In flowering plants, organic nutrients produced in mature leaves during photosynthesis are translocated to non-photosynthetic organs such as roots and growing fruits. Which mechanism drives the movement of sucrose solution through the phloem sieve tubes according to the mass flow (pressure-flow) hypothesis?
- Turgor pressure gradient generated by osmotic influx of water at the source tissueCevap
- BNegative tension pull created by evaporation of water through leaf stomata
- CCapillary action operating through dead, hollow lignified tracheary elements
- DUnidirectional root pressure pushing mineral ions through non-living conducting cells
Cevap
The movement of sucrose solution through phloem sieve tubes is driven by a turgor pressure gradient generated by osmotic influx of water at the source tissue.
According to the mass flow hypothesis, sucrose is actively loaded into phloem sieve tubes at source organs (leaves). This decreases the solute potential inside the sieve tube, drawing water in from adjacent xylem vessels via osmosis. The resulting high turgor (hydrostatic) pressure at the source pushes the aqueous sucrose solution toward sink tissues where pressure is lower.
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Anahtar Kavram
Mass Flow / Pressure-Flow Hypothesis of Phloem Translocation