Which one of the following regions in plants is responsible for the growth of its roots and shoots?

The correct answer is D, Apical meristem. Apical meristems sit at the tips of roots and shoots, and their dividing cells make the plant grow in length.

Meristems are groups of cells that keep dividing throughout a plant's life. Apical meristem, at the root tip and the shoot tip, causes primary growth, that is, increase in length of the root and the stem. Lateral meristem, such as the vascular cambium and cork cambium, adds to the girth of stems and roots, which is secondary growth. Intercalary meristem, found at the base of leaves or internodes in grasses, helps those parts grow back after grazing or cutting. New cells formed by meristems later change into permanent tissues.

A is wrong because collenchyma is a simple permanent tissue that gives flexible support, not growth. B is wrong because the endodermis is the innermost layer of the cortex that controls water entry into the vascular core. C is wrong because the cortex is a storage region between the epidermis and the vascular tissue.

Exam tip: apical meristem gives length, lateral meristem (cambium) gives girth, intercalary meristem regrows grasses.