Hint: Food is converted into energy by the process called cellular respiration. Energy is produced in the form of ATP. There are two types of respiration; one in presence of oxygen known as aerobic respiration and the other is anaerobic respiration in the absence of oxygen.
Complete answer: Food is converted into energy by the process of cellular respiration which may occur in the presence or absence of oxygen, i.e. aerobic and anaerobic respiration respectively. Aerobic respiration occurs in the cytoplasm and mitochondria. Examples of anaerobic respiration include alcoholic fermentation that leads to the formation of ethanol and energy and lactic acid fermentation that leads to the fermentation of lactic acid. Aerobic respiration occurs in the presence of oxygen and it occurs in the cytoplasm and mitochondria. Steps involved in aerobic respiration are as follows:
a) Glycolysis: One molecule of glucose (6 carbons) is broken down into two molecules of pyruvic acid. This process occurs in the cytoplasm. Two molecules of pyruvic acid, two molecules of ATP and two molecules of NADH are the end product of glycolysis.
b) Kreb’s cycle: Pyruvic acid after being transferred into the mitochondria, is converted into Acetyl CoA. Two molecules of ATP, two molecules of NADH and two molecules of FADH2 are produced. This cycle is also known as the tricarboxylic acid cycle or the citric acid cycle.
c) Electron transport chain and oxidative phosphorylation: Electrons are transferred through a chain of electron carriers that results in electron gradient in ETS, as a result of which produces ATP from ADP.
Note: ATP is regarded as the currency of the cell. It drives all the important biochemical reactions of the body. For example; ATP is required in the photosynthetic process in plants.