The partial pressure of oxygen in blood vessels from different parts of the body influences the percentage saturation of each haemoglobin molecule with oxygen. Blood vessel data: - vein from active muscle: partial pressure of oxygen $4\,\text{kPa}$, saturation $25\%$ - vein from resting muscle: partial pressure of oxygen $7\,\text{kPa}$, saturation $75\%$ - arteriole in lungs: partial pressure of oxygen $12\,\text{kPa}$, saturation $100\%$ Which statement explains the difference in saturation between active muscle and resting muscle?
- AA small decrease in partial pressure causes two atoms of oxygen to leave each haemoglobin molecule because the oxygen dissociation curve is sigmoid shaped.
- BA small decrease in partial pressure between $4\,\text{kPa}$ and $7\,\text{kPa}$ causes two molecules of oxygen to leave each haemoglobin molecule because the oxygen dissociation curve is steep.
- CLoading of oxygen is slower between $4\,\text{kPa}$ and $7\,\text{kPa}$ due to binding of one oxygen molecule to each haemoglobin molecule making the next one harder to bind.
- DLoading of oxygen is faster between $4\,\text{kPa}$ and $7\,\text{kPa}$ due to binding of one oxygen molecule to each haemoglobin molecule making the next one easier to bind.