Exchanging Substances Revision Notes and Practice Quiz
You need to know about a few examples of exchange surfaces. Mammals exchange gases in their lungs and absorb nutrients in their small intestines. In plants, gas exchange occurs in the leaves. In fish, gas exchange occurs in the gills.
The lungs are responsible for transferring oxygen to the blood and removing carbon dioxide from it. This is accomplished by millions of little air sacs called alveoli 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.
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