Sensory Reception

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  • Sensory Reception
    • Stimulus and response
      • A stimulus is a detectable change in the internal or external environment of an organism that produces a response in the organism
      • Increases the chances of survival of an organism.
        • Greater chance of raising offspring and of passing their alleles onto the next generation.
          • Selection pressure favouring organisms with more appropriate responses.
    • Taxes
      • A simple response whose direction is determined by the direction of the stimulus
        • A motile organism responds directly to environmental changes by moving its whole body either towards a favourable stimulus or away from an unfavourable one.
      • Single celled algae will move towards light - positive phototaxis
        • Need light to manufacture food
      • Earthworms move away from light - negative phototaxis
        • Takes them into soil where they are better able to conserve water, find food and avoid predation
    • Kineses
      • The organism moves more rapidly and changes direction more when the stimulus is unpleasant
        • Results in an increase in random movements
      • Woodlice move more rapidly in dry conditions and change direction more often. Increases chance of moving into a more suitable area.
    • Tropisms
      • Growth movemment of part of a plant in response to a directional stimulus.
      • Plant shoots grow towards light - positive phototropism. Can capture most light for photosynthesis
      • Plant roots grow towards water - positive hydrotropism.


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