Question

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

2) Organic substances (used as substrates).

Answer 1

1) Stepwise breakdown

In aerobic respiration, glucose is not directly converted to $C{O}_2$. The process of respiration occurs in multiple steps which includes - glycolysis, oxidative decarboxylation, krebs cycle, electron transport chain and oxidative phosphorylation.

Since in aerobic respiration, the organic molecules are broken down in the presence of oxygen with the help of many enzymes, it is called stepwise breakdown of organic materials.

2) Organic substances(used as substrates):

Carbohydrates, proteins, fats and other intermediates formed during the respiration are some of the organic substances that are used as respiratory substrates.