3. The Balancing Act of Life  Homeostasis – process by which an organisms maintains a relatively stable internal environment  Examples: Thermoregulation – maintaining body temperature Water regulation – keeping enough water in your body Regulating oxygen, blood sugar, and blood pH

4. Various methods of thermoregulation

5. Plasma Membrane  Function: The plasma membrane encloses the cell and protects it.  Function: It lets certain particles into and out of the cell.  Surrounds all cells

6. MOVEMENT THROUGH THE PLASMA MEMBRANE  How do materials or substances enter or leave cells?

7. THE PLASMA MEMBRANE IS PICKY!  Selective Permeability - the membrane can pick and choose what particles can pass through it.

8. PLASMA MEMRANE  Plasma membranes are made of phospholipids, proteins, and sometimes cholesterol.

9. THE PHOSPHOLIPID A A phospholipid - made up of a glycerol attached to 2 fatty acids and a phosphate group.  The fatty acids are hydrophobic (hate water).  The phosphate group is hydrophilic (likes water).

11. Reference

12. THE BILAYER STRUCTURE  The plasma membrane is a bilayer of phospholipids.

13. DRAW THIS IN NOTES!

15. THE BILAYER STRUCTURE  The plasma membrane is a bilayer of phospholipids.  Reference Reference

16. OTHER STRUCTURES IN THE MEMBRANE...  Animal plasma membranes have cholesterol in between phospholipids to slow their movement.

17. MEMBRANE PROTEINS  Proteins are embedded in membranes.  Some are on the inner or outer surfaces, some go the entire way through the bilayer.

18. MEMBRANE PROTEINS’ JOBS  Regulate which particles can pass through membrane (transport)  Act as enzymes in chemical reactions  Act as markers on outside and inside of cell to identify self

20. Membrane Video 0:45 – 1:57

21. WAYS TO MOVE THROUGH THE MEMBRANE:  1. Active transport requires energy to move the molecules through the plasma membrane.  2. Passive transport does not require energy, and occurs spontaneously.

22. PASSIVE TRANSPORT  The principle means of passive transport is diffusion.  Diffusion is the movement of molecules from a HIGH concentration to a LOW concentration.

24. Reference

25.  Equilibrium occurs when two opposing actions occur at the same rate.  Diffusion occurs when a system is not at equilibrium.

26. FACTORS THAT AFFECT DIFFUSION:  Temperature - higher temperature means more energy and molecules will diffuse faster.  Size - Smaller molecules will move more rapidly than larger molecules

27. REAL-LIFE EXAMPLES  CO 2 and O 2 diffuse across plasma membranes.  Oxygen moves from an area of high concentration to an area of low concentration from your lungs to your blood to your cells.

28.  As chemical reactions in the cell use up oxygen they produce CO 2.  The concentration of CO 2 inside the cell increases so that more CO 2 is inside of the cell.  Therefore CO 2 diffuses into your blood and then into your lungs where it is exhaled.

29. OSMOSIS  The movement of water from a high concentration to a low concentration.  It is the diffusion of water.  This can cause cells to burst or shrink.

30. Osmoregulation  Saltwater organisms have to get rid of salt and conserve water.  Freshwater organisms have to get salt and get rid of excess water.

31. FACILITATED DIFFUSION Helping diffusion along  Proteins help certain chemicals pass through a plasma membrane  Requires no energy (still moves from high to low)  Usually needed for slightly larger molecules like glucose

32. High Concentration Low Concentration Cell Membrane Glucose molecules Protein channel

33. High Concentration Low Concentration Cell Membrane Glucose molecules Protein channel

34. ACTIVE TRANSPORT  When a cell needs energy to move from low to high concentration.  Proteins pump molecules through membrane  Molecules move against diffusion (from low to high concentration)  Works against diffusion

35. Reference

36. OTHER WAYS CELLS GET MATERIALS...  Vesicles – a membrane-bound sac that is used to transport materials inside of a cell  Endocytosis – the plasma membrane engulfs and takes materials into the cell in a vesicle  Exocytosis – vesicles with chemicals move to plasma membrane and fuse with membrane. The chemicals are then released out of the cell  Endo and Exo are both forms of ACTIVE TRANSPORT

39. Exocytosis Video