Answer:
In cellular respiration, especially in the Krebs cycle, hydrogen is one of the many molecules present in glucose that become vital in order for energy, in the form of ATP, to be produced by the cell.
Originally, a molecule of glucose is conformed by 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms. Due to the chemical process of ATP production, which will give energy to cells, the hydrogen atoms from the glucose molecule will both procure the necessary electrons in order to energyze the process of ATP production, and generate waste products such as carbon dioxide and water. This happens thanks to the stimulating effects of the coenzymes NAD and FAD.
As such, the process would be: The hydrogen is bound to carbon molecules and oxygen, but given the right stimulus during cellular respiration, in the presence of further oxygen and coenzymes, in order to produce ATP, the bonds are broken and hydroxen is released from the glucose molecule. The chemical reactions, and the passage of the ions, will generate energy that will permit the production of ATP, and in the end, the leftover hydrogen atoms will combine with oxygen and carbon, again, to form carbon dioxide and water. This is, in a nutshell, what happens during the Krebs cycle.
