Phloem Loading

Question

Active phloem loading of sucrose into sieve elements raises osmotic pressure causing:

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1. **Munch's Mass Flow Hypothesis**: Explains how sugars are transported in phloem from 'source' to 'sink'.
2. **Phloem Loading**: Sugars are actively loaded into the sieve tube elements at the source (leaves).
3. **Osmosis**: This high concentration of sugar lowers the water potential in the sieve tube, causing water to diffuse in from the adjacent xylem by osmosis.
4. **Pressure Build-up**: The entry of water increases the **hydrostatic pressure (turgor pressure)** in the phloem.
5. **Bulk Flow**: This high-pressure area 'pushes' the sap toward the low-pressure 'sink' (roots/fruits), where sugars are unloaded.

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Phloem Loading

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