DP Biology (last assessment 2024)

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Question 23M.3.SL.TZ1.5

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Date May 2023 Marks available [Maximum mark: 7] Reference code 23M.3.SL.TZ1.5
Level SL Paper 3 Time zone TZ1
Command term Distinguish, Outline, Suggest Question number 5 Adapted from N/A
5.
[Maximum mark: 7]
23M.3.SL.TZ1.5

The graph shows the distribution of photoreceptors in the retinas of humans and mice. Distances from the centre of the retina (0°) are expressed as visual angles. The image shows the position of the optic nerve.

[Source: Volland, S., Esteve-Rudd, J., Hoo, J., Yee, C. and Williams, D.S., 2015. A Comparison of Some Organizational
Characteristics of the Mouse Central Retina and the Human Macula. PLOS ONE, [e-journal] 10(4), e0125631.
https://doi.org/10.1371/journal.pone.0125631. Open access.]

(a)

Outline one reason that no data is shown at the position of the optic nerve.

[1]

Markscheme

there are no photoreceptors/cones/rods
OR
it is the blind spot;

Examiners report

The blind spot at the position of the optic nerve was well known.

(b)

Suggest whether the data in the graph shows that mice have better colour vision than humans.

[2]

Markscheme
  1. mouse has greater photoreceptor density (than human);
  2. the graph does not distinguish between types of photoreceptor;
  3. cones detect colours
    OR
    rods provide monochromatic/night vision;
  4. there is no data about colour vision in mice;
Examiners report

Marking point a for photoreceptor density was frequently awarded, although some candidates did not read the key correctly. Fewer referred to rods and cones.

(c)

Outline the role of bipolar cells in the retina.

[2]

Markscheme
  1. bipolar cells interconnect/link photoreceptors to ganglion cells
    OR
    bipolar cells pass impulses from photoreceptors to ganglion cells;
  2. one bipolar cell receives signals from/synapses with one cone cell;
  3. one bipolar cell receives signals from/synapses with several rod cells;
Examiners report

Many knew that bipolar neurons connect photoreceptors to ganglion cells but few scripts were seen where the number of synapses was discussed.

(d)

Distinguish between chemoreceptors and mechanoreceptors, including an example of each.

[2]

Markscheme
  1. chemoreceptors stimulated by chemicals but mechanoreceptors are stimulated by movement/forces/pressure;
  2. valid example of each;

Chemoreceptors: taste buds, carotid/aortic bodies, pH, oxygen Mechanoreceptors: hair cells, stretch, touch, pressure

Accept other verified examples

Examiners report

Most candidates did not distinguish between the receptors in one sentence, but this was not penalised. There were not many good examples.