Exam qs

• Describe how a Pacinian corpuscle produces a generator potential when stimulated (3)

  • Increased pressure deforms / changes stretch-mediated sodium ion channel
  • Sodium channels open and sodium ions flow in
  • Depolarisation (leading to generator potential)
• Nocturnal mammals are active at night. Describe how the number and distribution of rods and cones across the retina would differ in a nocturnal mammal from the number and distribution in a human. Explain your answer (3)

  • more rods and fewer cones present
  • rods at the fovea / rods not mainly at periphery
  • rods have high sensitivity whereas cone cells do not
  • because rhodopsin is bleached at low light intensities
• Explain what causes vision using the fovea to be in colour (1)

  • three different wavelengths of cone cells
• Explain what causes vision using the fovea to have high visual acuity (1)

  • each receptor cell connects to a separate neurone
• Explain why it takes time for the rod cells to recover their sensitivity to light after moving into darkness (2)

  • rhodopsin bleached
  • time for resynthesis
• Explain why vision using other parts of the retina has high sensitivity to light (3)

  • many rods in other parts of retina
  • pigment in receptors work in low light
  • receptors connected in groups to ganglion cells
• Suggest and explain how the interaction between the radial muscle and circular muscle could cause the pupil to constrict (2)

  • circular muscle contracts
  • radial muscle relaxes
• The fovea of the eye of an eagle has a high density of cones. An eagle focuses the image of its prey onto the fovea. Explain how the fovea enables an eagle to see its prey in detail (3)

  • high visual acuity
  • each cone is connected to a single neurone
  • cones send separate sets of impulses to 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. (3)

  • high visual sensitivity
  • several rods connected to a single neurone
  • spatial summation to reach / overcome threshold
• Cone cells give higher visual acuity than rod cells. Explain how (2)

  • each cell has a separate bipolar neurone to brain
  • impulses from each cone kept separate / no summation of impulses