Energy Production Respiration and Fermentation

All living organisms get their chemical energy from ATP and a hydride a reduced form of nicotinamide adenosine nucleotide diphosphate, NADH + H+, or its phosphorylated analog, NADPH + H+(Fig. 1.5). 

Photosynthesis (action of sunlight on water and C02 in chloroplasts, Chap. 2) 

In respiration, substrate organic molecules containing carbon-hydrogen bonds (food) and oxygen are absorbed by prokaryotic cells or by the mitochondria of eukaryotic cells. The oxygen reacts with electrons that are derived from metabolic changes to the carbon-hydrogen bonds of the substrates. The final steps of substrate metabolism, the Krebs cycle, 

1 Necessary Basics Elements, Isotopes, Ions, Chemical Reactions, Energy Metabolism, and Bacterial Structures 

In fermentation, energy is obtained by shuffling organic molecules so that NADH produced in one step is oxidized by a subsequent product or products, which are reduced and excreted. Due to the small amount of energy obtained, only microbes can rely on fermentation as their sole energy source. More complex organisms utilize respiration alone or in combination with sunlight. 

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