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I tried an experiment. First, I placed grapes in pure water(hypotonic solution). The grapes burst because of endosmosis. Then, I placed new set of grapes in strong sugar solution(fully saturated) but they did not shrink. And then when I placed it in strong salt solution(fully saturated), they did shrink a little. Why does this occur?

How is this possible?

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What is a strong sugar solution? Grapes contain ~15-20% of sugar. – nico Sep 30 '12 at 10:50
According to Wikipedia fully saturated sucrose solution should be 2000g/L, way above the 15-20% sugar content of grapes. Interestingly the versions of this experiment that I can find online all use salt for a hypertonic solution. Of course this could be just because it is cheaper than sugar. – Alan Boyd Sep 30 '12 at 13:42
Why are we so sure that osmosis can happen in both directions in grapes? – rwst Sep 30 '12 at 13:47
@rwst - The grapes are probably dead, so any trans-membrane pumps would most likely be inactive. That leaves pores and other entry points for water to equilibrate. There's also evidence in the experiments above; because of the membrane potential maintained by ion concentrations (fewer in the cytosol) the saturated salt solution would cause water to leave the grapes and also cause the smaller ions to enter the grapes to dissipate the membrane potential. Sugar isn't small, though, and requires active transport (to the best of my memory). – MCM Sep 30 '12 at 19:58

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Well, without the details of your experiment to cross-check with the sugar and H2O content of your average grape, I'd say the saturated solution probably approximated the natural molarity of sugar in the grape. At least to the point it didn't make any advese effects noticeably on your time scale.

That seems the most apparent solution to me. I suppose it's also possible (though I don't know the mechanics behind it) that hypertonic solution might have acted as a preservative - similar to jam. It's not just water which will attempt to reach an equilibrium, but all compounds that can pass through the membrane - perhaps sucrose/fructose/glucose can do so, maintaining the structural integrity of the grape.

Both are guesses until you reveal more information, though.

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please see the question now .... I have added some more information and then help me! – Pranit Bauva Sep 30 '12 at 13:00

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