In the reactions of Krebs cycle no `O_2` is required. Inspite of that the reactions of this cycle stop in absence of `O_2` why ?

Explanation

Reaction of Krebs cycles require coenzymes `NAS+ and FAD`. Are reduced very shortly during the process. Presence of `O_2` in the cell help these reduced co-enzymes to be oxidised and thus take part again in the reactions. Without `O_2` in the cell, reduced co enzymes are not oxidised and the reactions of Krebs cycle stop.