What is the ultimate source of energy that moves water upward in the trunk of a tree?

• A. Contraction of xylem cells
• B. Pressure exerted by root cells
• C. Breakdown and release of energy of sugar molecules
• D. Osmotic changes caused by alterations in salt content
• E. Evaporation of water by the sun

Answer: (E)

Verified step by step guidance

1. Understand the process of transpiration: Transpiration is the movement of water through a plant and its evaporation from aerial parts, such as leaves, stems, and flowers. This process is crucial for moving water upward in the trunk of a tree.
2. Identify the role of the sun: The sun provides the energy necessary for evaporation. When sunlight hits the leaves, it causes water to evaporate from the leaf surfaces, creating a negative pressure that pulls water upward from the roots through the xylem.
3. Explore the cohesion-tension theory: This theory explains how water is transported in plants. Water molecules stick together (cohesion) and are pulled up the plant as water evaporates from the leaves, creating tension in the xylem vessels.
4. Consider the role of xylem: Xylem cells are specialized for transporting water and nutrients from the roots to the rest of the plant. They do not contract but facilitate the movement of water due to the pressure difference created by evaporation.
5. Evaluate the incorrect options: The contraction of xylem cells, pressure exerted by root cells, breakdown of sugar molecules, and osmotic changes are not the primary drivers of water movement in trees. The ultimate source of energy is the sun, which drives evaporation.