Plasma Membrane What is special about a membrane? Helper protein HYDROPHILIC HEAD Cell or Plasma Membrane Cell membranes are bilayered, dynamic structures that: Regulate cells Form boundaries between cells and environments Regulate movement of molecules into and out of cells Maintain HOMEOSTASIS! Selectively permeable phospholipid bilayer •Each has a hydrophilic region, where the phosphate groups are located, and a hydrophobic region, the fatty acid “tails.” Diffusion Molecules move from an area of high concentration to an area of low concentration Tendency to reach equilibrium Does not require cell energy Osmosis The passage of WATER through a selectively permeable biological membrane Substance travels from area of high concentration to an area of low concentration Permeability If a substance is able to diffuse across a membrane = Permeable If a substance is unable to diffuse across a membrane = Impermeable If only certain substances can diffuse across a membrane = Selectively Permeable Concentration Gradients Isotonic= Hypertonic= Solution containing equal concentration of solute No net movement of water Solution containing high concentration of solute Water moves into solution Hypotonic= Solution containing low concentration of solute Water moves out of solution Sugar and Water Types of movement through a membrane Passive Transport Active Transport Facilitated Diffusion Passive Transport “Going with the flow” or “with the concentration gradient” Does not require cell energy to occur Particles move from an area of high concentration to low concentration Includes osmosis and diffusion Particles move with the concentration gradient Facilitated Diffusion Molecules that cannot diffuse across a membrane on their own need “helper molecules” Carrier proteins are used to get needed molecules into the cell Does not require energy; just proteins Examples: Sugars and salts Active Transport “Going against the flow” or “against the concentration gradient” Requires ENERGY from the cell to accomplish Movement from area of low concentration to area of high concentration Particles move against the concentration gradient Active Transport Types of active transport Endocytosis- cells fold in their cell membrane and take in materials Exocytosis- cells removing materials Phagocytosis - cell eating/engulfing large particles Pinocytosis – cell drinking Na+/K+ Pumps – maintains an electrochemical gradient in cells; pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell Essential Functions of Membranes in Cells Barrier for the cell and organelles from the external environment Provides region for concentration gradients to form in cells. This allows for osmosis and diffusion to occur. Formation of vesicles for the transportation of materials in and out of the cell.