TONICITY

=Tonicity= Tonicity is a measure of the relative concentration of solute particles on either side of a semi-permeable membrane (e.g. inside a cell versus outside the cell). Only solutes that cannot cross the membrane contribute to tonicity. It determines the direction and extent to which water moves by osmosis. The higher the tonicity the greater the difference in the concentration of solutes (dissolved substances) and therefore the concentration of water. ==Hypertonic Solution== [image:http://i.imgur.com/ZUdPRLe.gif] A '''hypertonic solution''' will have higher concentration of dissolved solutes than the solution inside the cell. Therefore a hypertonic solution has a lower concentration of water than the solution within the cell. As a result a hypotonic solution will force water out the cell (there is a net movement of water out the cell). ==Hypotonic Solution== [image:http://i.imgur.com/uX3Ru7s.gif] A '''hypotonic solution''' will have a lower concentration of dissolved solutes than the solution inside the cell. Therefore a hypotonic solution has a higher concentration of water than the solution within the cell. As a result a hypotonic solution will force water into the cell (there is a net movement of water into the cell). ==Isotonic Solution== [image:http://i.imgur.com/NIz3a3c.gif] An '''isotonic solution''' will have an equal concentration of solutes to the solution inside the cell. Therefore an isotonic solution has an equal concentration of water to the solution within the cell. As a result, water moves in and out of the cell at an equal rate. There is no net movement of water ==Affect on Animal Cells (Red Blood Cells)== [image:http://i.imgur.com/KB0iH2W.png?2] A '''hypertonic solution''' causes water to move out of the cell and the cell becomes shrivelled. Red blood cells develop a star-shaped appearance that resembles a spiked ball (they become crenated). An '''isotonic solution''' does not result in any net movement of water in / out of the cell and so it remains unaffected. A '''hypotonic solution''' causes water to move into the cell. Animal cells do not have a tough cellulose wall and if water continues to move into the cell pressure builds until ultimately the cell bursts (cell lysis) ==Affect on Plant Cells== [image:http://i.imgur.com/MW1C6AH.png?1] A '''hypertonic solution''' causes water to move out of the cell and the cell membrane tears away from the cell wall in a process called ''plasmolysis'' An '''isotonic solution''' does not result in any net movement of water in / out of the cell, however, a plant cell may become flaccid (soft, drooping or inelastic). A '''hypotonic solution''' causes water to move into the cell. The tough plant cell wall limits the cells volume preventing it from bursting. Eventually no more water can move into the cell, but instead the internal pressure of the cell increases. The cell membrane starts to push against the cell wall. This is known as '''turgour pressure''' and it causes the plant cells to become '''turgid''' (swollen and firm). Plants rely on turgour pressure to maintain their rigidity. This is why placing flower stems in a hypotonic solution helps to prevent them from wilting.