Introduction of Photorespiration | Biology Class 11 - NEET PDF Download

Photorespiration 

Photorespiration is a plant metabolic process that primarily occurs in the cells of the leaves. It is considered a wasteful pathway that competes with photosynthesis, potentially impacting plant growth and productivity. This process is triggered under conditions where the concentration of carbon dioxide (CO₂) is low and the concentration of oxygen (O₂) is high.

What is Photorespiration?

Photorespiration is a metabolic process that occurs during the Calvin cycle, also known as the C2 Cycle. The enzyme RuBisCO plays a significant role in photorespiration. This process is particularly important in C3 plants as a mechanism to manage the inefficiencies of RuBisCO.

During photorespiration, oxygen (O₂) is utilized, and carbon dioxide (CO₂) is released in the presence of light. It shares similarities with the process of respiration, where O₂ is consumed, and CO₂ is produced.

Organelles involved in Photorespiration

Three cell organelles are implicated in photorespiration:

• Chloroplast
• Peroxisomes
• Mitochondria

Photorespiration is the Wasteful Product

• When the level of CO₂ surrounding the cell drops, photorespiration is initiated.
• Photorespiration commences with the oxygenation of ribulose-1,5-bisphosphate-carboxylase/oxygenase (RUBISCO), the key enzyme responsible for CO₂ fixation in nearly all photosynthetic organisms.
• Phosphoglycerate produced in the presence of oxygen is recycled in the Calvin cycle amidst phosphoglycerate in the Photorespiratory pathway.
• This process consumes excess energy and diminishes the yields, with a portion of the previously fixed carbon being released as CO2.
• Consequently, photorespiration has often been viewed as an inefficient process.
• In photorespiration, oxygen binds with the enzyme Rubisco, yielding 3-Phosphoglycerate in a reduced setting and requiring substantial energy expenditure.

Factors influencing Photorespiration

• In submerged, stressful conditions, higher light intensity leads to increased photorespiration.
• Temperature plays a significant role in influencing photorespiration.

Benefits of Photorespiration

• Photorespiration contributes to plant defense mechanisms, enhancing their resilience.
• It aids in maintaining the redox balance within the cell.

Significance of Photorespiration

• Photorespiration acts as the opposite process of photosynthesis.
• It reduces the efficiency of photosynthesis.
• Photorespiration is an inefficient cycle since it does not produce ATP or NADPH.