Solution

Breaking down of glucose involves two pathways aerobic and anaerobic. In the first step, glucose will be broken into three carbon molecules called pyruvate. The pyruvate is further broken down to release carbon dioxide and release energy in following different ways in various organisms. 1) Aerobic respiration: In this case, pyruvate is broken down into water and carbon dioxide along with the release of energy. It takes place mainly in the presence of oxygen. 2) Anaerobic respiration: In anaerobic respiration, Pyruvate will be converted to lactic acid and release water with a certain amount of energy. This reaction takes place in the lack of oxygen in muscles while exercising.