Q.The compound which links glycolysis and Krebs cycle is

Step 1. Glycolysis ends with pyruvic acid as its final product, formed in the cytoplasm.

Step 2. Pyruvic acid enters the mitochondrial matrix and is oxidatively decarboxylated in the link (transition) reaction, combining with coenzyme A to form acetyl CoA while releasing CO2 and reducing NAD+.

Step 3. This acetyl CoA is exactly the molecule that condenses with oxaloacetate to start the Krebs cycle, so it is the direct chemical bridge -- the 'link' -- between glycolysis and the Krebs cycle.

Step 4. The other options are Krebs-cycle intermediates themselves (succinic acid, citric acid) or the substrate that precedes acetyl CoA (pyruvic acid), not the actual linking compound.

Identify which molecule is both the end-product of the link reaction and the starting substrate of the Krebs cycle: acetyl CoA.

• Selecting pyruvic acid, which is glycolysis's end product but must first be converted to acetyl CoA before entering the Krebs cycle.
• Selecting citric acid or succinic acid, which are Krebs-cycle intermediates, not the connecting molecule between the two pathways.