Step 1 : Introduction to the question "4. Photosynthesis and cellular respiration are opposite cell processes. One puts this compound into the atmosphere and the other one takes it out. Which compound fits this description?"
...1. Nitrogen 2. Carbon Monoxide 3. Hydrogen 4. Carbon Dioxide Another substance that would have fit this description is oxygen, but it's an element, not a compound. Photosynthesis and cellular respiration are opposite processes because their chemical equations are reversed. Also, one stores energy while the other releases it.
