How does the active uptake of mineral ions in the roots cause the absorption of water by osmosis?

Sourav PanNovember 9, 2024

Answered

The active uptake of mineral ions in the roots plays a crucial role in facilitating the absorption of water by osmosis. Here’s how this process works:

Mechanism of Active Uptake and Water Absorption

1. Active Transport of Mineral Ions:
   • Root cells actively transport mineral ions (such as potassium, nitrate, and phosphate) from the soil into their cytoplasm against their concentration gradient. This process requires energy in the form of adenosine triphosphate (ATP) and involves specific transport proteins located in the plasma membrane of root cells.
2. Lowering Water Potential:
   • As mineral ions are actively absorbed, the concentration of solutes inside the root cells increases. This increase in solute concentration lowers the water potential (Ψ) of the root cells compared to that of the surrounding soil solution, which has a higher water potential. The water potential is a measure of the potential energy of water in a system, and it influences the movement of water.
3. Osmosis:
   • Water moves from an area of higher water potential (the soil) to an area of lower water potential (the root cells) through osmosis, which is the diffusion of water across a selectively permeable membrane . The osmotic gradient created by the active uptake of mineral ions effectively draws water into the root cells.
4. Water Movement into Xylem:
   • Once inside the root cells, water continues to move into the xylem vessels due to the established osmotic gradient. This movement is facilitated by both osmosis and capillary action within the xylem . The increase in turgor pressure within root cells also helps push water upward through the plant.
5. Continuity with Transpiration:
   • The process is further supported by transpiration, where water evaporates from leaf surfaces, creating negative pressure that pulls more water up through the xylem from the roots. This continuous cycle ensures that plants can absorb sufficient water to compensate for losses due to transpiration