DP Biology (first assessment 2025)

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Question 20N.2.HL.TZ0.a

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Date November 2020 Marks available [Maximum mark: 3] Reference code 20N.2.HL.TZ0.a
Level HL Paper 2 Time zone TZ0
Command term Explain Question number a Adapted from N/A
a.
[Maximum mark: 3]
20N.2.HL.TZ0.a

Using the graph, explain the Bohr shift.

[3]

Markscheme

a. respiring tissues produce CO2;

b. CO2 leads to an increase in H+/decrease in blood pH;

c. increased acidity/decreased pH shifts the oxygen dissociation curve to the right;

d. affinity of the hemoglobin for oxygen is reduced;

e. greater release of oxygen from hemoglobin (at the same partial pressure of oxygen) in tissues;

Examiners report

Most candidates did well in this question, but strongest candidates distinguished themselves with complete and very detailed answers. Although candidates did well, there were many inaccuracies in some answers. Bohr shift is the shift to the right of the oxygen dissociation curve in respiring tissues; it does not refer to the reverse process at lung level.

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