Respiration is an energy releasing

Respiration is an energy releasing and enzymatically controlled catabolic process which involves a
step-wise oxidative breakdown of organic substances inside living cells. In this statement about respiration explain the meaning of (i) step-wise oxidative breakdown (II) organic substances (used as substrates).

(i) Step-wise oxidative breakdown The series of reactions transfers the energy of glucose to ATP.
(ii) Organic substances (used as substrates) The organic substances, which are catabolised . in the living cells to release energy are called as respiratory substrates. Though any food
stuff-carbohydrate, fat or protein may act as a respiratory substrate, the common respiratory substrate is glucose because it can he oxidized easily and is present abundantly.