| Date | November 2011 | Marks available | 3 | Reference code | 11N.3.SL.TZ0.4 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Describe | Question number | 4 | Adapted from | N/A |
Question
A treadmill test was taken by 46 men and women who were inactive and overweight. During the test, the percentage of fat and carbohydrate (CHO) used for energy was measured at increasing levels of exercise intensity. The intensity of exercise was assessed by measuring VO2 and showing it as a percentage of VO2 max.
State the percentage contribution of the different sources of energy at 36% VO2 max in women.
Fat: ................................................................
CHO: ................................................................
Using the data in the graph, describe the relationship between the intensity of exercise and the source of energy.
Fat can only be used in aerobic respiration. Suggest reasons for the change in the percentage contribution of fats to energy supply during exercise as the intensity of exercise increases.
Markscheme
fat: 58 (%); (allow responses in the range of 57 to 59 %)
CHO: 42 (%); (allow responses in the range of 41 to 43 %)
(both needed)
fat contributes most energy/63 (±1)% at lower level of exercise intensity;
contribution of fat as an energy source decreases as exercise intensity increases / negative correlation;
contribution of CHO as an energy source increases as exercise intensity increases / positive correlation;
fats and carbohydrates used equally / crossover point is 41 % VO2 max;
little difference between men and women;
at lower exercise intensity (more) oxygen available for aerobic respiration;
(stored) fat will supply energy when oxygen is available;
as exercise intensity increases anaerobic respiration increases;
less oxygen available (in anaerobic respiration) means more CHO metabolism/ less fat metabolism (at higher exercise intensity);
Examiners report
Almost all candidates were able to get the mark for reading the correct values from the graph.
Many candidates found it difficult to use the data to describe the relationship between intensity of exercise and source of energy. Better candidates were able to score two or three marks.
Most candidates struggled with this section and did not relate their answers to oxygen availability for aerobic and anaerobic exercise.
