Table 1 shows measurements made during an altitude-training assessment. Two healthy people cycled for 12 minutes at the same workload. One test was carried ...
Question 1 Report
Table 1 shows measurements made during an altitude-training assessment. Two healthy people cycled for 12 minutes at the same workload. One test was carried out at sea level and the other in a chamber where the air had a lower oxygen concentration. Blood samples were taken immediately after exercise. The body cells of each person need oxygen for aerobic respiration.
| Test condition | Oxygen concentration in inhaled air (%) | Breathing rate (breaths per minute) | Oxygen concentration in blood leaving lungs (%) |
|---|---|---|---|
| Sea level | 21.0 | 22 | 19.2 |
| Low-oxygen chamber | 15.0 | 31 | 16.8 |
(a) Use Table 1 to state the difference in breathing rate between the two tests. [1]
(b) Explain why the person in the low-oxygen chamber breathed faster. [3]
(c) Describe the effect of the lower oxygen concentration in inhaled air on the oxygen concentration in blood leaving the lungs. [2]
(d) Explain how reduced oxygen delivery to body cells could affect the person’s cycling performance. [3]
(e) Suggest one control used in this assessment that makes the comparison between the two people more valid. [2]
Answer Details
(a) \[31 - 22 = 9\] The breathing rate is 9 breaths per minute higher in the low-oxygen chamber. [1]
(b) The inhaled air in the chamber contains less oxygen. Therefore less oxygen diffuses into the blood and blood oxygen concentration falls. Faster breathing increases ventilation, bringing more air, and therefore more oxygen, to the air spaces each minute. [3]
(c) Lower oxygen concentration in inhaled air decreases the oxygen concentration in blood leaving the lungs, from \(19.2\%\) to \(16.8\%\). This is a decrease of \(2.4\) percentage points. [2]
(d) Less oxygen delivered to body cells reduces the rate of aerobic respiration. Less energy is released for muscle contraction, so muscles fatigue sooner or produce less force. Cycling performance is therefore reduced. [3]
(e) Valid controls include making both people cycle at the same workload and for the same time. Using the same equipment and taking blood samples at the same time after exercise are also acceptable. These controls mean oxygen concentration is the main intended difference. [2]
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