Survival and response

• Define stimulus

  A change in the internal or external environment
• Define receptor

  Something that detects the stimulus
• Define coordinator

  Formulates a suitable response to the stimulus
• Define effector

  Produces the response, which increases the chance of survival
• Name the 3 simple responses

  • Taxis
  • Kinesis
  • Tropism
• Describe the taxis response

  Directional movement of a mobile organism towards or away from a stimulus
• Describe the kinesis response

  Non-directional movement of a mobile organism. The stronger the stimulus, the faster the rate of movements and turns until a favourable environment is reached.
• Describe the tropism response

  Directional growth of part of a plant towards or away from a stimulus
• Describe positive phototropism

  • Indoleacetic acid is an auxin that is produced in the shoot tip and is intially evenly distributed
  • Light causes IAA to diffuse to the shaded part of the shoot
  • IAA causes cells to elongate in the shoot
  • Cells on the shaded side grow faster than the illuminated side
  • The shoot bends toward light to increase the rate of photosynthesis
• Describe positive gravitropism

  • Indoleacetic acid is an auxin and produced in the root tip and is initally evenly distributed
  • Gravity causes IAA to diffuse to the lower side of the root
  • IAA inhibits cell elongation in the roots
  • Cells on the upper side grow faster than the lower side
  • The root bends toward gravity for anchorage and to increase rate of water, nitrates and phosphates uptake
• Name 3 features of reflexes

  • Rapid, as only consist of 3 neurons
  • Effective from birth, so you don't need to learn them
  • Automatic, so no decision-making is needed
• Describe how reflexes are important for survival

  • Allow escape from predators
  • Protect against tissue damage
  • Allow homeostatic environment
  • Allow control of balance and posture