doubt

i) Anaerobic respiration - In case of absence of oxygen, glucose is broken down into a three-carbon molecule called pyruvate in the cytoplasm. Further, the pyruvate gets  converted into ethanol and carbon dioxide. This process takes place in yeast during fermentation.

ii) In case of sufficient supply of oxygen - Sometimes, when there is a lack of oxygen in our muscle cells, glucose breaks down into a 3- carbon molecule of pyruvate in the cytoplasm, which further breaks down into lactic acid in our muscles with release of energy.

(iii) In case of sufficient supply of oxygen - Here glucose breaks up into a 3- carbon molecule of pyruvate which further breaks down into carbon dioxide and water with release of energy. Breakdown of pyruvate into carbon dioxide and water takes place in mitochondria.