Endodermis blocks apoplastic water flow in roots

Steps:

• Identify the apoplastic pathway as water movement through cell walls and intercellular spaces.
• Recall that in plant roots, a barrier forces water into the symplastic pathway for selective absorption.
• Examine the transverse section for root tissues: epidermis, cortex, endodermis, pericycle, and stele.
• Locate the endodermis, which contains the Casparian strip inhibiting apoplastic flow.

Why B is correct:

• The endodermis has the Casparian strip, a waxy band that seals cell walls, blocking apoplastic water movement per the symplast-apoplast route definition.

Why the others are wrong:

• A (epidermis): Outer layer absorbs water but allows apoplastic flow freely.
• C (cortex): Parenchyma tissue permits unrestricted apoplastic passage.
• D (pericycle): Inner layer initiates lateral roots, not involved in pathway inhibition.

Final answer: B