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Chapter 3 Cell Passive Transport (Osmosis, Cell Tonicity) Slide 132-147 Water Balance of Cells Without Walls Tonicity is the ability of a surrounding solution to cause a cell to gain or lose water Isotonic solution: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane Hypertonic solution: Solute concentration is greater than that inside the cell; cell loses water Hypotonic solution: Solute concentration is less than that inside the cell; cell gains water 2 Hypertonic solutions are those in which more solute (and hence lower water potential) is present. Hypotonic solutions are those with less solute (again read as higher water potential). Isotonic solutions have equal (iso-) concentrations of substances. Water potentials are thus equal, although there will still be equal amounts of water movement in and out of the cell, the net flow is zero. Water relations and cell shape in blood cells. Water relations in a plant cell. 3 Osmosis and tonicity https://www.youtube.com/watch?v=niuZJ2f2Cks 4 Keeping water balance Cell survival depends on balancing water uptake & water loss freshwater balanced saltwater 5 1Keeping right amount of water in cell Freshwater KABOOM! a cell in fresh water high concentration of water around cell cell gains water example: Paramecium problem: cells gain water, swell & can burst No problem, here freshwater water continually enters Paramecium cell solution: contractile vacuole pumps water out of cell 6 2Keeping right amount of water in cell saltwater Saltwater I’m shrinking, I’m shrinking! a cell in salt water low concentration of water around cell cell loses water example: shellfish problem: cell loses water I will survive! in plants: plasmolysis in animals: shrinking cell solution: take up water 7 Keeping right amount of water in 3 cell balanced Balanced conditions no difference in concentration That’s of water between cell & better! environment cell in equilibrium example: blood problem: none water flows across membrane equally, in both directions volume of cell doesn’t change I could be better… 8 Solute Concentration (b) Isotonic surroundingsH2O (a) Hypertonic surroundings (c) Hypotonic surroundings Animal cell: plasma membrane H2O H2O Plant cell: H2O plasma membrane cell wall wilted Net movement of water out of cell H2O H2O Balanced water movement turgid Net movement of water into cell 9 Osmosis and Tonicity https://www.youtube.com/watch?v=Y_w07A7chnk 10 Hypertonic-Isotonic-Hypotonic 11 12 13 Isotonic, Hypotonic, Hypertonic IV Solutions Made Easy | Fluid Electrolytes Nursing Students https://www.youtube.com/watch?v=51FkahHUBwc 14 Diffusion vs Osmosis • Passive diffusion is the net movement of gases or small uncharged polar molecules across a phospholipid bilayer membrane from an area of higher concentration to an area of lower concentration . Examples of gases that cross membranes by passive diffusion include N2, O2, and CO2; examples of small polar molecules include ethanol, H2O, and urea. • • Osmosis is the diffusion of water across a membrane from an area of higher water concentration (lower solute concentration) to lower water concentration (higher solute concentration). Osmosis is powered by the potential energy of a concentration gradient and does not require the expenditure of metabolic energy. In an isotonic environment, both the water and solute concentration are the same inside and outside the cell and water goes into and out of the cell at an equal rate. 15 Hypertonic-Hypotonic • If the environment is hypertonic, the water concentration is greater inside the cell while the solute concentration is higher outside (the interior of the cell is hypotonic to the surrounding hypertonic environment). Water goes out of the cell. • In an environment that is hypotonic, the water concentration is greater outside the cell and the solute concentration is higher inside (the interior of the cell is hypertonic to the hypotonic surroundings). Water goes into the cell. 16 Hypertonic Solutions: contain a high concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypertonic solution, the water diffuses out of the cell, causing the cell to shrivel. Hypotonic Solutions: contain a low concentration of solute relative to another solution (e.g. the cell's cytoplasm). When a cell is placed in a hypotonic solution, the water diffuses into the cell, causing the cell to swell and possibly explode. Isotonic Solutions: contain the same concentration of solute as another solution (e.g. the cell's cytoplasm). When a cell is placed in an isotonic solution, the water diffuses into and out of the cell at the same rate. The fluid that surrounds the body cells is isotonic.