The Outer Boundary of a Root's Vascular Cylinder is a Layer

Question

The outer boundary of a root's vascular cylinder is a layer of cells called ____.  
A) pericycle
B) cortex
C) epidermis
D) stele
E) endodermis

Accepted Answer

The endodermis is the outermost layer of cells in the vascular cylinder of a root, and it has a specialized structure with a casparian strip which regulates the movement of water and nutrients into and out of the root. The pericycle is a layer of cells located just inside the endodermis and is responsible for lateral root formation. The cortex is the layer of cells between the epidermis and the endodermis and is responsible for storage of nutrients. The epidermis is the outermost layer of cells in the root and is responsible for protecting the root from damage and absorbing water and nutrients. The stele is the collective term used to describe the entire vascular cylinder of a root, including the endodermis, pericycle, and vascular tissues.