Fact 1: Oxygen is essential for cellular respiration for all aerobic organisms.

Fact 2: Besides nitrogen and oxygen, the atmosphere contains many, many other molecules in trace amounts.

Given the two facts above, answer the question "What is essential for cellular respiration?" with the following options: 
- Veins and arteries.
 - kinetic energy
 - The atmosphere
 - Energy.
 - heat energy
 - Organic compounds
 - Chemical energy
 - flow of electrons


 

   The atmosphere      