CAIE A Level Biology 9700 · Transport in mammals
In a study of carbon dioxide transport, blood samples were analysed. The results are shown in the table below.
| Form of CO2 transport | Arterial blood (cm³ CO₂ per 100 cm³ blood) | Venous blood (cm³ CO₂ per 100 cm³ blood) |
|---|---|---|
| Dissolved in plasma | 2.6 | 3.1 |
| As bicarbonate ions | 43.7 | 52.5 |
| As carbaminohaemoglobin | 4.3 | 11.2 |
Explain the processes by which carbon dioxide is transported in the blood, using the data to illustrate the roles of red blood cells and plasma.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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