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Mass Flow through Sieve Tube Elements

Sucrose loaded into the sieve tubes causes the sieve tubes to have a lower water potential.Water moves from xylem vessels into the sieve tubes down the water potential gradient by osmosis.This creates a high hydrostatic pressure which causes the mass flow of water containing dissolved sucrose through the sieve tube elements.Although mass flow is a passive process, the whole process is driven by the active transport of hydrogen ions so as a whole the process is active.

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Specification: AQA Biology (7401), AS-level, 3.3.4.2 Mass transport in plants. Topic: Mass Transport in Plants.

Key terms in this lesson

osmosis
The net movement of water molecules from a region of higher water potential to a region of lower water potential through a selectively permeable membrane.
water potential
The pressure created by water molecules, a measure of the tendency of water to move out of a solution; pure water has a water potential of zero and solutes make it more negative.
active transport
The movement of molecules or ions across a membrane from a region of lower to higher concentration, against the concentration gradient, using ATP and carrier proteins.
xylem
Plant vascular tissue, made of dead, lignified tubular cells, that transports water and mineral ions from the roots to the leaves.

More in Mass Transport in Plants

All 15 lessons in Mass Transport in Plants · All AQA AS-level Biology topics