Respiration is an energy releasing adn enzymatically controlled catabolic process which involves a step-wise oxidative breakdown of organic process which involves a stet-wise oxidative breakdown of organic substances indside living . In this statament about respiration explain the meaing of
(a) Step-wise breakdown
(b) Organic substances (used as substrates).

Explanation

(i) Stepwise oxidative breakdown : Series reactions at many steps forms ATP during respiration of food.
(ii) Organic substances : They act as respiratory substrates. They may be carbohydrates, fats or proteins. Glucose is oxidised readily and easily.