Aerobic cellular respiration is the process by which cells use oxygen to help them convert glucose into energy. This type of respiration occurs in three steps: glycolysis; the Krebs cycle; and electron transport phosphorylation. Oxygen is not needed for glycolysis but is required for the rest of the chemical reactions to take place.
TL;DR (Too Long; Didn't Read)
Oxygen is necessary for the complete oxidation of glucose.
Cellular respiration is the process by which cells release energy from glucose and change it into a usable form called ATP. ATP is a molecule that provides a small amount of energy to the cell, which provides it fuel to do specific tasks.
There are two types of respiration: anaerobic and aerobic. Anaerobic respiration does not use oxygen. Anaerobic respiration produces yeast or lactate. When exercising, the body uses oxygen more quickly than it is taken in; anaerobic respiration provides lactate to keep the muscles moving. Lactate buildup and lack of oxygen are the reasons for muscle fatigue and labored breathing during hard exercise.
Aerobic respiration occurs in three stages where a glucose molecule is the source of energy. The first stage is called glycolysis and does not require oxygen. In this stage, ATP molecules are used to help break down glucose into a substance called pyruvate, a molecule that transports electrons called NADH, two more ATP molecules, and carbon dioxide. Carbon dioxide is a waste product and is removed from the body.
The second stage is called the Krebs cycle. This cycle consists of a series of complex chemical reactions that generate additional NADH.
The final stage is called electron transport phosphorylation. During this stage, NADH and another transporter molecule called FADH2 carry electrons to the cells. Energy from the electrons is converted to ATP. Once the electrons have been used, they are donated to atoms of hydrogen and oxygen to make water.
Glycolysis in Respiration
Glycolysis is the first stage of all respiration. During this stage, every molecule of glucose is broken down into a carbon-based molecule called pyruvate, two ATP molecules, and two molecules of NADH.
Once this reaction has occurred, the pyruvate goes through a further chemical reaction called fermentation. During this process, electrons are added to the pyruvate to generate NAD+ and lactate.
In aerobic respiration, the pyruvate is further broken down and combined with oxygen to create carbon dioxide and water, which are eliminated from the body.
Pyruvate is a carbon-based molecule; each molecule of pyruvate contains three carbon molecules. Only two of these molecules are used to create carbon dioxide in the final step of glycolysis. Thus, after glycolysis there is loose carbon floating around. This carbon binds to various enzymes to create chemicals used in other capacities in the cell. The Krebs cycle reactions also generate eight more molecules of NADH and two molecules of another electron transporter called FADH2.
Electron Transport Phosphorylation
NADH and FADH2 carry electrons to specialized cell membranes, where they are harvested to create ATP. Once the electrons are used, they become depleted and must be removed from the body. Oxygen is essential for this task. Used electrons bind with oxygen; these molecules eventually bind with hydrogen to form water.
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