Final answer:
The one-cell thick inner layer of the root cortex is the endodermis, which regulates substances entering the plant's vascular system. The option (A) is correct.
Step-by-step explanation:
The one-cell thick inner layer of the root cortex is called the endodermis. The endodermis is a critical layer in plant roots that separates the stele, which is the inner portion of the root containing the vascular tissue, from the outer ground tissue. The presence of the Casparian strip, a waxy substance on the walls of endodermal cells, ensures that the substances entering the plant's vascular system are strictly regulated.
It makes sure that water and solutes must cross the plasma membranes of the endodermal cells, which allows only necessary nutrients to pass through while blocking toxins and pathogens. The vascular tissue differs between dicot and monocot roots, with dicot roots having an X-shaped arrangement of xylem and phloem and monocot roots having a vascular ring around the pith. Therefore, option (A) is correct.
This question is not complete, Here I am attaching the complete question:
The one-cell thick inner layer of the root cortex is called the________.
A) Endodermis
B) Pericycle
C) Epidermis
D) Pith