DP Chemistry (last assessment 2024)

Test builder »

Question 17N.3.hl.TZ0.b

Select a Test
Date November 2017 Marks available [Maximum mark: 3] Reference code 17N.3.hl.TZ0.b
Level hl Paper 3 Time zone TZ0
Command term Explain Question number b Adapted from N/A
b.
[Maximum mark: 3]
17N.3.hl.TZ0.b

Vitamins can be water-soluble or fat-soluble.

Retinal is the key molecule involved in vision. Explain the roles of cis and trans-retinal in vision and how the isomers are formed in the visual cycle.

[3]

Markscheme

Any three of:

cis-retinal binds to «the protein» opsin

OR

cis-retinal «binds to opsin and» forms rhodopsin

rhodopsin extends conjugation in retinal

OR

rhodopsin allows absorption of visible/blue/green light

when visible light is absorbed cis-retinal changes to trans-retinal

change «to trans-retinal» triggers an electrical/nerve signal

trans-retinal detaches from opsin AND is converted back to cis-retinal

OR

trans-retinal is converted back to cis-retinal through enzyme activity

Do not accept “cis-retinal to trans-retinal” alone without reference to absorption of visible light.

[Max 3 Marks]

Syllabus sections