In a plant root, the one structure that water cannot move past via the apoplast is the __________.

• A. epidermis
• B. pericycle
• C. cortex
• D. vascular tissues
• E. endodermis

Answer: (E)

Verified step by step guidance

1. Understand the concept of apoplast and symplast pathways in plant roots. The apoplast pathway involves the movement of water through the cell walls and intercellular spaces, while the symplast pathway involves movement through the cytoplasm of cells connected by plasmodesmata.
2. Identify the role of the endodermis in plant roots. The endodermis is a layer of cells that surrounds the vascular tissues and acts as a selective barrier.
3. Recognize the presence of the Casparian strip in the endodermis. The Casparian strip is a band of cell wall material that is impregnated with suberin, a waxy substance that is impermeable to water and solutes.
4. Understand that the Casparian strip forces water and solutes to move from the apoplast into the symplast to cross the endodermis. This ensures that all substances entering the vascular tissues are filtered by the cell membranes.
5. Conclude that the endodermis, due to the Casparian strip, is the structure that water cannot move past via the apoplast pathway, thus requiring a shift to the symplast pathway.