Phloem Transports Organic Nutrients Downward

Steps:

• Bark includes phloem, which conducts organic nutrients from leaves to roots.
• Removing the phloem ring girdles the tree, blocking downward transport.
• Roots lack organic nutrients like sugars, starving the tree.
• Without root nourishment, the tree dies.

Why B is correct:

• Phloem sieve tubes transport organic nutrients (e.g., sucrose) from photosynthetic sites to non-photosynthetic tissues like roots, per vascular tissue function in plants.

Why the others are wrong:

• A: Mineral salts move upward in xylem, not affected by phloem removal.
• C: Oxygen reaches roots via diffusion through soil, not vascular transport.
• D: Water ascends through xylem vessels, independent of phloem.

Final answer: B