At What Stage in Cellular Respiration Is Most ATP Produced?


Quick Answer

In cellular respiration, the electron transport stage is when most adenosine triphosphate (ATP) is produced. Electron transport is the third stage in cellular respiration.

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Full Answer

Cellular respiration involves a series of complex reactions. The first phase of cellular respiration is glycolysis, which involves splitting glucose. This phase is carried out in several steps. The end result is the production of pyruvic acid. After pyruvic acid is produced, the Krebs cycle begins. The Krebs cycle, which is the second phase of cellular respiration, is sometimes referred to as the citric acid cycle. The Krebs cycle first produces citric acid, and it produces carbon dioxide as an end product. Electron transport is the last stage of aerobic respiration in cellular respiration. It results in the production of adenosine triphosphate, or ATP. ATP is a molecule that supports a variety of life functions. It is found in the nucleoplasm and cytoplasm of all cells, and helps organisms perform physiological functions. During anaerobic respiration, ATP is synthesized through glycolysis. In aerobic production, ATP is produced by mitochondria in addition to glycolysis.

Glycolysis and ATP Production
Glycolysis is produced in a cell's cytoplasm. During this phase, a molecule of glucose is broken down into two molecules of pyruvate. These two molecules then move on to the second phase of the cellular respiration process. The second phase, or the Krebs cycle, begins when the pyruvate molecules enter the mitochondrion. The Krebs cycle ends in a complete breakdown of the glucose molecule. During this phase, six carbon atoms combine with oxygen to produce carbon dioxide. The energy produced through chemical bonds in the Krebs cycle is then stored in a series of molecules. The electron transport phase involves the transformation of the energy produced in the Krebs cycle to ATP. As the energy is released, it travels down structures called electron transport chains, which are located in the mitochondrion. The energy makes hydrogen ions move across the inner membrane into the intermembrane space. Hydrogen ions then move back across the membrane with the help of channel proteins called ATP synthase. The end result of glycolysis is that it produces four molecules of ATP, which means that two molecules of ATP are gained during glycolysis.

Aerobic and Anaerobic Cellular Respiration
Cellular respiration can be performed with and without oxygen. Cellular respiration that requires oxygen is called aerobic respiration. Cellular respiration that does not need oxygen is called anaerobic respiration. Anaerobic respiration first appeared when the earliest life forms arose on Earth and did not have access to oxygen. Oxygen began appearing on Earth around two or three billion years ago. At that point, living organisms could begin using oxygen to produce ATP. Most organisms use aerobic respiration instead of anaerobic respiration.

Uses of Cellular Respiration
Plants and animals both use cellular respiration to perform life functions on a daily basis. Plants use it to perform photosynthesis, which provides the sustenance they need to stay alive. However, plants have a reverse cycle of cellular respiration, which produces oxygen as an end product. Animals take in oxygen and give off carbon dioxide. This delicate balance makes animals and plants dependent on each other for survival.

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