Question 19M.3.HL.TZ1.b
| Date | May 2019 | Marks available | [Maximum mark: 6] | Reference code | 19M.3.HL.TZ1.b |
| Level | HL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | b | Adapted from | N/A |
Explain how physical exercise affects the affinity of hemoglobin for oxygen. You could supplement your explanation with a labeled diagram.
[6]
a. diagram showing normal oxygen dissociation curve ✔
b. diagram showing curve with increased CO2 to the right ✔
c. both axes correctly labelled ✔
d. where tissues are respiring there is a higher concentration of CO2 ✔
e. exercise increases the amount of CO2 in the blood ✔
f. an increase in CO2 lowers the pH of the blood ✔
g. a lower pH causes hemoglobin to release oxygen ✔
h. lower pH decreases hemoglobin affinity for O2/changes hemoglobin conformation ✔
i. oxygen is released in tissue where it is required for respiration ✔
j. this is known as the Bohr effect/shift ✔
k. at the lungs the low concentration of CO2 means oxygen attaches to hemoglobin ✔
l. «Bohr» effect particularly important during exercise ✔
Apply [4 max] if no diagram.
Students who did well on this question tended to achieve all marking points, including correct information on the graphs. These students also composed detailed explanations, including the role of reduced pH and its effect on affinity. Some students remain unsure about how, where and why CO2 is produced and how this changes hemoglobin affinity for oxygen. Weaker students did not realise that the annotated diagram referred to in the question would be the dissociation curve; they often included caricatures of people exercising or attempts at drawing hemoglobin.
