MadSci Network: Botany

Re: Why/How does sugar affect the travel of dye through transpiration?

Date: Thu Apr 21 18:11:56 2005
Posted By: David Hershey, Faculty, Botany, NA
Area of science: Botany
ID: 1114097381.Bt

You are correct that a sugar solution is thicker than water but I don't think
that is why you failed to get the dye to move up the stem and into the flower. 

Plant cells attract water by having higher concentrations of salts or other
dissolved substances in their cells than in the soil solution. Water moves from
a high concentration of water (less salty) to a lower concentration of water
(more salty) across a cell membrane. Movement of water across a cell membrane is
termed osmosis. 

The osmosis website cited under References gives a good definition except for
the term "semipermeable", which is inaccurate and obsolete. The membrane is
selectively permeable, meaning water can freely cross the membrane but most
salts and sugars cannot freely cross. Salts and sugars would have to be actively
transported across.

Sugar works like salt so I think your sugar solution was more concentrated than
the solution in the flower cells so water (carrying dye) could not move into the
flower cells. It may be that some of the water in the cut flower moved out of
the cut flower and into the sugar solution. Did you notice any wilting of the
cut flower in the sugar solution? Cut flowers absorb dye solutions faster if
they are slightly wilted prior to placing their cut ends in a dye solution.

Smaller amounts of sugar are added to vase solutions for cut flowers after
dying. The sugar provides energy to the flower and helps them last longer.



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