Which of the following is a mechanism involved in soil-water uptake by the roots?

• A. Osmosis
• B. Transpiration
• C. Photosynthesis
• D. Respiration

Answer: (A)

Water uptake by roots occurs mainly through osmosis: water moves across the membranes of root cells from the soil, where water potential is higher, into the cells where water potential is lower. This movement is driven by a gradient in water potential between soil and root tissues, aided by root hairs that increase surface area and, at the cellular level, aquaporin channels that facilitate water passage. Once inside the roots, water can travel toward the xylem and be transported upward.

Transpiration is related to water movement but is not the mechanism of uptake itself—it’s the loss of water from leaves that helps pull water through the plant. Photosynthesis uses water as a reactant but does not govern how water enters roots, and respiration is a metabolic process that releases energy and does not drive water intake.