Respiration is the chemical process inside every living cell that releases energy from glucose. The released energy is transferred to ATP, which the cell can then spend on any process that needs energy
Some important things to notice about that definition:
- Respiration happens in every living cell, all the time. Plant cells respire just as much as animal cells, and they do it day and night.
- Respiration is not the same as breathing. Breathing (or gas exchange) is how oxygen gets into the body and carbon dioxide gets out. Respiration is the chemical reaction inside the cells that uses that oxygen to release energy.
- Energy is not produced or made by respiration. Energy is released from the bonds of glucose and transferred to ATP. Exam mark schemes are strict on this point, so never write "respiration produces energy".
What ATP does for the cell
The energy released by respiration is stored in the chemical bonds of a molecule called ATP (adenosine triphosphate). ATP is the "energy currency" of the cell. When ATP is broken down, the stored energy is released right where it is needed. Cells use ATP for:
- Building large molecules from smaller ones (proteins from amino acids, starch from glucose, DNA replication, etc.)
- Muscle contraction for movement
- Active transport across membranes (pumping ions against a concentration gradient)
- Cell division (mitosis and meiosis)
- Generating body heat in warm-blooded animals, to keep enzymes at their optimum temperature
- Nerve impulses (resetting the resting potential after each impulse)