AS Biology Unit 1: Osmosis part 1 Osmosis “Movement of ______ from a _____ water potential to a ____ water potential, through a ______________ permeable membrane.” Key facts about water potential (Ψ) 1.Water potential is a measure of the ability of water molecules to ________ freely. 2.Pure water has a water potential of _____. 3.Water always moves from an area of high Ψ to an area of low Ψ, ____ a Ψ _________. 4.Adding ______ always __________ the Ψ (making it more ________________, for example –100kPa becomes -300kPa). Osmosis in animal cells Animal cells are surrounded by a thin partially permeable membrane. Solutes such as glucose lower the water potential _____________ cells. If _______ cells are placed in a solution which has a high water potential, water will ________ by osmosis, causing them to _________ and potentially _______________. If animal cells are placed in a solution which has a low water potential, water will ______ by osmosis, causing them to ___________. The water potential of red blood cells is ______________________ with blood plasma, ensuring there is no __________ gain or loss of ________________ by osmosis for red blood cells. Osmosis in plant cells _________ such as salts and sugars _______ the water potential in plant cells. When placed in pure water plant cells become _______, as water ___________ by osmosis down the Ψ gradient. The extra water in the cytoplasm and vacuole pushes against the rigid cellulose ____ _____. Plant cells placed in a solution with a _________ Ψ, lose water by _______. As the cytoplasm and membrane shrink and pull away from the cell wall, the cell becomes _________________. Key term: Isotonic An _________ solution is one which shows ___ net gain or loss of water by osmosis.

AS Biology Unit 1: Osmosis part 1 Osmosis “Movement of water from a high water potential to a low water potential, through a partially permeable membrane.” Key facts about water potential (Ψ) 1.Water potential is a measure of the ability of water molecules to move freely. 2.Pure water has a water potential of zero. 3.Water always moves from an area of high Ψ to an area of low Ψ, down a Ψ gradient. 4.Adding solute always lowers the Ψ (making it more negative, for example –100kPa becomes -300kPa). Osmosis in animal cells Animal cells are surrounded by a thin partially permeable membrane. Solutes such as glucose lower the water potential inside cells. If animal cells are placed in a solution which has a high water potential, water will enter by osmosis, causing them to swell and potentially burst. If animal cells are placed in a solution which has a low water potential, water will leave by osmosis, causing them to shrink. The water potential of red blood cells is isotonic with blood plasma, ensuring there is no net gain or loss of water by osmosis for red blood cells. Osmosis in plant cells Solutes such as salts and sugars lower the water potential in plant cells. When placed in pure water plant cells become turgid, as water enters by osmosis down the water potential gradient. The extra water in the cytoplasm and vacuole pushes against the rigid cellulose cell wall. Plant cells placed in a solution with a lower water potential, lose water by osmosis. As the cytoplasm and membrane shrink and pull away from the cell wall, the cell becomes plasmolysed. Key term: Isotonic An isotonic solution is one which shows no net gain or loss of water by osmosis.

Osmosis part 2 Osmosis “chip” experiments Using a core borer helps to ensure the ____________ ____________ for osmosis is similar in each chip. Keeping “chips” _________ before use prevents ________________ and any subsequent changes in water potential to the tissues/cells. Often osmosis experiments are left to work over several hours. This allows _____________ to be reached between ________ and the solutions they are in, whilst ________________ any changes in mass/density. Blotting ______ the chips removes __________ solution, ensuring that only changes in ______ due to water gained or lost by osmosis from the tissue is measured. One of the main limitations in “chip” experiments is that the results may be unreliable due to natural __________ in the __________ ____________ of the tissues used. Making dilutions Calculate the volumes of water and sodium chloride needed to make 25 cm 3 of a 0.4 mol dm -3 sodium chloride solution from a 1.0 mol dm -3 sodium chloride solution. Calculate the volumes of water and sucrose needed to make 30 cm 3 of 5 % sucrose solution from a 50 % sucrose solution. Movement of water between adjacent cells Add arrows to show the direction of water movement between the cells. Ψ = -400kPa Ψ = -150kPa Ψ = -300kPa Percentage change in mass. Percentage change in mass rather than the change in mass is often used because it allows ____________ of data, even when ___________ ___________________ are different. If Start mass = 2.35g and Final mass = 1.80g 1. Calculate the percentage change in mass; 2. Suggest what type of solution the chip was in; 3. Explain the change in mass.

Osmosis part 2 Osmosis “chip” experiments Using a core borer helps to ensure the surface area for osmosis is similar in each chip. Keeping “chips” moist before use prevents evaporation and any subsequent changes in water potential to the tissues/cells. Often osmosis experiments are left to work over several hours. This allows equilibrium to be reached between cells and the solutions they are in, whilst maximising any changes in mass/density. Blotting dry the chips removes surface solution, ensuring that only changes in mass due to water gained or lost by osmosis from the tissue is measured. One of the main limitations in “chip” experiments is that the results may be unreliable due to natural variation in the water potential of the tissues used. Making dilutions Calculate the volumes of water and sodium chloride needed to make 25 cm 3 of a 0.4 mol dm -3 sodium chloride solution from a 1.0 mol dm -3 sodium chloride solution. 0.4/1 x 25 = 10 cm 3 of a 1.0 mol dm-3 sodium chloride solution. Plus (25-10) = 15 cm 3 water Calculate the volumes of water and sucrose needed to make 30 cm 3 of 5 % sucrose solution from a 50 % sucrose solution. 5/50 x 30 = 3cm 3 of 50 % sucrose solution. Plus (30-3) 27 cm 3 water Movement of water between adjacent cells Add arrows to show the direction of water movement between the cells. Ψ = -400kPa Ψ = -150kPa Ψ = -300kPa Percentage change in mass. Percentage change in mass rather than the change in mass is often used because it allows comparison of data, even when starting masses are different. If Start mass = 2.35g and Final mass = 1.80g Calculate the percentage change in mass. (“new” – “old”) / “old” x 100 = ( )/2.35 x100 = % Suggest what type of solution the chip was in. Concentrated salt/sugar solution Explain the change in mass. Water moves by osmosis out of chip, down the Ψ gradient, because there is a higher Ψ inside chip and a lower Ψ in the solution.