why respiration is amphibolic?

Amphibolic Pathway

glucose is the favoured substrate for respiration . All carbohydrates are usually first converted into glucose before they e used for respiration .
Other respired , but they do not enter the respiratory pathway at the first step .

Fats would need to be broken down into glycerol and fatty acids first . If fatty acids were to be respired they would first be degraded to acetyl CoA and enter the pathway . Glycerol would enter the pathway after being converted to PGAL . The proteins would be degraded proteases and the individual amino acids ( after deamination ) depending on their structure would enter the pathway at some stage within the Krebs ' cycle or even as pyruvate or acetyl CoA .

Since respiration involves breakdown of substrates , the respiratory process has traditionally been considered a catabolic process and the respiratory pathway as a catabolic pathway . But this is not completely true .

> When the organism needs to synthesise fatty acids , acetyl CoA would be withdrawn from the respiratory pathway for it . Hence , the respiratory pathway comes into the picture both during of fatty acids . Similarly during breakdown and synthesis of protein too , respiratory form the link .

> Breaking down processes within the living organism is catabolism and synthesis is anabolism . Because respiratory pathway is involved in both anabolism and catabolism , it would hence be better to consider the respiratory pathway as an amphibolic pathway .