Structures and Functions in Living Organisms · 7 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 18% of your exam marks.
Aerobic and anaerobic respiration equations and comparisons are consistently tested.
During exercise the muscles use far more ATP than at rest, so they need far more glucose and oxygen and produce far more CO₂. The body responds in several ways:
The combined effect is that more oxygen reaches the muscles per minute and more CO₂ is cleared per minute.
If the exercise is so intense that even maximal breathing cannot keep up with the muscles' oxygen demand, the muscles switch to anaerobic respiration and produce lactic acid. After the exercise is over, the body needs extra oxygen to break the lactic acid back down. This is the oxygen debt (sometimes called excess post-exercise oxygen consumption, EPOC).
You "pay back" the oxygen debt by continuing to breathe hard for several minutes after stopping, even though the muscles are no longer working. The extra oxygen is being used by your liver to convert lactic acid back into harmless products (glucose, CO₂ and water).
A simple practical to demonstrate this:
Expected result: breathing rate is markedly higher after exercise. The increase ranges from a few breaths per minute (for light exercise) to more than double the resting rate (for vigorous exercise).
Limitations: