I searched a lot in the net but don't found a clear answer. I just want to know if plasma membrane is permeable to sucrose.
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No, but yes.
Sucrose is a large polar solute. Because it is polar, it cannot easily pass the hydrophobic core of the membrane. So, if the lipids of the plasma membrane are mostly impermeable to sucrose, how do cells take in sucrose?
Plants
In biology, membrane-bound proteins are used for efficient transport across the membrane (Brian, 2011 from a review of Suc transport in plant cells). The specific group of membrane proteins used for sucrose transport are unimaginatively called Suc transporters (SUT).
So in a plant cell, sucrose can be moved across the membrane.
Humans
In mammals, there are no SUTs. Instead, sucrose is broken down into fructose and glucose by the enzyme sucrase.
From there, glucose transporters GLUT proteins carry glucose and fructose across the plasma membrane.
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$\begingroup$ What I don't understand is that in the osmosis experiment, potatoes shrink for a long time in the solution of sucrose. if plant cells were permeable to sucrose the potatoes will gain their initial size $\endgroup$ – med morad Sep 12 '19 at 18:04
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1$\begingroup$ @medmorad it depends on sucrose concentration and whether sucrose transporters are expressed in that particular tissue. $\endgroup$ – WYSIWYG Sep 13 '19 at 15:20
