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Methods of Transport Across Membranes

Methods of Transport Across Membranes. 1. Diffusion 2. Osmosis 3. Facilitated Diffusion 4. Active Transport. Osmosis and Diffusion. Learning Objectives. To understand Diffusion and osmosis, osmotic pressure. To learn how to calculate osmotic pressure

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Methods of Transport Across Membranes

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  1. Methods of Transport Across Membranes 1. Diffusion 2. Osmosis 3. Facilitated Diffusion 4. Active Transport

  2. Osmosis and Diffusion

  3. Learning Objectives • To understand Diffusion and osmosis, osmotic pressure. • To learn how to calculate osmotic pressure • To understand hemolysis & crenation • To know the applications of osmosis in living organisms & everyday life • To learn the difference between osmosis & dialysis

  4. Osmosis and Diffusion Have very important role in our daily life.

  5. In our daily life • Daily we perform various activities . We just do them and do not pay any attention to the science behind these activities. • Let us see a few examples and try to understand the science behind these activities.

  6. Rooh Afza , jame sheerin or Sharbati Anar in water.The color spreads out the entire glass slowly. The red color diffuses throughout water. Addition of sugar to tea in cup

  7. Examples of diffusion • Aroma of food from kitchen • Smell of perfume • This happens because the gas molecules from the kitchen and perfume diffuse into the air and spread . • In plants, carbon dioxide gas diffuses through the stomata of the leaves for photosynthesis. • Oxygen gas diffuses out of the stomata and lenticels of the leaves during photosynthesis.

  8. Think of • How we absorb nutrients from food through the intestines and deliver them to individual cells. This obviously is essential to the survival of a cell. • It is through Osmosis, which is stabilizing the internal environment of an organism by keeping the water and intercellular fluids levels balanced.

  9. Cell Membrane • Living cells of both plants and animals are enclosed by cell membrane,which is semi-permeable. • This regulates the flow of liquids and of dissolved solids and gases into and out of the cell. • This is called Osmosis

  10. Osmosis • It influence the distribution of nutrients and the release of metabolic waste products. • The membrane forms a selective barrier between the cell and its environment; • Not all substances can pass through the membrane with equal ease.

  11. Without this selectivity • The substances necessary to the life of the cell would diffuse uniformly into the cell's surroundings, and toxic materials from the surroundings would enter the cell.

  12. Another most important function • Cells get rid of their waste by osmosis. • This process also happens in the kidneys, that filter the blood to get rid of any toxic chemicals.

  13. Osmosis is a special type of diffusion. • It is the diffusion of water molecules from a solution with a lower solute concentration to a higher solute concentration through a semi permeable membrane until an equilibrium condition is reached. • Osmosis take place in the liquid medium. • Osmosis is a passive transport as no external energy is required.

  14. In both diffusion and osmosis • There is movement of particles from higher concentration to lower concentration.  • Both require no external energy. • Diffusion takes place in liquids and gases.

  15. We feel thirsty after eating salty food. Why? • Salt is a solute. Our cells become concentrated with salt after we eat salty food. So our cells draw water in its direction. So we feel thirsty and we drink water to bring stability in our cells.

  16. In plants • Absorption of water by roots of the plants is an example of osmosis.  Roots of the plants absorb water and minerals from soil and transport it to various parts of the plant . • They use osmosis to maintain minerals and water equilibrium in their cells. There is lower concentration of water molecules in the roots than in the surrounding soil.

  17. In severe sore throat • We are advised to gargle salt water. • The cells and the tissues surrounding the throat will be swollen up because of excess of water when there is sore throat. • The salt water has lower concentration of water molecules than the cells of our throat. • So water molecules move from the swollen cells of the throat to the salt water and reduces the pain and swelling of the throat.

  18. In Diarrhoea • it is advised to drink ORS / fresh fruit juices. • Why? • ORS and fresh fruit juices have salt and sugar in addition to water and fruit extracts. • Our intestines would have lost water and there would be no water in the cells due to Diarrhoea. • When ORS is taken it diffuses through the cells and revive the intestines and put them back into action.

