are growth factors produced?


  In the growing regions of the plant (EG shoots tips, leaves) and they move to where they are needed in the other parts of the plant
• what do growth factors called auxins do?

  stimulate the growth of shoots by cell elongation
• what is cell elongation?

  this is where cell walls become loose and stretchy, so the cells get longer?
• what do high concentrations of auxins do?

  inhibit growth in roots
• what does IAA stand for?

  Indoleacetic acid
• what is IAA?


  An important auxin that is produced in the tips of shoots in flowering plants
• where is IAA produced?


  in the tips of shoots in flowering plants
• Where does IAA move?

  IAA is moved around the plant to control tropisms
• how does IAA move?

  by diffusion and active transport over short distances, and via the phloem over long distances

  • THIS RESULTS IN different parts of the plant having different concentrations of IAA
  • this uneven distribution of IAA means there is uneven growth of the plant
• IAA- phototropism- describe?


  IAA moves to the more shaded parts of the shoots and roots, so there is uneven growth
• where does IAA concentration increase in the SHOOT(phototropism) ?

  increases on the shaded side- cells elongate and the shoot bends TOWARDS the light
• where does IAA concentration increase in the ROOT(phototropism) ?

  Increases on the shaded side- growth is inhibited so the root bends away from the light
• Gravitropism- IAA - describe>?

  IAA moves to the underside of shoots and roots, so there is uneven growth
• Shoot- gravitropism- where does IAA concentration increase?

  Increases on the lower side- cells elongate so the shoot grows upwards
• Root- gravitropism- where does IAA concentration increase?


  Increases on the lower side- growth is inhibited so the root grows downwards