Biology
Water Absorption in Plants
Quick fact
A single mature corn plant can absorb and transpire over 200 liters of water during its growing season—yet only about 1% is used for photosynthesis.
Why this is interesting
Have you ever watered a plant and wondered where all that water goes? How does it travel from the soil all the way to the highest leaves?
Read the full explanation
Understanding Water Absorption in Plants
Water absorption begins at the roots, specifically through tiny hair-like extensions called root hairs that increase surface area. These root hairs are in close contact with soil water. Water moves into the root hairs by osmosis—it flows from an area of higher water potential (the moist soil) to an area of lower water potential (the inside of the root cells). This happens because the root cells have a higher concentration of dissolved salts and sugars, making their water potential lower. Once inside, water travels through the root cortex, either moving between cells (apoplastic route) or through them (symplastic route), until it reaches the xylem vessels—the plant's water-conducting tubes.
A deeper explanation
The journey of water upward is primarily driven by transpiration pull. Water evaporates from the leaves through stomata, creating a negative pressure at the top of the xylem. Because water molecules are cohesive (they stick to each other) and adhesive (they stick to the xylem walls), this tension is transmitted all the way down to the roots, pulling a continuous column of water upward—a process described by the cohesion-tension theory. Early in the day or in humid conditions, root pressure can also push water upward, sometimes causing guttation (water droplets on leaf tips). This entire mechanism is crucial not just for hydration, but also for transporting dissolved minerals from the soil and for cooling the plant through transpiration.