GCSE Biology · Biology
Respiration: a clear study guide
Respiration is an exothermic chemical reaction that transfers energy from glucose for cells to use. Keep the word equation, location and exercise response separate in longer answers.
Aerobic respiration
Aerobic respiration uses glucose and oxygen to release energy, producing carbon dioxide and water. It takes place in mitochondria and supplies energy for active transport, muscle contraction and other cell processes.
The energy is transferred rather than created. A useful equation is energy transferred = power x time when a question describes a device or process using the energy.
- Word equation: glucose + oxygen -> carbon dioxide + water.
- Aerobic respiration releases more energy than anaerobic respiration.
- It happens continuously in living cells, not only during exercise.
Anaerobic respiration
When muscles cannot receive enough oxygen during vigorous exercise, anaerobic respiration releases energy from glucose without oxygen. In animal cells it produces lactic acid, which can contribute to fatigue and creates an oxygen debt that must be repaid after exercise.
In plants and microorganisms, anaerobic respiration can produce ethanol and carbon dioxide. Use the organism named in the question before writing the products.
Exercise and recovery
During exercise, heart rate, breathing rate and breath volume increase so more oxygen and glucose reach muscles and carbon dioxide is removed. After exercise, continued deeper breathing supplies oxygen for breaking down lactic acid.
Quick check
Where does aerobic respiration mainly take place?
Answer: In the mitochondria of cells.
What product of anaerobic respiration builds up in exercising muscles?
Answer: Lactic acid.
Common questions
Why does breathing stay fast after exercise?
Extra oxygen is needed to help break down lactic acid and repay the oxygen debt.
Does anaerobic respiration release no energy?
No. It releases some energy from glucose, but less than aerobic respiration.