Cellular respiration is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products. It is one of the key ways a cell gains useful energy.
|Definition||Aerobic respiration uses oxygen.||Anaerobic respiration is respiration without oxygen; the process uses a respiratory electron transport chain but does not use oxygen as the electron acceptors.|
|Cells that use it||Aerobic respiration occurs in most cells.||Anaerobic respiration occurs in bacteria, yeasts, some prokaryotes, erythrocytes (red blood cells), and in muscle cells.|
|Production of lactic acid||Does not produce lactic acid||Produces lactic acid (in lactic acid fermentation but not in alcoholic fermentation)|
|Amount of energy released||High (36-38 ATP molecules)||Low (2 ATP molecules)|
|Products||Carbon dioxide, water, ATP||Lactic Acid Fermentation - lactic acid, ATP Alcoholic Fermentation - ethyl alcohol, ATP, carbon dioxide|
|Site of reactions||Cytoplasm and mitochondria||Cytoplasm|
|Stages||Glycolysis, Krebs cycle, Electron Transport Chain||Glycolysis, Fermentation|
The process of aerobic vs anaerobic respiration
The sugar molecules stored in the food are broken apart through enzyme-mediated reactions and the energy released is absorbed by cells. This process is much more effective in the presence of oxygen through aerobic respiration.
Aerobic respiration requires oxygen in order to generate energy (ATP). It is the preferred method of pyruvate breakdown from glycolysis and requires that pyruvate enter the mitochondrion in order to be fully oxidized by the Krebs cycle. The product of this process is energy in the form of ATP (Adenosine Triphosphate), by substrate-level phosphorylation, NADH and FADH2.
Anaerobic and aerobic respiration share the initial pathway of glycolysis but aerobic metabolism continues with the Krebs cycle and oxidative phosphorylation. The post glycolytic reactions take place in the mitochondria in eukaryotic cells, and in the cytoplasm in prokaryotic cells.
Fermentation in anaerobic respiration
Without oxygen, pyruvate is not metabolized by cellular respiration but undergoes a process of fermentation. The pyruvate is not transported into the mitochondrion, but remains in the cytoplasm, where it is converted to waste products that may be removed from the cell. This serves the purpose of oxidizing the hydrogen carriers so that they can perform glycolysis again and removing the excess pyruvate.
This waste product varies depending on the organism. In skeletal muscles, the waste product is lactic acid. This type of fermentation is called lactic acid fermentation. In yeast, the waste products are ethanol and carbon dioxide. This type of fermentation is known as alcoholic or ethanol fermentation. The ATP generated in this process is made by substrate phosphorylation, which is phosphorylation that does not involve oxygen.
Krebs cycle in aerobic respiration
The Krebs cycle (also known as the citric acid cycle, or the tricarboxylic acid cycle) is a series of enzyme-catalysed chemical reactions, which is of central importance in aerobic respiration. the citric acid cycle is part of a metabolic pathway involved in the chemical conversion of carbohydrates, fats and proteins into carbon dioxide and water to generate a form of usable energy. Other relevant reactions in the pathway include those in glycolysis and pyruvate oxidation before the citric acid cycle, and oxidative phosphorylation after it. Therefore, carbohydrates break into sugar and then into ATP. The overall process of aerobic respiration can be understood by the following reaction. C6H12O6 + 6O2 + 6H2O ——> 6CO2 + 12H2O + energy.
Energy efficiency of aerobic vs anaerobic respiration
Aerobic metabolism is 19 times more efficient than anaerobic metabolism (which yields 2 mol ATP per 1 mol glucose). Anaerobic respiration is less efficient at using the energy from glucose since 2 ATP are produced during anaerobic respiration per glucose, compared to the 38 ATP per glucose produced by aerobic respiration. This is because the waste products of anaerobic respiration still contain plenty of energy. Ethanol, for example, can be used in gasoline (petrol) solutions. Glycolytic ATP, however, is created more quickly.
For prokaryotes to continue a rapid growth rate when they are shifted from an aerobic environment to an anaerobic environment, they must increase the rate of the glycolytic reactions. Thus, during short bursts of strenuous activity, muscle cells use anaerobic respiration to supplement the ATP production from the slower aerobic respiration, so anaerobic respiration may be used by a cell even before the oxygen levels are depleted, as is the case in sports that do not require athletes to pace themselves, such as sprinting.
Video comparing Aerobic Respiration vs Anaerobic Respiration