By: DC A cell membrane A fluid mosaic of proteins, carbohydrates and lipids. What is a selectively permeable membrane? . Answer: Small, non polar molecules can pass relatively easily, large, polar, or charged molecules cannot pass the membrane A: Carbohydrates B: Glycoprotein (receptors for signal molecules) C: Glycolipid D: Phospholipid E: Phospholipid Bilayer F: Cellular Membrane G: Cytoskeleton (microfilaments, i.e. protein) I: Cholesterol (provides rigidity) J: Channel Protein (allows molecules to pass) Diffusion Diffusion is the RANDOM movement of molecules from high concentration to low concentration. Movement is always from high concentration to low concentration. Concentration gradient is the difference in concentration across a selectively permeable membrane. 3 Types of Diffusion Passive Molecules moves by themselves Hi to Lo concentration Facilitated Membrane proteins facilitate (help) movement of molecules across a membrane Hi to Lo concentration Active Transport Requires energy in the form of ATP Lo to Hi Concentration Osmosis The net movement of water across a selectively permeable membrane. A solution is composed of a solute (e.g. salt, sugar) dissolved in a solvent (water). Water is the universal solvent. Hypotonic, Hypertonic, Isotonic Hypo-, hyper-, and isotonic- are used to compare to solutions. The solution with the lower concentration is hypotonic, while the other solution is hypertonic. Isotonic means the movement across the membrane is balanced, the concentration gradient is at equilibrium. wning/Membranes/diffusion animation.html Example of Active Transport Sodium/Potassium Pump Animal Cells Cells in your body need to maintain a higher concentration of Sodium (Na) outside the cell and a higher concentration of Potassium (K) on the inside of your cell. Steps 1: Three sodium ions bond to the carrier protein. 2: ATP is used to open the gate (a change in the shape of the protein) to allow Na to enter the cell 3: Two potassium Ions bond to the carrier protein, which changes the shape and passes the potassium to the outside of the cell. Purpose of the Na/K Pump? Na/K Pump is used by nerve cells as electrical impulses to send messages from one cell to another Three Types of Endocytosis 1) Phagocytosis: Active movement to devour prey 2) Pinocytosis: Engulfing large amounts of fluid Endocytosis Pinocytosis Receptor-mediated Endocytosis Exocytosis Contractile Vacuoles. Freshwater animals, like Elodea live in a hypotonic environment. Contractile vacuoles are used to expel excess water.