Response To Stimuli

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  • Response To Stimuli
    • Kineisis
      • Kineisis- A form of response in which the organisms does not move towards or away the stimulus. Instead it changes the speed at which it moves and the rate at which is changes direction.
      • If the organism crosses a sharp dividing line between favourable and unfavourable. it's rate of turning increases.  This raises the chance of a quick return to a favourable envrionment.
      • If it moves a large distance into the unfavourable environment the the rate of turning may slowly decrease so it moves in long straight lines before it turns often sharply. This response tends to bring the organism into new environments with favourable conditions.
    • Key Terms
      • Stimulus- A detectable change to the internal or external environment of an organism that leads to a response of an organism.
      • Receptor- Specific to one type of stimulus.
      • Coordinator- Formulates a suitable response to a stimulus. Can be at molecular level or include a large organ such as the brain.
      • Effector- Where the response is produced. This could be at molecular level or could involve the whole organism.
    • Tropism
      • Tropisms is the growth of a plant in response to a directional stimulus. They almost always grow towards a positive stimulus or away from a negative stimulus.
      • Plant shoots grow towards light and roots grow away from gravity so the leaves are in the light .  Plant roots grow away from the light and towards gravity. It increases the chance of the roots growing down into the soil to absorb water and minerals.


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