Oxygen is essential for cellular respiration for all aerobic organisms, and besides nitrogen and oxygen, the atmosphere contains many, many other molecules in trace amounts. Given these facts, what is essential for cellular respiration among the following options:
- Veins and arteries.
 - kinetic energy
 - The atmosphere
 - Energy.
 - heat energy
 - Organic compounds
 - Chemical energy
 - flow of electrons


 

   The atmosphere      