Which of the following processes relies heavily on the function of xylem?

Transpiration is the process that relies heavily on the function of xylem, making it the correct answer. Xylem is a type of vascular tissue in plants responsible for the transport of water and dissolved minerals from the roots to the rest of the plant. During transpiration, water evaporates from the leaf surfaces, creating a negative pressure within the xylem vessels that helps pull water upward from the roots through the plant. This process not only supplies essential moisture to the leaves for photosynthesis but also aids in the movement of nutrients, making it a critical aspect of plant physiology.

In contrast, photosynthesis, while influenced by water availability supplied via the xylem, is primarily a process that converts light energy into chemical energy using carbon dioxide and water. Pollination and fertilization are reproductive processes in plants that do not directly involve the xylem's function in water transport. Pollination is the transfer of pollen from male to female reproductive structures, and fertilization occurs when male and female gametes unite, neither of which relies on xylem for operation.