2. Active & Passive Transport Across Cell Membranes Active & Passive Transport Across Cell Membranes

3. Cells Need to Exchange Materials with the Extracellular Fluid Take in nutrients or Dispose of wastes Take in nutrients or Dispose of wastes - CO 2 - Urea - CO 2 - Urea

4. Membrane Permeability Size Size - the smaller the particle, the more permeable - the smaller the particle, the more permeable - small molecules (O 2, CO 2, H 2 O) can - small molecules (O 2, CO 2, H 2 O) can - large molecules (proteins, DNA) cannot - large molecules (proteins, DNA) cannot Lipid Solubility Lipid Solubility - Yes: nonpolar molecules (O 2, cholesterol) - Yes: nonpolar molecules (O 2, cholesterol) - No: charged ions, polar molecules (Na +, Cl -, - No: charged ions, polar molecules (Na +, Cl -, large molecules (glucose) large molecules (glucose)

5. Passive Transport No energy expended by the cell No energy expended by the cell Goes “ downhill ” with the concentration gradient Goes “ downhill ” with the concentration gradient Substances move from Substances move from [HIGH] [LOW] [HIGH] [LOW] Examples: diffusion, osmosis, facilitated diffusion Examples: diffusion, osmosis, facilitated diffusion Active Transport Requires cell to expend energy Goes “uphill” or against the concentration gradient Involves embedded proteins (transport proteins) acting like pumps Other examples: Exocytosis, endocytosis, pinocytosis, phagocytosis

6. Diffusion Solution = solute + solvent Solution = solute + solvent Solute- substance that is dissolved Solute- substance that is dissolved Solvent- substance that does the dissolving (fluid) Solvent- substance that does the dissolving (fluid) Solute particles dissolved in a solvent are constantly in motion. Temperature motion Solute particles dissolved in a solvent are constantly in motion. Temperature motion This constant motion causes DIFFUSION This constant motion causes DIFFUSION Diffusion- movement of particles from areas of high concentration to areas of low concentration Diffusion- movement of particles from areas of high concentration to areas of low concentration [HIGH] [LOW]

7. Solvent transport is from right to left.

8. The net flow of solute continues until equilibrium is reached. The net flow of solute continues until equilibrium is reached. Solute continue to move across the membrane, but for every one that moves in one direction, another moves in the opposite direction, so there is no net movement. Solute continue to move across the membrane, but for every one that moves in one direction, another moves in the opposite direction, so there is no net movement. [HI] [LOW] [MED] [MED] Diffusion

11. Diffusion not all substances can pass through a cell membrane.

12. Facilitated Diffusion Diffusion “ made easy ” Diffusion “ made easy ” No energy required, goes with the concentration gradient No energy required, goes with the concentration gradient Embedded proteins (channels) provide a convenient pathway for LARGE and/or charged substances to pass thru cell membrane. Also called “ passive diffusion ” Embedded proteins (channels) provide a convenient pathway for LARGE and/or charged substances to pass thru cell membrane. Also called “ passive diffusion ” Another type of embedded protein, a carrier/transport protein, grabs hold and carries the substance thru a cell membrane. Still, no energy required Another type of embedded protein, a carrier/transport protein, grabs hold and carries the substance thru a cell membrane. Still, no energy required Ions, sugars, etc… now can enter and leave cells Ions, sugars, etc… now can enter and leave cells

13. Facilitated Diffusion

14. Facilitated Diffusion Can involve embedded protein channels OR Embedded protein carrier/transport molecules

15. Facilitated Diffusion Substances move from areas of high concentration to areas of low concentration NO ENERGY REQUIRED IT IS A PASSIVE PROCESS

16. Factors Affecting the Rate of Diffusion Magnitude of the gradient  gradient  rate Permeability of the membrane  permeability  rate Temperature of the Solution  temperature  rate The surface area of the membrane through which diffusion is taking place  SA  rate

17. OSMOSIS Diffusion of water Diffusion of water Passive process, does not require energy Passive process, does not require energy The membrane is permeable to water, the solvent. The membrane is permeable to water, the solvent. The membrane is not permeable (impermeable) to the solute. The membrane is not permeable (impermeable) to the solute.

18. Osmosis

19. Osmosis and Tonicity Hypertonic- the solution that has [solute and less water] Hypertonic- the solution that has [solute and less water] Water flows toward the hypertonic environment Hypotonic- the solution that has [solute and more water] Hypotonic- the solution that has [solute and more water] Water flows away from a hypotonic environment Isotonic- the solutions have equal concentrations of solute (no net osmosis)

20. Water Balance in Animal Cells If the animal cell is in a hypotonic environment… If the animal cell is in a hypotonic environment… …the cell gains water, swells, and may even pop like an overfilled balloon! …the cell gains water, swells, and may even pop like an overfilled balloon! Osmosis can kill cells Osmosis can kill cells Hypo – more water Hyper – less water

21. Water Balance in Animal Cells If the cell is in a hypertonic environment… The environment has higher [solute] than the cell… The cell loses water (osmosis) and shrivels and may die Osmosis kills

22. Water Balance in Plant Cells Plant cells like a hypotonic environment (water flows in) Plant cells like a hypotonic environment (water flows in) Their strong cell walls withstand the osmotic pressure that can cause animal cells to burst or shrivel Their strong cell walls withstand the osmotic pressure that can cause animal cells to burst or shrivel

24.  Cells use energy (ATP) to move large molecules or ions thru a cell membrane  Usually, these substances are moved “ uphill ” or against the concentration gradient. In other words, the substances are moved in the opposite direction of diffusion (passive transport)  The embedded proteins involved are often called PUMPS  Examples: pumps, exocytosis, endocytosis, phagocytosis, pinocytosis. Active Transport

25. Active Transport: Pumps

28. Facilitated Diffusion Facilitated Diffusion- molecules move down a concentration gradient with the aid of special proteins. Facilitated Diffusion- molecules move down a concentration gradient with the aid of special proteins.

29. Active Transport Requires Energy. Requires Energy. ATP (form of energy made by mitochondria). ATP (form of energy made by mitochondria). Moves against the concentration gradient. Moves against the concentration gradient.

30. Active Transport: Exocytosis For really LARGE molecules, vesicles form and fuse to the plasma membrane & spills its contents out

31. Active Transport: Exocytosis

32. Active Transport: Endocytosis 1.Vesicles bud inward 2.Opposite ends of the cell membrane meet & connect 3.Vesicle pinches off & brings LARGE substances into cell

33. An Amoeba feeding via the process of endocytosis. Active Transport: Endocytosis

34. Active Transport: Pinocytosis Cells actively engulf large quantities of fluid (water) Vesicles/vacuoles

35. Active Transport: Phagocytosis Solid particles

36. 35