The plasma membrane acts as a gatekeeper that regulates what enters and exits the cell. It uses both passive and active transport. Passive transport relies on diffusion and moves substances along concentration gradients, while active transport requires energy and can move substances against concentration gradients using mechanisms like the sodium-potassium pump. The plasma membrane is a lipid bilayer with embedded proteins that gives cells structure and allows for selective permeability and transport of molecules in and out of the cell.

1. Plasma Membrane: The Gate Keeper Ms. Polson Biology October 18,2009

2. Plasma Membrane Lesson Objectives Students will be able to: Use vocabulary related to transport across the plasma membrane Differentiate between active and passive transport Identify membrane structures that permit transport Understand the function of the plasma membrane as a “gate keeper”

3. What is a Plasma Membrane? All living cells have them Selective permeability Asymmetric Gives cell structure Cell-cell recognition Fluid mosaic model Lipid movement in bilayer Maintains homeostasis

4. Animal and Plant Plasma (cell) Membrane

5. Plasma Membrane Function Separate inside organelles from external environment Regulate entrance and exit of substances Transfer information Establishment of electric potential difference Site of biological activities Attachment between cells Removal of waste

6. Plasma Membrane Photograph: Cell Membrane

7. Plasma Membrane Structure Lipids Phosphlipids, Glycolipids, Steroids Hydrophilic and hydrophobic properties Gives flexibility Proteins Integral - transport channels Peripheral - recognition sites Determines membranes specific functions Sugars

8. Lipid Bilayer Model Cross Section Gorter and Grendel, 1925 Two sheets of lipids 7.5 nm thick Found around cell Embedded with proteins Strengthened with cholesterol molecules (animal)

9. Lipid Bilayer Model Phospholipid Hydrophilic Water loving Phosphate end Outside and inside Hydrophobic Water fearing Lipid tail region Center

10. Plasma Membrane Hydrophilic and Hydrophobic

11. Passive Transport Simple Diffusion Result of inherent kinetic energy Thermal motion or heat No energy needed Diffusion and osmosis High concentration to low concentration: small molecules O 2 , CO 2 , H 2 O

12. Simple Diffusion

13. Passive Transport Facilitated Diffusion Proteins act as tunnels Carrier proteins help larger polar molecules cross membrane Glucose Moves materials along concentration gradient

14. Active Transport Energy is needed Low concentration to high concentration Movement of molecules up concentration gradient Sodium-potassium pump

15. Active Transport Movement of large substances by vesicles Endocytosis – taking into cell Phagocytosis Pinocytosis Receptor mediate Exocytosis – expelling from cell ER or Golgi Apparatus

16. Types of Solutions Isotonic Concentration of dissolved substances are the same inside and outside the cell Hypotonic Concentration of dissolved substances are lower outside than inside Hypertonic Concentration of dissolved substances are higher outside than inside

17. Homeostasis Plasma Membrane Maintains constant internal environment Controls movement of materials in and out of the cell as a “gate keeper” Dynamic equilibrium Separates cellular organelles from external environment

18. Vocabulary Review Plasma Membrane Homeostasis Passive Transport Simple Diffusion Facilitated Diffusion Active Transport Hydrophilic Hydrophobic Endocytosis Exocytosis Isotonic Hypertonic Hypotonic

19. Questions… Comments… Thoughts?