Cell Transport

1. Cell Transport

2. Ch. 9: Cell Transport • Passive Transport • Targets • Distinguish between diffusion & osmosis • Define equilibrium & explain how it is established • Explain what is meant by a concentration gradient • Explain how substances cross the cell membrane through facilitated diffusion • Explain how ion channels assist the diffusion of ions across the cell membrane

3. Concentration • how much of a given substance there is mixed with another substance

4. Kinetic Motion • All particles of matter are in constant (random) motion • Molecules travels in a straight line until they hit something, bounce off, and travel in a new direction • Molecules move down the concentration gradient from an area more concentrated to an area less concentrated

5. Concentration Gradient • Difference in concentration of a substance across a space

6. Animations of Active Transport & Passive Transport Weeee!!! high low This is gonna be hard work!! high low Types of Cellular Transport • Passive Transport cell doesn’t use energy • Diffusion • Facilitated Diffusion • Osmosis • Active Transport cell does use energy • Protein Pumps • Endocytosis • Exocytosis

7. Passive Transport • Diffusion • Movement of molecules from an area of higher concentration to an area of lower concentration • Driven entirely by the kinetic motion of molecules • Continues until the concentration of molecules is the same throughout the space they occupy

8. Factors Affecting Diffusion Rate

9. Equilibrium • Exists when the concentration of the molecules of a substance is the same throughout a space • Random motion of molecules continues so equilibrium is maintained (no concentrated gradient)

10. Diffusion Across Membranesright guard commercial • Cell membranes are selectively permeable • Phospholipidbilayer (non-polar) • Diffusion depends on size, type of molecule, & chemical nature of molecule

11. About Cell Membranes (continued) • Structure of cell membrane Lipid Bilayer -2 layers of phospholipids • Phosphate head is polar (water loving) • Fatty acid tails non-polar(water fearing) • Proteins embedded in membrane Phospholipid Lipid Bilayer

13. Diffusion Across Membranes • Non-polar molecules (O2 & CO2) can dissolve in lipid bilayer and thus pass through by diffusion • Very small insoluble molecules may pass through membrane pores by diffusion • Large or Polar substances move through membrane with help from transport proteins as do ions

15. Osmosis • Osmosis • Diffusion of water molecules through a cell membrane from an area of higher water molecule concentration to an area of lower concentration • Quick Fact! • Process of osmosis was first described in 1748 by French scientist Abbé Jean Antoine Nollet. He observed that water spontaneously diffused through a pig bladder membrane into alcohol!

16. Direction of Osmosis • Depends upon the relative concentration of solutes on the two sides of the membrane

17. Osmotic Potential • The tendency of water to move across a membrane into a solution • The lower the solute concentration, the higher the osmotic potential

18. Isotonic Solution • A solution in which the concentration of dissolved substances is the same as the concentration inside the cell; therefore, the concentration of water is the same on both sides of the plasma membrane • Diffusion of water in = water out

19. Turgor Pressure • Pressure that exists inside a cell

20. Hypotonic Solution • A solution in which the concentration of a dissolved substance is lower than the concentration inside the cell; therefore, the concentration of water is greater outside the cell than inside the cell • Water diffuses into the cell & the cell swells-Turgor Pressure increases • Cytolysis – cell bursts • Plant v. Animal

21. Osmosis (Cell in Hypotonic Solution

22. Hypertonic Solution • A solution in which the concentration of dissolved substances is higher than the concentration inside the cell; the concentration of water is greater in the cell than outside • Result: water moves out of the cell & the turgor pressure decreases & the cell shrivels • Plasmolysis – loss of water pressure in a cell

23. Osmosis (Cell in Hypertonic Environment)

24. Click for animation

25. How Cells Deal with Osmosis • Example: Paramecia (freshwater protozoan) • Live in a hypotonic environment • Water constantly diffuse into them • Contractile vacuoles (organelle) removes the excess water • A common remedy for a sore throat is to gargle with salt water. Using the concept of osmosis, explain how this remedy might work. • Quick Fact! • Wooden drawers in cabinets absorb water from the air on humid days causing the wood to swell & hard to open!

26. Osmotic Pressure • Pressure required to stop osmosis in a solution • Pressure that builds up as water diffuses into a cell • If a physical barrier prevents expansion of a hypertonic solution as water moves in by osmosis, a buildup of pressure is created as water continues to flow in • As pressure ↑, the net flow of water molecules will slow (stops in plants due to cell wall – turgor pressure)

27. Reverse Osmosis • The movement of water particles from an area of lower concentration to an area of higher concentration with the • Addition of pressure

28. Facilitated Diffusion • Used for molecules that cannot diffuse rapidly across the membrane (size, polarity) • Molecules are assisted by membrane proteins • 2 Types • Carriers & Channels • Move down the concentration gradient (High [ ] to low [ ]) no energy is used by cell

29. Facilitated Diffusion • Molecule binds to carrier protein • Protein changes shape shielding molecule from lipids as it crosses • Molecule is released to cell interior • Carrier protein returns to original shape • Accelerates glucose movement • Carrier proteins are specific to the molecules they carry

30. Facilitated Diffusion Carriers Channels

31. Diffusion through Ion Channels • Membrane proteins • Passageway through membrane for ions to pass through (Na+, Ca2+, Cl-) • Each ion channel is specific to one type of ion • Some channels are always open, others have gates • Gates open in response to stimuli • Stretching of cell membrane • Electrical signals • Chemical signals

32. Ion Channels

33. Active Transport • Differentiate between active & passive transport • Compare & contrast endocytosis & exocytosis

34. Active Transport • Movement of materials up a concentration gradient, from an area of low concentration to an area of higher concentration • Requires cell to use energy • Uses carrier proteins • [ ] = Concentration

35. Active Transport • Endocytosis & Exocytosis • Transport of macromolecules & food particles too large to pass to pass through cell membrane

36. Endocytosis • Process by which cells ingest large materials by surrounding them with the cell membrane forming a pouch • Pouch pinches off from membrane & forms a vesicle

37. Endocytosis • Types: • Pinocytosis • Transports solutes or fluids (cell drinking)

38. Endocytosis • Phagocytosis • Ingestion large particles or whole cells (cell eating) • Many unicellular organisms feed this way • Used to ingest bacteria & viruses • Cells called phagocytes – allows lysosomes to fuse with vesicles containing bacteria & viruses to destroy them

39. Exocytosis • Reverse of endocytosis • Cell excretion • Vesicles in cytoplasm fuse with cell membrane to release contents to external environment • Releases proteins packaged in Golgi apparatus

40. ENDOCYTOSIS/EXOCYTOSIS

41. Kidspiration by: Riedell