Introduction to Cell Membranes and Transport
PHOSPHOLIPIDS Polar / Hydrophillic head and Nonpolar / Hydrophobic tail! Amphipathic (literally “dual-sympathy” = Glycerol linked to phosphate group and two fatty acid chains
PHOSPHOLIPIDS Polar / Hydrophillic head and Nonpolar / Hydrophobic tail! Amphipathic (literally “dual-sympathy”)
PHOSPHOLIPID BILAYERS ARE SELECTIVELY PERMEABLE! Very small molecules, especially nonpolar molecules like 02 will be able to get across easily macromolecules, ions cannot get across without help!
Variation in Membrane Fluidity: Bond Saturation Can pack saturated more tightly = increased hydrophobic interactions; also longer the tail = increased hydrophobic interactions
Variation in Membrane Fluidity: Bond Saturation
Atherosclerosis
Variation in Membrane Fluidity: Cholesterol
THE CELL MEMBRANE IS SELECTIVELY PERMEABLE!
Facilitated Diffusion Types of Transport: Diffusion Osmosis Facilitated Diffusion Active Transport What is moving? Concentration gradient? Energy? Proteins?
Osmosis
Plant Cells Are Complicated…
Water Potential Water Potential = Quantification of the tendency of water to diffuse from one area to another w.p. = the potential energy that water has in a particular environment compared with the potential energy of pure water at room temp and atmospheric pressure; under these conditions, pure water has a water potential of 0 water flows from areas of high water potential to areas of lower water potential; Greek letter sigh; measured in bars
Water Potential Solute Potential ( ) = As solute potential goes up, water concentration goes down, there are fewer water molecules to diffuse, so water potential must go down; solute potential must be either zero (for pure water), or negative, if the water contains a solute Solute Potential ( ) =
Water Potential Pressure Potential ( ) = Force exerted by the wall is called wall pressure; as water moves into the cell, the pressure inside the cell known as turgor pressure, increases until wall pressure is induced. Cells that are firm and that experience wall pressure are said to be turgid; pressure potential = any pressure on water; measured in megapascals (Mpa) car tire = 0.2MPa, and 0.2 and 0.3 MPa Pressure Potential ( ) =
Water Potential: The Soil Can also think about water potential of leaves, stem, roots, soil and air: in soil – water contains fewer solutes than water in roots of plants; soil has higher potential in soil than in roots (exceptions: very dry soils, salty soils)
Water Potential and Potatoes
Design an Experiment to Test the Effect of _________ on Diffusion / Osmosis Hot plate Water bath Sucrose solutions Salt Starch Cork Borer Potatoes Chicken