Name the epithelial cell type indicated by label lines A and B.
Describe the way the elastic fibres of the alveoli help the lungs function properly.
The true diameter of the alveolus along line X-Y is $220\ \mu\text{m}$. Calculate the magnification of Fig. 6.1. Show your working and give your answer rounded to the nearest whole number.
Outline two gas exchange-surface features visible in Fig. 6.1.
Fig. 6.2 is a simplified view of the human circulatory system, with gas exchange shown in the lungs and in respiring tissue. The partial pressures of oxygen ($pO_2$) and carbon dioxide ($pCO_2$) at four points are also displayed. Using Fig. 6.2, explain how differences in $pO_2$ and $pCO_2$ between the alveoli and the blood make gas exchange possible in the lungs and respiring tissue.