Oxygen carriage and the dissociation curve — practice questions

Question 1 · difficulty L1 · recall

Approximately what percentage of oxygen is transported by haemoglobin in normal blood?

• A. About 3%
• B. About 70%
• C. About 25%
• D. About 97%

Question 2 · difficulty L2 · understanding

A rise in carbon dioxide and hydrogen ions generally shifts the oxygen dissociation curve:

• A. nowhere
• B. to the right
• C. up without horizontal shift
• D. to the left

Question 3 · difficulty L2 · understanding

The approximate fraction of oxygen transported bound to haemoglobin:

• A. about 7 percent
• B. about 97 percent
• C. about 23 percent
• D. about 70 percent

Question 4 · difficulty L2 · understanding

The shape of the oxyhaemoglobin dissociation curve:

• A. parabolic only
• B. sigmoidal
• C. linear
• D. rectangular

Question 5 · difficulty L2 · understanding

Which combination of conditions in actively respiring tissues promotes dissociation of oxygen from oxyhaemoglobin?

• A. Low pO2, high pCO2, high H+ concentration and higher temperature
• B. High pO2, low pCO2, low H+ concentration and lower temperature
• C. High pO2 and high pH only
• D. Low pCO2 and low temperature only

Question 6 · difficulty L2 · understanding

Frogs respire in water by skin and buccal cavity and on land by skin, buccal cavity and lungs. Choose the correct answer from the following :

• A. The statement is false for water but true for land
• B. The statement is false for both the environment
• C. The statement is true for water but false for land
• D. The statement is true for both the environment

Question 7 · difficulty L3 · understanding

A rise in the carbon dioxide concentration of blood shifts the oxygen dissociation curve in which direction, and with what effect on haemoglobin?

• A. To the left; haemoglobin binds oxygen more tightly
• B. To the right; haemoglobin releases oxygen more readily
• C. To the left; haemoglobin releases oxygen more readily
• D. To the right; haemoglobin binds oxygen more tightly

Question 8 · difficulty L3 · application

Blood entering an actively respiring muscle encounters low oxygen partial pressure and elevated carbon dioxide. What should happen to haemoglobin?

• A. Its affinity for oxygen increases sharply
• B. Its affinity for oxygen decreases and more oxygen is released
• C. It converts oxygen into carbon dioxide
• D. It stops binding hydrogen ions

Question 9 · difficulty L3 · application

Blood sample P is exposed to high pO2, low pCO2 and low H+ concentration, while sample Q is exposed to low pO2, high pCO2 and high H+ concentration. Which outcome is most likely?

• A. Neither sample can carry oxygen
• B. P unloads more oxygen and Q binds more oxygen
• C. Both samples bind oxygen equally
• D. P shows greater oxyhaemoglobin formation and Q shows greater oxygen unloading

Question 10 · difficulty L3 · understanding

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R. Assertion A: During the transportation of gases, about 20-25 percent of CO$$_2$$ is carried by Haemoglobin as carbamino-haemoglobin. Reason R: This binding is related to high pCO$$_2$$ and low pO$$_2$$ in tissues. In the light of the above statements, choose the correct answer from the options given below.

• A. A is true but R is false.
• B. A is false but R is true.
• C. Both A and R are true and R is the correct explanation of A.
• D. Both A and R are true but R is NOT the correct explanation of A