Diffusion and Osmosis

1. Diffusion and Osmosis

2. Functions of Cell Membrane 1. Protect cell • Control incoming and outgoing substances • Selectively permeable - allows some molecules in, others are kept out

3. Phospholipid Bilayer

4. Plasma membrane components Phospholipid bilayer polar head P – cytosol hydrophobic molecules hydrophilic molecules nonpolar tails

5. Membrane Permeability • Selective permeability • The ability of a cell membrane to control which substances and how much of them enter or leave the cell • Allows the cell to maintain a difference between its internal environment and extracellular fluid • Supplies the cell with nutrients, removes wastes, and maintains volume and pH

6. The Selectively Permeable Nature of Cell Membranes

8. Types of Membrane Proteins

9. Methods of Transport Across Membranes 1. Diffusion -passive transport – no energy expended 2. Osmosis - Passive transport of water across membrane 3. Facilitated Diffusion - Use of proteins to carry polar molecules or ions across 4. Active Transport- requires energy to transport molecules against a concentration gradient – energy is in the form of ATP

10. Concentration and Gradients • Concentration • The number of molecules (or ions) of substance per unit volume of fluid • Concentration gradient • The difference in concentration between two adjacent regions • Molecules always move from a region of higher concentration to one of lower concentration

11. Diffusion • Solute molecules moving from an area of high concentration to an area of low concentration • Random motion drives diffusion • Equilibrium is reached when there is an even distribution of solute molecules (water)

12. Diffusion

17. Osmosis • Diffusion of water through a semi-permeable membrane • Semi-permeable: permeable to solvents (WATER), but not to large molecules • High [water] to low [water] • Dissolved molecules (i.e. glucose, starch) are called solutes • REMEMBER: Water = solvent Glucose, Starch = solutes

18. Osmosis

19. Effect of Water on Cells • Hypertonic Environment • High [solute], low [water] • Hypotonic Environment • High [water], low [solute] • Isotonic Environment • [water] = [solute] Hypertonic Hypotonic Isotonic Part 3 pg. 85

20. Cellulose in cell wall Osmosis in Living Cells

21. Isotonic Predictions? Hypertonic Hypotonic Osmosis in Red Blood Cells • Observe sheep RBCs via a wet mount of the sample • Aliquot one drop the following solutions with a ½ drop of RBC to a slide • 0.9% saline • 10% NaCl • Distilled water • Record observation in the table on page 85 Crenation

23. Effect of Water on RBC

24. Hypertonic Predictions? Hypotonic Osmosis in Plant Cells Plasmolysis • Observe Elodea leaves via a wet mount of the sample • Aliquot two drops the following solutions with a new Elodea leaf to a slide. Incubate for 10 minutes @ room temp. • 10% NaCl • Distilled water • Record observation in the table on page 85

25. Hydrostatic Pressure in Plants • Normal tomato on left – salt water gives effect (r) in 30min • Iris petal cells • Iris petal cells in wilted stage

26. Types of Transport

27. Transportation of Molecules • Passive Transport • Movement of molecules across a semi-permeable membrane • no energy required • Active Transport • Movement of molecules across a semi-permeable membrane against a concentration gradient • ENERGY – ATP • Facilitated Diffusion • Movement of molecules across a semi-permeable membrane with a protein • no energy required

29. FLUIDOUTSIDECELL Phosphorylated transport protein Transportprotein • Active transport in two solutes across a membrane • Na+/K+ pump • Protein shape change Firstsolute 1 First solute, inside cell, binds to protein 2 ATP transfers phosphate to protein 3 Protein releases solute outside cell Second solute 4 Second solute binds to protein 5 Phosphate detaches from protein 6 Protein releases second solute into cell Figure 5.18

31. Exocytosis and endocytosis transport large molecules exocytosis = vesicle fuses with the membrane and expels its contents FLUID OUTSIDE CELL CYTOPLASM Figure 5.19A

32. or the membrane may fold inward, trapping material from the outside (endocytosis) Figure 5.19B

33. Receptor-mediated endocytosis

34. Cholesterol can accumulate in the blood if membranes lack cholesterol receptors Phospholipid outer layer LDL PARTICLE Receptor protein Protein Cholesterol Plasma membrane Vesicle CYTOPLASM Figure 5.20

35. Membrane-Crossing Mechanisms