which carbohydrate does the body use for energy production during respiration
Carbohydrate metabolism Although humans consume a variety of carbohydrates, digestion breaks down complex carbohydrates into a few simple monomers (monosaccharides) for metabolism: glucose, fructose, and galactose.[4] Glucose constitutes about 80% of the products, and is the primary structure that is distributed to cells in the tissues, where it is broken down or stored as glycogen.[3][4] In aerobic respiration, the main form of cellular respiration used by humans, glucose and oxygen are metabolized to release energy, with carbon dioxide and water as byproducts.[2] Most of the fructose and galactose travel to the liver, where they can be converted to glucose.[4]
Lipid Triglycerides, stored in adipose tissue, are a major form of energy storage both in animals and plants. They are a major source of energy because carbohydrates are fully reduced structures. In comparison to glycogen which would contribute only half of the energy per its pure mass, carbohydrate carbons are all bounded to hydrogens unlike in carbohydrates.[66] The adipocyte, or fat cell, is designed for continuous synthesis and breakdown of triglycerides in animals, with breakdown controlled mainly by the activation of hormone-sensitive enzyme lipase.[67] The complete oxidation of fatty acids provides high caloric content, about 38 kJ/g (9 kcal/g), compared with 17 kJ/g (4 kcal/g) for the breakdown of carbohydrates and proteins. Migratory birds that must fly long distances without eating use stored energy of triglycerides to fuel their flights.[68]