A level Biology 8.2 Transport of oxygen and carbon dioxide – Exam style question – Paper 1

Question

An increase in carbon dioxide in human blood shifts the oxyhaemoglobin dissociation curve to the
right.
What is the explanation for this effect?
A      An increase in carbon dioxide concentration increases the ventilation rate.
B      Carbon dioxide is more soluble than oxygen and displaces it.
C      Diffusion of carbon dioxide between the alveoli and the blood is more rapid.
D     Increasing the H+ concentration decreases haemoglobin affinity for oxygen.

▶️Answer/Explanation

Answer     D

The correct answer is D.

An increase in carbon dioxide concentration causes a decrease in pH, which in turn leads to an increase in H+ concentration. This increase in H+ concentration causes haemoglobin to release oxygen more readily, which shifts the oxyhaemoglobin dissociation curve to the right. This is known as the Bohr effect. Option A is incorrect because an increase in carbon dioxide concentration would actually decrease the ventilation rate, as the body attempts to retain more carbon dioxide. Option B is incorrect because carbon dioxide does not displace oxygen in the blood. Option C is incorrect because the diffusion of carbon dioxide between the alveoli and the blood is not affected by changes in carbon dioxide concentration in the blood.

Question

Haemoglobin can bind to carbon dioxide, carbon monoxide and oxygen.

Which statement about the binding sites of haemoglobin is correct?

  1. Carbon dioxide and carbon monoxide bind to one site, oxygen binds to a different site.
  2. Carbon dioxide and oxygen bind to one site, carbon monoxide binds to a different site.
  3. Carbon monoxide and oxygen bind to one site, carbon dioxide binds to a different site.
  4. Carbon monoxide, oxygen and carbon dioxide all bind to different sites.
Answer/Explanation

Ans:

C

The correct that option C is the correct answer. Haemoglobin has four heme groups, each of which can bind to one molecule of oxygen. Carbon dioxide and oxygen both bind to the heme iron ion, while carbon monoxide binds to the heme iron ion with a much higher affinity than oxygen. Therefore, carbon monoxide and oxygen bind to one site, while carbon dioxide binds to a different site. Option C is the correct answer. Option A is incorrect because carbon dioxide and oxygen do not bind to different sites. Option B is incorrect because carbon dioxide does not bind to the same site as oxygen. Option D is incorrect because carbon monoxide and oxygen bind to the same site.

Question

Which substances will displace oxygen from oxyhaemoglobin?

  1. carbon dioxide
  2. carbon monoxide
  3. hydrogen carbonate ions
  4. hydrogen ions

A 1 and 2 only               B 1 and 4 only                C 2 and 3 only                D 2 and 4 only

Answer/Explanation

Ans:

D

The correct that option D is the correct answer. Oxyhaemoglobin is formed when oxygen binds to the iron ion of the heme group in haemoglobin. Several factors can cause the oxygen to be released from oxyhaemoglobin, including an increase in hydrogen ion concentration (decrease in pH), an increase in carbon dioxide concentration, and the presence of carbon monoxide. Hydrogen carbonate ions do not directly displace oxygen from oxyhaemoglobin. Therefore, options 2 and 4 are correct, which means the correct answer is D. Option A is incorrect because hydrogen carbonate ions do not displace oxygen from oxyhaemoglobin. Option B is incorrect because hydrogen ions do not displace oxygen from oxyhaemoglobin, and carbon dioxide does not directly displace oxygen from oxyhaemoglobin in the same way that carbon monoxide does. Option C is incorrect because carbon dioxide does not directly displace oxygen from oxyhaemoglobin in the same way that carbon monoxide does.

Question

Which reactions will be taking place in blood in a capillary next to an alveolus?

  1. Hb + 4O2 → HbO8
  2. H2 O + CO2 → H2 CO3
  3. HHb + 4O2 → HbO8 + H+

A 1 only          B 2 only           C 1 and 2           D 2 and 3

▶️Answer/Explanation

The correct that option A is the correct answer.

In the capillaries next to an alveolus, oxygen and carbon dioxide will be exchanged between the blood and the air in the alveolus. As a result, the concentration of oxygen in the blood will increase, while the concentration of carbon dioxide will decrease. This will cause the following reactions to occur:

Hb + 4O2 → HbO8

The reaction occurs when oxygen in the alveolus diffuses into the red blood cells and binds to haemoglobin to form oxyhaemoglobin. Therefore, only option 1 is correct, which means the correct answer is A. Option B is incorrect because it only includes the reaction for the formation of carbonic acid, which is not the only reaction that occurs in the capillaries next to an alveolus. Option C is incorrect because it includes both the reaction for the binding of oxygen to haemoglobin and the formation of carbonic acid, which is not the only reaction that occurs in the capillaries next to an alveolus. Option D is incorrect because it only includes the reaction for the formation of carbonic acid, which is not the only reaction that occurs in the capillaries next to an alveolus.

Question

Which statement describes the Bohr effect?

  1. In high partial pressure of oxygen and high partial pressure of carbon dioxide, the affinity of haemoglobin for oxygen increases.
  2. In high partial pressure of oxygen and low partial pressure of carbon dioxide, the affinity of haemoglobin for oxygen decreases.
  3. In low partial pressure of oxygen and high partial pressure of carbon dioxide, the affinity of haemoglobin for oxygen decreases.
  4. In low partial pressure of oxygen and low partial pressure of carbon dioxide, the affinity of haemoglobin for oxygen is unchanged.
▶️Answer/Explanation

Ans:

C

The correct answer is C.

The Bohr effect is a phenomenon that describes how the affinity of haemoglobin for oxygen changes in response to changes in the partial pressure of oxygen and carbon dioxide. When carbon dioxide is produced during cellular respiration, it diffuses into the blood and reacts with water to form carbonic acid. Carbonic acid then dissociates into hydrogen ions and bicarbonate ions. The hydrogen ions combine with haemoglobin to form HHb, which helps to buffer the decrease in pH caused by the formation of hydrogen ions.

This decrease in pH causes a conformational change in the haemoglobin molecule, which decreases its affinity for oxygen. This means that, in low partial pressure of oxygen and high partial pressure of carbon dioxide, the affinity of haemoglobin for oxygen decreases.

Option A is incorrect because it describes the opposite of the Bohr effect. In high partial pressure of oxygen, the affinity of haemoglobin for oxygen is already high, so it cannot increase further. Option B is incorrect because it describes the opposite of the Bohr effect. In high partial pressure of oxygen, the affinity of haemoglobin for oxygen is already high, so it cannot decrease. Option D is incorrect because it does not describe any change in the affinity of haemoglobin for oxygen.

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