Photorespiration

Definition

Photorespiration is a metabolic process in plants that occurs when the enzyme RuBisCO oxygenates RuBP, leading to the consumption of energy and the release of CO2 instead of producing glucose during photosynthesis. This process typically happens under conditions of high oxygen levels and low carbon dioxide concentrations, causing inefficiency in the plant's ability to fix carbon and produce organic molecules using light energy.

5 Must Know Facts For Your Next Test

1. Photorespiration can reduce the overall efficiency of photosynthesis by as much as 25% in C3 plants due to the loss of fixed carbon.
2. This process occurs when oxygen levels are high relative to carbon dioxide, often during hot, dry conditions when plants close their stomata to conserve water.
3. Photorespiration results in the production of a two-carbon compound called glycolate, which is then processed through a series of reactions that can lead to energy loss.
4. Plants have developed different mechanisms, such as C4 and CAM pathways, to minimize photorespiration and improve carbon fixation efficiency.
5. Understanding photorespiration is crucial for improving crop yields, especially in changing climate conditions where elevated CO2 levels and temperature fluctuations can affect plant productivity.

Review Questions

• How does photorespiration affect the efficiency of photosynthesis in plants, particularly in C3 species?
  • Photorespiration negatively impacts photosynthesis efficiency by causing RuBisCO to fix oxygen instead of carbon dioxide, which leads to a decrease in glucose production. In C3 species, this process can reduce overall productivity by about 25% because it competes with the normal carbon fixation pathway. High oxygen levels and low carbon dioxide concentrations drive this process, especially during hot, dry conditions when stomata are closed.
• Discuss the role of RuBisCO in both photosynthesis and photorespiration. How does its activity change based on environmental conditions?
  • RuBisCO plays a central role in photosynthesis by catalyzing the fixation of carbon dioxide into ribulose bisphosphate during the Calvin cycle. However, its dual activity also allows it to react with oxygen instead of carbon dioxide under certain environmental conditions, leading to photorespiration. When oxygen levels are high and carbon dioxide levels are low—such as during drought stress—RuBisCO's affinity for oxygen increases, promoting photorespiration over efficient carbon fixation.
• Evaluate the implications of photorespiration on agricultural practices and crop yield improvement strategies in changing climates.
  • Photorespiration has significant implications for agriculture as it reduces the efficiency of photosynthesis and thus crop yields. In changing climates characterized by higher temperatures and fluctuating CO2 levels, understanding and mitigating photorespiration becomes crucial. Strategies such as developing genetically modified crops with reduced photorespiration rates or utilizing C4 and CAM pathways can enhance carbon fixation efficiency. By addressing photorespiration, agricultural practices can be optimized to improve crop resilience and productivity under stressful environmental conditions.

Related terms

RuBisCO:

Ribulose-1,5-bisphosphate carboxylase/oxygenase, an enzyme that catalyzes the first major step of carbon fixation in the Calvin cycle.

Calvin Cycle: A series of biochemical reactions occurring in the stroma of chloroplasts where CO2 is fixed into organic molecules using ATP and NADPH generated during photosynthesis.

C3 Plants: Plants that utilize the C3 pathway for photosynthesis, which involves the direct fixation of carbon dioxide into a 3-carbon compound, but are more susceptible to photorespiration.