Explain the mass flow hypothesis of transport in phloem.

(N/A) The mass flow hypothesis,also known as the pressure-flow hypothesis,is the most widely accepted theory for the translocation of sugars in plants.
$1$. Source and Sink: Glucose produced in the leaves (source) is converted into sucrose. This sucrose is loaded into the companion cells and then into the sieve tube elements of the phloem by active transport.
$2$. Osmotic Gradient: The high concentration of sucrose in the phloem creates a hypertonic condition,causing water to move from the adjacent xylem into the phloem by osmosis.
$3$. Hydrostatic Pressure: This influx of water increases the hydrostatic pressure (turgor pressure) within the sieve tubes at the source.
$4$. Mass Flow: The pressure difference between the source and the sink (where sucrose is being utilized or stored) causes the sap to flow through the phloem sieve tubes towards the sink.
$5$. Unloading: At the sink,sucrose is actively removed from the phloem into the cells where it is needed. As the solute concentration decreases,water moves back into the xylem,reducing the hydrostatic pressure at the sink,thus maintaining the pressure gradient.