What is photorespiration?

What is photorespiration?

• A. A wasteful process that uses energy and decreases sugar synthesis; occurs when Rubisco binds to oxygen.
• B. The process by which plants split water during photosynthesis.
• C. The light-dependent reactions of photosynthesis.
• D. A pathway that fixes CO2 into glucose.

Answer: (A)

Photorespiration happens when the enzyme Rubisco binds oxygen instead of carbon dioxide during carbon fixation. This tends to occur when the leaf’s internal O2/CO2 ratio is high, such as in bright, hot conditions when stomata close to conserve water. The oxygenation reaction starts a salvage pathway that uses ATP and NADPH and releases CO2, so no net sugar is produced. Because it burns energy and reduces carbon gain, it’s considered wasteful relative to productive sugar synthesis. It’s distinct from splitting water, the light-dependent reactions, or fixing CO2 into glucose, and some plants have strategies (like C4 or CAM pathways) to minimize this loss.

Photorespiration happens when the enzyme Rubisco binds oxygen instead of carbon dioxide during carbon fixation. This tends to occur when the leaf’s internal O2/CO2 ratio is high, such as in bright, hot conditions when stomata close to conserve water. The oxygenation reaction starts a salvage pathway that uses ATP and NADPH and releases CO2, so no net sugar is produced. Because it burns energy and reduces carbon gain, it’s considered wasteful relative to productive sugar synthesis. It’s distinct from splitting water, the light-dependent reactions, or fixing CO2 into glucose, and some plants have strategies (like C4 or CAM pathways) to minimize this loss.