O-LevelBiologyTransport in Humans5090/22 · May/June 2017 · Q610 Marks
Section B Answer both questions in this section.
- (a)Describe the journey made by a molecule of carbon dioxide after its production by respiration in a body cell, to the moment it enters the air in the lungs.[7]
- (b)Explain how blood is kept flowing from the foot to the heart.[3]
Mark scheme
Marking points from the official mark scheme (May/June 2017). The mark or mark type is shown in brackets.
- [7] (a) 1 correct reference to (CO2) diffusion ; 2 cytoplasm ; 3 (across) cell membrane ; 4 tissue fluid; 5 * capillary; 6 plasma / (red) blood (cell); 7 vein / vena cava ; 8 heart + right (side of heart); 9 reference to atrium / auricle + followed by ventricle ; 10 pulmonary artery / arch; 11 * capillary; 12 alveolus / alveoli;
- [3] (b) 1 (blood is under) pressure ; 2 (moved) by (contraction of skeletal) muscles ; 3 reference to veins / correct named vein; 4 reference to valves (in veins) ; 5 (valves) prevent backflow of blood AW ;
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