Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Molecular Movement Across Membranes What you need to know! • How water will move if a cell is placed in an isotonic, hypertonic, or hypotonic solution • How electrochemical gradients are formed. Diffusion • The movement of molecules from an area of high concentration to an area of low concentration • Resulting in even distribution when equilibrium is reached • Reason: random movement of all molecules driven by kinetic energy (temperature/pressure) • Cells do not invest energy (no ATP) Diffusion in and out of cells • Plasma membrane is selectively permeable (semi-permeable) • Permeable for very small, uncharged, hydrophobic molecules and gases • Impermeable for ions and large molecules • Use of transport proteins/pores embedded in the membrane • No energy needed due to concentration gradient Examples of Diffusion • O2/CO2 exchange between blood and cells • Sugar molecules/pores • Small waste molecules-urea • Amino acids/pores • Lipids Osmosis • Definition: diffusion of water molecules across a semi-permeable membrane • All water movements in cells or organisms through osmosis • Water molecules use aquaporin proteins • Water will always go in the direction of lower water concentration (high solute concentration) or lower water potential Osmosis in Cells • 2 parameters: 1. Solute concentration (salt, sugar, other substances…) 2. Water concentration: – High solute (salt, sugar, etc.) concentration usually means low water concentration – Low solute (salt, sugar, etc.) concentration usually means higher water concentration – Distilled water is solute free (100% water) How to answer Osmosis Questions • Compare the inside water concentration with the outside water concentration: • Isotonic: inside and outside same concentration of solute (and water) • Hypertonic: solution with higher solute concentration (lower water) • Hypotonic: solution with lower solute concentration (higher water) Living Cells in solutions a) Low salt water (same salt concentration inside and outside the cell = isotonic) no change in shape b) Strong salt water (more salt outside the cell = hypertonic; inside = hypotonic) cell shrivles c) Distilled water (no salt outside = hypotonic; inside = hypertonic) cell explodes