Assertion (A) : In C₄ plants photorespiration does not occur.

Reason (R) : They have a mechanism in which C₄ acid from mesophyll cell is transported to bundle sheath cell thereby increasing CO₂ concentration in the site of RuBisCO.

This assertion is correct. C₄ plants indeed exhibit a significantly reduced rate of photorespiration compared to C₃ plants. The biochemical and anatomical adaptations in C₄ plants help minimize the wasteful effects of photorespiration, making it a much less prominent process in these plants. 

This reason is correct. C₄ plants have evolved a unique carbon fixation mechanism known as the C₄ pathway. In this pathway, C₄ plants initially fix carbon dioxide into a 4-carbon compound called oxaloacetate in the mesophyll cells of the leaves. 

The 4-carbon compounds are then transported to bundle sheath cells, which are arranged in a ring around the vascular bundles within the leaf. In the bundle sheath cells, the 4-carbon compounds are decarboxylated to release carbon dioxide, which diffuses into the vicinity of RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) enzyme. RuBisCO then fixes this carbon dioxide into the Calvin cycle to produce sugars.

By concentrating carbon dioxide around RuBisCO in the bundle sheath cells, the C₄ pathway helps reduce the wasteful oxygenation of RuBisCO that leads to photorespiration. The higher CO₂ concentration and reduced oxygen concentration in the vicinity of RuBisCO favor carboxylation (fixation of CO₂) over oxygenation (formation of phosphoglycolate), reducing the occurrence of photorespiration.

A and R are true and R is the correct explanation of A.