| Date | May 2013 | Marks available | 2 | Reference code | 13M.3.HL.TZ1.12 |
| Level | Higher level | Paper | Paper 3 | Time zone | Time zone 1 |
| Command term | Explain | Question number | 12 | Adapted from | N/A |
Question
The effects of normal and hypoxic (lower than normal) oxygen concentrations on the oxygen levels in blood and muscles of athletes were investigated in a study. Healthy male non-athletes and athletes performed 30 seconds of intense maximal exertion exercise on a stationary bicycle. The data displayed below show the arterial oxygen saturation levels before, during and after the exercise.
Estimate the change in the arterial oxygen saturation between 30 and 60 seconds in non-athletes under hypoxic conditions.
. . . . . . . . . . . . . . . . . . . . . .%
Compare the effect of hypoxic concentrations on athletes and non-athletes during exercise.
Suggest a reason for the differences.
Explain how the body prevents oxygen saturation levels from falling by more than a small amount during maximal exertion exercise.
Hypoxic concentrations also occur at high altitudes. Explain one effect of high altitude on oxygen transport by blood.
Markscheme
accept range 3.8–4.2 (%)
a. percentage saturation of O2 drops in both during exercise;
b. decrease is greater/more rapid in athletes than in non-athletes;
a. athletes exercise more vigorously/at higher intensity;
b. athletes use more oxygen during exercise;
a. ventilation rate/tidal volume increased;
b. more oxygen absorbed (per minute);
c. heart rate increased;
a. altitude causes formation of more red blood cells/more haemoglobin so/thus the capacity to carry oxygen increases; Idea of capacity is essential although can be OWTTE.
b. the % saturation of blood is lower because there is less oxygen in the atmosphere;
Examiners report
Most used the graph correctly to estimate the change in arterial saturation. However, some candidates are incorrectly giving a range of values rather than calculating a single value. Perhaps this comes from looking at past paper mark schemes in which a range of values is given within which examiners can accept an answer as correct.
Most candidates earned 1 out of the 2 marks, and many received both marks.
Fewer candidates were able to suggest a reason and get the mark for this section.
Some candidates were incorrectly discussing myoglobin and missed the simpler points available for such modifications as increased ventilation rate.
Few candidates could clearly explain an effect of high altitude on oxygen transport by the blood. Answers were vague or talked about symptoms of altitude sickness.
