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
1) Step-wise oxidative breakdown, and
2) Organic substances (used as substrates).
1) Step-wise oxidative breakdown:
During cellular respiration, all the energy which is contained in the respiratory substrate is not released all at once. Instead, it is released in a step-wise manner.
The energy is released by a series of slow steps which are controlled and moderated enzymatically. It is synthesized in the chemical energy in the form of ATP. Therefore, the energy release cannot occur directly, and it follows a series of steps of catabolic breakdown only when energy is required.
2) Organic substances (used as substrates):
Organic substances like carbohydrates used as substrates and oxidized during the respiratory process for releasing energy. Organic substances like protein, fats and organic acids are used as organic respiratory substances in some organisms and plants.