The role of the cell membrane in transport

1. The role of the cell membrane in transport Section 2.2 Unit C

2. Objectives • define and give examples for movement of matter through the cell membrane • passive and active transport, • facilitated diffusion, • osmosis, • endocytosis and exocytosis

3. Review • Cell membrane/plasma membrane is a phospholipidbilayer • Phospholipids arranging so centre of bilayer is hydrophobic and outside is hydrophilic • How are they arranged? Which way do each part of the phospholipid arrange itself? • Proteins are embedded or attached to the membrane • Fluid-mosaic model

4. Diffusion: Introduction • Movement of particles from an area of high concentration to an area of low concentration • Moving towards equilibrium/sameness • How can we increase the rate of diffusion (i.e. how fast diffusion is occurring)? • Add energy- ex. Stir or heat • Ex. Opening a bag of coffee  releases aroma molecules

5. Demonstration • What direction is the water moving? • Why is it moving this way? • How could I increase the rate of diffusion here? • How do these principles apply to the smell of popcorn?

6. Diffusion in Cells • Occurs across the cell membrane (water or solutes) • Difference between concentrations over the cell membrane = concentration gradient • Process called passive transport • No energy required for movement

7. Permeability of membranes • Cell membrane is called selectively permeable • Allows only certain particles pass (not all) • Essential to maintain equilibrium and function • Semi-permeable passage of materials determined by size, charge, and solubility • Ex. Membranes used in water treatment and desalination • What kinds of molecules might not get through? Why not?

8. Fig C2.15 p. 277

9. Osmosis • Diffusion of water across a semi-permeable membrane • Example of passive transport • From area of higher concentration to lower concentration of water

10. Predicting movement of water • The movement of water can predicted by determining what the amount of solute is relative to the cell • A large amount of solute (high concentration) = low amount of water • A small amount of solute (low concentration) = high amount of water • Recall: water moves from high to low

11. Predicting movement of water • Compare solute solution (3 types) • 1) hypertonic- higher concentration of solutes than that in the cell • Ex. Cell is in a salt solution: solution has less water than the cell • 2) hypotonic- lower concentration of solutes than that in cell • Ex. Solution has more water than cell • 3)isotonic- same concentration of solutes in solution as in cell • Ex. Solution has same amount of water as the cell What would be the net movement of water in a hypertonic solution? Hypotonic? Isotonic?

12. Hypertonic solution

13. Hypotonic solution

14. Isotonic

15. How Osmosis works: an animated tutorial • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

16. Osmosis and animal cells • When cells lose water, they shrink (plasmolysis) • When cells gain water, they swell and may even burst (cytolysis) • When there is no net change in water, cells remain in homeostasis, or a state of equilibrium (i.e. no change)

17. Example: blood cells • http://highered.mcgraw-hill.com/sites/0073377988/student_view0/chapter3/hemolysis_and_crenation.html

18. Example • Identify each picture below as hypertonic, hypotonic or isotonic (which one is experiencing plasmolysis, cytolysis, equilibrium?) Isotonic (equilibrium) Hypotonic (cytolysis) Hypertonic (plasmolysis)

19. Osmosis in Plant Cells • Plant cells have a maximum amount of water that can hold • What makes it different than animal cells? What different structure does it have? • Movement of water into plant cell increases turgor pressure • Turgor pressure supports plant’s structure • High turgor pressure cells are turgid (firm) • Low turgor pressure  cells are flaccid (soft, floppy)

20. Example: Plasmolysis in onion cells http://www.youtube.com/watch?v=gYbt7hhIxPo&feature=related&safety_mode=true&persist_safety_mode=1&safe=active • Plasmolyseoignon rouge (red onion plasmolysis) – note how the cell contents pulls in from the cell wall:

21. Example: Plasmolysis in elodea plant • http://www.youtube.com/watch?v=VK-_YHakvho&safety_mode=true&persist_safety_mode=1&safe=active

22. Facilitated Diffusion • For particles that are soluble with water • Why would they need a special way across the membrane? • Uses proteins for diffusion – still passive transport • Channel proteins: pores for small molecules to pass through • Carrier proteins: attach to larger molecules, change shape and physically brings it inside the cell • http://www.youtube.com/watch?v=s0p1ztrbXPY&safety_mode=true&persist_safety_mode=1

23. Active Transport • Movement against concentration gradient • What does this mean? • Carrier proteins- act like a pump and use energy • Like swimming upstream • Energy from mitochondria • Uses energy molecules called ATP • http://www.youtube.com/watch?v=STzOiRqzzL4&feature=related

24. Endocytosis and Exocytosis • For very large molecules • Cell uses vesicles • Sac surrounding large particle • Like vacuoles, but smaller and temporary

25. Endocytosis • Movement into the cell • Steps: • 1) vesicle forms around particle • 2) cell membrane pinches off • 3) vesicle now inside cell

26. Exocytosis • Movement out of the cell • For waste particles or cell products Steps: • 1) vesicle surrounds particle in cell • 2) moves to membrane and fuses with it • 3) vesicle ruptures, releasing contents

27. Animation • http://www.youtube.com/watch?v=4gLtk8Yc1Zc&feature=related

28. Summary video • http://www.youtube.com/watch?v=kfy92hdaAH0

29. The Cell • Watch the following video and write down the organelles and transport systems that you recognize. Find at least 3 • “Inner Life of a Cell” • http://www.studiodaily.com/main/technique/tprojects/6850.html