Dye Uptake and Xylem Transport in Plants

Steps:

• Roots absorb water and dissolved dye from the soil via osmosis and active transport.
• Dye moves upward through the xylem vessels in the vascular tissue.
• After 4 hours, dye reaches the stem but not leaves, as transport is unidirectional.
• Cross-sections reveal dye in root and stem vascular bundles, appearing as dark spots.

Why A is correct:

• Diagram A shows black dye concentrated in the central vascular cylinder of roots and scattered upward in stem xylem, matching xylem transport pathway.

Why the others are wrong:

• B: Dye only in roots, ignores upward transport to stem.
• C: Dye throughout entire stem cross-section, contradicts confinement to xylem.
• D: No dye in roots, violates initial absorption site.

Final answer: A