OSMOSIS DIFFUSION Unit 4 Diffusion Through Cell Membranes

OSMOSIS & DIFFUSION Unit 4

Diffusion Through Cell Membranes � � � Every living cell exists in a liquid environment. One of the functions of the cell membrane is to regulate the movement of molecules from one side of the membrane to the other. Diffusion-The movement of molecules from an area where they are more concentrated to an area where they are less concentrated.

Diffusion

Diffusion Continued � � In solutions particles constantly and randomly move. Concentration- The concentration of a solute in a given volume of solution. M/V (Examples: 12 g/3 L, 4 g/1 L) Diffusion moves particles from an area where they are more concentrated (4 g/1 L) to areas of less concentration (2 g/1 L). Diffusion depends upon random particle movements. � � � Substances diffuse without using energy. Diffusion uses the concentration gradient to move particles instead of using energy. The concentration gradient is the differences in concentrations from one area to another.

Osmosis � Osmosis- The diffusion of water (and dissolved substances) through a selectively permeable membrane. � Works like diffusion (moves from higher to lower concentration, without energy) � The selectively permeable membrane lets some things pass through it (water) and not others (sugar). � Osmosis continues until the concentration on both sides of the membrane is the same (no gradient). When this happens the two solutions are said to be Isotonic.

Solutions � � Hypertonic- High concentration of particles in solution. Hypotonic-Low concentration of particles in solution. Isotonic- When the concentration of particles in two solutions are the same (equal). Osmotic Pressure- Produces net movement, this is created by the pressure on the hypertonic side of the membrane.

Facilitated Diffusion � � The diffusion of (larger) substances with the aid of protein channels. Happens at a faster pace then regular diffusion. Hundreds of different protein channels have been found, each is specific to the substances they move. Even though facilitated diffusion is fast and specific via protein channels, it still requires a concentration gradient and doesn’t use energy.

Active Transport � � The movement of materials against the concentration gradient Requires Energy Generally carried out by transport proteins called protein pumps, that are found in the membrane. The movement of large molecules or clumps of material can be done using this process.

Types of Active Transport � Endocytosis- The process of taking material into the cell by means of inner folds, or pockets in the cell membrane. � Exocytosis- The release of large molecules or material, vacuole membrane fuses with the cell membrane forcing the material out. � Phagocytosis- Process in which an extension of the cytoplasm surrounds and engulfs a particle. � Pinocytosis- The process of forming fluid filled vacuoles along the membrane.