Leaf water transport via osmosis, evaporation, and diffusion

Steps:

• Stage 1-2: Water moves from xylem into mesophyll cells across a semi-permeable membrane due to lower water potential inside cells.
• Stage 3-4: Water evaporates from moist cell walls into air spaces within the leaf.
• Stage 4-5: Water vapor diffuses from high concentration in air spaces to low concentration outside through stomata.
• Match processes to stages: osmosis for uptake, evaporation for liquid-to-gas change, diffusion for vapor exit.

Why D is correct:

• Osmosis is passive water movement down a potential gradient into cells (definition); evaporation converts liquid water to vapor at mesophyll surfaces; diffusion moves vapor along its concentration gradient per Fick's law.

Why the others are wrong:

• A: Misplaces diffusion and osmosis; diffusion doesn't drive initial cell entry.
• B: Swaps diffusion and evaporation; evaporation precedes vapor diffusion.
• C: Starts with evaporation, but osmosis initiates cellular uptake before evaporation.

Final answer: D