BRAINCAKEPressure Flow Hypothesis
The pressure flow hypothesis is another name for the mass flow model of translocation. It states that phloem sap is pushed from source to sink by a difference in hydrostatic pressure, created by loading sucrose at the source and unloading it at the sink. Scientists test the hypothesis by comparing its predictions with evidence.
Evidence supporting the hypothesis
1. If an aphid feeding on phloem is cut off, leaving its stylet (mouthpart) in the sieve tube, sap flows out of the stylet. This shows that the phloem contents are under pressure. The sap flows out faster near the leaves than near the roots, suggesting a pressure gradient.
Sign in free to see the rest of this lesson, the R.E.C.I.P.E. recall steps and the quiz
BrainCake is free. Make an account in seconds and pick up where this page stops.
Key terms in this lesson
- hydrostatic pressure
- The pressure a fluid exerts on the walls of its container; in a capillary it pushes fluid out through the gaps between the endothelial cells.
More in Transport in Plants
- Factors Affecting Transpiration
- Root Pressure
- Translocation in the Phloem
- Phloem Loading
- The Symplast Pathway
- The Apoplast Pathway
- Phloem Unloading
- Mass Flow Hypothesis
All 21 lessons in Transport in Plants · All Edexcel AS-level Biology topics