The lungs

• Gas exchange is the exchange of oxygen and carbon dioxide between the bloodstream and the atmosphere. Oxygen passes from atmosphere to bloodstream while carbon dioxide passes from bloodstream to atmosphere.
• Oxygen moving through the wall of the alveoli to the bloodstream is called diffusion.
• Once in the bloodstream oxygen diffuses into red blood cells and binds to haemoglobin.
• Breathing rate= number of breaths/ time