1.2 Evaluate the conditions required for effective gaseous exchange.

Gas exchange is the movement of oxygen into the bloodstream and carbon dioxide out of the bloodstream. Inside the lungs, gas exchange takes place between the air and the blood. This process is called Diffusion.
For effective gaseous exchange to take place there are certain requirements needed. The Lungs are attached to the inner chest wall surface by pleural membranes, between these are pleural fluids. The pleural fluid keeps the lungs moist to allow flexibility and prevents friction (www.bbc.co.uk/dna/hzg2/A27019505).
The alveoli provide a very large surface area in which a greater amount of gaseous exchange can take place. The alveolus is 1 cell thick allowing for the diffusion to happen easy. The lining of the alveoli are kept moist because in order for the gases to be defused across the membranes they need to be in solution. Each alveolus is supported by a network of blood capillaries; these carry the incoming oxygen away quickly maintaining a diffusion gradient (Wright, D (2000) Human Physiology and Health, Cambridge publishing management, page 52). If the surface tension of the alveoli walls is too high then it reduces the airflow and this means oxygen is not getting transported to the capillaries but if the surface tension is too low then this results in the alveoli becoming floppy during exhalation and decreases ventilation. Your body constantly fights to maintain balance and homeostasis in order for this to happen the oxygen levels inside the body need to remain high and the carbon dioxide needs to able to disperse. The concentration gradients across the respiratory surface are the boundary between the external environment and the interior body.

(http://www.biologymad.com/master.html?http://www.biologymad.com/GaseousExchange/GaseousExchange.htm