Osmosis and Diffusion

1. Osmosis and Diffusion Cell Processes- Cellular Transport

2. Weeee!!! high low This is gonna be hard work!! high low Types of Cellular Transport • Passive Transport cell doesn’t use energy • Diffusion • Facilitated Diffusion • Osmosis • Active Transport cell does use energy • Protein Pumps • Endocytosis • Exocytosis

3. Active Transport Transport of large particles- (whole cells or solids) a.Endocytosis- • cell membrane folds in and forms a small pouch • The pouch then pinches off from the cell membrane to become a vesicle b.Exocytosis- • Vesicle moves to the cell membrane-fuses with it and then releases its contents to the outside of the cell

4. Amoeba Feeding

5. Passive Transport- Diffusion Diffusion is the movement of molecules from an area of high concentration to an area of low concentration, until evenly spread out.

6. Why is Diffusion Important? All living cells rely on diffusion to live. Cells use it for: • Getting raw materials for respiration (dissolved substances and gases) • Removing waste products (eg. from respiration) • Photosynthesis in plants (raw materials in, waste products out) Examples…

7. Respiration- Gas Exchange In breathing you exchange carbon dioxide (CO2) and oxygen (O2) between alveoli in the lungs and the blood. This is an example of diffusion.

9. Cellular Respiration- In Cells food + oxygen  carbon dioxide + water + energy

10. Cellular Respiration and Diffusion

11. Photosynthesis and Diffusion • Carbon dioxide diffuses in through the stomata carbon dioxide + water  oxygen + glucose • Oxygen and water diffuse out of the stomata

12. Osmosis • Osmosis is a special case of diffusion. • It is the movement of WATERacross a selectively permeable membrane from a high concentration to a low concentration.

13. Selectively Permeable? • The cell membrane has very small holes in it. • Small molecules like water can pass through it easily. • Larger molecules like sugar, salt and starch can not fit through easily.

14. Model of a Selectively Permeable Membrane Water Starch Small molecules, such as watercan pass through it. Large molecules likestarchcan notpass through the membrane Diagram shows the net flow of water

15. Osmosis What is Happening? The water molecules pass both ways through the membrane The overall flow of water molecules is from a region with lots of water molecules to region of less water molecules. Water is described as moving down a concentration gradient – from a high concentration to a low concentration Water Starch Lots of water molecules Few water molecules

16. Osmosis what is happening? Water molecules move from the high water concentration to the low water concentration. Until both sides have an evenly balanced water concentration. Water is described as moving down a concentration gradient – from a high concentration to a low concentration Water Starch Lots of water molecules Few water molecules

18. Osmosis in Action Have a look at this video and answer the questions on the next slide: http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

19. 1 Osmosis is best defined as the movement of A) molecules from an area of high concentration to an area of lower concentration. B) molecules from an area of low concentration to an area of higher concentration. C) water molecules across a membrane from an area of low water to an area of higher concentration. D) water molecules across a membrane from an area of high water concentration to an area of lower concentration. E) water molecules inside a container. 2Which of the following will pass through a cell membrane most easily? A) small polar molecules B) small nonpolar molecules C) large polar molecules D) large nonpolar molecules E) large neutral molecules 3 A red blood cell placed in a hypertonic medium will A) expand. B) burst. C) shrink. D) have no change in shape. E) become a white blood cell. 4 A 5% urea solution is hypotonic to a 10% urea solution. A) True B) False If a cell is placed in an isotonic medium, there will be no net movement of water. A) True B) False

20. In pure water – water will move in swelling the vacuole which pushes out against the cell wall. The plant cell is described as TURGID. The cell does not burst because of the cell wall. Plant Cell in Different Solutions Plant cell placed in pure water Water moves Into the cell

21. Plant Cell in Strong Sugar Solution In a strong salt or sugar solution – water will move out of the vacuole causing it to shrink. The cytoplasm can also shrink away from the cell wall. The plant cell is described as Plasmolysed or Flaccid. Strong Sugar/Salt Solution

22. Animal Cells in Different Solutions • A red blood cell in pure water, water will move into the cell and the cell will BURST(there is no cell wall to prevent this happening) • In a strong salt/sugar solution water will move out and the cell will SHRINK (the cell in described as CRENATED)

25. Some terms when comparing two solutions • Hypotonic – one that has a high water concentration compared to surrounding solution • Hypertonic– one that has a low water concentration compared to surrounding solution • Isotonic– one that has a water concentration equal to the surrounding solution

26. What Type of Solution are These Cells In? B C A Hypertonic Isotonic Hypotonic

27. Act it out! • Nominate some sugar molecules • Everyone else is a water molecule • Draw a dashed line down the middle of the parking lot with chalk (your selectively permeable membrane!) • Arrange your water molecules either side of the membrane • Add your sugar molecules to one side and see if equilibrium can be restored by water moving in the right direction! • What happens if you remove some of the water molecules?