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Transport. Across Biological Membranes. Review for Transport. What are the two parts of a solution? In cells, what is normally the solvent? How would you describe the activity of solute particles in solutions?. Passive Transport. Concentration Gradient
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Transport Across Biological Membranes
Review for Transport • What are the two parts of a solution? • In cells, what is normally the solvent? • How would you describe the activity of solute particles in solutions?
Passive Transport • Concentration Gradient • A difference in concentrations across a membrane
Simple Diffusion Mainly small, nonpolar • Particles diffuse through lipid bi-layers to reach equilibrium
Facilitated Diffusion • Membrane proteins carry materials through the lipid bilayer. • Particle binds to membrane protein. • Membrane protein changes shape. • Particle is released on the other side.
Channel Proteins • Membrane protein opens a passage for materials through the lipid bilayer.
HYPOTONIC HYPERTONIC H2O H2O H2O H2O H2O H2O HYPERTONIC HYPOTONIC H2O H2O H2O H2O H2O H2O H2O H2O H2O H2O Osmosis • Diffusion of water • When solute cannot cross membranes to reach equilibrium, the solvent (water) does • Water moves from where it is purest (hi conc.) to where it is least pure (lo conc.)
Transport Review • What two things are always true of passive transport? • What are the examples of passive transport we discussed? • Why shouldn’t we drink salt water? • How do we regulate the amount of water (and concentration of solutes) in our bodies?
HI LO HI LO LO HI No E req'd E req'd
Pump • Similar to facilitated diffusion except it’s AT ADP + P ATP
Active Transport • Exocytosis • Pre-packaged materials are released from the cell.
Active Transport • Endocytosis • Cells engulf large materials (nutrients, enemies) with cell membrane.
Active Transport • Endocytosis • Cells engulf large materials (nutrients, enemies) with cell membrane.
Review Questions • What’s the difference between active and passive transport? • In what direction will particles always diffuse? • What happens to a wall-less cell in a hypotonic solution? • Why might a cell want to build up a concentration gradient?