-the movement of dissolved substances from source to sink.
-substances are moved from source to sink
source - for sucrose is the leaves where it is made
sinks - where the sucrose is made up (roots, stems + leaves)
-enzymes maintain a concentration gradient between sources and sinks by dissolving the substances at the sink.
1) Sucrose is loaded into the seive tubes by active transport
2) this lowers the water potential - water enters the tubes by osmosis - the pressure increases
3) solutes are used up at the sinks - increasing the water potential inside - water leaves by osmosis - the pressure decreases
4) the result is a pressure gradient
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