Answer the following question: 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, what is essential for cellular respiration?

Select from the following.
1). Veins and arteries.;
2). kinetic energy;
3). The atmosphere;
4). Energy.;
5). heat energy;
6). Organic compounds;
7). Chemical energy;
8). flow of electrons;
Answer:
3).