DP Chemistry (last assessment 2024)

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Question 20N.3.hl.TZ0.c(ii)

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

Proteins are polymers of amino acids.

Explain why the affinity for oxygen of foetal hemoglobin differs from that of adult hemoglobin.

 

[2]

Markscheme

Any two of:

contains two gamma/γ units «instead of two beta/β units found in adults»
OR
differs in amino acid sequence «from the two beta//β units found in adults» ✔

less sensitive to inhibitors/2,3-BPG/DPG ✔

receives O2 from «partly deoxygenated» blood so can work at low pO2 ✔

low pCO2 in foetal blood increases affinity for O2 ✔

hemoglobin concentration in foetal blood greater than in the mother ✔

Examiners report

This question required an explanation as to why the affinity for oxygen of foetal hemoglobin differs from that of adult hemoglobin. This question was poorly answered and only the stronger candidates managed to score both marks, usually by stating that foetal hemoglobin contains two gamma units instead of the two beta units found in adult hemoglobin, required for M1 and often by stating that there is less sensitivity to inhibitors for M2.

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