3.6.1.1

• Taxis

  A response to a stimulus that is directional

  • Movement towards or away from a stimulus
• Tropism

  The growth response of a plant to directional stimulus
• Organisms increase their chance of survival by responding to changes in their environment.
• Auxin

  A class of plant hormones that control cell elongation

  • Not secreted.
• Indoleacetic Acid (IAA)

  A plant growth factor that is a type of auxin and controls cell elongation.

  • Stimulates elongation in shoots
  • Inhibits elongation in roots
• Kinesis

  A response to a stimulus that is non-directional, changing the speed at which an organisms moves and the rate at which its direction changes.
• Negative tropism

  The growth of a plant away from a stimulus.
• Phototropism

  A plant’s growth response to light.
• Plant growth factors

  Hormone-like substances that control the growth of plants in response to external stimuli
• Positive tropism

  The growth of plant towards a stimulus
• Reflex

  A rapid, automatic response to a sensory stimulus by the body

  • Acts as a protective mechanism
• Reflex Arc

  The pathway of neurons involved in a reflex action

  • Stimulus - Receptor - Sensory Neurone - Intermediate Neurone - Motor Neurone - Effector - Response
• Taxis

  A response to a stimulus that is directional

  • i.e. the movement of an organism towards or away from a stimulus
• Tropism

  The growth response of a plant to a directional stimulus
• Gravitropism

  A plant’s growth response to gravity
• Central Nervous System (CNS)

  The brain and spinal cord
• Peripheral Nervous System (PNS)

  Pairs of nerves that originate from the CNS and carry nerve impulses into and out of the CNS.

  • Divided into sensory and motor nervous system.
• Response

  A change in an organism as a result of a stimulus