Diffusion & Osmosis Cell exist in a constantly changing environment. Homeostasis: Biological balance, or stability that a cell maintains with its environment. MOLECULES TEND TO MOVE INTO THOSE AREAS THAT ARE LESS CONCENTRATED! Diffusion Process by which molecules spread from an area of greater concentration to an area of lesser concentration. Diffusion Continued. Concentration Gradient Difference in concentration of a substance across space. Equilibrium When the concentration of the molecules of a substance is the same throughout the space. Diffusion Across Membranes Permeable: Membranes that allow substances to pass through them. Not all molecules pass through the membrane SSize TType MMolecular Structure of membrane Osmosis The process by which water molecules diffuse through a membrane from an area of greater concentration to an area of lesser concentration. Direction of Osmosis Hypertonic Greater solute concentration Hypotonic Lesser solute concentration Isotonic Equal solute concentration Direction of Osmosis Condition Environment solution is: Cell Solution is: Water will move: If solute concentration in env. is less than the cell hypotonichypertonic Into the cell If solute concentration in env. is more than in cell hypertonichypotonic Out of the cell If solute concentration in env. is equal to the cell isotonic Water will not move Passive & Active Transport Passive Transport Greater concentration to lesser concentration. No use of energy Example: facilitated diffusion, simple diffusion Active Transport Lesser concentration to greater concentration Use of energy (against concentration gradient) Example: Sodium-Potassium pump; Endo- & Exocytosis Passive Transport vs. Active Transport Carrier Molecules Proteins that function in transport. Each is specialized to allow the movement of only one type of molecule across a membrane. Carriers used in gated channels & facilitated diffusion Passive Transport Simple Diffusion Movement through lipid bi-layer Gated Channel Protein controlled passage that permits cell to be as permeable as needed. Facilitated Diffusion Carrier molecules transport solute molecules through a membrane without expending energy. Endocytosis & Exocytosis Endocytosis: process by which cells engulf substances that are too large to pass through the membrane. Pinocytosis: Solute or fluids into the cell. Phagocytosis: Large food particles or whole microorganisms into the cell. Exocytosis: passage of large molecules out of the cell. The Role of Osmosis Plasmolysis: Condition in which water leaves the cell, and cell wilts. Cytolysis: Condition in which a cell takes in so much water that they burst.