Tamilnadu BoardEnglish MediumSTD 11Bio ZoologyRespiration5 Marks
Question
Explain the transport of oxygen In blood.
✓
Answer
Molecular oxygen is carried in blood in two ways: bound to hemoglobin within the red blood cells and dissolved in plasma. Oxygen is poorly soluble in water, so only $3 \%$ of the oxygen is transported in the dissolved form. $97 \%$ of oxygen binds with haemoglobin in a reversible manner to form oxyhaemoglobin $\left( HbO _2\right)$. The rate at which haemoglobin binds with $O _2$ is regulated by the partial pressure of $O _2$.
Each haemoglobin carries maximum of four molecules of oxygen. In the alveoli high $pO _2$, low $pCO _2$, low temperature and less $H +$ concentration, favours the formation of oxyhaemoglobin, whereas in the tissues low p02, high $pCO _2$, high $H +$ and high temperature favours the dissociation of oxygen from oxyhaemoglobin.
A sigmoid curve ( $S$-shaped) is obtained when the percentage saturation of haemoglobin with oxygen is plotted against $pO _2$. This curve is called the oxygen haemoglobin dissociation curve. This S-shaped curve has a steep slope for $pO _2$ values between 10 and $50 mm Hg$ and then flattens between 70 and $100 mm$ $Hg$. Under normal physiological conditions, every $100 mL$ of oxygenated blood can deliver about $5 mL$ of $O _2$ to the tissues.
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