Traditionally, respiration has been considered a catabolic process because it involves the breakdown of substrates to derive energy. However, this understanding is incomplete as the respiratory pathway serves dual functions.

The respiratory pathway is called an amphibolic pathway because it is involved in both anabolism and catabolism. Catabolism refers to breaking down processes within the living organism, while anabolism refers to synthesis processes.

During catabolism, various substrates enter the respiratory pathway at different points. Fats are broken down into glycerol and fatty acids; fatty acids are degraded to acetyl CoA before entering the pathway, while glycerol enters after being converted to PGAL. Proteins are degraded by proteases, and amino acids enter at various stages within the Krebs' cycle or as pyruvate or acetyl CoA.

During anabolism, the same respiratory intermediates are withdrawn for synthesis. For instance, when an organism needs to synthesise fatty acids, acetyl CoA is withdrawn from the respiratory pathway. Similarly, during synthesis of proteins, respiratory intermediates form the link.

Hence, since the respiratory pathway comes into the picture both during breakdown and synthesis of various substrates like fatty acids and proteins, it is better to consider the respiratory pathway as an amphibolic pathway rather than as merely a catabolic one.