Which gas is produced as a byproduct of photosynthesis that is essential for aerobic respiration?

• A. Carbon dioxide
• B. Nitrogen
• C. Hydrogen
• D. Oxygen

Answer: (D)

Oxygen is produced during photosynthesis as a byproduct. In the light-dependent reactions, water molecules are split to replace electrons, and this process releases oxygen gas. That oxygen becomes available to living organisms for aerobic respiration, where it serves as the final electron acceptor in the mitochondria to fully oxidize glucose into carbon dioxide and water, yielding a large amount of ATP. Without oxygen, cells must rely on less efficient pathways that generate far less energy. So the gas released by photosynthesis that’s essential for aerobic respiration is oxygen. The other gases listed don’t fit this role here: carbon dioxide is a reactant in photosynthesis, while nitrogen and hydrogen aren’t produced as the byproduct in this context.