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Osmosis 1 of 17 © Boardworks Ltd 2012 2 of 17 © Boardworks Ltd 2012 What is osmosis? Osmosis is the diffusion of water molecules from a low sugar concentration solution to a high sugar concentration solution across a partially-permeable membrane. A partially-permeable membrane has holes in it that permit water molecules through, but are too small to allow larger molecules through. Osmosis can be demonstrated using visking tubing filled with a solution and placed in a beaker of pure water. partiallypermeable membrane (visking tubing) water Glucose (solute) 3 of 17 © Boardworks Ltd 2012 4 of 17 © Boardworks Ltd 2012 Dilute vs. concentrated During osmosis, water molecules diffuse from pure water or dilute solution to more concentrated solutions. Dilute solutions have a high concentration of water molecules. Concentrated solutions have a low concentration of water molecules. pure water 5 of 17 dilute solution concentrated solution © Boardworks Ltd 2012 Predicting osmosis 6 of 17 © Boardworks Ltd 2012 Osmosis in action 7 of 17 © Boardworks Ltd 2012 The concentration of solutes inside your body cells needs to stay at the same level for them to work properly. However, the concentration of the solutions outside your cells may be very different to the concentration inside them. This concentration gradient can cause water to move into or out of the cells by osmosis 8 of 17 © Boardworks Ltd 2012 • If the concentration of solutes in the solution outside the cell is the same as the internal concentration the solution is ISOTONIC to the cell 9 of 17 © Boardworks Ltd 2012 • If the concentration of the solutes in the solution outside the cell is higher than the internal concentration the solution is HYPERTONIC to the cell 10 of 17 © Boardworks Ltd 2012 • If the concentration of the solutes in the solution outside the cell is lower than the internal concentration the solution is HYPOTONIC to the cell 11 of 17 © Boardworks Ltd 2012 In Plants If more water is lost by osmosis the vacuole and cytoplasm shrink and eventually the cell membrane pulls away from the cell wall. This is PLASMOLYSIS Plasmolysis cells die very quickly unless the osmotic balance is restored. 12 of 17 © Boardworks Ltd 2012 Osmosis and cells Plant and animal cells are surrounded by a partiallypermeable plasma membrane. This allows water and other small molecules to diffuse across. Plant cells additionally have a strong cell wall surrounding the membrane which offers support and protection. plasma membrane cell wall plant cell 13 of 17 red blood cell © Boardworks Ltd 2012 OSMOSIS IN PLANTS • Plants rely on osmosis to support their stems and leaves • When water moves into a cell by osmosis this causes the vacuole to swell which presses against the cytoplasm against the cell wall – this pressure is called TURGOR PRESSURE • This pressure makes the cell hard and rigid 14 of 17 © Boardworks Ltd 2012 • If more water is lost by osmosis, the vacuole and cytoplasm shrink, and eventually the cell membrane pulls away from the cell wall. • This is PLASMOLYSIS. • Plasmolysed cells die quickly unless osmotic balance is restored. 15 of 17 © Boardworks Ltd 2012 Osmosis and plant cells 16 of 17 © Boardworks Ltd 2012 Osmosis and plants Root cells in plants absorb water through osmosis. Many fine root hairs increase the surface area of a plant’s roots, allowing them to draw in more water from the surrounding soil. The presence of water in plant cells gives the plant structural support 17 of 17 © Boardworks Ltd 2012 Osmosis and animal cells Animal cells do not have a cell wall. This means they respond differently to plant cells to the gain and loss of water. In dilute solutions, osmosis can cause animals cells, such as red blood cells, to swell up and burst. This is called lysis. In concentrated solutions, water loss causes the cells to shrink. When this happens to red blood cells, it is called crenation. 18 of 17 © Boardworks Ltd 2012 Osmosis and animal cells 19 of 17 © Boardworks Ltd 2012 Osmosis and animal cells In order to remain healthy, animal cells need to maintain an isotonic water balance. This means that the water concentration both inside and outside the cell is equal. hypothalamus The concentration of water and salt in the blood is controlled by the kidneys. The kidneys are controlled by the portion of the brain called the hypothalamus. 20 of 17 © Boardworks Ltd 2012 • PRACTICAL 21 of 17 © Boardworks Ltd 2012 OSMOSIS and DIFFUSION 22 of 17 © Boardworks Ltd 2012 Concentration gradient Concentration Gradient - change in the concentration of a substance from one area to another. 23 of 17 © Boardworks Ltd 2012 24 of 17 © Boardworks Ltd 2012 PLANT CELLS Hypotonic Solution Turgor Pressure builds in the cell and causes 25 ofosmosis 17 to stop Hypertonic Solution Plants will wilt when cells lose water through osmos © Boardworks Ltd 2012 ELODEA CELLS As viewed under the microscope 26 of 17 © Boardworks Ltd 2012 27 of 17 © Boardworks Ltd 2012 Glossary 28 of 17 © Boardworks Ltd 2012 Anagrams 29 of 17 © Boardworks Ltd 2012 Which process? 30 of 17 © Boardworks Ltd 2012 Multiple-choice quiz 31 of 17 © Boardworks Ltd 2012