Osmosis
Osmosis is the diffusion of water through a semipermeable membrane down its concentration gradient. If a membrane is permeable to water, though not to a solute, water will equalize its own concentration by diffusing to the side of lower water concentration (and thus the side of higher solute concentration). In the beaker on the left, the solution on the right side of the membrane is hypertonic.
Source
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"OpenStax College, The Cell Membrane. October 23, 2013."
http://cnx.org/content/m46021/latest/
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