Stroma of chloroplast and peroxisomes .Photorespiration is a process the rate of which increases under the influence of light CO2, is released and O2 is used but no ATP is formed. It involves three organelles chloroplasts, mitochondria and peroxisomes.

During photorespiration, the oxygen-consuming reaction occurs in the stroma of chloroplasts and peroxisomes.

Introduction:
Photorespiration is a metabolic process that occurs in plants when there is a high ratio of oxygen to carbon dioxide. It is considered to be a wasteful process as it reduces the efficiency of photosynthesis. Photorespiration mainly takes place in the chloroplasts and peroxisomes of plant cells.

Explanation:

1. Chloroplasts:
Chloroplasts are responsible for photosynthesis, the process by which plants convert light energy into chemical energy in the form of glucose. However, under certain conditions, such as high temperatures or low carbon dioxide levels, the oxygen-consuming reaction of photorespiration occurs in the stroma of chloroplasts.

2. Peroxisomes:
Peroxisomes are membrane-bound organelles found in plant cells. They play a crucial role in various metabolic processes, including photorespiration. During photorespiration, peroxisomes help in the oxidation of glycolate, a byproduct of the oxygen-consuming reaction. This oxidation reaction occurs in the peroxisomes, leading to the production of hydrogen peroxide.

3. Oxygen-consuming reaction:
The oxygen-consuming reaction of photorespiration involves the enzyme Rubisco, which is found in the stroma of chloroplasts. Rubisco normally functions as a carboxylase during photosynthesis, but under high oxygen conditions, it acts as an oxygenase. This oxygenase activity leads to the production of glycolate, which is then metabolized in the peroxisomes.

Conclusion:
In conclusion, the oxygen-consuming reaction during photorespiration occurs in both the stroma of chloroplasts and peroxisomes. The stroma of chloroplasts is where the initial oxygenation of ribulose-1,5-bisphosphate (RuBP) takes place, while peroxisomes are involved in the subsequent oxidation of glycolate. Understanding the molecular mechanisms of photorespiration is important for improving crop productivity and developing strategies to mitigate the negative impacts of this metabolic pathway on plant growth and yield.