Diffusion & Osmosis

Diffusion The movement of molecules from an area in which they are highly concentrated to an area in which they are less concentrated.

Diffusion

Sugar molecules dissolve in water to make a homogeneous mixture. Sugar is the solute. H2O is the solvent. The mixture is a solution.

Net movement of molecules stops when equilibrium is reached

MEMBRANE STRUCTURE AND FUNCTION Membranes organize the chemical activities of cells Membranes provide structural order for metabolism Forms most of the cell's organelles Compartmentalizes chemical reactions The plasma membrane forms a boundary between a living cell and its surroundings Exhibits selective permeability Controls traffic of molecules in and out

Cell Membrane Controls movement of molecules into and out of the cell Selectively permeable Some substances can pass freely. Some substances can pass to an extent. Some not at all. Allow cells to maintain homeostasis. Appears as a double layer under the electron microscope

Fluid-Mosaic Model of Cell Membrane Has two layers (a bilayer) of phospholipids (fats with phosphorous attached), in which protein molecules float, and which at body temperature are fluid. Why is it called a mosaic?

The membrane is a fluid mosaic of phospholipids and proteins A membrane is a mosaic because proteins and other molecules are embedded in a framework of phospholipids. A membrane is fluid. Most protein and phospholipid molecules can move laterally. Membrane glycoproteins and glycolipids function in cell identification.

Passive transport is diffusion across a membrane Passive transport across membranes occurs when a molecule diffuses down a concentration gradient. Like moving down a hill, it requires no energy.

Osmosis The diffusion of water across a selectively permeable membrane. Osmosis is a type of Passive Transport. Osmosis requires NO ENERGY.

Osmosis

Osmosis Tonicity Hypotonic- a solution that causes a cell to swell because of Osmosis. Hypertonic- a solution that causes a cell to shrink because of Osmosis. Isotonic- a solution that causes no change in the size of the cell

Hypotonic Solution In this picture a red blood cell is put in a glass of distilled water. Because there’s a higher concentration of water outside the cell, water enters the cell by OSMOSIS. In this case too much water enters and the cell swells to the point of bursting open. 

Concentration of H20 depends on a amount of dissolved solute So, answer this question….Why do establishments” offer free popcorn, peanuts, and pretzels to their patrons if they are serving beverages? What changes are taking place in the body to initiate the need for more beverages?

Selectively Permeable A membrane that allows only certain materials to cross it. Materials pass through pores in the membrane. What determines whether molecules can pass through a cell membrane? If a molecule is too large it cannot pass. The molecule has to be fairly small, O2, H2O, CO2 and a couple others can easily pass through the membrane. Also it depends on the concentration of a specific substance inside the cell. Similarly, if a molecule is polar it cannot penetrate the phospholipid bilayer.

Summary Diffusion is the movement of molecules from an area of higher concentration to an area of lesser concentration. Osmosis is the movement of water thru a semi permeable membrane. Passive transport needs NO ENERGY! (molecules move from an area of higher to lesser concentration). Active transport requires energy. (molecules move from an area of lesser to higher concentration)

Why are osmosis & diffusion important? All living things have certain requirements they must satisfy in order to remain alive – maintain homeostasis These include exchanging gases (usually CO2 and O2), taking in water, minerals, and food, and eliminating wastes. These tasks happen at the cellular level. Molecules move through the cell membrane by diffusion A balance, or EQUILIBRIUM, must be maintained.