Mass flow in phloem from leaves to roots

Steps:

• Recognize W as the transport tissue for organic solutes: phloem.
• Identify X as the tissue for water and minerals: xylem.
• Label Y as the source of sugars: leaves.
• Label Z as the sink for storage: roots.
• Determine flow in W: downward from source to sink.

Why B is correct:

• Phloem translocation moves sugars via mass flow from source (leaves) to sink (roots), driven by pressure gradients.

Why the others are wrong:

• A: Reverses direction; phloem flows from leaves to roots, not roots to leaves.
• C: Swaps phloem/xylem labels and inverts flow direction.
• D: Misassigns phloem to X and reverses sink-to-source flow.

Final answer: B