Compare and contrast aerobic and anaerobic respiration.
Aerobic respiration requires oxygen to completely break down glucose and produce energy. The equation is C6H12O6 + 6O2 → 6CO2 + 6H2O. Anaerobic respiration, on the other hand, does not require oxygen as it does not fully break down glucose. However, this also means that it releases 19 times less energy than respiring aerobically. In human muscles, anaerobic respiration results in the production of lactic acid (equation: C6H12O6 → 2C3H6O3) whereas in plants and fungi, it produces carbon dioxide and ethanol (equation: C6H12O6 → 2C2H5OH + 2C02). The requirement of an oxygen supply means aerobic respiration is slower than anaerobic, so in muscles, the latter is preferred during bursts of hard exercise, whereas the former is better suited for lower intensity endurance exercise. Lactic acid buildup during hard exercise leads to an oxygen debt, where excess oxygen must be consumed after exercise in order to oxidise muscle lactic acid. Anaerobic respiration in yeast is used to brew alcoholic beverages and provide rise in bread.(Extra detail beyond the scope of the GCSE course:When there is aerobic respiration in humans, NADH from glycolysis supplies electrons to the mitochondrial electron transport chain, allowing oxidative phosphorylation to occur. However, when oxygen is limited, ATP cannot be produced via oxidative phosphorylation. Glycolysis itself produces 2 molecules of ATP, but uses up the cell's pool of NAD+, as the resulting NADH is not oxidised in the absence of oxygen. The conversion of pyruvate into lactate oxidises one molecule of NADH, producing NAD+. Thus, the production of lactic acid in anaerobic respiration does not itself produce energy, but instead maintains a pool of NAD+ such that glycolysis can continue.)
