Mass Flow Hypothesis
This suggests that there is a passive movement of sucrose from the phloem (the source), where it is most concentrated, to other areas, such as growing tissues, where sucrose is less concentrated (the sink).
1. The source cells, such as the mesophyll cells of the leaves, produce sucrose during photosynthesis, which decreases the water potential of the cell. Therefore, water diffuses in by osmosis from the xylem, down the water potential gradient.
2. This causes the hydrostatic pressure to build and sucrose molecules to be forced out of the cell into the phloem.
3. The pressure pushes the sucrose downwards towards the sink cells. This is called mass flow.
4. At the sink cell, the sucrose is either used for respiration or converted into insoluble starch for storage.
5. The increased pressure forces…