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 $(a)$ Step-wise oxidative breakdown $(b)$ Organic substances (used as substrates).

(N/A) Step-wise oxidative breakdown: Respiration is a phase-wise or step-wise oxidation of organic substances,which includes three main phases:
$(i)$ Glycolysis
$(ii)$ Krebs' cycle
$(iii)$ Electron transport system $(ETS)$.
Glucose undergoes a series of enzyme-catalyzed reactions,and at the end,it forms $H_2O$,$ATP$,and $CO_2$.
$(b)$ Organic substances: These are carbon-containing compounds found in living systems,typically in ring or long-chain forms,bonded with hydrogen,oxygen,and nitrogen atoms. Examples include glucose,fatty acids,and amino acids.
These substances are oxidized to release energy. The respiration of glucose and fatty acids is called floating respiration,while the respiration of amino acids is called protoplasmic respiration.