1. Title: Water potential and diffusion 14 March 2016 Learning question: what is diffusion and why is it important? Homework: Learning package 2 due 23 rd September

2. Key words Diffusion Osmosis Passive transport Facilitated diffusion Hydrophilic Hydrophobic Water potential Osmosis Equilibrium Isotonic Hypotonic Hypertonic Electrolytes Anions Cations

3. Aims from specification (i)explain the mechanisms of diffusion, facilitated diffusion (to include channel and carrier proteins) and osmosis (to include channel proteins), with reference to the structure of the red blood cell membrane; (j) describe the mechanism of active transport, with reference to the structure of the red blood cell membrane;

4. Diffusion Net movement of molecules from a region of high concentration to a region of lower concentration until those molecules are evenly distributed Does not require energy – a passive process Small, lipid-soluble molecules can diffuse across the plasma membrane (phospholipid bilayer)

5. Facilitated diffusion Protein channels help small ions (charged particles) or water soluble molecules to cross the plasma membrane As protein channels help, this is called as facilitated diffusion Some protein channels remain permanently open to allow substances to pass through

6. Facilitated diffusion Carrier proteins are a form of facilitated diffusion “flip-flop” method of transport – Molecule binds to protein – One side opens, other side closes – E.g. glucose entering RBCS

7. Osmosis

8. Highest water potential is zero, therefore water has the highest water potential. Adding molecules to water e.g. sugar/salt, decreases the water potential (less than zero) Osmosis is the movement of water molecules from a region of high water potential to a region of lower water potential until both sides reach equilibrium (equal)

9. Arrange these products in order of lowest water potential to highest

10. 35g Arrange these products in order of lowest water potential to highest 33g 27g 13g 24g

11. Highest water potential, no bad stuff

12. Osmosis in cells Water is so small it can get through the phospholipid bilayer. Permeability to water can be increased by the addition of protein channels that allow water to enter and exit the cell rapidly

14. Describe the number of solute molecules inside and out side of the cell in these three pictures Hypotonic: LESS solute molecules outside the cell than inside Isotonic: EQUAL number of solute molecules inside and outside Hypertonic: MORE solute molecules outside the cell than inside

15. These drinks have NO place in a healthy diet! Linked to obesity, diabetes and heart disease. Refers to gatoraide when it is drunk as per instructions!

16. Keeping the osmotic balance Electrolytes – ions with positive or negative charge – Positive ions – cations – Negative ions – anions Mostly the job of electrolytes to maintain the water potential in cell plasma Electrolytes in blood stream need to kept within a narrow range – deviation from set point can result in tachycardia, bradycardia or heart failure

17. Task 1 Complete all questions on page 19 of the textbook in complete sentences! Self assess – mark your answers in a different coloured pen. If you have missed anything out, fill it in. Read pages 20-21 on active transport

18. Imagine you are going the other way from the rest of the crowd. Would it be easy to get through the crown? What would you have to do to get through the crowd?

19. Active Transport The movement of molecules against the concentration gradient Requires energy for this to happen Energy for cells is in the form of ATP Most common protein pump that uses active transport is the sodium-potassium pump.

20. Exocytosis and Endocytosis Use Figure 3 at the top of page 21 to write a description of the terms endocytosis and exocytosis Give examples of molecules that are taken into the cell and removed from the cell by these methods.

21. Task 2 Complete all questions on page 21 of the textbook in complete sentences! Self assess – mark your answers in a different coloured pen. If you have missed anything out, fill it in.