Breathing and gas exchange — Biology, 11–13 years
Breathing moves air, but gas exchange is the important meeting between air and blood. Oxygen enters the blood and carbon dioxide leaves it through thin surfaces in the lungs.
Air meets blood
When you breathe in, air travels through branching tubes to tiny air sacs called alveoli. Their walls are very thin, and many small blood vessels surround them. Oxygen moves from the air into the blood, while carbon dioxide moves the other way to be breathed out.
Why exchange gases?
Cells need oxygen to release energy from nutrients, and they produce carbon dioxide as waste. The problem is getting the first gas in and the second gas out without mixing the two jobs. Lungs solve it with a huge, thin exchange surface; scientists found this by studying breathing, blood and tissue under microscopes.
After running
Run for one minute and notice your breathing. Your leg muscles are using more energy, so they need more oxygen and produce more carbon dioxide. Sensors in the body detect the change; your brain makes breathing faster and deeper. More fresh air reaches the alveoli, speeding up gas exchange.
Breathing is not the same as gas exchange
A reasonable mistake is to treat breathing as simply filling the lungs with air. We can feel the chest moving, but we cannot feel oxygen crossing into blood. Breathing moves air in and out; gas exchange happens at the alveoli, where oxygen and carbon dioxide cross between air and blood.
At altitude and in sport
This idea matters when people exercise, climb mountains or use medical oxygen. At high altitude, each breath contains fewer oxygen molecules, so the body may breathe faster and make more red blood cells over time. It does not mean lungs create oxygen; they only exchange the gases available.
Keep exploring
Other languages
Loading MyLeoNes™…