Six athletes trained for four weeks at high altitude, where the air contains less oxygen than at sea level. The number of red blood cells in their blood was measured before and after the training.
Table: The number of red blood cells in 1 mm3 of blood for six athletes, before and after four weeks of training at high altitude
| Athlete | Number of red blood cells in 1 mm3 before training | Number of red blood cells in 1 mm3 after training |
|---|---|---|
| 1 | 4 900 000 | 5 400 000 |
| 2 | 5 100 000 | 5 500 000 |
| 3 | 4 700 000 | 5 300 000 |
| 4 | 5 000 000 | 5 600 000 |
| 5 | 4 800 000 | 5 000 000 |
| 6 | 5 200 000 | 5 200 000 |
Calculate the mean number of red blood cells in 1 mm3 of blood after training.
Give the number of the athlete whose red blood cell count did not change.
Suggest why training at high altitude increases the number of red blood cells in an athlete's blood.
179 exam-style questions on AQA GCSE Biology 2.2 Animal tissues, organs and organ systems, covering 2.2.1 The human digestive system, 2.2.2 The heart and blood vessels, 2.2.3 Blood, 2.2.4 Coronary heart disease: a non-communicable disease, 2.2.5 Health issues, 2.2.6 The effect of lifestyle on some non-communicable diseases, and 2.2.7 Cancer. Each one has a worked solution and a mark scheme showing where the marks go.