Respiration and ATPSpec 2.34, 2.35
In short
Respiration is the chemical process in every living cell that releases energy from food molecules such as glucose. The energy is used to join a phosphate group onto ADP to make ATP. ATP is then broken down to release energy for muscle contraction, active transport, making large molecules, cell division and nerve impulses. Respiration is not breathing.
Respiration is the process that releases energy from food molecules such as glucose. It happens in every living cell, all the time. It is a chemical reaction in cells, so it is not the same as breathing.
Cells cannot use the energy in glucose directly. Instead, the energy released when glucose is broken down is used to make a molecule called ATP (adenosine triphosphate).
- Glucose is broken down in respiration and energy is released.
- This energy is used to join a phosphate group onto ADP (adenosine diphosphate), making ATP.
- ATP moves to the part of the cell where energy is needed.
- ATP is broken down back to ADP and phosphate, and this releases energy for the cell to use.
- ADP and phosphate are then used again in respiration to make more ATP.
So ATP is the energy carrier of the cell. ATP provides energy for cells to carry out the processes of life.
- Muscle contraction, so that movement is possible.
- Active transport, which moves substances against a concentration gradient.
- Making large molecules from small ones, such as proteins from amino acids.
- Cell division and growth.
- Sending nerve impulses.
- ATP
- The molecule that provides energy for cells. It is made during respiration.
- Respiration
- The chemical process in cells that releases energy from food, such as glucose, and uses it to make ATP.
Do not say that respiration 'makes energy'. Energy cannot be made. Say that respiration releases energy from glucose to make ATP, and ATP provides energy for cells.
Written and checked against the Edexcel IGCSE Science Double Award (4SD0) specification · Updated October 2026