Q.Differentiate: Xylem and Phloem functioning

Step 1. Composition and living state: xylem's conducting cells (tracheids, vessels) are dead at maturity; phloem's conducting cells (sieve tubes) are alive, though they lose their nucleus, and are actively kept functioning by their companion cells.

Step 2. What is conducted: xylem conducts water and dissolved minerals absorbed by the roots, moving them upward to the shoot and leaves; phloem conducts organic food (mainly sugars) manufactured in a source tissue (usually a photosynthesising leaf) to sink tissues (roots, growing points, developing fruits/seeds, storage organs) — so phloem transport can run in different directions depending on where the current source and sink are.

Step 3. Mechanical role: because xylem cell walls are heavily lignified, xylem doubles as the plant's main mechanical/support tissue, giving rigidity to stems, leaves and other organs; phloem, being mostly living and thin-walled (aside from its fibres), contributes comparatively little mechanical support — what support it does provide comes from phloem fibres, which are largely confined to secondary phloem. …

Contrast xylem and phloem on living state, direction/substance conducte …

• Saying phloem transport is always 'downward' — it actually runs from wherever the current source is to wherever the current sink is, which is not fixed to one direction. …