Final answer:
c) Endodermis. The endodermis is the innermost layer of the root cortex that acts as a selectively permeable barrier to control the movement of water and dissolved minerals. It contains the Casparian strip, which forces substances to cross the endodermal cells' plasma membranes. This helps maintain the integrity of the root's vascular system and prevents the entry of harmful substances.
Step-by-step explanation:
The innermost layer of the root cortex, known as the endodermis, is a selectively permeable barrier that helps control the movement of water and dissolved minerals. It separates the stele, or vascular tissue, from the ground tissue in the outer portion of the root. The endodermis contains a waxy substance called the Casparian strip that forces water and solutes to cross the plasma membranes of endodermal cells, ensuring that only necessary materials pass through while excluding toxic substances and pathogens.