Cellular respiration is the set of
metabolic reactions and processes that take place in the
cells of
organisms to convert biochemical energy from
nutrients into
adenosine triphosphate (ATP), and then release waste products. The reactions involved in respiration are
catabolic reactions, which break large molecules into smaller ones, releasing energy in the process, as weak so-called "high-energy" bonds are replaced by stronger bonds in the products. Respiration is one of the key ways a cell gains useful energy to fuel cellular activity. Cellular respiration is considered an
exothermic redox reaction which releases heat. The overall reaction occurs in a series of biochemical steps, most of which are redox reactions themselves. Although technically, cellular respiration is a
combustion reaction, it clearly does not resemble one when it occurs in a living cell due to slow release of energy from the series of reactions.