A-LevelBiologyTransport in mammals9700/21 · Oct/Nov 2024 · Q211 Marks

In the mammalian circulatory system, red blood cells travel through different types of blood vessel as they pass from the heart to respiring tissues and back to the heart. Fig. 2.1 shows the types of blood vessels through which red blood cells travel in the circulatory system. [Figure 2.1]

(a)Complete Fig. 2.1 by writing the names of the missing types of blood vessels through which red blood cells travel.[2]
(b)With reference to Fig. 2.2, explain how water acts as a solvent for sodium chloride.[3]
(c)(i)Draw a line on Fig. 2.4 to suggest the position of the oxygen dissociation curve for penguin haemoglobin.[2]
(c)(ii)Penguin haemoglobin is very sensitive to a decrease in pH caused by an increase in the carbon dioxide concentration in the blood. Explain how a decrease in pH affects penguin haemoglobin, and suggest how this helps the penguin to swim underwater for a long time.[3]
(d)Name the group of specialised cells in the wall of the right atrium that regulates heart rate.[1]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.

2(a) arteriole/s;
venule/s;
2(b) any three from:
(because) water is, polar/ a polar molecule / polar / dipolar ; A delta positive hydrogen atom / Hδ+, and, delta negative oxygen atom / Oδ-
ref. to attraction between, (negatively charged) chloride ions / Cl-, and Hδ+ ;
ref. to attraction between, (positively charged) sodium ions / Na+ and Oδ- ;
if both ideas (mp2 and mp3) stated, then this is also mp1
water molecules collect around sodium chloride (and separate ions);
AVP; e.g. ionic bond broken (between sodium and chloride atom) ref. to hydration shell(s) idea that ions are separated (and spread through the water)
If no marks gained allow one mark for idea of attraction between water and, ions/NaCl
2(c)(i) line drawn to the left ;
sigmoid shape of line and starting at 0, 0;
2(c)(ii) any three from:
oxygen can be released (from haemoglobin to supply respiring tissues);
increase in H+ ions so more, hydrogen ions bind to haemoglobin / haemoglobinic acid forms;
haemoglobin affinity for oxygen reduces (when the pH decreases) ;
aerobic respiration in muscle cells can continue for longer ;
AVP; e.g. ref. to Bohr shift / curve shifts to right providing ATP for muscle contraction
2(d) sinoatrial node; I SAN

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