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Efficiency Of Cellular Respiration

One can easily determine the energy efficiency of cellular respiration by calculating the standard free energy change, a thermodynamic quantity, between the reactants and products. On this basis, biochemists often quote the overall efficiency of cellular respiration as about 40%, with the additional 60% of the energy given off as heat.

However, many cells regulate the different enzymes of respiration so that they are in nonequilibrium states, leading to a higher overall efficiency. Calculations of the free energy change, a different thermodynamic quantity, account for these regulatory effects and show that cellular respiration often has an efficiency of 60% or more.

Interestingly, some plants have two separate electron transfer chains in their mitochondria. The alternate electron transfer chain only operates occasionally, but when it does, it gives off most of its energy as heat, rather than ATP. This seemingly wasteful generation of heat is so great in some species that it volatilizes chemicals in their flowers which attract insect pollinators.

See also Respiratory system.



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Nicholls, P. The Biology of Oxygen. Burlington, NC: Carolina Biological, Inc., 1982.

Randall, D. J., et al. The Evolution of Air Breathing in Vertebrates. Cambridge: Cambridge University Press, 1981.

Salisbury, F.B., and C.W. Ross. Plant Physiology. 4th ed. Belmont, CA: Wadsworth Inc., 1991.

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Peter A. Ensminger


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—Adenosine triphosphate; a high energy molecule that cells use to drive energy-requiring processes such as biosynthesis, transport, growth, and movement.


—Process in which a difference in H+ concentration on different sides of the inner mitochondrial membrane drives ATP synthesis.


—Random movement of molecules which leads to a net movement of molecules from a region of high concentration to a region of low concentration.


—A cell whose genetic material is carried on chromosomes inside a nucleus encased in a membrane. Eukaryotic cells also have organelles that perform specific metabolic tasks and are supported by a cytoskeleton which runs through the cytoplasm, giving the cell form and shape.

Fetal alcohol syndrome

—Suite of developmental abnormalities of an infant, caused by exposure to alcohol as a fetus.


—An iron-containing, protein complex carried in red blood cells that binds oxygen for transport to other areas of the body.

Mitochondrion (plural, mitochondria)

—Cellular organelle of eukaryotes which produces ATP.

Additional topics

Science EncyclopediaScience & Philosophy: Reason to RetrovirusRespiration - External Respiration, Internal Respiration, Cellular Respiration, Glycolysis, Cirtric Acid Cycle, Electron Transfer Chain