Sensory Reception
- Created by: Megan Cameron
- Created on: 26-02-13 09:46
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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.
- Greater chance of raising offspring and of passing their alleles onto the next generation.
- 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
- A simple response whose direction is determined by the direction of the stimulus
- 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.
- The organism moves more rapidly and changes direction more when the stimulus is unpleasant
- 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.
- Stimulus and response
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