First 228 words of the document:
Ventilation and gas exchange.
Rearrange the statements into the correct order.
1. The intercostals muscles contract pulling the ribs up, and the diaphragm contracts
It then diffuses back into the bronchioles.
The intercostals muscles and diaphragm relax, and the elasticity of the lungs respond by
decreasing the volume.
Oxygen diffuses into the alveoli down a diffusion gradient, and dissolves in the thin film of
water covering the surface.
The atmospheric pressure is higher, so air is forced down the trachea, bronchi, and
The carbon dioxide now diffuses down a diffusion gradient back out of the cell to the blood.
The blood circulates, this maintains the diffusion gradient at the alveoli, and reaches an area
where respiration is occurring.
The volume of the thoracic cavity increases, and pressure decreases.
The oxygen diffuses across the short distance of two cells, the alveolar and capillary walls,
and combines with haemoglobin in a red blood cell.
It is carried back to the lungs where it diffuses into the alveoli, as they have little carbon
The oxygen is released by the haemoglobin, and diffuses through the cell to a mitochondrion,
where aerobic respiration takes place.
12. This increase the pressure above atmospheric, and the air is exhaled.