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Photorespiration is a process that involves the release of carbon dioxide in the presence of light.The process occurs when the enzyme responsible for carbon fixation in the Calvin cycle, Rubisco, binds oxygen instead of carbon dioxide (CO₂) and uses the fixed carbon to release carbon dioxide using ATP.

Thus, photorespiration is considered a wasteful pathway that uses up fixed carbon and wastes energy.

The majority of plants are C₃ plants. These plants fix carbon in the Calvin cycle by attaching CO₂ to RUBP (ribulose 1,5-diphosphate). C₃plants perform photorespiration and lose water through this process.

C₄ plants fix carbon dioxide in the cytoplasm by attaching CO₂ to phosphoenolpyruvate (PEP). These plants do not perform photorespiration, so they lose less water. Tropical grasses like sugarcane and corn are C₄ plants.

CAM plants fix carbon in the night to synthesize organic molecules. They do this to avoid water loss through transpiration. Succulents and pineapple are CAM plants.

Photorespiration is not a problem for C₃ plants because they lack specific traits. The C4 and CAM pathways, on the other hand, are two adaptations that aid some animals in reducing photorespiration. In these plants, Rubisco is constantly exposed to high levels of CO₂, preventing it from attaching to oxygen.

Carbon fixation happens in C₄ plants in the mesophyll cell, which is then broken down into bundle sheath cells to release CO₂. As a result, C4 plants reduce photorespiration by conducting initial CO₂ fixation and the Calvin cycle in different cell types.

On the other hand, carbon is fixed by CAM plants at night, whileCO₂is released during the day. By dividing these steps between night and day, CAM plants reduce photorespiration and conserve water.

As a result, most of the C₃ species would be replaced by C₄ and CAM species if the climate became hotter.