Photorespiration

Definition

Photorespiration is a process that occurs in plants when the enzyme RuBisCO oxygenates ribulose bisphosphate instead of carboxylating it, leading to the production of a two-carbon molecule that must be converted back to three-carbon compounds. This process is often considered wasteful as it consumes energy and carbon, reducing the efficiency of photosynthesis, particularly under conditions of high light intensity and low carbon dioxide concentrations.

5 Must Know Facts For Your Next Test

1. Photorespiration can occur more frequently in hot, dry conditions when plants close their stomata to conserve water, which limits carbon dioxide intake.
2. This process can reduce the overall efficiency of photosynthesis by up to 50% in some species, impacting plant growth and agricultural yields.
3. Plants have evolved various adaptations to minimize photorespiration, including C4 and CAM pathways that concentrate carbon dioxide around RuBisCO.
4. Photorespiration produces one molecule of glycolate, which is then metabolized in a series of reactions that ultimately recycle some of the carbon lost during the initial reaction.
5. Understanding photorespiration is crucial for improving crop efficiency and yield, as researchers explore genetic engineering and selective breeding to enhance photosynthetic pathways.

Review Questions

• How does photorespiration affect the efficiency of photosynthesis in plants?
  • Photorespiration negatively impacts photosynthesis by causing RuBisCO to bind with oxygen instead of carbon dioxide. This leads to the production of a two-carbon compound instead of three-carbon sugars, reducing the overall output of energy and biomass. The occurrence of photorespiration can significantly lower the efficiency of photosynthesis, especially under stressful environmental conditions such as high temperatures and low CO2 levels.
• What adaptations do plants utilize to mitigate the effects of photorespiration and how do they function?
  • To counteract photorespiration, some plants have developed adaptations like C4 and CAM pathways. C4 plants initially fix carbon dioxide into four-carbon compounds that are then transported to specialized cells where they release CO2 for use in the Calvin cycle, effectively reducing oxygenation by RuBisCO. CAM plants, on the other hand, open their stomata at night to take in CO2 and store it as organic acids, releasing it during the day when light is available for photosynthesis. These strategies help maintain higher efficiency in photosynthesis under varying environmental conditions.
• Evaluate the implications of photorespiration on global agriculture and how advancements in plant biology might address these challenges.
  • Photorespiration poses significant challenges to global agriculture by reducing crop yields, particularly in environments prone to heat stress or water scarcity. With growing concerns about food security due to climate change, understanding photorespiration is vital. Advancements in plant biology, such as genetic modification and selective breeding aimed at enhancing C4 traits or minimizing photorespiration pathways, hold promise for developing crops that can thrive under adverse conditions. By increasing photosynthetic efficiency through these innovations, farmers may be able to achieve greater yields while using fewer resources.

Related terms

RuBisCO: Ribulose bisphosphate carboxylase/oxygenase, the enzyme responsible for fixing carbon dioxide during photosynthesis, but also has the potential to catalyze a reaction with oxygen.

C3 Photosynthesis: A type of photosynthesis where carbon fixation occurs through the Calvin cycle, using RuBisCO as the primary enzyme, and is the most common form found in many plants.

Stomata: Small openings on plant leaves that regulate gas exchange, allowing carbon dioxide to enter and oxygen to exit, playing a key role in photosynthesis and photorespiration.