Respiration: ATP

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The total of all the biochemical reactions needed for an organism to stay alive is it's metabolism.

metabolism = anabolism + catabolism

Anabolism is the building up of more complex molecules from simpler ones e.g. synthesis of nucleic acids and carbohydrates. Enzymes are needed for growth and anabolic reactions are energy consuming.

Catabolism is the enzymic breakdown of complex molecules. These yield energy.

All living organisms need a continuous supply of energy to maintain metabolism. They must absorb light energy or chemical potential energy to do work to stay alive. This includes:

  • synthesising complex molecules from simpler molecules (anabolic) e.g. polypeptides to amino acids
  • active transport of substances across cell membranes against concentration gradient e.g. sodium-potassium pump.
  • movement of the whole organism by the action of cilia, undulipodia or muscles, and movement within the organism e.g. organelles in cells.
  • maintenance of body temperature which release thermal energy to maintain body temperature of that in the environment.

Photosynthesis transfers light energy into chemical potential energy, which can then be released for work by respiration. Both use adenosine triphosphate. In many living organism's, most energy transferred to ATP is derived originally from light energy, a few prokaryotes are nor dependent on light energy but use energy from inorganic chemical reactions.


Processes in cells that require energy are linked to chemical reactions that yield energy by an intermediary molecule, ATP. Using one type of molecule to transfer energy to many different energy-requiring processes makes it easier for processes to be


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