Osmosis

9.1 PLASMA MEMBRANE I. All cells must maintain homeostasis in order to live. - they do this by controlling what materials can enter and leave II. All cells have a plasma membrane that is SELECTIVELY PERMEABLE - this only allows for specific things to enter and leave the cell A. Selective permeability is achieved by the structure of the plasma membrane (fig.9.3, pg 220) 1. The cell membrane is composed of 2 layers of PHOSPHOLIPIDS - "phospho" = phosphate "lipid" = …

…do all the work, and no energy is required from the cell 3. ACTIVE TRANSPORT - moves particles against the concentration gradient - takes energy - Transport proteins bind to the particles (pg 231, fig 9.15) - Large particles are transported by Endocytosis = cell surrouds the particles, they are engulfed and enclosed by the membrane - Reverse of endocytosis is Exocytosis = process in which the cell expels waste - Both endocytosis and exocytosis use large amounts of energy