What part of an animal cell breaks down sugar to release energy?  

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Organic molecules like glucose provide the chemical energy or fuel that animals and other eukaryotic organisms use for the process of aerobic cellular respiration. The organelle where this process occurs is the mitochondria where ATP is produced as a result of respiration. ATP is a high energy compound that helps a cell to perform work including cell division, synthesis of organelles and growth.

During aerobic cellular respiration, glucose and oxygen are combined chemically and in this reaction, glucose is oxidized while oxygen is reduced. When glucose is oxidized, electrons are transferred to a lower energy state. Some of this energy is available for the production of ATP.

Glycolysis is the first step where glucose is broken down into two molecules of pyruvate. This occurs in the cytoplasm of the cell.

Next, pyruvate enters the mitochondrion and the citric acid cycle occurs which is followed by the electron transport chain and oxidative phosphorylation. As glucose is slowly broken down in a series of steps, eventually, electrons are accepted into the electron transport chain until they combine with oxygen and hydrogen ions to form water. The energy released at each step is used to make ATP. Specifically, ATP is created by the pumping of protons back into the inner mitochondrial membrane.

By the end of the process, a molecule of glucose is broken down to carbon dioxide, water and up to around 32 molecules of ATP. 



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