Plasma Membrane, Osmosis, Diffusion and Water Balance

Membrane Structure & Function

Membrane structure, I Constructed of Phospholipids Selective permeability Amphipathic polar vs. non-polar regions hydrophobic & hydrophilic regions “fluid mosaic” model currently widely accepted

Phospholipid Structure

Membrane structure, II Phospholipids membrane fluidity Cholesterol membrane fluidity and stabilization “Mosaic” Structure Integral proteins trans-membrane proteins transport materials Peripheral proteins surface of membrane

Plasma Membrane

Diffusion, Osmosis, Facilitated Diffusion High Concentration Active-Need ATP (against or with gradient) Active Transport Passive (with gradient) Diffusion, Osmosis, Facilitated Diffusion Low Concentration

Diffusion movement of a substance from an area of high concentration of that substance to an area of low concentration of that substance. Concentration gradient imbalance in concentration Passive transport diffusion of a substance across a biological membrane without the need for energy Osmosis the diffusion of water from an are of high concentration of water to an are of low concentration of water across a selectively permeable membrane

Water balance Osmoregulation control of water balance Hypertonic higher concentration of solutes Hypotonic lower concentration of solutes Isotonic equal concentrations of solutes Cells with Walls: Turgid (very firm) Flaccid (limp) Plasmolysis plasma membrane pulls away from cell wall

Specialized Transport Transport proteins Facilitated diffusion passage of molecules and ions with transport proteins across a membrane down the concentration gradient Active transport movement of a substance against its concentration gradient with the help of cellular energy