* Osmosis: You're right, water moves into phloem cells by osmosis. This happens because the sugar concentration inside the phloem cells is higher than the surrounding cells. Water naturally moves from areas of high water concentration to areas of low water concentration, following the concentration gradient.
* Increased pressure: As water moves into phloem cells, it increases the pressure inside. This increased pressure creates a force that pushes the sugar-water mixture, called phloem sap, through the phloem.
* Movement to the rest of the plant: The pressure gradient drives the phloem sap from areas of high pressure (where sugars are loaded) to areas of low pressure (where sugars are unloaded). This movement delivers sugars to different parts of the plant, including roots, stems, leaves, flowers, and fruits.
To summarize:
The pressure-flow hypothesis explains how sugar, made during photosynthesis in leaves, is transported to other parts of the plant through the phloem. This movement is driven by a combination of osmosis and the resulting pressure gradient.
