Response to stimuli

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  • Created by: ggmonkey
  • Created on: 22-11-16 10:16
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  • Response to stimuli
    • Plant growth factors - Tropisms
      • Light
        • IAA (an auxin) as positive tropism
          • 1. Cells in the tip produce IAA.
          • 2. IAA transported evenly through all parts of shoot.
          • 3. Light causes IAA to move to dark side.
          • 4. Larger concentration of IAA on shaded side.
          • 5. Greater elongation on darker side, tip bends towards the light so get more light for photosynthesis.
      • Water
      • Gravity
        • IAA as a positive geotropism
          • 1. Cells in the tip produce IAA.
          • 2. IAA transported evenly through all parts of root.
          • 3. Gravity pulls IAA to lower side.
          • 4. Larger concentration of IAA on lower side.
          • 5. Greater inhibition of cells on lower side so upper side elongates more and cells grow down.
    • Stimulus and response
      • Taxes
        • Direction determined by stimulus
        • Positive taxis - Towards a favourable stimulus
          • Single celled algae will move towards light as light is used in photosynthesis.
        • Negative taxis - Away from an unfavourable stimulus
          • Earthworms move away from light as this moves them into the soil where they will find food.
      • Kineses
        • Changes speed and rate of change in direction.
        • Usually a response to humidity and temperature
        • Woodlice rapidly move and change direction in dry conditions to try and find warm conditions.
    • Reflex arc
      • Stimulus - Receptor - Sensory - Relay  - Motor - Effector - Response
    • Receptors
      • Pacinian Corpsucle
        • Specific to a single stimulus
          • Transducer - produces a generator potential
        • Stretch mediated sodium channel
          • 1. Pressure deforms channel so sodium ions can flow.
          • 2. Membrane becomes depolarised producing the generator potential and in turn the impulse (action potential).
    • The eye
      • Rod cells
        • Can't distinguished different wavelengths
        • One pigment - rhodopsin
          • 1. Breaks down into opsin and retinal.
          • 2. Cisretinal changes to transretinal.
          • 3. This causes a stretch mediated sodium channel response.
        • Convergence as more than one rod cell can be connected to one bipolar cell
          • Threshold for generator potential
      • Cone cells
        • Have their own bipolar cell.
          • Only respond to high light intensity as no threshold can be releases.
        • Can distinguish between colours. 3 pigments - iodopsin
          • Iodopsin breaks down to create a generator potential.
        • Only cone cells in fovea in the macula
    • Control of heart rate
      • The autonomic nervous system
      • The parasympathetic pathway
        • Inhibits effectors and slows down activity
        • Controls activity under normal resting conditions
        • Cardioinhibitory centre
        • The sympathetic pathway
          • Stimulates effectors and speeds up activity
          • In control when we excersise
          • Fight or flight
          • Cardioacceleroratory centre
          • Example
            • Increased muscular activity
              • More carbon dioxide from respiration
                • Blood pH lowered
                  • Chemoreceptors in the carotid arteries increaese frequency of impulses to medulla oblongata
                    • Cardioacceleratory centre increases frequency of impulses to the SA node.
                      • SA node increases heart rate.
      • Chemoreceptors and pressure receptors in carotid artery and aorta.
      • The sympathetic pathway
        • Stimulates effectors and speeds up activity
        • In control when we excersise
        • Fight or flight
        • Cardioacceleroratory centre
        • Example
          • Increased muscular activity
            • More carbon dioxide from respiration
              • Blood pH lowered
                • Chemoreceptors in the carotid arteries increaese frequency of impulses to medulla oblongata
                  • Cardioacceleratory centre increases frequency of impulses to the SA node.
                    • SA node increases heart rate.
  • Antagonistic

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