Phloem Pressure Flow — The Münch Mechanism

Plants transport the sugars made during photosynthesis from source leaves to sinks like roots, fruit and growing shoots without a heart or a pump — they use osmosis to build hydrostatic pressure and let that pressure push the sap through. This simulator models the source and sink ends of a phloem sieve tube as two coupled compartments: active sucrose loading at the source raises local osmotic pressure, which draws water in from the xylem and builds turgor; unloading at the sink drains sucrose and lets water leave, keeping its pressure low. The resulting pressure gradient, resisted by the sieve tube's hydraulic resistance, drives real bulk mass flow — rendered as sucrose particles streaming from source to sink while water recirculates back through the xylem to close the loop. Adjust source loading, sink demand and tube resistance to see flow velocity and pressures respond exactly as the Münch pressure-flow hypothesis predicts.