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PASSIVE TRANSPORT A.K.A. THE LAZY ONE THAT DOESN’T NEED ENERGY Przeworski HOMEOSTASIS • https://www.youtube.com/watch?v=9RLnlXNlfdk • Why do we want to keep a constant internal environment? • Temperature • pH • Salt/Potassium/Ion content In passive transport: oMolecules always move across the cell membrane without the use of energy oMolecules always move from high to low concentration (from where there are more to where there are fewer) Low High High Low ATP Diffusion oDiffusion is the most basic form of passive transport o Occurs everywhere, not just across membranes oEquilibrium is reached when diffusion has caused molecules to spread out evenly Facilitated Diffusion In facilitated diffusion, molecules move through the membrane with help from proteins o Channel proteins are open doors o Carrier proteins open and close Osmosis In Osmosis, water molecules diffuse through a membrane oSolute: a substance dissolved in a liquid oSolvent: liquid that dissolves the solute oSolution: mixture of solute and solvent Osmosis Tonicity describes relative concentrations of solute: o Hypertonic: Concentration is higher relative to something else o Hypotonic: Concentration is lower relative to something else o Isotonic: Both concentrations are equal In which beaker would we expect to see the greatest movement of particles? (list the percents as your answer) Cell in Hypertonic Solution 15% Solute 85% H2O CELL 5% Solute 95% H2O WHICH DIRECTION WILL THE WATER MOVE? Cell in Hypotonic Solution 20% Solute 80% H2O CELL 30% Solute 70% H2O WHICH DIRECTION WILL THE WATER MOVE? Cell in Isotonic Solution 10% Solute 90% H2O CELL 10% Solute 90% H2O WHICH DIRECTION WILL THE WATER MOVE? What happens when plant cells are placed in solutions of different tonicity? ? ? • Plasmolyzed: Water leaves plant cells, causes the cell membrane to pull away from the cell wall (plasmolysis), plant wilts • Turgid: Water moves into plant cells, makes cells plump, plant remains rigid VIDEO-BIO • https://www.youtube.com/watch?v=IaZ8MtF3C6M • Video: Pre-AP (first 5 minutes) • https://www.youtube.com/watch?v=dPKvHrD1eS4 EXIT TICKET: A student measures the mass of each of six potato cores and places one core in each of six different unknown solutions. After a period of time, the student removes the potato cores and measures the mass of each one. Solution 1 2 3 4 5 6 Potato Core Mass Increase Decrease No Change No Change Decrease Increase Which two potato cores were placed in an isotonic solution?