A-LevelBiologyTransport in mammals9700/21 · May/June 2018 · Q410 Marks

Fig. 4.1 is a ribbon model of a molecule of haemoglobin. [Figure 4.1]

(a)State the term that matches each of the descriptions given in boxes E, F, G, H and J in Fig. 4.1. E F G H J[5]
(b)(i)The pO₂ in alveolar air is 13.0 kPa and the pCO₂ is 5.3 kPa. Use Fig. 4.2 to suggest the percentage saturation of haemoglobin in blood entering the pulmonary veins.[1]
(b)(ii)Use the information in Fig. 4.2 to state and explain the effect of increasing pCO₂ in muscle tissues during strenuous exercise.[4]

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Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[5] E - haem / porphyrin (ring); I iron / iron-containing group A conjugated group / prosthetic group F a helix; R a helix G - tertiary structure ; A 3° structure H - primary structure ; A 1º structure J - quaternary structure / 4° structure / 2α and 2ẞ globins ; A polypeptides for globins
[1] 98 (%);
[4] four from: 1 Bohr, shift / effect; 2 (at any pO2 on the left of graph) percentage saturation of haemoglobin decreases / haemoglobin releases more oxygen (to muscle tissue) / increases dissociation of oxyhaemoglobin ; A any comparative data quote for any one value of pO2 between 1 and 5 kPa 3 (increase in carbon dioxide) increases production of carbonic acid; 4 increase in hydrogen ions (in red blood cells); 5 haemoglobin accepts hydrogen ions / formation of haemoglobinic acid (HHb) ; A haemoglobin has an affinity for hydrogen ions 6 decreases the affinity between haemoglobin and oxygen ;

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