The figure below shows a part of the circulatory system of a human being.
a) Identify the parts labelled A to D
b) Name the site of gaseous exchange in man.
ii) Identify two ways in which the part named in [ b)] is suitable for gaseous exchange
c) How does a malfunctioning valve at X affects pulmonary circulation?
d) Kara recently joined the track team at her school. She finds it difficult to complete her 100m sprints because soon after running her heart beats much faster and she gets pain in her leg muscles.
i) Briefly explain why her heart rate increases during the sprint.
ii) Account for the pain she feels in her leg muscles.