1. The Plasma Membrane 1

2. I. Maintaining Balance 2

3. How do cells maintain balance? Cells need to maintain a balance by controlling material that move in and out of the cell  HOMEOSTASIS 3

4. I. Maintaining Balance Small molecules, like water, oxygen, and carbon dioxide can move in and out of the cell freely. Large molecules like proteins and carbohydrates cannot. Eliminating wastes 4

5. I. Maintaining balance 5

6. Structure of the plasma (cell) membrane All cells are surrounded by a plasma membrane. Functions like a GATE, controlling what ENTERS and LEAVES the cell. The cell membrane is semipermeable or selectively permeable. 6

7. Structure of the plasma (cell) membrane A semipermeable membrane only allows certain molecules to pass through Some substances easily cross the membrane, while others cannot cross at all. 7

8. Structure of the plasma (cell) membrane Made of a thin layer of lipids and proteins Made mostly of phospholipid molecules (phosphate and lipid) Phospholipids are a kind of lipid that consists of 2 FATTY ACIDS (tails) and a PHOSPHATE GROUP (heads) Hydrophilic head Hydrophobic tail 8

9. Structure of the plasma (cell) membrane Cell membranes consist of TWO phospholipid layers called a PHOSPHOLIPID BILAYER Phosphate head Cytoplasm inside cell Outside cell 9

10. Structure of the plasma (cell) membrane Water molecules surround both sides of the cell membrane. Polar phosphate heads sticking TOWARD the water (hydrophilic) Nonpolar lipid tails pointing AWAY from the water (hydrophobic) 10

11. Structure of the plasma (cell) membrane The cell membrane is constantly being formed and broken down in living cells. cytoplasm 11

12. III. Lipid Bilayer Moving with and among the phospholipids are cholesterol, proteins, and carbohydrates. Cholesterol: Nonpolar, found among the phospholipids to help prevent the fatty acid tails from sticking together Helps with structure and homeostasis Gives cell its fluidity Fact: The model of the cell membrane is affectionately called the Fluid Mosaic model 12

13. III. Lipid Bilayer 13

14. III. Lipid bilayer Proteins: Found on the surface of the plasma membrane = transmits signals to the inside of the cell Embedded in the plasma membrane = structure and support of cell’s shape, and move large substances in and out of cell 14

15. III. Lipid Bilayer 15

16. III. Lipid bilayer Carbohydrates Attached to proteins; helps cells identify chemical signals Ex: help disease fighting cells recognize and attack a potentially harmful cell 16

17. Cellular Transport Types 17 Active vs Passive

18. Cellular Transport All particles move and have kinetic energy (energy of motion). Movement is random and usually in a water solution Cells are mostly made of water and there is a constant flow of ions and particles. 18

19. IV. 2 types of cellular transport 1.Passive transport = movement of molecules across the membrane by using the molecules kinetic energy. The cell exerts NO energy! 2.Active transport = transport of materials against the concentration gradient and requires cellular energy. 19

20. V. Passive Transport 3 types of passive transport 1.Diffusion = the net movement of particles from an area of higher concentration of particles to an area of LOWER concentration of particles. 20

21. Diffusion… Molecules move randomly until they are equally distributed (equilibrium). Diffusion continues until the concentration of substances is uniform throughout. 21

22. Diffusion… Dynamic equilibrium = continual movement but no overall change in concentration. Movement of materials into and out of the cell at equal rates maintains its dynamic equilibrium with its environment. 22

23. Diffusion… Diffusion depends on the concentration gradient. Concentration gradient is the difference between the concentration of a particular molecule in one area and the concentration in an adjacent area. Ex: gas exchange in the lungs (oxygen from air to blood and carbon dioxide from blood to air) 23

24. 24

25. V. Passive Transport 2.Facilitated Diffusion = type of passive transport that increase the rate of diffusion with the use of a carrier protein (transport) Usually because molecules are too large to pass through the membrane. Would pass too slowly without the use of a carrier protein Ex: Facilitated diffusion of glucose 25

