Cellular respiration is a set of metabolicreactions and processes that take place in the cells of organisms to convertbiochemical energy from nutrients intoadenosine 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 releases chemical energy to fuel cellular activity. Cellular respiration is considered anexothermic redox reaction which releases heat.