Chapter 3, Section 4

1. Chapter 3, Section 4 Passive Transport: Diffusion and Osmosis

2. Preview • Passive Transport through • diffusion • osmosis

3. Types of Passive Transport Passive transport: the movement of certain molecules across the cell membrane without energy input from the cell. • Diffusion • Osmosis

4. DEMO P.E.O.E. (a demonstration activity) Predict: predict what you think will happen Explain: explain why you believe this will happen Observe: watch the demonstration and record what happened Explain: explain what actually happened

5. Diffusion Diffusion: fluid or gas molecules move from a region of high concentration to areas of low concentration (molecules spread out) • this is the result of random motion of molecules causing them to collide and scatter • eventually the concentration of the molecules is the same throughout the solution (dynamic equilibrium)

6. Diffusion in the Cell Diffusion plays an important role is moving substances across the cell membrane • small lipids (fats) and other nonpolar substances (CO2 and O2) can easily diffuse across the cell membrane • Example: cells consume O2, which means the O2 concentration outside the cell is always higher. O2 diffuses into the cell through the membrane

7. DEMO P.E.O.E. (a demonstration activity) Predict: predict what you think will happen Explain: explain why you believe this will happen Observe: watch the demonstration and record what happened Explain: explain what actually happened

8. Osmosis Osmosis: water molecules move from areas of high concentration to areas of low concentration

9. Osmosis • Solutions in which water molecules can move are said to be • Hypotonic, • Isotonic , • or Hypertonic

10. Osmosis • Hypotonic • when the cell has higher concentration of solutes than the solution • water molecules are more concentrated outside the cell • water diffuses into the cell • if too much water enters the cell, it can burst like an overfull balloon

11. Osmosis • Isotonic • when the cell and solution have the same concentration of solutes • water molecules move in and out of the cell through the cell membrane at an equal rate (dynamic equlibrium) • the cell does not expand or shrink

12. Osmosis • Hypertonic • when the solution has a higher concentration of solutes than the cell • the water concentration is higher in the cell • water moves out of the cell • if too much water leaves the cell, it can shrivel or even die

13. Osmosis

14. Osmosis

15. Facilitated Diffusion • Some molecules cannot easily diffuse across a membrane • they may be allowed to enter the cell by passing through a transport protein • this process is called facilitated diffusion

16. Facilitated Diffusion • Facilitated diffusion is still considered a form of passive transport because no energy is expended by the cell