Stimuli are detected by the body and lead to a response

Important points about stimuli and response made from my aqa syllabus unit 5 notes

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  • Stimulus
    • detectable change in environment (internal or external) of any organism that produces a response in that organism
  • Receptor
    • Cells or organs that detect stimuli
  • Effector
    • Cells, tissues, organs or systems that carry out the response
  • Tropism
    • a growth movement of part of a plant in response to a directional stimulus.
  • Phototropism
    • Response to light.
  • Geotropism
    • Response to gravity
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Glossary Cont

  • Hydrotropism
    • Response to water
  • Taxis
    • Movement that is orientated in relation to the direction of a stimulus
  • Kineses
    • behaviour pattern in which the animal responds ti a change in stimulus intensity or decreasing it activity.
      • Orthokinesis
        • speed of movement depends on stimulus intensity
      • Klinokinesis
        • rate of turning depends on stimulus intensity
  • Central Nervous system (CNS)
    • consists of brain and spinal cord
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Glossary cont

  • Peripheral nervous system
    • made up of pairs of nerves that originate from either the brain or the spinal cord which link to receptors and effectors
  • Sensory neurones
    • Carry nerve impulses from receptors to CNS
  • Motor neurones
    • Carry nerve impulses from CNS to effectors.
  • Voluntary Nervous System
    • carries nerve impluses to body muscles
  • autonomic Nervous System
    • carries impulses to glands, smooth muscle and cardiac muscle.
  • Reflex
    • An involuntary respnse to a sensory stimulus
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Glossary Cont

  • Reflex Arc
    • pathway of neurones involved in a reflex
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Organisms respond to stimuli

  • Responding to a stimulus increases organism chances of survival
    • this increases chances of reproduction and passing alleles to next generation
    • Therefore, there is always a selection pressure favouring organisms with more appropriate responses
    • Animals use the nervous system as a more rapid method of communication

Stimulus--> Receptor --> Co-ordinator --> Effector --> Response

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Tropisms in flowering plants

  • Plants often respond to an external stimulus acting from a particular direction
    • movement involves directional growth
      • caused by more growth in one region than another
    • such growth is caused tropism
  • Type of response named after stimulus:
    • Phototropism
      • Shoots = positively phototropic
      • roots =negatively phototropic
    • Geotropism
      • Shoots = negatively geotropic
      • Roots = Positively geotropic
      • allows seeds to be orientated correctly.
    • Hydrotropism
      • Roots = positive hydrotropism
      • Within soil root systems will grow where most water.
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Taxes and Kineses

  • Taxis
    • motile organism responds to environmental changes
    • classified according to whether movement is away or towards stimulus.
      • positive or negative taxis
  • Kineses
    • the more unpleasant the stimulus, the more rapidly it changes direction.
    • Kineses causes increase in random movement
    • designed to bring organism into favourable conditions.
    • Types of kinesis:
      • Orthokinesis
      • Klinokinesis
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Simple Reflec arc

Nervous system divided into two parts:

  • Central Nervous system
  • Peripheral Nervous System

Peripheral Nervous system is divided into:

  • Sensory neurones
  • Motor neurones

The motor nervous system can be further subdived into:

  • Voluntary nervous system
  • Autonomic nervous system
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Spinal cord

Column of nervous tissue that runs along the back and lies inside the vertebral colomn for protection.

  • emerges at intervals along the spinal cord as a pair of nerves.

1. Nerve from receptor

2. to sensory neurone

3. to intermediate neurone

4. to effector.

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Reflex Arc

Receptor --> Peripheral nerve --> CNS --> Peripheral nerve --> Effector

  • Reflex passes along a reflex arc
    • involves 3 neurones
      • e.g spinal reflex
    • main stages of spinal reflex:-

stimulus-->receptor-->sensory neurone --> intermediate neurone --> motor neurone --> effector -->response

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Importance of reflex actions

  • involuntary
    • means brain is left for more complex disicisions
  • Protects body from harmful stimuli
  • Fast
    • short neurone pathway
    • 1 or 2 synapses
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