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Definition

A series of metabolic processes that take place within a cell in which biochemical energy is harvested from organic substance (e.g. glucose) and stored as energy carriers (ATP) for use in energy-requiring activities of the cell.

Supplement

Simplified Reaction: C₆HA₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O δH_c -2880 kJ

It consists of:
(1) Glycolysis
(2) Citric Acid cycle or Krebs Cycle
(3) Oxidative phosphorylation

The cell seems to “respire” in a way that it takes in molecular oxygen (as an electron acceptor) and releases carbon dioxide (as an end product), hence, the process is described to be aerobic. There are organisms that use other organic molecules as electron acceptors instead of oxygen. This type of respiration in which oxygen is not used as a final electron acceptor is referred to as anaerobic.

In anaerobic respiration (respiration in absence of oxygen), pyruvate is not metabolized by cellular respiration but undergoes a process of fermentation. The pyruvate is not transported into the mitochondrion, but remains in the cytoplasm, where it is converted to waste products that may be removed from the cell.

Cellular respiration is essential to both eukaryotic and prokaryotic cells since biochemical energy is produced to fuel many metabolic processes, such as biosynthesis, locomotion, transportation of molecules across membranes.

The entire process occurs in the cytoplasm of prokaryotes. In eukaryotes, glycolysis occurs in the cytoplasm whereas the Krebs Cycle and oxidative phosphorylation in the mitochondrion. Prokaryotic cells can yield a maximum of 38 ATP molecules while eukaryotic cells can yield a maximum of 36.

Word origin: NL cellulāris, equiv. to cellul(a) live cell + late ME respiracioun < L respīrātiōn- (s. of respīrātiō) a breathing out, equiv. to respīrāt(us) (ptp. of respīrāre to respire) + -iōn.

Variant: cell respiration.