we need energy for various body activities the energy comes from the food we eat every day in our body chemical energy stored in food is released through a process called respiration respiration can take place with or without oxygen respiration that requires oxygen is called called aerobic respiration it occurs in three main stages namely glycolysis kreb cycle and oxidative [Music] phosphorilation glycolysis is the first stage of aerobic respiration it occurs in the cytoplasm of the cell first glucose is activated by phosphorilation two molecules of ATP are used next the activated glucose is broken down into two molecules of trios phosphate which is a three carbon compound each trios phosphate molecule is then oxidized to another three carbon compound called pyruvate in this process ATP is formed and NAD is reduced to nadh glycolysis is completed the crebs cycle is the second stage of aerobic respiration before proceeding to it the pyruvate forming glycolysis enters the mitochondrian in the mitochondrial Matrix a carbon atom is removed from the pyruvate and released as carbon dioxide the remaining two carbon compound loses hydrogen which is accepted by NAD to form nadh the two carbon compound then combines with co-enzyme a to form acetal COA the acetal COA then enters the Krebs cycle the kreb cycle also occurs in the mitochondrial Matrix the acetal COA formed before combines with a four carbon compound already present in the mitochondrial Matrix to form a six carbon [Music] compound co-enzyme a is regenerated in the process the six carbon compound is then oxidized step by step to regenerate the four carbon compound during the oxidation two carbon atoms are removed from the six carbon compound and released as carbon dioxide the six carbon compound also loses hydrogen atoms which are accepted by NAD and fad to form nadh and fad H ATP is also formed the four carbon compound then accepts other acetal COA to form the six carbon compound the cycle is [Music] repeated oxidative phosphorilation is the final stage of aerobic respiration it occurs on the inner membrane of the mitochondrion the nadh and fadh formed in glycolysis and the kreb cycle lose hydrogen and are oxidized to NAD and fad respectively the NAD and fad are regenerated to accept hydrogen in glycolysis and the Krebs cycle again the hydrogen atom split into hydrogen ions and electrons the electrons take part in a series of Redux reactions along the electron transport chain forming ATP finally the hydrogen ions and electrons are transferred to oxygen the final electron acceptor to form water [Music]