Lab 6 Diffusion/osmosis

Intro to Lab 6

Solutions Molecules (solutes) dissolved in a liquid (solvent) All molecules are constantly in motion Molecules in solution move randomly Random motion causes mixing

Brownian Motion Random tendency of ALL molecules to move due to their inherent kinetic energy. Kinetic energy: energy of motion

Concentration Gradient Concentration is the amount of solute in a solvent Concentration gradient: more solute in one region of a solvent than in another

Concentration gradients Concentrations of some key ions are very different on the inside versus the outside of cells creating a gradient IN: [Na+] = low [K+] = high [Ca2+] = very low [Cl-] = low OUT: [Na+] = high [K+] = low [Ca2+] = low (blood, interstitial fluid)

Passive transport: Diffusion Due to: random motion and collision of molecules Movement “down” a concentration gradient (from area of high concentration to area of low concentration) Occurs until a dynamic equilibrium is reached

Diffusion – solid in water

Animation

What factors Affect Diffusion Rates? Distance Molecule size Temperature Gradient Electrical force

What can/can’t diffuse through the cell membrane?

Lab exercise 6 Transport Activities 6.1 – 6.4 1 Brownian motion – view in scope up front 2 Diffusion of a liquid – view demo 4 Dialysis – I’ll start it, come and look later

Exercise 4. Dialysis Starch + iodine = purple Purple will be inside or outside bag

Osmosis Osmosis is the net diffusion of water across a membrane. Osmosis only occurs when solutes cannot cross a selectively permeable membrane (no diffusion) so the solvent, water, crosses instead

Osmosis = Water Movement Water molecules diffuse across membrane toward solution with more solutes Volume increases on the side with more solutes Can think of it like diffusion of water: water moves from an area in which it is more concentrated (less solute) to area where it is less concentrated (more solute)

Osmosis

How Osmosis Works More solute molecules = lower concentration of water molecules Key to osmosis: membrane must be freely permeable to water, selectively permeable to solutes. (i.e. some solutes must be impermeable. Otherwise, diffusion would occur)

Osmosis in cells

Osmosis Isotonic  cell ok Hypotonic  Swelling or hemolysis (burst). Like in the bathtub Hypertonic  crenation (shrinkage)

Osmosis Osmosis is the net “diffusion” of water across a membrane. Osmosis only occurs when solutes cannot cross a selectively permeable membrane (no diffusion) so the solvent, water, crosses instead Osmotic Pressure = a pulling force exerted by the side with more solutes that pulls water in.

Egg lab Eggs are very large single cells, allow us to measure osmosis easily We will place eggs into solutions of unknown concentration to determine what type of solution each is (hypertonic, isotonic, hypotonic) What will happen to the egg if the solution is hypertonic and why? What about hypotonic?

Lab 6 Assignment Lab Exercise #6 Parts: B C:1,2,4 D