GCSE-ready- Home
- Lessons
- KS3 Science
- Breathing and gas exchange
Breathing and gas exchange
🎬 The doodle video for this lesson is coming soon. Subscribe on YouTube to see it first.
Every cell needs oxygen and must get rid of carbon dioxide. Your lungs swap these gases with the air.
Inside the lungs
Air goes down the trachea (windpipe), held open by rings of cartilage. It splits into two bronchi, then smaller bronchioles, ending in tiny air sacs called alveoli.
In the alveoli, oxygen diffuses into the blood and carbon dioxide diffuses out.
Alveoli are good at this: a huge surface area, walls one cell thick, a rich blood supply, and a moist lining.
In plants, gases move in and out of leaves through tiny holes called stomata, opened and closed by guard cells.
In the alveoli, oxygen diffuses into the blood and carbon dioxide diffuses out.
Alveoli are good at this: a huge surface area, walls one cell thick, a rich blood supply, and a moist lining.
In plants, gases move in and out of leaves through tiny holes called stomata, opened and closed by guard cells.
Breathing in and out
Breathing in: the muscles between the ribs (intercostal muscles) contract, so the ribs move up and out. The diaphragm contracts and flattens. The chest gets bigger, so the pressure inside falls below the air pressure outside, and air rushes in.
Breathing out: the muscles relax, the ribs move down and in, the diaphragm moves up. The chest gets smaller, pressure inside rises, and air is pushed out.
You can measure how much air you breathe out by blowing into an upside-down bottle full of water and seeing how much water is pushed out.
Breathing out: the muscles relax, the ribs move down and in, the diaphragm moves up. The chest gets smaller, pressure inside rises, and air is pushed out.
You can measure how much air you breathe out by blowing into an upside-down bottle full of water and seeing how much water is pushed out.
Exercise, asthma and smoking
Exercise: you breathe faster and more deeply to get more oxygen. Regular exercise strengthens the breathing muscles.
Asthma: the airways become inflamed and narrow, and make extra mucus, so breathing is hard. An inhaler relaxes the airway muscles.
Smoking: tar damages the cilia that sweep mucus out, so people cough. Smoke can break down alveolus walls (less surface area) and causes lung cancer. Carbon monoxide in smoke reduces how much oxygen the blood can carry.
Asthma: the airways become inflamed and narrow, and make extra mucus, so breathing is hard. An inhaler relaxes the airway muscles.
Smoking: tar damages the cilia that sweep mucus out, so people cough. Smoke can break down alveolus walls (less surface area) and causes lung cancer. Carbon monoxide in smoke reduces how much oxygen the blood can carry.
A student blows out fully into a bottle holding 5.0 litres of water. Afterwards 1.8 litres of water are left. What volume of air did they breathe out?
- The air pushed out the water.
- Volume of air = 5.0 − 1.8
Answer: 3.2 litres
Air passes trachea, bronchi, bronchioles, alveoli. Alveoli have a large surface area, thin walls and a good blood supply. Breathing in: ribs up and out, diaphragm flattens, volume up, pressure down, air in. Smoking and asthma damage or narrow the airways.
Check you have got it
Answer 8 quick questions with instant marking. If you get one wrong, GCSE-ready shows you why and gives you another go. It is free, and you do not need an account.