Membrane Transport Chapter 5.14+

What you need to know! The role of diffusion (osmosis), active transport, and bulk flow in the movement of water and nutrients in plants. How water will move if a cell is placed in an isotonic, hypertonic, or hypotonic solution How electrochemical gradients are formed.

Diffusion The movement of molecules from an area of high concentration to an area of low concentration Results in an even distribution: equilibrium Reason: random movement of all molecules driven by kinetic energy (temperature/pressure)

Diffusion in and out of cells The Cell membrane is selectively permeable (semi-permeable) Permeable for very small, uncharged, hydrophobic molecules and gases (simple diffusion) Impermeable for ions and large molecules

Diffusion in and out of cells Facilitated Diffusion: Cells can build transport proteins to allow large molecules to permiate the membrane Permeable molecules move down their concentration gradient (high to low) across the membrane

Diffusion Test: Setup At your lab stations: Fill Dialysis Tubing with Starch & Water. Record the mass. Fill your cup with tap water Add iodine to the cup (just enough for the liquid to turn a light yellow Place the Dialysis Tubing into the cup with the iodine and water Record the initial colors of both liquids Wait (come back to your seats)

Osmosis Definition: diffusion of water molecules across a semi-permeable membrane All water moves via osmosis Water molecules travel through aquaporin proteins (facilitated diffusion/osmosis) Water will always go down the concentration gradient (high to low)

Passive Transport When molecules move across the membrane without the cell investing energy (doing work) Ex: diffusion, facilitated diffusion, osmosis

Diffusion Test: Results At your lab stations: Observe the liquid in the cup and in the dialysis tubing. Mass the tubing. Record the color of each liquid in your notes. Record the mass. On a separate sheet of paper: Diagram the before and after molecules (see page 136) What diffused across the dialysis tubing? What did not diffuse across the dialysis tubing? Write a short paragraph explaining what happened. A diagram can (and should) be used. Include relevant vocabulary.

Osmosis in Cells Water concentration: High solute (salt, sugar, etc.) concentration means low water concentration Low solute (salt, sugar, etc.) concentration means higher water concentration Distilled water is solute free (100% water) Compare the inside water concentration with the outside water concentration: Isotonic Solution: inside and outside same concentration of solute (and water) Hypertonic Solution: solution has a higher solute concentration (lower water) Hypotonic Solution: solution has a lower solute concentration (higher water)

Active Transport Cell expends energy to pump molecules against their concentration gradient (up hill) Molecular Transport: Exocytosis move large molecules out of the cell: vesicles fuse with the cell membrane Endocytosis move large molecules into the cell: vesciles pinch off from the membrane