Cells of which of the following region of root is responsible for the growth of the root in length?

Zone of elongation is responsible for the growth of the root in length.

The cells of the region of the root known as the zone of maturation show protoplasmic modifications and attain maximum size in terms of cell wall thickening.

The zone of maturation is the region of the root where fully differentiated, specialized cells are found. In this region, the cells undergo protoplasmic modifications, such as the development of specialized organelles and the formation of subcellular structures, to carry out specific functions.

In addition, the cells in the zone of maturation also undergo maximum cell wall thickening, which helps to provide mechanical support and protect the root as it grows through the soil.