People who live at high altitude breathe air with a lower concentration of oxygen.
The table shows the mean number of red blood cells in two groups of people.
Table
| Group of people | Mean number of red blood cells per mm3\text{mm}^3mm3 of blood |
|---|---|
| Live at sea level | 5.0 × 106 |
| Live at high altitude | 6.5 × 106 |
Which statement explains the difference shown in the data?
More red blood cells means more plasma to carry dissolved oxygen to cells.
More red blood cells means more haemoglobin, so more oxygen can be carried.
More red blood cells means each cell carries less oxygen, so less is wasted.
More red blood cells means the blood flows faster, so oxygen arrives sooner.
114 exam-style questions on OCR GCSE Biology 2.2 The challenges of size, covering 2.2.1 Exchange surfaces and surface area : volume ratio, 2.2.2 Substances transported in organisms, 2.2.3 The human circulatory system, 2.2.4 The heart and blood vessels, 2.2.5 Red blood cells and plasma, 2.2.6 Uptake of water and mineral ions by plants, 2.2.7 Transpiration and translocation, 2.2.8 Xylem and phloem, 2.2.9 Environmental factors and water uptake, and 2.2.10 Using a potometer. Each one has a worked solution and a mark scheme showing where the marks go.