Using energy

Energy released during respiration is used by the organism in several ways. It may be used to build up larger molecules from smaller ones. For example:

• Plants make amino acids from sugars, nitrates and other nutrients
• These amino acids are then built up into larger molecules - proteins

Energy is used by animals to enable the muscles to contract so that the animals can move. Mammals and birds keep their body temperature steady. Energy from respiration is used to do this when their surroundings are colder than they are.