Cellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients intoadenosine triphosphate (ATP), and then release waste products. The reactions involved in respiration are catabolic reactions that involve the redox reaction (oxidation of one molecule and the reduction of another). Respiration is one of the key ways a cell gains useful energy to fuel cellular changes.
Nutrients that are commonly used by animal and plant cells in respiration include sugar, amino acids and fatty acids, and a common oxidizing agent (electron acceptor) is molecular oxygen (O2). Bacteria and archaea can also be lithotrophsand these organisms may respire using a broad range of inorganic molecules as electron donors and acceptors, such as sulfur, metal ions, methane or hydrogen. Organisms that use oxygen as a final electron acceptor in respiration are described as aerobic, while those that do not are referred to as anaerobic.[1]

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Aerobic respiration

Aerobic respiration (red arrows) is the main means by which both plants and animals utilize energy in the form of organic compounds that were previously created through photosynthesis (green arrow).
Aerobic respiration requires oxygen in order to generate energy (ATP). Although carbohydrates,fats, and proteins can all be processed and consumed as reactant, it is the preferred method ofpyruvate breakdown in glycolysis and requires that pyruvate enter the mitochondrion in order to be fully oxidized by the Krebs cycle. The product of this process is energy in the form of ATP (Adenosine triphosphate), by substrate-level phosphorylation, NADH and FADH2 Simplified reaction: | C6H12O6 (aq) + 6 O2 (g) → 6 CO2 (g) + 6 H2O (l) | | ΔG = -2880 kJ per mole of C6H12O6 |
The negative ΔG indicates that