C4-plants show Kranz anatomy. In the leaves of C4-plants the vascular bundles are surrounded by bundle sheath of parenchymatous cells, which in turn are surrounded by mesophyll cells. In C4-plants the Hatch and Slack pathway involves two carboxylation reaction one taking place in chloroplast of mesophyll cells and other in chloroplast of bundle sheath cells. The initial CO2 fixation occurs in mesophyll cells where primary CO2 acceptor is phosphoenol pyruvate and formed oxaloacetate. The oxaloacetate is reduced to malic acid. From chloroplasts of mesophyll cells the malic acid is transferred to chloroplast of bundle sheath cells and decarboxylated to form CO2 and pyruvic acid. The CO2 is again fixed by C3 cycle. In plants, stoma is surrounded by two small, specialized, green epidermal cells called guard cells. The guard cells are small in size and therefore, rapidly influenced by turgor changes.