Mitochondrion
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Diagram of a mitochondria.
The mitochondrion (plural is mitochondria) is also crucial to the survival of a cell and plant. Its main function is to provide energy to the cell and plant in the form of ATP, or adenosine triphosphate. It is made of a adenine molecule, a ribose molecule, and three phosphate groups. Mitochondria are shaped like kidney beans, with a inner and outer membrane. The inner membrane is folded many times, and it encloses a fluid called the matrix. Mitochondria are sometimes called the "powerhouse" of the cell, because it is the site of cellular respiration, where energy for the cell and the plant is produced. Cellular respiration requires glucose, a sugar, which comes from photosynthesis in chloroplasts, along with oxygen to produce water, carbon dioxide, and ATP. The process starts outside the mitochondrion with glycolysis, where the glucose is broken down into two pyruvic acid molecules. This requires an initial input of two ATP. It also fills up NAD+ molecules with electrons to make them NADH molecules. The next stage is called the Krebs Cycle. It takes place in the matrix. The Krebs Cycle uses the pyruvic acid, which was converted into acetyl coenzyme A, to combine with a four carbon chain to produce carbon dioxide and ATP. It also fills more NAD+ molecules with electrons. The NADH molecules then go to the folded inner membrane for the last step of cellular respiration. The electrons go through an electron transport chain, which pumps H+ ions across the membrane into the space between the inner and outer membrane. These then flow back through a structure called ATP synthase, which produces ATP from ADP and a phosphate group.