Key Processes in Transpiration Stream

Steps:

• Recall water moves from roots to atmosphere via xylem as a continuous column driven by transpiration.
• Evaporation from leaf mesophyll cells creates tension pulling water upward.
• Cohesion between water molecules maintains the column against gravity.
• Diffusion enables water vapor to exit stomata into the atmosphere.
• Verify which option marks all three processes as required.

Why A is correct:

• All three processes are essential per the cohesion-tension theory, where evaporation drives pull, cohesion sustains the column, and diffusion releases vapor.

Why the others are wrong:

• B marks none required, ignoring their roles in water transport.
• C omits cohesion, which is vital for unbroken xylem flow.
• D omits cohesion, which is vital for unbroken xylem flow.

Final answer: A