A graph plots the percentage saturation of haemoglobin with oxygen (y-axis) against the partial pressure of oxygen in mm Hg (x-axis). The normal curve is S-shaped. A second curve has the same shape but lies to the right of the normal one. Which conditions favour the shift to the right?
A
Low pCO2, low H+ concentration and lower temperature, as in the alveoli
B
High pCO2, high H+ concentration and higher temperature, as in the tissues
C
High pO2 alone, as in the alveoli
D
Low pCO2 and higher temperature only
Show the answer
The answer is B.
The oxygen dissociation curve is sigmoid. In the tissues, low pO2, high pCO2, high H+ concentration and higher temperature favour release of oxygen from oxyhaemoglobin. This shifts the curve to the right.
A.
These conditions, found in the alveoli, favour the formation of oxyhaemoglobin and shift the curve to the left.
C.
High pO2 is a point further along the x-axis, not a cause of shifting the curve. High pO2 favours binding of oxygen.
D.
Low pCO2 favours binding of oxygen. Dissociation is favoured by high pCO2, high H+ and higher temperature together.
NCERT: Class 11 Biology, Chapter 14
Sample 2NEET level
Consider the following statements about the transport of gases in humans: I. About 97 per cent of O2 is transported by RBCs in the blood. II. Every 100 ml of oxygenated blood delivers around 4 ml of O2 to the tissues under normal physiological conditions. III. About 70 per cent of CO2 is carried as bicarbonate. IV. Every 100 ml of deoxygenated blood delivers approximately 4 ml of CO2 to the alveoli. Which of the statements above are correct?
A
I and III only
B
I, III and IV only
C
II, III and IV only
D
I, II and IV only
Show the answer
The answer is B.
About 97 per cent of O2 is carried by RBCs, about 70 per cent of CO2 travels as bicarbonate, and 100 ml of deoxygenated blood delivers about 4 ml of CO2 to the alveoli. Every 100 ml of oxygenated blood delivers around 5 ml of O2, not 4 ml, so II is wrong.
A.
Leaves out IV, which is correct.
C.
Includes II (the figure is 5 ml of O2) and leaves out the correct I.
D.
Includes II and leaves out the correct III.
NCERT: Class 11 Biology, Chapter 14 (Breathing and Exchange of Gases), Transport of Gases
Practise Breathing and exchange of gases
Practice at the level you choose, with the answer after every question; timed tests with the answers when you submit. Every question is verified against NCERT first.