Plasma membrane = the flexible boundary between the cell and its environment Allows: Things in the cell Things out of the cell Maintains BALANCE in the cell
What is maintaining balance in the cell called? Homeostasis!
How does the plasma membrane maintain homeostasis? Plasma membranes are selectively permeable Selective permeability = process in which a membrane allows some molecules to pass while keeping others in/out.
Structure is the KEY! The specific structure of the plasma membrane allows it to be selectively permeable
Plasma Membrane Structures: Thin layer of phosopholipds, proteins, and cholesterol Phospholipid = kind of lipid found in the cell membrane – Glycerol, 2 fatty acids, and phosphate (PO4) – Phospholipids have 2 parts
What does the polarity mean about the passage of water in/out of the cell? Water CAN pass through the polar part, but CANNOT pass through the nonpolar part. This allows the cell to prevent water loss and prevent “drowning”
Cell membranes consist of 2 phospholipid layers called a bilayer (think bicycle has 2 wheels)
Plasma Membrane Made of: phospholipid bilayer – Phosphate head hydrophilic – Lipid tail hydrophobic – Carrier proteins – Cholesterol (good kind) Called the fluid mosaic model – Moves fluidly – Mosaic of proteins scattered in membrane – http://www.youtube.com/watch?v=Qqsf_UJcfBc&feat ure=related http://www.youtube.com/watch?v=Qqsf_UJcfBc&feat ure=related
Diffusion = movement across a plasma membrane from HI to LO concentration Osmosis = diffusion of water across a plasma membrane from HI to LO concentraion
Solution Solution = homogeneous mixture of 2 or more substances Made up of: – Solute = part that gets dissolved – Solvent = part that does the dissolving Water is the UNIVERSAL SOLVENT
Types of Cell Transport Water can move freely through the plasma memebrane, but can Solute??? NO! Water will move to reach equilibrium since the solute cannot Which way will the water move? Depends on the TYPE OF SOLUTION the cell is in
Types of Solution Hypertonic – Solute concentration is higher in solution than cell – Water moves OUT – Cell shrinks Hypotonic – Solute concentration is lower in solution than cell – Water moves IN – Cell Swells Isotonic – Solute concentration is equal in solution and in cell – Water moves IN and OUT – Cell stays the same
Cell Transport Active transport = movement of substances across membrane; requires ATP Passive transport = movement of substances across membrane; does NOT require ATP
Active Transport Goes against concentration gradient Exocytosis = move particles OUT of cell Endocytosis = move particels IN cell – 2 kinds of endocytosis: – Pinocytosis = movement of liquid IN cell – Phagocytosis = movement of solids IN cell – http://www.youtube.com/watch?v=4gLtk8Yc1Zc&NR=1 http://www.youtube.com/watch?v=4gLtk8Yc1Zc&NR=1
Passive Transport Goes with concentration gradient Osmosis = movement of water across a membrane with concentration gradient Facilitated Transport = movement of substances across a membrane with concentration gradient with the help of a carrier protein http://www.youtube.com/watch?v=s0p1ztrbX PY&feature=related http://www.youtube.com/watch?v=s0p1ztrbX PY&feature=related