Breathing and gas exchange
Every cell in your body needs oxygen delivered and carbon dioxide removed, continuously. The gas exchange system is built almost entirely around making that swap fast.
Part of your national curriculum
- Biology: structure and function: Understand the structure and functions of the gas exchange system and the effects of exercise, asthma and smoking
Lesson overview
What you'll learn in this lesson
Understand the structure and functions of the gas exchange system and the effects of exercise, asthma and smoking
Key learning points
- • The pathway of air
- • Why alveoli are shaped as they are
- • Breathing in and out
- • Exercise, asthma and smoking
This lesson at a glance
- 30 minutes
- 27 parts to scroll through
- 4 quick checks
- Marked quiz at the end
- Gentle pace: short sittings with pauses
Words to know
Scroll down — the lesson carries on below
Watch & discover
Part 1 of 27
Visual introductionPicture this
Breathing and gas exchange
Every cell in your body needs oxygen delivered and carbon dioxide removed, continuously. The gas exchange system is built almost entirely around making that swap fast.
In a nutshell
Understand the structure and functions of the gas exchange system and the effects of exercise, asthma and smoking
What you already know
Part 2 of 27
Before we start
What you already know
You should already know that cells need oxygen, that the lungs sit inside the ribcage, and that diffusion moves particles from where there are many to where there are few.
Key words
Part 3 of 27
Key words
Words you'll need today
- Alveolus
- A tiny air sac in the lung where gases swap between air and blood.
- Diffusion
- Particles spreading from a high concentration to a low one.
- Trachea
- The windpipe, held open by rings of cartilage.
- Diaphragm
- The sheet of muscle below the lungs that flattens when you breathe in.
- Concentration gradient
- The difference in amount between two places, which drives diffusion.
Reset break
Part 4 of 27
Pause
That's sitting 1 of 7 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Learning cycle
Part 5 of 27
Learning cycle 1 of 2
How air reaches the blood
A short piece of teaching, then a check to make sure it has landed.
Explore the idea
Part 6 of 27
Learn
The pathway of air
Air travels through the trachea, which is held open by rings of cartilage, into two bronchi, then into finer bronchioles and finally into tiny air sacs called alveoli. Ciliated cells and mucus along the airway trap dust and microbes and sweep them upwards, away from the lungs.
Explore the idea
Part 7 of 27
Learn
Why alveoli are shaped as they are
Millions of alveoli give an enormous surface area. Their walls are one cell thick, giving a short diffusion path, and they are wrapped in capillaries that carry oxygen away as fast as it arrives, maintaining a steep concentration gradient. A moist lining lets gases dissolve before crossing. Each feature exists to make diffusion faster.
Reset break
Part 8 of 27
Pause
That's sitting 2 of 7 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 9 of 27
Quick check
Part 10 of 27
Learning cycle
Part 11 of 27
Learning cycle 2 of 2
Breathing, exercise and damage
A short piece of teaching, then a check to make sure it has landed.
Reset break
Part 12 of 27
Pause
That's sitting 3 of 7 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Explore the idea
Part 13 of 27
Learn
Breathing in and out
Breathing is not the same as respiration. To inhale, the diaphragm flattens and the intercostal muscles pull the ribcage up and out, increasing chest volume and reducing pressure inside the lungs so air flows in. Exhaling reverses this. Respiration, by contrast, is a chemical reaction inside cells.
Explore the idea
Part 14 of 27
Learn
Exercise, asthma and smoking
During exercise the breathing rate and depth rise because muscles need more oxygen and produce more carbon dioxide. In asthma the airways narrow and produce extra mucus, reducing airflow. Smoking damages cilia so mucus collects, and tar can break down alveolar walls, cutting the surface area available for exchange permanently.
Quick check
Part 15 of 27
Reset break
Part 16 of 27
Pause
That's sitting 4 of 7 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Quick check
Part 17 of 27
Explore the idea
Part 18 of 27
Worked example
Worked answer: explain how alveoli are adapted for efficient gas exchange (4 marks)
There are millions of alveoli, giving a very large total surface area for diffusion (1). Their walls are one cell thick, so the diffusion distance is short (1). A dense capillary network constantly removes oxygen and delivers carbon dioxide, keeping a steep concentration gradient (1). The lining is moist, so gases dissolve and cross the membrane easily (1). Saying only that alveoli are 'small' scores nothing without the effect on diffusion.
Common mix-ups
Part 19 of 27
Common mix-ups
Things people often get wrong
- People often think breathing and respiration are the same thing. Breathing moves air; respiration is a chemical reaction inside every cell.
- People often think lungs pull air in like a pump. Muscles change the size of the chest, and air flows in because the pressure inside drops.
Reset break
Part 20 of 27
Pause
That's sitting 5 of 7 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Challenge round
Part 21 of 27
Game · Sort it
Which of these are true?
Drag each card into the right column. Tap a card first if dragging is fiddly.
True
Not true
Challenge round
Part 22 of 27
Game · Fill the gaps
Finish the sentences
Choose the word that belongs in each gap.
Smoking damages cilia so mucus collects, and tar can break down alveolar walls, cutting the surface area available for ____ permanently.
Challenge round
Part 23 of 27
Game · Recall cards
Why do alveoli have very thin walls and a huge combined surface area?
Card 1 of 4
Reset break
Part 24 of 27
Pause
That's sitting 6 of 7 done
Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.
Exit quiz
Part 25 of 27
Exit quiz
Show what you've learned
6 questions, marked together at the end. Nothing is timed.
1. Which feature of alveoli gives the shortest diffusion path?
2. What holds the trachea open?
3. When you breathe in, the diaphragm...
4. Why does breathing rate rise during exercise?
5. Smoking damages cilia. The direct result is that...
6. Capillaries around alveoli help gas exchange because they...
Mastery quiz
Part 26 of 27
Marked quiz
End of lesson quiz: Breathing and gas exchange
4 questions, marked with the reasoning shown. No timer.
1. Why do alveoli have very thin walls and a huge combined surface area?
2. Where does gas exchange happen in the lungs?
3. Why does breathing rate increase during exercise?
4. How does smoking damage the lungs?
Lesson round-up
Part 27 of 27
Lesson round-up
Ready when you are
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Understand the structure and functions of the gas exchange system and the effects of exercise, asthma and smoking