What is the hypothesis that explains the movement of fluid through phloem in a plant?

The hypothesis that explains the movement of fluid through phloem in plants is known as the "pressure flow hypothesis." It posits that the movement of sap, which contains sugars and nutrients, occurs due to differences in turgor pressure between source tissues (where sugars are produced or stored) and sink tissues (where they are utilized). As sugars are actively loaded into the phloem at the source, water enters osmotically, creating high pressure that drives the flow of the sap toward areas of lower pressure at the sinks.