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Unformatted text preview: K+, CA++, CI); water molecules CI Selectively Permeable Barrier 6 PASSIVE TRANSPORT (1) A. Simple Diffusion The net movement of like molecules or ions down a concentration gradient molecules collide randomly, but net movement is away from the place with the most collisions (down gradient) Factors Affecting Diffusion Rate
1. Steepness of concentration gradient Steeper gradient, faster diffusion 2. Molecular size Smaller molecules, faster diffusion 3. Temperature Higher temperature, faster diffusion 4. Charge (like ions strongly repel each other) 5. Electrical or pressure gradients 7 B. Transport Proteins: Facilitated Diffusion
transport protein with binding site for molecule or ion of a specific substance (the solute) (Passive Transport - 2) Proteins span pan the lipid bilayer Interior is able to open to both sides Change shape when they interact with solute Move water-soluble substances across a membrane solute
lipid bilayer of cell membrane C. Passive and Active Transport
Passive Transport Doesn't require energy inputs Solutes diffuse through a channel inside the protein's interior (facilitated) Active Transport Requires ATP Protein is an ATPase pump Pumps solute against its concentration gradient Low High Net movement is down concentration gradient High Low 8 Membrane Transport
high Concentration gradient ATP low Diffusion of lipid-soluble lipidsubstances - SIMPLE Passive transport of water-soluble watersubstances - FACILITATED Active transport through ATPase D. Osmosis Water molecules tend to diffuse down water concentration gradient Total number of molecules or ions dictates concentration of water Tonicity: relative solute concentration of two fluids
1. Hypertonic - having more solutes 2. Isotonic - having same amount 3. Hypotonic - having fewer solutes 9 Tonicity and Osmosis
2% sucrose hyper water 10% sucrose 2% sucrose Hypo- Hyper- Iso- hypo Hydrostatic Pressure Pressure that a fluid exerts against structure enclosing it (wall, membrane) Eg: Turgor Pressure in plants Increases with increased solute concentration Influences the osmotic movement of water 10 Increase in Fluid Volume compartment 1 compartment 2 HYPOTONIC SOLUTION membrane permeable to water but not to solutes HYPERTONIC SOLUTION fluid volume increases In compartment 2 F. Membrane Traffic (Bulk Transport) Endocytosis Membrane sinks inward around a substance, bringing it into the cell in a vesicle Phagocytosis; Phagocytosis; Pinocytosis cytoplasm Exocytosis Vesicle carrying substance fuses with membrane, releasing it into the intracellular fluid
plasma membrane Cyclical processes!!! cytoplasm 11...
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- Spring '09