AP BIOLOGY

Detailed explanation-1: -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-2: -A key factor that helps create the pull of water up the tree is the loss of water out of the leaves through a process called transpiration. During transpiration, water vapor is released from the leaves through small pores or openings called stomates.

Detailed explanation-3: -Once water is in the xylem, it travels upwards-against the force of gravity-towards the rest of the plant. Water is able to move against gravity due to two forces: tension and cohesion. Tension is a ‘sucking force’ which is created when water evaporates from leaves (transpiration), pulling more water into the leaf.

Detailed explanation-4: -Thus, transpiration helps in the upward movement of water and dissolved minerals from the roots to the leaves through the stem.

Detailed explanation-5: -Osmosis plays a central role in the movement of water between cells and various compartments within plants. In the absence of transpiration, osmotic forces dominate the movement of water into roots.