 Phospholipids  Give membrane hydrophilic and hydrophobic properties  Phosphate – hydrophilic, face aqueous exterior or interior  Fatty acid – hydrophobic, face each other inside the membrane  Proteins  Cholesterol, Glycolipids, and Glycoproteins

 Phospholipids  Proteins: many different roles  Hydrophilic  Have charged and polar side groups  Hydrophobic  Have nonpolar side groups  Cholesterol, Glycolipids, and Glycoproteins

 Phospholipids  Proteins  Cholesterol, Glycolipids, and Glycoproteins  Cholesterol: resists changes in membrane fluidity caused by changes in temperature  Glycolipids & Glycoproteins: have a carbohydrate attached; cell-cell recognition

 Can Pass Through:  Small, Uncharged polar  Small Nonpolar  Can NOT Pass Through (without assistance):  Hydrophilic substances  Large  Polar  Ions  Water Note: Plant Cell Walls are made of cellulose and are external to the cell membrane. They are also found in Prokaryotes and Fungi.

 Does not require the input of energy  Net movement of molecules from high to low concentration  Used to import resources and export wastes  Water moves across the membrane through proteins called “aquaporins.”  Osmosis: the diffusion of water across a selectively permeable membrane.  Tonicity: the ability of a solution to cause a cell to gain or lose water

 Solutions outside a cell may be…  Isotonic – same concentration of solutes as the interior of the cell; water moves across membrane at the same rate in both directions

KEY: term – exterior solution; effect – direction of water flow

 Solutions outside a cell may be…  Hypotonic – lower concentration of solute than the interior of the cell; water moves across membrane into the cell faster than it flows out, causing it to swell and lyse (burst)

KEY: term – exterior solution; effect – direction of water flow

 Solutions outside a cell may be…  Hypertonic - higher concentration of solute than the interior of the cell; water moves across membrane out of the cell faster than it flows in, causing it to shrivel and possibly die

KEY: term – exterior solution; effect – direction of water flow

 Requires energy to move molecules from low to high concentration  Free energy often from ATP  Uses membrane proteins  Example: Sodium-potassium pump

 Exocytosis – internal vesicles fuse with the plasma membrane to secrete macromolecules out of the cell  Endocytosis – the cell takes in macromolecules and other particles by forming vesicles from the plasma membrane