Active transport is used to pump sugars from the

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Unformatted text preview: Sugars are stored in the roots, and sometimes in the stems, fruits, or leaves of a plant. • Active transport is used to pump sugars from the source cells into the phloem cells. • Once a phloem cell is loaded with sugar, water moves in by osmosis. This raises pressure in the cell. • Osmotic pressure moves the sap (sugar dissolved in water) toward the sink (roots, fruits, or other place that the sugars will be stored). • Sugars move into sink cells and enter the cells by diffusion. The sugar molecules are linked together to make starch, which is less soluble in water. This keeps the concentration of sugar low in the cell, to keep the diffusion gradient high. Notes Biology 103, Spring 2008 Dr. Karen Bledsoe • The same process can be used to move sugars out of sink cells to other cells that need sugars for energy. Starch can be broken apart into sugar again, and the sugars can then be pumped into the phloem cells by active transport. Common misconceptions: • Students sometimes compare plant transport to animal c...
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