Photosynthesis in Higher Plants

In $\mathrm{C}_3$ plants, all the reactions of $\mathrm{C}_3$ or Calvin cycle occur in mesophyll cells of leaves while $\mathrm{C}_4$ plants show a distinct type of anatomy called as Kranz anatomy, where two different regions mesophyll cells and bundle sheath, are involved in this process.

The assertion is true, but the reason is false. In $\mathrm{C}_3$ cycle, the first stable compound is $3 \mathrm{C}$ compound - the phosphoglycerate, which is formed by the carboxylation of RuBP by one molecule of $\mathrm{CO}_2$ in the presence of RuBP carboxylase.

In $\mathrm{C}_4$ plants, the first $\mathrm{CO}_2$-fixation product is a $4 \mathrm{C}$-oxaloacetic acid, but they use $\mathrm{C}_3$ pathway or Calvin cycle as the main biosynthetic pathway for carbon-fixation (carboxylation), which occurs in the bundle sheath cells of leaves.

A plant with the $\mathrm{C}_4$ pathway is advantageous over a plant with a $\mathrm{C}_3$ pathway as the former can occur in low $\mathrm{CO}_2$ concentrations. When the weather is hot and arid, the leaves close their stomata to reduce water loss. This closure results in low $\mathrm{CO}_2$ concentrations and thus, leading to both loss of RuBP and inhibition of Calvin-Benson cycle.

Non-cyclic photophosphorylation occurs in granum of chloroplast. It is an association of photosystem-I and II. In this process, electron continuously flows from water to PS-II to PS-I and then to final electron acceptor. In this process, ATP is formed from ADP and O$_2$ is evolved.