Q80 - Species Differences in Oxygen Dissociation and the Bohr Effect

Theoretical B Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Figure Q.80 demonstrates the relationship between oxygen concentration and oxygen partial pressure (PO2) in blood of two species of vertebrates (species a and b). Each sample was subjected to two levels of carbon dioxide pressure (PCO2): curve I represents the values measured at normal PCO2 and curve II represents the values measured at elevated PCO2. The blood having passed through the lungs of the two species normally has a PO2 of 100 mm Hg and the deoxygenated blood leaving the tissues has a PO2 of 40 mm Hg.

Figure Q.80

Figure 1. Figure 1.

Using the information and data, determine which of the statements are true or which are false.

A. While comparing curve I of species a with curve I of species b, you can predict that the O2 concentration of the blood in the lungs of species a will be higher than that of species b.

B. If you expose deoxygenated blood of the two species at the same level of PCO2 to increasing PO2, the first blood to become saturated with O2 would be that of species a.

C. In species b, if curves I and II represent the PCO2 of oxygenated and deoxygenated blood, respectively, there will be less than 160 mL of O2 released from a litre of blood as it passes through the tissues.

D. In species a, an increase in PCO2 in the blood reduces the affinity of hemoglobin for oxygen but has no effect on the maximum oxygen-carrying capacity in the blood.

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Question reproduced from IBO 2016, Theoretical Paper B, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)