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Solutions

Solutions. Water is considered the solvent. The substance(s) dissolved in water is / are the solute(s). Together, solvent + solute  solution. Concentration is the number of solutes in each volume of solvent. Osmosis.

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Solutions

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  1. Solutions • Water is considered the solvent. • The substance(s) dissolved in water is / are the solute(s). • Together, solvent + solute  solution. • Concentration is the number of solutes in each volume of solvent

  2. Osmosis • The diffusion of water across a semipermeable membrane is called osmosis. • In a solution, there are water molecules and dissolved particles (the solute). • The more dissolved particles there are, the lower the concentration of water molecules. ANIMATION

  3. Comparing Solutions • A solution may be desribed as isotonic, hypertonic or hypotonic relative to another solution • These are comparisons; they require a point of reference (ie, my hair is shorter… …than it was last year). • The comparison in biology is usually to the inside of a cell.

  4. Isotonic • A solution is isotonic to a cell if it has the same concentration of dissolved particles as the cell. • This means the water concentration is also the same. • Water molecules move into and out of the cell at an equal rate in an isotonic solution. • The cell size remains the same.

  5. Hypertonic • A hypertonic solution has a higher concentration of dissolved particles than a cell. • This means the water concentration is lower than that of the cell. • Thus, water flows out of the cell – so, the cell will shrivel and eventually die. ANIMATION

  6. Hypotonic • A hypotonic solution has a lower concentration of dissolved particles than a cell. • Therefore the water concentration is higher than that of the cell. • Thus, water diffuses into the cell – causing the cell to expand and potentially burst.

  7. Impact on Cells • In an isotonic solution (center), water enters / exits red blood cells at equal rates. • In a hypertonic solution (like salt water – right), water rushes out and the cell shrivels. • In a hypotonic solution (like distilled water – left), water rushes in and the cell swells / bursts (lysis). Video clips: RBC in isotonic solution RBC in hypertonic solution RBC in hypotonic solution

  8. Adaptations - Plants • Plant cells use the cell wall to prevent bursting. At center, the plant cell is in an isotonic solution. Water moves in / out at equal rates (no NET movement) At left, the plant cell is in a hypotonic solution. Water rushes in, filling the vacuole. This cell is turgid / has high turgor pressure. At right, the plant cell is in a hypertonic solution. Water rushes out of the cell, draining the vacuole. This is called plasmolysis. Video: Elodea in isotonic / hyper / hypo

  9. Adaptations - Protists • Paramecia live in freshwater • This makes paramecia hypertonic to their surroundings • Water is constantly rushing into the paramecium • So the paramecium uses a contractile vacuole to pump the water back out (and prevent bursting) Video: The contractile vacuole in action

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