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The Effects of Isotones on a Cell

In biological research, isotonic solutions are critical to the success of many tests. They are used to dilute or buffer samples while protecting cells and organelles from damage. A solution's tonicity depends on the concentration of solutes or particles dissolved in the solution. This concentration must match the concentration within the cell for the solution to be isotonic.

  1. What Are Isotones?

    • The Latin root "iso-" means "same." "Tonic" refers to the osmotic pressure between two solutions. Osmotic pressure is the amount of pressure needed to prevent osmosis into a cell completely contained by a semipermeable membrane. Therefore, isotonic solutions have equivalent osmotic pressures, and would not flow into one another if separated by such a membrane. In medicine and biology, a solution is often called isotonic if it has the same osmotic pressure as a typical human cell.

    Isotonic Solutions

    • Most common isotonic solutions have the same amount of solutes --- such as salt --- as cells or blood. Because the solutions have the same osmotic pressures as the cells, they have no effect on the cells' volume. The cells neither take on nor lose water or fluid, because their surrounding environment is neutral, and neither pushes in nor pulls out fluid across the cell membrane. Many sports drinks are isotonic, designed to replace fluids and electrolytes without damaging cells.

    Hypertonic Solutions

    • If a solution is hypertonic, it has a higher osmotic pressure than the cells or solutions it is being compared to. When cells are placed in hypertonic solutions, the higher concentration of solutes outside the cell causes the cell to lose fluid in an attempt to match the concentration of its environment. This makes cells shrink and wrinkle, a phenomenon known as "crenation." In plant cells, this causes the cell membrane to shrink back and pull away from the sturdier cell wall.

    Hypotonic Solutions

    • Hypotonic solutions have lower osmotic pressures than whatever they are being compared to. Therefore, they have a lower concentration of salt or solutes than the cells. In order to match the lower concentration, cells will take in fluid to dilute the concentration of solutes within themselves. This causes the cells to expand, but the membranes can only extend so far. After a certain point, the membranes burst and the cells die. This is known as "osmotic shock."

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