O-LevelBiologyRespiration5090/21 · May/June 2014 · Q26 Marks
Fig. 2.1 shows the mean distance that molecules must travel during gas exchange between air in the lungs and blood in the circulatory system in birds and mammals. This distance is known as the thickness of the blood-gas barrier. [Figure 2.1]
- (a)Name two gases that cross the blood-gas barrier during gas exchange. 1. 2.[1]
- (b)(i)Use information from Fig. 2.1 to compare the thickness of the blood-gas barrier in birds and mammals.[2]
- (b)(ii)Explain how the difference in thickness of the blood-gas barrier suggests that movement of a bird by flying requires more energy than movement by a mammal on land.[3]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (May/June 2014). The mark or mark type is shown in brackets.
- [1] carbon dioxide + oxygen ;
- [2] thicker in mammals/ora;
- by 2.5 times/use of comparative figures ;
- [3] (thinner barrier) results in faster/greater gas exchange/diffusion;
- more oxygen supplied/more carbon dioxide removed ;
- ref. (aerobic) respiration;
- ref. increased (respiration);
- ref. muscles ;
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