question_answer 3)

Even though a very few cells in a plant carry out the biosynthetic-Calvin pathway, yet they are highly productive. Can you discuss why?  

Answer:

plants chemically fix carbon dioxide in the cells of the mesophyll by adding it to the three-carbon molecule phosphoenolpyruvate (PEP), a reaction catalysed by an enzyme called PEP carboxylase. It creates the four-carbon organic acid, oxaloacetic acid. Oxaloacetic acid or malate synthesised by this process is then translocated to specialized bundle sheath cells where the enzyme, RuBisCO and other Calvin cycle enzymes are located and where CO2 released by decarboxylation of the four-carbon acids is then fixed by RuBisCO activity to the three-carbon sugar 3-phosphoglyceric acids. The physical separation of RuBisCO from the oxygen-generating light reactions reduces photorespiration and increases CO2 fixation and thus photosynthetic capacity of the leaf.