Fig. 1 shows part of a study of carbon dioxide production during exercise. Four students cycled at the same resistance. Their expired air was collected in b...
Question 1 Report
Fig. 1 shows part of a study of carbon dioxide production during exercise. Four students cycled at the same resistance. Their expired air was collected in bags for one minute and analysed. Table 1 shows the results. Student D had completed endurance training for six months.
| Student | Volume of expired air collected / dm3 | Carbon dioxide concentration in expired air / % |
|---|---|---|
| A | 42 | 4.2 |
| B | 45 | 4.0 |
| C | 40 | 4.5 |
| D | 36 | 3.8 |
(a) Use Table 1 to identify the student with the greatest carbon dioxide volume in the collected air. Show your working. [3]
(b) Describe one difference between the results for student D and student A. [2]
(c) Explain why carbon dioxide concentration in expired air is greater than in inspired air. [3]
Answer Details
(a) Carbon dioxide volume is calculated using:
\[\text{volume of expired air}\times\text{carbon dioxide fraction}\]
\[\text{A: }42\times0.042=1.764\text{ dm}^3\]
\[\text{B: }45\times0.040=1.80\text{ dm}^3\]
\[\text{C: }40\times0.045=1.80\text{ dm}^3\]
\[\text{D: }36\times0.038=1.368\text{ dm}^3\]
Student B and student C have the greatest carbon dioxide volume, equal at 1.80 dm3 [3]. A high percentage alone is not enough: the volume of air must also be considered.
(b) Student D expired less air than student A, 36 compared with 42 dm3 [1]. Student D also had a lower carbon dioxide concentration, 3.8% compared with 4.2% [1].
(c) Carbon dioxide is made by respiration in body cells [1]. It is transported in the blood to the lungs [1], where it diffuses from the blood into the alveoli and is breathed out [1]. This makes expired air contain more carbon dioxide than inspired air.
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