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All living things carry out the seven life processes:

• movement
• respiration
• sensitivity
• growth
• reproduction
• excretion
• nutrition

The process of respiration provides the energy required for these processes. It also provides energy for:

• muscle contraction, required for movement
• nerve impulses, required for sensitivity and responding
• cell division and protein synthesis, required for growth

The process of respiration also releases energy in the form of heat. The heat is used to maintain the relatively high body temperature of mammals and birds.

Respiration involves chemical reactions that break down nutrient molecules in living cells to release energy.

Aerobicrespiration needs oxygen. It is the release of a relatively large amount of energy in cells by the breakdown of food substances in the presence of oxygen.

It can be summarised by this equation.

Adenosine triphosphate (ATP) – Higher tier

If the energy stored in glucose were released all at once it would be very difficult to contain. Therefore, the energy stored in the glucose molecule is released gradually during respiration and used to form ATP. ATP is the energy currency of the cell. It temporarily stores the energy in a high energy bond, and when this bond is broken, small amounts of energy are released and used by the body.

Mitochondria

Note that respiration is different to breathing (ventilation). The oxygen dependent reactions involved in aerobic respiration happen inside mitochondria in cells.

The inner membrane is folded inwards, providing a large surface area for the attachment of enzymes which catalyse the process of respiration.