Question

Grasses have an adaptive mechanism to compensate photorespiratory lossesName and describe the mechanism.

Answer 1

The photorespiratory losses are checked by certain grasses by having physiological adaptation. The process of photosynthesis occurs in mesophyll cells and bundle sheath cells.

• Mesophyll cells:

1. Initially, CO₂ is taken up by Phosphoenolpyruvate (PEPA) (3C) and changed to oxaloacetate (4C) in the presence of PEP carboxylase.
2. Oxaloacetate is reduced to Malate/Aspartate. The product formed reaches the bundle sheath.

• Bundle Sheath:

1. The oxidation of Malate and Aspartate occurs with the release of carbon dioxide and the formation of Pyruvate (3C)
2. Due to increased CO₂ concentration RUBISCO functions as a carboxylase and not as Oxygenase.
3. The photosynthetic losses are prevented.
4. RUBP operates now under the Calvin cycle and pyruvate transported back to Mesophyll cells is changed into Phosphoenolpyruvate to keep the cycle going.