(a)[4]
Complete the table by putting a tick $\checkmark$ or a cross $\times$ in each box to show whether the structure has that feature or not. Two boxes have already been done for you.
(b)[2]
State the two ways in which the concentration gradients of oxygen and carbon dioxide are kept up for efficient gas exchange.
(c(i))[1]
State one role of the elastic fibres.
(c(ii))[1]
Name the medical condition that results from breakdown of the elastic fibres.
(d)[3]
Cigarette smoke contains tar, a substance with several harmful effects on the cells lining the gas exchange system. Outline three of these effects.