Energy is generated by glyolysis and aerobic respiration which contributes to approximately 252kcal. This is only 37% of total energy of glucose i.e 686kcal/mol.
According to the second law of thermodynamics all of the energy cannot be converted into work done i.e most of the energy is lost in the form of heat.
So, there 63% of the energy present in glucose is lost in the form of heat and 37% of the total energy is used for cellular respiration
