Question

Choose the correct answer from the alternatives given.
A decrease in the pH of human blood would

• A. decrease breathing rate
• B. increase heart rate
• C. decrease the amount of $O_2$ unloaded from haemoglobin
• D. decrease cardiac output

Answer 1

The correct option is C decrease the amount of $O_2$ unloaded from haemoglobin

In response to a decrease in blood pH, the respiratory centre (in the medulla ) sends nervous impulses to the external intercostal muscles and the diaphragm, to increase the breathing rate and the volume of the lungs during inhalation. Under such conditions, the chemoreceptors do not respond to changes in oxygen levels (which actually change much more slowly), but to pH, which is dependent upon plasma carbon dioxide levels. Thereby a decrease in the amount of oxygen unloaded from haemoglobin is seen. So, the correct option is 'decrease the amount of O${}_2$ unloaded from haemoglobin'.