Breathing and gas exchange Edexcel International GCSE Biology revision
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In plain words
Every cell needs oxygen and has to get rid of carbon dioxide. The swap happens in your lungs, in millions of tiny air sacs wrapped in blood vessels. Breathing just keeps fresh air arriving and stale air leaving.
Three things to know
- Air goes in through the trachea, the bronchi and the bronchioles to the alveoli (air sacs). Alveoli are good at gas exchange: a huge surface area, walls one cell thick, a rich blood supply, and fresh air always arriving.
- Breathing in: the diaphragm contracts and flattens, and the intercostal muscles pull the ribs up and out. The chest gets bigger, the pressure inside falls, and air is pushed in. Breathing out is the reverse.
- Breathed-out air has less oxygen (about 16%), more carbon dioxide (about 4%) and more water vapour than breathed-in air. Exercise makes breathing faster and deeper. Mucus traps dust and microbes, and cilia sweep it up out of the airways.
Tips and tricks
- Breathing in: volume up, pressure down, air in. Give the chain in that order.
- Breathing is moving air. Respiration is the chemical reaction in cells. Gas exchange is the swap in the alveoli. Use the right word.
It lands in your notebook with its questions as flashcards.
Breathing and gas exchange: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Where does gas exchange happen in the lungs?
The alveoli are tiny air sacs surrounded by capillaries.
What happens to the diaphragm when you breathe in?
This makes the chest bigger.
Which gas is there more of in expired air than in inspired air?
It is a waste product of respiration.
What do cilia do in the airways?
The mucus carries trapped dust and microbes with it.
Why do alveoli have walls one cell thick?
Gases cross quickly.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 8 marks. Write your answers on paper, then check them.
Breathing and gas exchange
Edexcel International GCSE Biology 4BI1 · 8 marks · papermunch.org
Name ______________________________ Date ______________
Explain how the alveoli are adapted for gas exchange.[3]
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They provide a very large surface area; their walls are one cell thick, giving a short diffusion distance; they have a rich blood supply, and are well ventilated, which keeps the concentration gradients steep.
Describe what happens to the diaphragm and the ribs when you breathe in, and how this draws air in.[3]
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The diaphragm contracts and flattens, and the ribs move up and out. The volume of the chest increases, so the pressure inside falls below the pressure outside, and air moves in.
State two differences between inspired air and expired air.[2]
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Any two: expired air has less oxygen, more carbon dioxide, more water vapour, and is warmer.
Answers: Breathing and gas exchange
- 1. They provide a very large surface area; their walls are one cell thick, giving a short diffusion distance; they have a rich blood supply, and are well ventilated, which keeps the concentration gradients steep.
- 2. The diaphragm contracts and flattens, and the ribs move up and out. The volume of the chest increases, so the pressure inside falls below the pressure outside, and air moves in.
- 3. Any two: expired air has less oxygen, more carbon dioxide, more water vapour, and is warmer.