| Date | May 2015 | Marks available | 1 | Reference code | 15M.3.HL.TZ1.4 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Identify | Question number | 4 | Adapted from | N/A |
Question
Regions of the brain that perceive pain also contain receptors for pain-killers, such as morphine (from poppy plants) or endorphins (produced in the brain). Teams of young men competed in pain-endurance tests by repeatedly squeezing hand-springs until reaching unbearable pain.
During pre-competition training, some teams received injections of morphine. During competition, no morphine was administered. However, some teams thought they were receiving morphine injections. Instead, they were injected with a placebo (a saline solution) or the placebo plus naloxone (an endorphin blocking drug) as shown in the following data.
State the effect of morphine during pre-competition training for team C.
Identify which team showed the greatest tolerance to pain on competition day.
Analyse the effect of the placebo as seen in the data.
Suggest a reason for the reduced pain tolerance in team D during competition.
Analyse the data collected in the week following competition.
Markscheme
increases tolerance to pain (when given in weeks 2 and 3)
team C
a. placebo has no effect in team B where morphine was not administered previously;
b. team B thought they were getting morphine but their performance was the same as team A;
c. placebo has a greater effect if morphine has been administered previously as in team C;
d. naloxone negates the (expected) effect of placebo (even if morphine administered previously) in team D;
e. error bars overlap so results may not be statistically significant/no difference;
naloxone (an endorphin blocking drug) blocks the receptors for endorphins / stops endorphins from acting as pain killers
a. pain tolerance goes down in all groups / all have same level of pain tolerance;
b. morphine-like effect/morphine effect is temporary;
c. endorphins/naturally produced pain-killers levels/number of receptors for pain-killers decreases;
d. decrease in pain tolerance is evidence for motivation/determination during competition and training / lack of motivation when no competition;
Examiners report
(a) and (b) Almost all candidates were able to correctly answer both parts which involved directly identifying information from the data provided. Very few did not score both points.
(a) and (b) Almost all candidates were able to correctly answer both parts which involved directly identifying information from the data provided. Very few did not score both points.
Candidates did not do well on section (i) as they did not notice that Team A was not given a placebo. Most saw or invented effects of the placebo, with many thinking it was effective in all cases, when in fact the placebo did not have an effect.
For section (ii) many simply repeated what was already in the stem so did not gain the mark.
A large number of candidates were able to gain 1 mark for seeing that pain tolerance went down in all groups during the week after competition but few were able to get a second mark.
