1. The Working Cell: Membrane Function CHAPTER 5
Passive Transport
Osmosis and Water Balance
Active Transport
Bulk Transport
Exo- and Endocytosis
Cell Signaling

2. Membrane Function
Working cells must control the flow of materials to and from the environment.
A cell membrane or wrapper made of phospholipids is relatively impermeable
Proteins embedded in the membrane provide for selective permeability and transport of materials into and out of the cell, among other things
Membrane Selectivity

3. Functions of Membrane Proteins
Figure 5.11

4. The Working Cell: Membrane Function CHAPTER 5
Passive Transport
Osmosis and Water Balance
Active Transport
Bulk Transport
Exo- and Endocytosis
Cell Signaling

5. Passive Transport: Diffusion Across Membranes
Molecules contain heat energy.
They vibrate and wander randomly.
Diffusion is movement of molecules from regions of high concentration to low concentration
Molecules tend to spread into the available space.
Diffusion Across A Membrane
Passive transport of small or hydrophobic molecules
Facilitated diffusion of larger and polar molecules
Diffusion

6. Examples of Passive Transport Across a Phospholipid Bilayer

7. The Working Cell: Membrane Function CHAPTER 5
Passive Transport
Osmosis and Water Balance
Active Transport
Bulk Transport
Exo- and Endocytosis
Cell Signaling

8. Osmosis and Water Balance in Cells
Osmosis is the passive transport of water across a selectively permeable membrane.
Water moves across a membrane from high concentration (high purity) to low concentration (low purity)

9. Terms Used to Compare the Purity of Water Solutions
A hypertonic solution
Has a higher concentration of dissolved substances (solute)
5% salt
1% salt
A hypotonic solution
Has a lower concentration of dissolved substances (solute)
1% salt
5% salt
An isotonic solution
Has an equal concentration of dissolved substances (solute).
1% salt
1% salt

10. Cells Must Regulate Salt and Water Balance
Turgid Elodea
Plasmolysis

11. The Working Cell: Membrane Function CHAPTER 5
Passive Transport
Osmosis and Water Balance
Active Transport
Bulk Transport
Exo- and Endocytosis
Cell Signaling

12. Active Transport: The Pumping of Molecules Across Membranes
Active transport is the movement of molecules from low concentration to high concentration
Active transport requires energy to pump molecules across a membrane, into more a more crowded space
Active Transport

13. The Working Cell: Membrane Function CHAPTER 5
Passive Transport
Osmosis and Water Balance
Active Transport
Bulk Transport
Exo- and Endocytosis
Cell Signaling

14. Bulk Transport: Exocytosis and Endocytosis
Dumping molecules out of the cell (export)
Exocytosis and Endocytosis Introduction

15. Bulk Transport: Exocytosis and Endocytosis
Bringing molecules into the cell (import)
Includes pinocytosis, phagocytosis, and receptor-mediated endocytosis
Pinocytosis: cell “drinking”
Phagocytosis: cell “eating”

16. Receptor-mediated endocytosis

17. The Working Cell: Membrane Function CHAPTER 5
Passive Transport
Osmosis and Water Balance
Active Transport
Bulk Transport
Exo- and Endocytosis
Cell Signaling

18. The Role of Membranes in Cell Signaling
Cellular communication
Begins with the reception of an extracellular signal.
The signal is transduced or passed across the membrane
A response is elicited from the transduced signal

19. The Working Cell: Membrane Function CHAPTER 5
Passive Transport
Osmosis and Water Balance
Active Transport
Bulk Transport
Exo- and Endocytosis
Cell Signaling