Estimate the difference between the highest and lowest mean body temperatures.

Compare and contrast the changes in mean ambient and body temperatures during 2012.

Explain the change in heart rate during the period of hibernation.

Distinguish between the changes in porosity of the bones in humans and bears as age increases.

The life expectancy of a human at the time of the study was 80 years. Estimate the porosity of the bones of the individual who was approximately 32 years old.

The researchers assessed age as a proportion of normal life span, rather than in years. Suggest one reason for this.

Describe what is happening to the bone during hibernation.

Suggest how the graph would differ for a human during a long period of inactivity.

Calculate the percentage increase in the mean concentration of osteocalcin from pre-hibernation to hibernation.

A hypothesis has been proposed that an increase in parathyroid hormone concentration causes an increase in osteocalcin in bears. Evaluate the evidence for this hypothesis provided by the data.

Discuss how helpful these studies of bears can be in developing an understanding of osteoporosis in humans.

5 °C;

Units required. Accept answers in the range 4.5 to 5.5 °C.

  Accept one similarity:

1. both rise and then fall / both fall with hibernation and rise with activity
2. both reach minimum during hibernation and maximum during activity;
3. both lowest in January/February / both rise from January/February;
   
   Accept one difference:
   
   
4. one peak of ambient temp but body temp has two peaks / OWTTE;
5. body temp remains maximal for longer/plateaus whereas ambient peaks;
6. body temperature is always higher than ambient temperature;
7. ambient range is greater than body temperature range / OWTTE;

1. decreased/slower heart rate because bears less active/use less energy;
2. less (cell) respiration / lower (rate of) metabolism;
3. less oxygen/glucose required / less CO₂ produced/needing to be removed;
4. less muscle contraction/muscles require less blood;
5. conserves energy;

porosity increased in humans and decreased in bears;

Both needed.

6 %;

Accept answers in the range 6.0 to 6.5 %.
Percentage sign required.

1. to allow comparison of bears and humans;
2. bears have a different life span to humans / bears do not live to 80 years;
3. because they age at different rates;

1. resorption/breaking down occurs and formation/rebuilding occurs;
2. at similar rates / more resorption at most times;
3. no/little (overall) change (in bone mass);
4. lag between bone resorption rising and formation rising / OWTTE;
5. bone resorption rising towards end as formation dropping / OWTTE;

1. more resorption than formation;
2. PICP/bone formation (always) lower (than in bears);
3. ICTP/bone resorption (always) higher (than in bears);
4. ICTP above PICP by a greater amount in humans (than in bears);

250 % (Allow 240 to 260 %)

1. (hypothesis supported by)
   positive/direct correlation/direct relationship (between parathyroid hormone and osteocalcin)
   OR
   osteocalcin rises as parathyroid hormone rises/vice versa;
2. no evidence for causal link / causal link cannot be assumed / correlation does not prove causation;
   OR
   no evidence that parathyroid hormone causes change in osteocalcin;
   OR
   other factors may cause change in osteocalcin;

  Accept one reason for the studies being helpful:

1. (helps us understand how)) bears avoid osteoporosis;
2. bone structure of bears and humans is similar / both are mammals;
3. suggests that hormones/osteocalcin/parathyroid hormone might be a (preventative) treatment;
   
   Accept one reason for the studies not being helpful:
4. humans do not hibernate / are not inactive for long periods;
5. humans live for much longer;

70 % of candidates were able to read two temperatures from the graph and subtract the higher from the lower correctly.

Many candidates realized that they were expected to give similarities and differences between the curves, but most struggled to do this clearly. Rather than make eclectic statements about the data that may be correct but are not significant, the aim with a question such as this is to make comments that would allow someone who has not been shown the curves to sketch them. Some students confused maxima or minima with increases and decreases, so for example stating that ambient body temperature increased in July, when it reached a maximum in July and stopped increasing.

Many candidates mentioned lack of activity as a reason for lower heart rate and some went on to mention reduced respiration rates or other aspects of physiology. Other candidates failed to offer an explanation and instead just described the data. A few claimed wrongly that bone porosity was directly proportional to age, in which case all those of a certain age would have the same degree of osteoporosis, which is plainly not the case.

Well answered with most candidates referring to the positive and negative correlations.

This question was very unusual in that the discrimination index was negative — stronger candidates were slightly less likely to answer correctly than weaker candidates, for reasons that are not obvious! Only a minority gave the expected answer of 6 %. A very common answer was 7 %, which is reached by calculating the age proportion correctly as 0.4 but using the trend line rather than the data point for the individual who was 32 years old. Careful reading of the question was needed to avoid this mistake.

Most candidates were successful here, using the argument that humans and bears have different life spans.

In this question candidates were expected to deduce the changes to bone from the concentrations of the markers. Given that neither of them reaches zero, we can assume that bone formation and resorption both continue throughout the hibernation period. Few candidates made this point clearly. The other 'best' answer was to comment on relative overall amounts of formation and resorption, either by stating that they are approximately equal or that there is slightly more resorption.

Candidates were expected to suggest a difference between the bears and humans in the concentration of one or both of the markers, that would result in loss of bone mass. A common fault was to predict changes in the markers during a period of inactivity in humans, but changes over time were not the issue — it was differences between humans and bears that were relevant to the question.

A very small proportion of candidates correctly calculated the percentage difference. There were many different incorrect answers, with 350 % being the most popular, which is the amount of osteocalcin during hibernation as a percentage of the amount pre-hibernation.

This type of question is increasingly well answered with more candidates understanding that two variables being positively correlated does not prove a causation. The situation would have been different if an experiment had been done with the levels of parathyroid hormone as the independent variable controlled by the researchers.

Answers here were very varied. The best included the idea that an understanding of how bears maintain bone mass despite inactivity during hibernation might lead to preventative treatments for humans. Because this was a discuss question, some counterargument was expected, based on differences between bears and humans.