  19. Functions of Membranes 1. Protection of cell 2. Control incoming and outgoing substances 3. Maintain ion concentrations of various substances 4. Selectively permeable - allows some molecules in and some others are kept out

  20. Phospholipid Bilayer

  21. Blood-Brain Barrier • Allows some substances into the brain, but screens out toxins and bacteria • Substances allowed to cross or can cross BBB include: water, CO2, Glucose, O2, Amino Acids, Alcohol, and antihistamines. HIV and bacterial meningitis can cross the barrier.

  22. Solutions • Solutions are made of solute and a solvent • Solvent - the liquid into which the solute is poured and dissolved. We will use water as our solvent today. • Solute - substance that is dissolved or put into the solvent. Salt and sucrose are solutes.

  23. Methods of Transport Across Membranes 1. Diffusion -passive transport - no energy expanded 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

  24. Diffusion • Movement of molecules from an area of high concentration to an area of low concentration. • Movement from one side of a membrane to another, un-facilitated

  25. Diffusion

  26. OSMOSIS • It is the flow of solvent through a semi- permeable membrane such as cell membrane, from a dilute solution to concentrated solution. Osmosis is a selective process.

  27. Osmosis • Semipermeable membrane: permits passage of some components of a solution. • Example: cell membranes and cellophane , plasma membrane , cell org membranes , peritoneum and urinary bladder • The movement of a solvent from low solute concentration to high solute concentration. • There is movement in both directions across a semi-permeable membrane.

  28. Osmosis • Eventually the pressure difference between the arms stops osmosis.

  29. Osmotic Pressure Force per unit area that prevents water from passing through membrane

  30. Osmotic Pressure • The hydrostatic pressure at equilibrium which prevents the passage of more solvent through the semi permeable membrane is called osmotic pressure.

  31. P If applied pressure is too low, H2O flows into the region of higher solute concentration... “Down the concentration gradient” for H2O. P Membrane Pure H2O H2O + Solutes

  32. P If applied pressure is too high, H2O flows into the region of lower solute concentration... Against the natural concentration gradient for H2O. --Reverse Osmosis P Membrane Pure H2O H2O + Solutes

  33. P P Minimum pressure required to maintain equal flow rates (to prevent infusion of H2O). Proportional to solute concentration differences across membrane. Membrane Pure H2O H2O + Solutes

  34. Units of Osmotic Pressure OSMOLE Non electrolyte: 1 M Solution = 1 osmole = 22.4 atmospheres = 22.4 x 760 mm Hg = 17024 mm Hg. Electrolyte: Dissociates into ions Bimolecular double osmotic pressure….NaCl Tri molecular tripple osmotic pressure…..CaCl2

  35. Osmotic pressure of some biological fluids • Human plasma • Gastric Juice • Hepatic bile and • CSF all exert nearly equal osmotic pressure which is about 3.7 milli osmoles / liter.

  36. Osmotic Pressure • Osmotic pressure, , is the pressure required to stop osmosis: Π = osmotic pressure M = Molarity (mol/L) R = Ideal Gas Constant T = Temperature (K)

  37. Problem #1 Calculate osmotic pressure for 0.10 M Na3PO4 at 20°C. Na3PO4 ionizes into 4 particles, (3 Na + 1 PO4), Ion conc. is = 0.40 M p = MRT = (0.40) (0.0821) (293) = 9.6 atm

  38. (3.00 atm) [0.0821 atm.L / mol) (300K)] = 0.122M Problem #2: Calculate molarity if soln. in water (300K) has osm. pressure of 3.00 atm M = p / RT

  39. Osmotic Pressure • Osmotic pressure is force per unit area that prevents water from passing through membrane! • Osmosis: Solvent passes through membrane. • Dialysis: Solute passes through membrane

  40. Hemolysis: • Red blood cells placed in a hypotonic solution; • There is a higher solute concentration in the cell; • Osmosis occurs and water moves into the cell. • The cell bursts.

  41. Crenation

  42. Crenation of Red Blood Cells, Electron Micrograph

  43. To prevent crenation or hemolysis, IV (intravenous) solutions must be isotonic.

  44. Drinking Seawater will Cause Dehydration of Body Tissues

  45. Reverse Osmosis Water Purification

  46. Home water purification by reverse osmosis

  47. Kidney and Dialysis

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