Osmosis is said to be the tendency of a fluid, usually water, to pass through a semi permeable membrane (as of a living cell) into a solution where the solvent concentration is higher thus equalizing the concentrations of materials on either side of the membrane.
When sugar is placed on a straw berry, the thin film of moisture on the berry skin begins to dissolve the sugar. Once this happens, the dissolved sugar forms a higher solute concentration on the skin of the berry than that found in the (plant) cells of the berry. A concentration gradient is formed and water molecules from the berry cells move down that gradient to the outside of the berry skin and dissolve the sugar to form a gooey solution.