How energy is formed from oxidation of carbohydrates, fats and proteins ? Correct the diagram given below :[Diagram to be corrected: at the top ‘Pyruvic Acid’; below it an empty box, then ‘Acetyl Co-Enzyme A’; below it an empty box; then ‘Glycolysis’…

Answer: Carbohydrates, fats and proteins are broken down into simpler substances which enter a common pathway (pyruvic acid → acetyl-CoA → Krebs cycle) and are oxidised to CO₂ and water with the release of energy (ATP).

Carbohydrates: glucose is oxidised step by step in the cytoplasm (glycolysis) to two molecules of pyruvic acid, with 2 ATP and 2 NADH₂. Pyruvic acid is converted into acetyl-coenzyme-A, which enters the mitochondria and is completely oxidised in the Krebs (tricarboxylic acid) cycle to CO₂ and H₂O; NADH₂ and FADH₂ formed give ATP through the electron transfer chain.

Fats (lipids): when carbohydrates are insufficient, lipids are converted into fatty acids (and glycerol); the fatty acids are converted into acetyl-CoA, which is oxidised in the Krebs cycle.

Proteins: proteins are converted into amino acids, which are converted into acetyl-CoA (or intermediates of the Krebs cycle) and oxidised to release energy.

Corrected diagram (arrows point upwards; read from bottom to top):

                    [ Kreb's cycle ]  --> CO2 + H2O + energy (ATP)
                           ^
                 [ Acetyl Co-Enzyme A ]
                 ^         ^          ^
                 |   [ Pyruvic acid ] |
                 |         ^          |
          [ Amino acids ] [ Glycolysis ] [ Fatty acids (Lipid) ]
                 ^         ^          ^
           [ Proteins ] [ Carbohydrates ] [ Fats ]

Corrections made: Kreb’s cycle goes at the top (not at the bottom); pyruvic acid goes between glycolysis and acetyl CoA (not at the top); the bottom row is proteins – carbohydrates – fats, with proteins → amino acids and fats → fatty acids (lipid), and both amino acids and fatty acids join at acetyl CoA.