Chapter 5: Homeostasis and Transport

1. Chapter 5:Homeostasis and Transport

2. Section 5-1:Passive Transport • Cell membrane helps organisms maintain homeostasis by controlling what enters/exits cell • Some substance can cross cell membrane with out using energy from cell • PASSIVE TRANSPORT

3. Diffusion • Simplest • movement of substances from area of high concentration to area of low concentration

4. Driven by kinetic energy that molecules posses • kinetic energy = molecules constantly in motion • Move randomly in straight line until they hit an object  Move in straight line in concentration gradient because to molecule to bounce off of

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

6. Equilibrium • When the concentration of molecules of a substance is the same throughout a space • Even at equilibrium the random motions of molecules still occur • Random motions on one direction balance out those of the other direction

7. Diffusion Across Membrane • If molecules can diffusion across cell membrane it will move from high concentration to low concentration

8. Ability of molecule to move across membrane depends on: • size • type of molecule • chemical nature of membrane

9. Membrane = phospholipids • THUS any substance that can dissolve in lipids will pass through membrane • Also VERY small molecule can fit through pores even if they are not soluble in lipids

10. REMEMBER • Chapter 2: Solution = solute dissolved in solvent • CELLS: Solutes = organic and inorganic moleculesSolvents= water

11. Osmosis • Process by which water molecules diffuse across cell membrane from high concentration to low concentration • Does not cost cell energy to occur

12. Direction of Osmosis • Net direction of osmosis depends on relative concentration of solutes on either side of membrane

15. Put it together... • If a solution is hypotonic then the cytosol is hypertonic • If solution is hypertonic then cytosol is hypotonic

16. Cell Environments • Isotonic environment  cells are fine(cells of vertebrate animals on land or sea animals) • Cells in hypotonic environment  cells must rid themselves of excess water (unicellular organisms in FRESH water)

17. How do cells deal with osmosis? 1- Contractile vacuoles 2- Solute Pumps 3- Cell Walls

18. Contractile Vacuoles • How some unicellular organisms rid themselves of excess water • Organelle which removes water • How? Collect excess water and then contract, pumping water out of cell **REQUIRES ENERGY**

19. Solute Pumps • Mostly in multicellular organisms • Pump solutes OUT of cytosol • Bring cytosol solute concentration closer to that of the solution • water less likely to move into cell

20. Cell Walls • Plant roots swell as they absorb water • Swelling stops when cell membrane is pressed against cell wall

21. Cells walls able to withstand pressure of water • Turgor pressure: pressure that water molecules exert against cell wall

22. Plasmolysis • In hypertonic environment water leaves cells • Cells shrink away from cells walls • Turgor pressure is lost • Plants wilt

23. Cytolysis • Bursting of cells • Cells which lack contractile vacuoles, solute pumps, and cells walls • Water continuously moves into cells

24. Facilitated Diffusion • Process used for molecules that cannot diffuse rapidly through cell membranes • Why not? • Not soluble in lipids • Too large to pass through pores

25. Carrier Proteins • Assist in diffusion of insoluble/large molecules across membrane • STILL PASSIVE! • Molecules moved from high concentration to low concentration

26. How carrier proteins work… 1. Carrier proteins binds to molecules it transports 2. Carrier protein changes shape

27. 3. Protein shields molecules from hydrophobic area of membrane 4. Molecule transported through membrane 5. Molecule released into/out of cell 6. Protein returns to original shape

28. Transport of Glucose • Facilitated diffusion • Glucose molecules too large • Cells need for energy • Carrier proteins are specific for certain molecules

29. Diffusion through Ion Channels • Passive transport involving membrane proteins • Ions: Na+, K+, Ca2+, and Cl- • Each type of ion has specific ion channel

30. Some ion channels always open • Others have “gates” that open to allows OR close • Gates may open due to three kinds of stimuli • Stretching of cell membrane • Electrical signals • Chemicals in cytosol or external environment

31. 5-2: Active Transport • Sometimes cells must move materials against concentration gradient[low]  [high] • Active transport: requires cell to use energy

32. Cell Membrane Pumps • Some carrier proteins also help active transport • Same “Bind-Change shape-Transport-Return shape” process

33. Sodium-Potassium Pump • Transport Na + and K + • Most animals cells must have high Na + outside of cells and low K + inside cell

34. Process • Three Na + ions bind to sodium-potassium pump WHILE carrier protein split phosphate group from ATP molecule • Phosphate group binds to carrier protein and changes carrier protein shape

35. 3. Now has shape need to bind two K + ions 4. When K + ions bind, phosphate group releases and carrier protein changes shape again 5. K + ions released into cell 6. Ready to do it again!

37. Summary of Sodium-potassium Transport… • 3 Na + ions now outside • 2 K + ions now inside • Usually about 450 Na + ions and 300 K +PER SECOND!

38. Movement of 3:2 Na + :K + ions create electrical gradient • Outside :positively charged • Inside :negatively charged • IMPORTANCE: conduction of electrical impulses along nerve cells

39. For things too large… • Macromolecules • Food particles • Types: • Endocytosis (endo in/enter) • Exocytosis (exo out/exit)

40. Endocytosis • Cells ingest external fluid, macromolecules, and large particles (including other cells) • Pouch formed  Materials enclosed by portion of cell

41. Vesicle: membrane bound organelle consisting of pinched off pouch from cell membrane • Some vesicles fuse with lysosomes to digest materials

42. Type of Endocytosis Based on kind of material taken in: • Pinocytosis • Phagocytosis

43. Pinocytosis • transport of solutes or fluids

44. Phagocytosis • movement of large particles or whole cells • how some organisms feed • how animal cells ingest bacteria and viruses • Phagocytes: cells that allow lysosomes to fuse with vesicles that contain harmful things

45. Exocytosis • Reverse of endocytosis • Vesicle fuse with cell membrane and release content’s into cell environment • Cell may use to release proteins