Gas exchange surfaces and the lungEdexcel International A Level Biology: Mind map

Exam questions on Gas exchange surfaces and the lung

1. Flatworms are flat, leaf-shaped animals less than 1 mm thick. They have no lungs or gills and take in oxygen directly across their body surface. A much larger animal, such as a rabbit, is made of the same types of cell but cannot obtain enough oxygen in this way.
   Explain why the flatworm does not need a specialised gas exchange system.2 marks
2. A patient has a lung disease in which the walls of the alveoli have become thickened by scar tissue. Doctors measure the rate at which oxygen diffuses from the alveoli into the blood and find that it is lower than normal.
   Use Fick's law to explain why the rate of diffusion of oxygen into the blood is reduced in the first patient.2 marks
3. The wall of each alveolus in a healthy lung is only one cell thick, and each alveolus is surrounded by a dense network of capillaries. Blood entering these capillaries has a low oxygen concentration and a high carbon dioxide concentration, while the air in the alveoli is repeatedly replaced by breathing.
   Describe how the structure of the alveoli and the surrounding capillaries is adapted for rapid gas exchange.3 marks