Exchanging Substances Revision Notes and Practice Quiz

The gas exchange in humans is in the following way. The lungs are responsible for transferring oxygen to the blood and removing carbon dioxide. Millions of little air sacs, called alveoli, accomplish this within the lungs.

Capillaries surround the alveoli, which are microscopic blood vessels. The air contains a higher concentration of oxygen than the blood, so oxygen diffuses from the air into the blood through the capillaries. Carbon dioxide diffuses the opposite way. A small tube called a bronchiole transports air between the alveoli and the outside world.

Alveoli has the following specialised features: