Respiration: the continuous exothermic reaction
Every living cell respires constantly to release energy from glucose. It is EXOTHERMIC — energy is transferred OUT to the surroundings/cell.
Respiration is the set of chemical reactions in cells that transfer energy from glucose so the organism can use it for life processes.
Three key facts the AQA spec wants you to memorise:
- Continuous — happens in every living cell 24/7, even when you are asleep.
- All organisms — animals, plants, fungi, bacteria. Not just animals!
- Exothermic — energy is transferred FROM the chemicals TO the surroundings (and to other useful processes in the cell). Note: this is the OPPOSITE of photosynthesis, which is endothermic.
What the organism uses the energy for (AQA list):
- Building larger molecules from smaller ones (e.g. amino acids → proteins; glucose → starch/cellulose; glycerol + fatty acids → lipids).
- Movement — muscle contraction in animals (and beating cilia in some single-celled organisms).
- Keeping warm — mammals and birds maintain a constant body temperature using heat released from respiration.
- Active transport — moving substances against concentration gradients (e.g. mineral ion uptake in root hair cells, glucose absorption in the small intestine).
Where it happens. Most respiration takes place in the mitochondria of cells — the powerhouses. Cells that need lots of energy (muscle, liver, sperm) contain many mitochondria; cells with low energy needs have fewer.
Exothermic — energy released OUT to surroundings/cell.
Continuous in ALL living cells.
Mostly happens in mitochondria.
Energy used for: building molecules, movement, warmth, active transport.