question_answer

         The diagrams of the thorax below show the mechanisms involved during breathing. (a)Which phase of breathing does diagram A and B each represent? (b) List the structures through which air passes in diagram A. (c) If the atmospheric pressure is 760 mmHg, what would you expect the alveolar air pressure in diagram B to be? Explain your answer. (d) Describe three ways in which the alveoli are adapted for efficient gaseous exchange.

Answer:

                  (a) Diagram A shows inhalation and diagram B shows exhalation.                                            (1) (b) Nostrils nasal cavitypharynx larynx tracheabronchibronchioles alveoli                                                          (1) (c) The alveolar air pressure in diagram B would be higher than 760 mmHg. During exhalation, the ribs move downwards and inwards, decreasing the volume of the thoracic cavity. This causes the lungs to be compressed and increases the air pressure in the lungs. (d) The alveoli are numerous, which provides a large surface area for gaseous exchange. The walls of alveoli are thin (only one-cell thick), which allows gases to diffuse across easily. The walls of the alveoli are lined with blood capillaries, which maintain the concentration gradients needed for the diffusion of gases.