AP BIOLOGY

Detailed explanation-1: -Transpiration i.e., evaporation of water molecules from the cells of the leaf creates a suction force (transpiration pull) which pulls water in the xylem vessels.

Detailed explanation-2: -Transpiration is ultimately the main driver of water movement in xylem. The cohesion-tension model works like this: Transpiration (evaporation) occurs because stomata are open to allow gas exchange for photosynthesis.

Detailed explanation-3: -Root pressure is caused by active distribution of mineral nutrient ions into the root xylem. Without transpiration to carry the ions up the stem, they accumulate in the root xylem and lower the water potential. Water then diffuses from the soil into the root xylem due to osmosis.

Detailed explanation-4: -The greatest contribution of root pressure may be to re-establish the continuous chains of water molecule in the xylem vessel which often break under enormous tension created by transpiration.

Detailed explanation-5: -Xylem is a complex permanent tissue which is responsible for the transportation of water and minerals from the roots to different parts of the plant.