Survival + Response, Control Of Heart Rate, Receptors

• Use knowledge of indoleacetic acid to explain growth curvature?

  1. IAA produced in tip of shoot
  2. IAA diffuses into shoot
  3. More elongation of cells on one side
• Suggest 2 advantages of simple reflexes?

  1. Rapid
  2. Do not have to be learnt
• Explain how the fovea enables an eagle to see its prey in detail?

  1. High visual acuity
  2. Each cone is connected to a single neuron
  3. Cones send separate sets of impulses to the brain
• The retina of an owl has a high density of rod cells. Explain how this enables an owl to hunt its prey at night?

  1. High visual sensitivity
  2. Many rods connected to a single neurone
  3. Spatial summation to reach threshold
• Explain how the resting potential of -70mV is maintained in the sensory neurone when no pressure is applied?

  1. Membrane more permeable to potassium ions and less permeable to sodium ions
  2. Sodium ions actively transported out and potassium ions in
• Explain how applying pressure to the Pacinian Corpuscle produces changes in membrane potential?

  1. Pressure causes membrane to become deformed
  2. (Stretch mediated) sodium ion channels open and sodium ions move in
  3. Greater pressure means more channels open
• Membrane potential stayed the same whether medium or heavy pressure was applied to the fingertip. Explain why?

  1. Threshold has been reached
  2. Threshold or above causes maximal response (all or nothing principle)
• Multiple sclerosis is a disease in which parts of the myelin sheaths surrounding neurones are destroyed. Explain how this results in slower responses to stimuli?

  1. Impulse unable to ‘jump’ from node to node
  2. More depolarisation over area of membranes
• Give 2 safety precautions that should be followed when dissecting a heart?

  1. Use a sharp scalpel
  2. Wash hands
• Exercise causes an increase in heart rate. Describe the role of receptors and of the nervous system in this process?

  1. Baroreceptors detect an increase in blood pressure
  2. Send impulses to cardiac centre
  3. More impulses to SAN
  4. By parasympathetic nervous system
• When the heart beats, both ventricles contract at the same time. Explain how this is coordinated in the heart after initiation of the heartbeat by the SAN?

  1. Electrical activity only through Bundle of His
  2. Wave of electrical activity passes through both ventricles (Purkinje fibres) at same time