Question 22N.1A.HL.TZ0.25
| Date | November 2022 | Marks available | [Maximum mark: 1] | Reference code | 22N.1A.HL.TZ0.25 |
| Level | HL | Paper | 1A | Time zone | TZ0 |
| Command term | Question number | 25 | Adapted from | N/A |
Melatonin controls circadian rhythms and is involved in the sleep-wake cycle. The pineal gland, which secretes melatonin, is inhibited by light. The graph shows a normal cycle where bedtime is around 10pm.
Using data from the graph, what might be the effect(s) of screen light from a laptop, tablet or phone at bedtime?
I. Delay in melatonin production
II. Lower peak concentration of melatonin
III. Peak of melatonin earlier in the evening
A. I only
B. III only
C. II and III only
D. I, II and III
[1]
B
This was the most problematic question on the paper. For multiple-completion questions to work satisfactorily, each of the possibilities must be unequivocally right or wrong. Here it was clear that use of a bright screen at bedtime is likely to delay melatonin production because the pineal gland would be inhibited. It was also clear that the peak of melatonin production would not be earlier in the evening. It was not clear whether there would be a lower peak of melatonin in the night. Given that a plateau in melatonin concentration is reached during the night, it seems more likely that the peak would not be lower, even if the rise took place later, leading to answer A. However, more candidates chose answer B, showing that they expected a lower peak. This is not unequivocally wrong, so the examining team decided to accept both answers A and B. Over 90% of candidates gained the mark and inevitably the discrimination index was low.
