In photosynthesis, what is the fate of the oxygen atoms present in CO₂? They end up __________.

• A. as molecular oxygen
• B. in sugar molecules
• C. in water
• D. as molecular oxygen and in sugar molecules
• E. in sugar molecules and in water

Answer: (E)

Verified step by step guidance

1. Understand the process of photosynthesis: Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy stored in glucose. The general equation for photosynthesis is: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
2. Identify the role of CO₂: In photosynthesis, carbon dioxide (CO₂) is one of the reactants. The carbon atoms from CO₂ are used to form the backbone of glucose molecules (C₆H₁₂O₆).
3. Determine the fate of oxygen atoms in CO₂: The oxygen atoms in CO₂ are incorporated into the glucose molecule and also into water molecules. This is because during the Calvin cycle, CO₂ is fixed into organic molecules, and the oxygen atoms are rearranged to form both glucose and water.
4. Clarify the formation of water: During the light-dependent reactions of photosynthesis, water molecules are split (photolysis) to release oxygen gas (O₂), but the oxygen atoms from CO₂ are not involved in this process. Instead, they are used in the formation of glucose and water in the Calvin cycle.
5. Conclude the fate of oxygen atoms: Therefore, the oxygen atoms from CO₂ end up in sugar molecules (glucose) and in water, as they are incorporated into these compounds during the Calvin cycle of photosynthesis.