How is energy generated from carbohydrates?

The breakdown of carbohydrates from foodstuffs produces mono and disaccharides. These sugars are converted into glucose to be respired for energy generation. Respiration catabolises (breaks down) glucose, to produce energy as ATP. In the presence of oxygen, glucose is respired aerobically to produce ATP, carbon dioxide and water. Aerobic respiration involves four main steps: glycolysis, the link reaction, the Kreb's cycle (also known as the citric acid cycle), and oxidative phosphorylation. Glycolysis occurs in the cell cytoplasm. The link reaction and Kreb’s cycle occur in the mitochondrial matrix. Oxidative phosphorylation generates a proton gradient across the inner mitochondrial membrane via electron transport chain proteins and reduced cofactors from prior respiration steps. The proton gradient facilitates chemiosmosis via an ATP synthase channel to generate a large amount of ATP.If oxygen is absent, glucose can be respired anaerobically, however this produces a smaller amount of energy (as ATP). Glycolysis is followed by alternative routes; lactate fermentation or ethanol fermentation. Long periods of intense exercise cause anaerobic lactate fermentation in our muscles. This is because there is a high energy requirement in the muscles during exercise, whilst oxygen consumption is too low to maintain aerobic respiration. If this process is prolonged it can cause accumulation of lactic acid, resulting in muscle pain. Ethanol fermentation is the anaerobic respiration method used by yeast and bacteria.