Transpiration occurs via evaporation in leaf air spaces

Steps:

• Water moves from soil through roots and xylem to leaf veins.
• From veins, water diffuses into mesophyll cells and surrounding air spaces.
• In air spaces, water molecules gain energy and evaporate from cell walls.
• Water vapor then exits through stomata to the atmosphere.

Why C is correct:

• Evaporation happens in the intercellular air spaces of the mesophyll, where high surface area and humidity gradient drive transpiration per the cohesion-tension theory.

Why the others are wrong:

• A: Xylem conducts liquid water upward but lacks evaporation sites.
• B: Veins transport water without exposing it to air for evaporation.
• D: Stomata allow vapor exit but evaporation precedes this in internal spaces.

Final answer: C