Heat of Respiration
Converting one form of energy into another always generates waste energy. In the case of respiration, chemical energy of organic molecules is converted into chemical energy of ATP, but most of the energy ends up somewhere else.
In the process of the respiration of glucose, 36 molecules of ATP is generated. Efficiency is simply the useful energy that results from a process, divided by the total energy that enters the process, times 100. In this case
The total efficiency is 38%. The energy not conserved as ATP energy, is lost as heat as demonstrated to the left.
While the generation of heat is unavoidable, in certain cases, the heat may be of benefit to the organism.
Follow the links below for two examples: