The Movement of Molecules: Diffusion, Osmosis & Active Transport

3. The Movement of Molecules: Diffusion, Osmosis & Active Transport For additional resources on this lecture topic, see the Diffusion, Osmosis & Active Transport main page on SPO. Images: Diffusion Animation, Biology Corner; Diffusion, J Krieger

4. Cellular Transport Foldable Fold your paper in half, then half again, then half again like me! Open it up. You should have 8 equal-sized squares. Fold the “doors” into the center, so that your paper looks like a window with closed “shutters”. Cut the “shutters” so that you have four total doors. 1 2 3 4

5. Cellular Transport Foldable

6. Cellular Transport Foldable • On the inside of each door, explain each process • Under each door, correctly illustrate the process. Worth 100 points and to be TURNED IN tomorrow! After I grade them you will glue them to page 38.

7. Plasma Membrane • Separates the cell from its environment. • Phospholipid molecules oriented so that hydrophilic(waterloving) heads directed outward and hydrophobic(waterhating) tails directed inward. • Proteins embedded in two layers of phospholipids(lipid bilayer). • Membrane is semi-permeable (also called selectively permeable). From the Virtual Cell Biology Classroom on ScienceProfOnline.com Image: Cell Membrane diagram, Wiki

8. Semi-Permeable Membranes • Selectively Permeable - some substances can pass through the membrane while others cannot

9. Passive Transport Primary function of plasma membrane →regulate movement of molecules entering or leaving cell. Passive Transport – is the movement of dissolved materials through a cell membrane without using cellular energy – like riding a bike downhill Two types of passive transport: 1. Diffusion (simple and facilitated) 2. Osmosis _Diffusion (simple)_ = when molecules move down a concentration gradient, from a higher to a lower concentration. Images: Diffusion Animation, Biology Corner; Diffusion, J Krieger From the Virtual Cell Biology Classroom on ScienceProfOnline.com

10. Passive Transport Facilitated Diffusion Protein channels assist in diffusion of molecules across plasma membrane. Movement only occurs in the presence of a concentration gradient. Some molecules move across the membrane more quickly during facilitated diffusion than simple diffusion. DOES NOT USE ENERGY!!! From the Virtual Cell Biology Classroom on ScienceProfOnline.com Image: Facilitated Diffusion, M. Ruiz

11. Passive Transport - Osmosis Osmosis – diffusion of water across the cell (plasma) membrane Environment surrounding cells may contain amounts of dissolved substances (solutes) that are… - equal to - less than - greater than …those found within the cell. Plasma membrane CELL Liquid environment inside the cell. Liquid environment outside the cell. From the Virtual Cell Biology Classroom on ScienceProfOnline.com Images: Osmosis animation

12. Passive Transport - Osmosis Tonicity and Osmosis Isotonic : equal concentration of a solute inside and outside of cell. Hypertonic : a higher concentration of solute. Hypotonic : a lower concentration of solute. Water will always move toward a hypertonic environment!! From the Virtual Cell Biology Classroom on ScienceProfOnline.com Images: Osmosis with RBCs, M. Ruiz

13. Passive Transport - Osmosis • Hypertonic and hypotonic solutions separated by a semipermeable membrane! Water molecules Hypotonic Large molecule, such as starch Hypertonic

14. Passive Transport - Osmosis • The large molecules will try to cross the membrane, but they can’t!

15. Osmosis • Since the big molecules can’t move across, the water molecules WILL in order to make both sides be isotonic.

16. Is This Confusing? • If it is difficult to remember that water flows from the hypotonic side to the hypertonic side, just remember the following rule: water always flows to where there is more solute. • Solutes are often salts or sugars, so you can just remember: • Water follows the salt.

17. Osmosis • Think of the water molecules as kids and the salt molecules of potato chips- which way would you go if you had a choice?

18. Osmosis can Work Against Gravity!

19. Red Blood Cells and Osmosis

20. Active Transport • How most molecules move across the plasma membrane. • Analogous to a pump moving water uphill. • Two types of Active Transport: • Transport by proteins • Transport by engulfing (Endocytosis) • Exocytosis • REQUIRES ENERGY!!! ATP = usable energy Active Transport by proteins Energy from adenosine triphosphate (ATP) drives substances across the plasma membrane with aid of carrier molecules. From the Virtual Cell Biology Classroom on ScienceProfOnline.com Image: Sodium-potassium pump, M. Ruiz

21. Active Transport • Transport by Engulfing – the cell membrane surrounds and engulfs, or encloses, a particle. • Once the particle is engulfed, the cell membrane wraps around the particle and forms a vacuole within the cell • Also called Endocytosis

22. Exocytosis • In exocytosis, materials are exported out of the cell via secretory vesicles. • Requires energy (ATP)