Glucose is broken down through cellular respiration, which involves a large number of chemical reactions. At the end of the cellular respiration process, a large number of ATP molecules are generated, but yet, not all of the possible energy that is contained in a molecule of glucose can be harnessed through these chemical reactions to generate ATP. In other words, during cellular respiration, not all of the energy that is contained in a molecule of glucose is converted into the energy stored in ATP. What happens to the remaining energy?

A. It is destroyed

B. It is used to drive exergonic reactions

C. It is donated to molecules in the cellular respiration process to reduce them

D. It is lost as heat

Lost as heat

Explanation:

Cellular respiration follows the laws of thermodynamics and is not a 100% efficient process of energy transformation. The process stores the energy released from the breakdown of glucose in the form of ATP. Since none of the energy transformation processes is 100% efficient and part of the energy is always lost as heat, cellular respiration also loses part of the energy of glucose as heat.

The total energy content of one glucose molecule is 686 kcal. The energy content of one ATP molecule is 7.3 kcal and a total of around 36 ATPs are produced by the breakdown of one glucose molecule through cellular respiration. Therefore, a total of 36 x 7.3 = 263 kcal energy is stored in the form of ATP while the rest of the energy of glucose is lost as heat.