Survival and response

• What is taxis?

  Taxis is a behavioral response in which the entire organism moves towards or away from a directional stimulus. Positive taxis=towards stimulus, Negative taxis=away from stimulus
• Types of taxis:

  Phototaxis = light

  Chemotaxis = chemical

  Aerotaxis = air (oxygen)

  Rheotaxis = resistance (moving against/towards currents/wind etc)
• What is kinesis?

  A non-directional movement response where the rate if movement is related to the intensity of the stimulus not the direction

  Unfavourable environment = moves faster, turns less

  Favourable environment = moves slower, turns more
• What is a tropism?

  A tropism is a growth response of a plant in response to a directional stimulus, such as light or gravity.

  Positive tropism = growing towards the stimulus

  Negative tropism = growing away from the stimulus
• Describe phototropism in shoots:

  • Main areas of cell division/cell elongation in plants is in meristem tissue in the tips of shoots/roots
  • Indoleacetic acid (IAA) is a growth factor (auxin) that makes cells elongate
  • In shoots, IAA is produced in high concentration in meristem tissue. It diffuses down the shaded side of the shoot, elongating the cells on that side, allowing the shoot to grow towards the light. Shoots are postively phototropic
• Describe phototropism in roots:

  • Roots are negatively phototropic, and positively geotropic
  • IAA collects on the shaded side of the root, and inhibits growth.
  • This causes the cells on the top to elongate more than the lower side of the root, therefore the root curves down
  • IAA is transported to the roots via the phloem