Passive Transport

1. Passive Transport SBI3C Ms. De Sousa

2. Cell membrane What molecules make up the cell membrane? Largermoleculesthat are not able to diffuse through the membrane on theirown, requireproteinsthatact as channels or pumps. The structural composition causes the cell to besemi-permeable,onlyallowing certain moleculesthrough.

3. Cell Transport Overview • -Energyisrequired • Molecules move across the cellagainsttheir concentration gradient • -No energyisrequired • Molecules move across the cellwiththeir concentration gradient

4. Passive Transportation Passive Diffusion – molecules are able to cross the cell membrane withoutenergy. • Molecules have a tendency to move from an area of high concentration to an area of low concentration • Thus, molecules move withtheirconcentration gradient Concentration Gradient: Difference in concentration of solutes in twodifferent areas.

5. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis There are 3 main types of passive transport: • Simple Diffusion • Osmosis • Facilitated Diffusion

6. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis • The cell membrane isselectivelypermeable, suchthatitonlyallows certain molecules to go through. • The hydrophobic portion of the cell membrane restricts the moleculesthat go into the cell. • Small, unchargedmoleculesare able to cross (i.e. H2O, O2, CO2) • Lipids are also able to cross the membrane.

7. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis During Simple diffusion: • The molecules move withtheirconcentration gradientsfrom an area of high concentration to an area of low concentration • Thesemolecules are able to diffuse across the cell membrane withoutany help fromproteins. (becausethey are small and uncharged)

8. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis • Molecules move across the membrane becausethey are in constant motion. • Molecules move in either direction untiltheiris an equal concentrations on bothside of the membrane. « DynamicEquilibrium »

9. Demonstration/Activity

10. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis • The movement of the molecules down their concentration gradient can be affected by temperature. What happens to the dye molecule when the temperature is hot? What happens to the dye molecule when the temperature is cold? The molecules have more kinectic energy and are able to move at a quicker rate. Thus the process of diffusion occurs much faster. The molecules lose kinetic energy resulting in a decrease rate. Thus the process of diffusion occurs much slower.

11. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis • Ions, polar, smallchargedmolecules and large moleculesare not able to cross the hydrophobic center of the membrane. • Theyrequiretransmembraneproteinsto getacross the cell membrane. • Transmembraneprotein: protein in the membrane thatspans the thickness of the phospholipidbilayer. • The proteins help transport thesemoleculesacross the bilayer. Why does this occur? Transmembrane protein in its quaternary structure.

12. Passive Transportation Facilitated diffusion Simple Diffusion Facilitated Diffusion Osmosis Large, polar molecules cross the membrane throughchannel or carrierprotein. The inner portion of the proteinishydrophilic, allowing the molecules to move across the hydrophobicbilayer.

13. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis Carrier Protein: When the moleculebinds to the carrier protein, the proteinchanges shapeand flips to allow the molecule to enter the cell.

14. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis Example of protein channel: Aquaporin The inside portion of the channel is hydrophilic/polar allowing it to interact (hydrogen bonds) with the water molecules.

15. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis Identify which process is illustrated in each diagram.

16. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis Osmosis: • Osmosis: net movement of wateracross a selectivelypermeable membrane. Water moves withits concentration gradient. • The cellremains the same size because H2O molecules move in and out of the celluntilDynamicEquilibriumisreached.

17. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis  Water will move from an area with low solute concentration (high water concentration) to an area of high solute concentration (low water concentration). There is a low concentration of water whenthereis a high concentration of solute.

18. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis • Osmosisoccurswhenthereis a difference in solute concentrationacross a membrane. • There are 3 keytermsthat are used to describesolute concentration. • IsotonicSolution • HypertonicSolution • HypotonicSolution

19. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis • Isotonic solution: when the solutions inside and outside of the cell have an equal concentration of solutes. What direction will water move?

20. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis 2) Hypertonic Solution: When one side of the solution has a higher concentration of solutethen the other area. What direction will water move?

21. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis 3) Hypotonic Solution: When one area of the solution has a lower concentration of solutesthan the otherside. What direction will water move?

22. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis The process of osmosis is occuring within everyone of our cells.

23. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis • When a cellisisotonic, both the cell and the envrionment have an equal concentration of solute. • Thus water will move at an equal rate inside and outside of the cell. • This is an optimal environmentbecause the celldoes not expand or shrink.

24. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis • When the solution ishypertonic, it has a highsolute concentration in comparison to the cell. • Water will have a tendency to move withits concentration gradient, from an area of lowsolute concentration to an area of highsolute concentration. • This causes the water to move out of the cell,thusleading to cellshrinkage.

25. Passive Transportation Simple Diffusion Facilitated Diffusion Osmosis • When a solution ishypotonic, thereis a lowersolute concentration in comparison to the cell. • Water has a tendency to move withits concentration gradient from an area of lowsolute concentration to an area of highsolute concentration. • Thus water will move into the cell, causingcellswelling.