In oxygenic photosynthesis (as in plants, algae, and cyanobacteria), which substance is released as a waste product when water is split during the light reactions?

• A. Carbon dioxide ($C_{O}2$)
• B. Water ($H_{2}O$)
• C. Oxygen ($O_2$)
• D. Glucose ($C_6{H}_{12}{O}_6$)

Answer: (C)

Verified step by step guidance

1. Understand that oxygenic photosynthesis occurs in plants, algae, and cyanobacteria, where light energy is used to split water molecules during the light reactions.
2. Recall the light reactions involve the splitting of water (H\_2O) molecules to provide electrons and protons for the photosynthetic electron transport chain.
3. Recognize that when water is split, it produces electrons, protons (H\^+), and a waste product.
4. Identify the waste product released during this process as molecular oxygen (O\_2), which is released into the atmosphere.
5. Note that carbon dioxide (CO\_2) is actually used in the Calvin cycle (dark reactions) to produce glucose (C\_6H\_{12}O\_6), not released as a waste product during water splitting.