The cell membrane controls what enters and exits the cell to maintain homeostasis. It is a selectively permeable bilayer made of phospholipids and embedded proteins. Small hydrophobic molecules and gases can pass through by diffusion down their concentration gradients, but most ions and larger molecules require transport proteins. Active transport uses ATP to move substances against their concentration gradients, such as the sodium-potassium pump. Endocytosis and exocytosis allow cells to ingest and secrete larger particles and molecules.

1. The Plasma Membrane - Gateway to the Cell

2. Photograph of a Cell Membrane

7. Structure of the Cell Membrane

8. Phospholipids Cholesterol Proteins ( peripheral and integral) Carbohydrates (glucose) Membrane Components

12. Cell Membrane Polar heads are hydrophilic “water loving ” Nonpolar tails are hydrophobic “water fearing” Makes membrane “Selective” in what crosses

14. Cell Membrane Hydrophobic molecules pass easily ; hydrophilic DO NOT The cell membrane is made of 2 layers of phospholipid s called the lipid bilayer

16. Semipermeable Membrane Small molecules and larger hydrophobic molecules move through easily. e.g. O 2 , CO 2 , H 2 O

17. Ions , hydrophilic molecules larger than water, and large molecules such as proteins do not move through the membrane on their own. Semipermeable Membrane

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28. Types of Transport Across Cell Membranes

31. Diffusion of Liquids

32. Diffusion through a Membrane Cell membrane Solute moves DOWN concentration gradient (HIGH to LOW)

34. Diffusion of H 2 O Across A Membrane High H 2 O potential Low solute concentration Low H 2 O potential High solute concentration

36. Cell in Isotonic Solution CELL 10% NaCL 90% H 2 O 10% NaCL 90% H 2 O What is the direction of water movement? The cell is at _______________. equilibrium ENVIRONMENT NO NET MOVEMENT

37. Cell in Hypotonic Solution CELL 10% NaCL 90% H 2 O 20% NaCL 80% H 2 O What is the direction of water movement?

38. Cell in Hypertonic Solution CELL 15% NaCL 85% H 2 O 5% NaCL 95% H 2 O What is the direction of water movement? ENVIRONMENT

39. Cells in Solutions

40. Isotonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) Hypotonic Solution CYTOLYSIS Hypertonic Solution PLASMOLYSIS

41. Cytolysis & Plasmolysis Cytolysis Plasmolysis

42. Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic

43. What Happens to Blood Cells?

44. hypotonic hypertonic isotonic hypertonic isotonic hypotonic

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57. Three Forms of Transport Across the Membrane

60. Proteins Are Critical to Membrane Function

62. Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins .

67. Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential

68. Moving the “Big Stuff” Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. Exocytosis - moving things out. This is how many hormones are secreted and how nerve cells communicate with one another .

69. Exocytosis Exocytic vesicle immediately after fusion with plasma membrane.

70. Moving the “Big Stuff” Large molecules move materials into the cell by one of three forms of endocytosis .

71. Pinocytosis Most common form of endocytosis . Takes in dissolved molecules as a vesicle .

73. Example of Pinocytosis pinocytic vesicles forming mature transport vesicle Transport across a capillary cell (blue).

74. Receptor-Mediated Endocytosis Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol , etc.

75. Receptor-Mediated Endocytosis

77. Endocytosis – Phagocytosis Used to engulf large particles such as food, bacteria , etc. into vesicles Called “Cell Eating”

79. Phagocytosis About to Occur

80. Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)

81. Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane . Inside Cell Cell environment