Cellular respiration

All organisms respire in order to release energy to fuel their living processes. The respiration can be aerobic, which uses glucose and oxygen, or anaerobic which uses only glucose. Respiration must happen all of the time so that the organism can survive.

Releasing energy in the form of ATP

Respiration releases energy - it is an exothermic process. The energy is stored in molecules of ATP. ATP can be broken down in other processes in cells to release the stored energy.

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Don't confuse respiration with photosynthesis.

Photosynthesis is the process by which plants, and some bacteria, synthesise food molecules - which they then use, in addition to other things, for respiration. The process of photosynthesis requires energy - it is endothermic.

Don't confuse respiration with breathing, which is ventilation. Respiration happens inside cells. Breathing is the movement of air into and out of the respiratory system, which involves organs like the lungs.

Why organisms need energy in the form of ATP

  • To drive the chemical reactions needed to keep organisms alive - the reactions to build complex carbohydrates, proteins and lipids from the products of photosynthesis in plants, and the products of digestion in animals, require energy.
  • Movement - in animals, ATP is needed to make muscles contract, while in plants, it is needed for transport of substances in the phloem.

All organisms need ATP to live.

Respiration is only around 40 per cent efficient. As animals respire, heat is also released.

In birds and mammals, this heat is distributed around the body by the blood. It keeps these animals warm and helps to keep a constant internal temperature.

ATP is also required:

  • For cell division.
  • To maintain constant conditions in cells and the body. This is called homeostasis.
  • To move molecules against concentration gradients in active transport.
  • For the transmission of nerve impulses.