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  4. The given graph shows an oxygen dissociation curve for haemoglobin. <img class=img-fluid question-image alt=image src=https://cdn.tardigrade.in/img/question/biology/1225fdeec19e695436b0a086bc71485d-.jpeg /> Where in the body will haemoglobin be saturated at the percentages shown at points 1, 2 and 3 on the graph? Left ventricle Pulmonary vein Vena cava (a) 1 2 3 (b) 2 1 3 (c) 2 3 1 (d) 3 2 1

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Q. The given graph shows an oxygen dissociation curve for haemoglobin.
image
Where in the body will haemoglobin be saturated at the percentages shown at points $1$, $2$ and $3$ on the graph?
$\,\,\,$ Left ventricle$\,\,\,$ Pulmonary vein$\,\,\,$ Vena cava$\,\,\,$
(a)$\,\,\,$ 1$\,\,\,$ 2$\,\,\,$ 3$\,\,\,$
(b) 2$\,\,\,$ 1$\,\,\,$ 3$\,\,\,$
(c) 2$\,\,\,$ 3$\,\,\,$ 1$\,\,\,$
(d) 3$\,\,\,$ 2$\,\,\,$ 1$\,\,\,$

Breathing and Exchange of Gases

Solution:

The relationship between the partial pressure of $O_2 \,(PO_2)$ and percentage saturation of the $Hb$ with $O_2$ is graphically illustrated by a curve called oxygen dissociation curve. The haemoglobin is most saturated with oxygen in the pulmonary vein, as this vein is carrying oxygenated blood from the lungs towards the left auricle of the heart. From the left auricle the blood moves to the left ventricle where saturation of $Hb$ with $O_2$ slightly reduces. Vena cava carries deoxygenated blood from all the organs of the body towards right auricle, thus, $Hb$ is less saturated with $O_2$.