<span> Oxygen is produced by plants and green-blue algae and consumed by weathering and burning. And yes, also by animals breathing, but that's actually pretty marginal. Oxygen levels are far from constant. There is evidence that in the last 500 million years it fluctuated between 15% and 30% percent.
B.) ATP contains a 5-carbon sugar, three phosphate groups, and an adenine base. Energy is released when the bond between the second phosphate group and the third phosphate group is broken.
Every action has an equal and opposite reaction. I would assume that the energy in the other direction would be an action.. though I'm not entirely sure. I hope it helps.
