ReceptorsAQA A-Level Biology: Subtopic test

1. 1
   Pacinian corpuscles are receptors found in the skin of the fingertips. Each one is the ending of a sensory neurone wrapped in several layers of connective tissue, with a gel between the layers.

   (a)

   To which type of stimulus does a Pacinian corpuscle respond?

   [1 mark]

   • ALight
   • BTemperature
   • CPressure
   • DChemicals

   (b)

   When pressure deforms a Pacinian corpuscle, which ion movement leads to the generator potential?

   [1 mark]

   • APotassium ions diffuse out through voltage-gated channels
   • BSodium ions diffuse into the neurone ending through stretch-mediated channels
   • CSodium ions are actively transported out of the neurone ending
   • DChloride ions diffuse into the neurone ending through voltage-gated channels

   (c)

   Suggest how the structure of the corpuscle allows pressure on the skin to produce a response in the sensory neurone.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A hiker walks at dusk. In the dim light she can make out the outline of the path and the trees but cannot tell what colour her jacket is. At midday she can read the fine print on her map and see colours clearly.

   (a)

   Which type of photoreceptor is mainly responsible for her vision at dusk?

   [1 mark]

   • ARods
   • BCones
   • CBipolar neurones
   • DGanglion cells

   (b)

   Which statement explains why she can read fine print at midday?

   [1 mark]

   • AMany cones share one bipolar neurone
   • BCones contain rhodopsin, which is very sensitive
   • CCones are more numerous than rods at the edge of the retina
   • DEach cone in the fovea has its own bipolar neurone, so adjacent points of light are seen separately

   (c)

   Explain why she could not tell what colour her jacket was at dusk.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A researcher records the potential difference across the membrane of the sensory neurone ending inside a Pacinian corpuscle while different stimuli are applied. Light pressure produced a small depolarisation but no action potentials. Moderate pressure produced a larger depolarisation and a short series of action potentials in the sensory neurone. Strong pressure produced an even larger depolarisation and a more rapid series of action potentials, each the same size as before. A bright light shone on the corpuscle produced no change at all.

   (a)

   Explain why strong pressure produced a larger depolarisation than light pressure.

   [3 marks]

   (b)

   Use the information to explain the effects of light, light pressure and strong pressure on the corpuscle.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An optometrist is explaining the human retina to a patient. In the fovea, at the centre of the retina, there are only cones, and each cone is connected to its own bipolar neurone. In the periphery of the retina there are mostly rods, and many rods are connected to the same bipolar neurone. The patient says that in bright light she can read small print and tell red, green and blue objects apart, but in dim light she sees only shades of grey and cannot read.

   (a)

   Explain why vision in the fovea has high visual acuity but is not sensitive in dim light, whereas vision in the periphery of the retina has low acuity but is sensitive in dim light.

   [6 marks]

   (b)

   Explain how the retina allows this patient to distinguish colours in bright light but only shades of grey in dim light.

   [6 marks]

   Total for question 4: 12 marks

End of questions