How does heartwood (duramen) fundamentally differ from sapwood (alburnum) in an old dicot tree trunk?

Answer and explanation

Correct answer: C. Heartwood is central, dead, and clogged with resins; sapwood is peripheral and conducts water

  1. Step 1: As a tree ages, the central older layers of secondary xylem become heavily infiltrated with organic compounds such as tannins, resins, oils, gums, and aromatic substances, turning dark brown (heartwood).
  2. Step 2: The lumens of heartwood tracheids and vessels become blocked by balloon-like parenchymatous ingrowths called tyloses, preventing water conduction.
  3. Step 3: Heartwood provides mechanical support and is highly resistant to decay and termites.
  4. Step 4: The peripheral, lighter-colored secondary xylem is sapwood (alburnum), which actively conducts water and mineral nutrients from roots to leaves.
Answer
Heartwood is dead, dark-colored, non-functional in water transport due to tyloses and organic deposits, but provides mechanical strength; sapwood is living, peripheral, and actively conducts water
Why not the others: 'Heartwood actively conducts sap upward...' inverts the physiological roles of heartwood and sapwood; 'Heartwood consists solely of primary phloem...' is false because both heartwood and sapwood are secondary xylem; 'Heartwood contains living parenchymatous cells...' is incorrect because all parenchyma cells in heartwood are dead.

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