Cellular respiration of carbohydrates using glycolysis releases pyruvate, which enter the 'tricarboxylic acid cycle' as acetyl coenzyme-A with the release of carbon dioxide. It is at the mitochondria that the pyruvate breaks down to give carbon dioxide, water and energy. This process is called as pyruvate decarboxylation and is catalysed by pyruvate dehydrogenase.

So, the correct answer is 'Mitochondria'