26. Facilitated Diffusion 26

27. V. Passive Transport 3. Osmosis = the diffusion of water molecules from an area of HIGH water concentration to an area of LOW water concentration across a semi-permeable membrane 27

28. V. Passive Transport: Osmosis Occurs in response to the concentration of solutes dissolved in water! Solutes are dissolved substances in a solution. Solvent is usually water in cells. Cytoplasm of cells is mostly water containing many dissolved solutes. 28

29. V. Passive Transport: Osmosis Because no TWO molecules can occupy the same space at the same time, the MORE solutes there are in a certain volume of water; the FEWER water molecules there can be in the same volume. 29

30. V. Passive Transport: Osmosis Plant and animal cells behave differently because plant cells have a large water vacuole and a cell wall 30

31. V. Passive Transport: Osmosis A.Isotonic Solution = a solution in which the concentration of dissolved substances (solutes) is the SAME as the concentration of solutes inside the cell. Osmosis DOES NOT occur since a concentration gradient(difference) is not established. 31

32. What happens to cells when places in an isotonic solution? Plant cells – become flaccid (limp) Plant wilts because no net tendency for water to enter Animal Cell – normal (preferred condition) 32

33. Animal cell Plant cell 33

34. V. Passive Transport Osmosis B.Hypotonic Solution = a solution in which the concentration of solutes is LOWER than the concentration of solutes inside the cell. 34

35. What happens to cells when placed in a hypotonic solution? Animal cell – water moves through plasma membrane into the cell. This causes the cell to swell and the internal pressure increases. Cell lyses (bursts)! 35

36. What happens to cells when placed in a hypotonic solution? Plant cell – normal The vacuole and cytoplasm increase in volume The cell membrane is pushed harder against the cell wall causing it to stretch a little The plant tissue becomes stiffer (turgid). 36

37. V. Passive Transport: Osmosis C.Hypertonic Solution = a solution in which the concentration of dissolved substances is HIGHER than the concentration inside the cell 37

38. What happens to cells when placed in a hypertonic solution? Animal cell - will shrivel because of decreased turgor pressure 38

39. What happens to cells when placed in a hypertonic solution? Plant Cell – will lose water from vacuole and a decrease in turgor pressure will occur: so it is plasmolyzed. Turgor pressure = internal pressure of a cell due to water held there by osmotic pressure Plasmolysis = the loss of turgor pressure causing the plasma membrane to pull away from the cell wall. Causes the plant to wilt. 39

40. Animal cell Plant cell 40

41. Summary of Cell Behavior in Different Environments 41

42. VI. Active Transport Movement of molecules from an area of Low to an area of HIGH concentration (opposite of passive transport!) REQUIRES cellular energy! Moves large, complex molecules such as proteins across the cell membrane. 42

43. VI. Active Transport Large molecules, food, or fluid droplets are packaged in membrane- bound sacs called vesicles. 43

44. 3 types of active transport 1.Endocytosis = process by which a cell surrounds and takes in material from its environment Used by ameba to feed and white blood cells to kill bacteria 44

45. Endocytosis Two Types 1.Pinocytosis = cell taking in liquids 2.Phagocytosis = cell taking in solids (food) 45

46. 3 types of active transport 2.Exocytosis = expels materials out of the cell, reverse of endocytosis Used to remove wastes, mucus, and cell products Proteins made by the ribosomes in a cell are packaged into transport vesicles by the Golgi apparatus Transport vesicles fuse with the cell membrane and then the proteins are secreted out of the cell (ex: insulin) 46

47. 3 Types of Active Transport 3.Pumps Proteins pump ions against concentration gradient. (Ca +2, Na +1, K +1 ) 47

48. Summary of the types of transport 48

49. Which process is used to transport these? Liquids, gasses, dyes, small uncharged molecules Water Glucose Ions such as sodium, potassium, calcium Hormones, enzymes, solids, food entering Hormones, enzymes, wastes leaving Diffusion Osmosis Facilitated diffusion Active (pumps) Active (Endocytosis) Active (Exocytosis) 49

50. Crash Course Video: Membranes and Transport 50