Cambridge IGCSE Biology (0610) · Gas exchange & respiration
Mini-Lesson
Gas exchange & respiration
This mini-lesson walks you through Cambridge IGCSE Gas exchange & respiration: gas exchange surfaces and the lungs, aerobic & anaerobic respiration and their equations, oxygen debt, and the effect of exercise.
Work through each screen, answer the questions as you go (some wordy, some calculations) and collect ⭐ stars. Watch for the Key term flags. Press Start when you're ready.
Gas exchange · the lungs
Gas exchange surfaces & the lungs
We breathe air down the trachea, which branches into bronchi and then tiny bronchioles, ending in millions of air sacs called alveoli. This is where gas exchange happens:
Oxygen diffuses from the air in the alveoli into the blood.
Carbon dioxide diffuses from the blood into the alveoli, to be breathed out.
Alveoli are adapted for fast diffusion: huge surface area, thin moist walls and a good blood supply.
Adaptations to learn: large surface area, thin (one-cell) walls, moist lining and a rich blood supply — all speed up diffusion of gases.
Quick check
Which way do the gases go?
?At an alveolus, which describes the correct direction of diffusion for the two gases?
Respiration · aerobic
Aerobic respiration
Respiration is the release of energy from food (glucose) inside every living cell. Aerobic respiration uses oxygen and releases a large amount of energy. It mostly happens in the mitochondria.
The energy released is used for muscle contraction, growth, making molecules, active transport, and keeping warm.
Careful wording: respiration releases (transfers) energy — it does not "make" or "produce" energy. Energy cannot be created; it comes from the glucose.
Respiration · anaerobic
Anaerobic respiration
Anaerobic respiration releases energy from glucose without oxygen. It releases much less energy per glucose than aerobic respiration, because the glucose is only partly broken down.
in muscles: glucose → lactic acid+ a small amount of energy released
In yeast and plants, anaerobic respiration is different — it forms alcohol (ethanol) and carbon dioxide (this is fermentation, used in brewing and bread-making):
Anaerobic respiration is a quick backup, but it wastes most of the glucose's energy.Sort it
Aerobic or anaerobic?
Tap a statement, then tap the type of respiration it describes. (Some are true of both.)
🔁 Both
🌬️ Aerobic
🚫 Anaerobic
Key term · oxygen debt
Oxygen debt & exercise
During hard exercise, muscles can't get enough oxygen, so they respire anaerobically, building up lactic acid. This causes muscle fatigue and cramp.
The extra oxygen needed afterwards to break down this lactic acid is called the oxygen debt. This is why you keep breathing hard and fast after you stop exercising — to "repay" the debt.
Exercise raises breathing rate, heart rate and depth of breathing to supply more oxygen and remove CO₂.Quick check
Why keep panting?
?After a sprint, an athlete keeps breathing deeply for several minutes. What is the main reason?
Calculate
Your turn — breathing rate
1A student takes 9 breaths in 30 seconds while resting. Calculate the breathing rate in breaths per minute.