(a)[3]
Table 3.1 gives some characteristics of these three blood vessel types. Finish Table 3.1 by placing a tick ($\checkmark$) if the feature is found in the blood vessel, or a cross ($\times$) if the feature is not found. Enter a tick ($\checkmark$) or a cross ($\times$) in every box.
(b(i))[1]
Draw two labelled arrows on Fig. 3.1 to indicate the direction in which oxygen moves and the direction in which carbon dioxide moves during gas exchange in the lungs.
(b(ii))[4]
Suggest and explain how a steep oxygen concentration gradient is kept up in the lungs.
(c)[3]
The passage describes the functions of the blood vessels linked to the heart. Complete the passage with the most suitable scientific terms.