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Osmosis, diffusion, active transport


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Osmosis, diffusion, active transport

  1. 1. Substances pass through the cell membrane by: 1.DIFFUSION 2.OSMOSIS 3.ACTIVE TRANSPORT
  2. 2. To remain alive, a cell needs:to take in the gas:to eliminate the gas: WHY? WHY?
  3. 3. To remain alive, a cell needs FOOD:Name TWO examples GLUCOSE AMINO ACIDS Name the material which also enters a cell & is used as a SOLVENT. water
  4. 4. Salts are also neededexample in plant cells: Nitrates
  5. 5. By which process do these materials enter or leave a cell? Gases by: DIFFUSION Water by: OSMOSIS Glucose Amino acids ACTIVE Salts TRANSPORT
  6. 6. Active or Passive transport?- No energy is needed
  7. 7. The cell membrane is semi-permeable / selectively permeable. Explain. Outside a cell Inside a cell CELL MEMBRANE
  8. 8. The cell membrane allows only certain substances to pass throughOutside a cell Porous membrane Inside a cell Only small molecules pass
  9. 9. Is the movement of molecules from aregion of high concentration to a region of lower concentration
  10. 10. Liquids & Gases diffuse
  11. 11. Draw arrows to show direction of molecules:Concentrationgradient forred moleculesConcentrationgradient forblue molecules
  12. 12. Fig. 1 Diffusion in a liquid.
  13. 13. Why does oxygen keep on entering an amoeba? Due to a concentration gradient.
  14. 14. Examples of ‘where’ diffusion occurs:  Diffusion of CO2 into stomata of leaves during photosynthesis.
  15. 15. Diffusion of: O2 into the alveoli of the lungs CO2 out of capillaries.
  16. 16. The rate of diffusion depends on:1. Concentration  the higher the concentration, the faster is the rate of diffusion
  17. 17. The rate of diffusion depends on:2. Temperature  the higher the temperature, the faster is the rate of diffusion
  18. 18. The rate of diffusion depends on:3. Size of molecules  the smaller the size, the faster is the rate of diffusion
  19. 19. Is the diffusion of water across a semi- permeable membrane from a weak solution to a strong solution. Strong Weak solution solution
  20. 20. Two conditions for osmosis to occur: 1. A semi-permeable membrane.Dilute salt Strong salt or sugar or sugar solution solution 2. A difference in concentration.
  21. 21. Red blood cells are placed in solutions of a different sugar concentration. Explain the result. Sugar molecule Let’s explain each:
  22. 22. RBC & and external solution are at the SAME concentration 1. Water entering RBC = water leaving. What happens? No change in RBC size.
  23. 23. RBC are placed in a very concentrated sugar solution2. RBC are dilute compared to external solution & lose water. What happens? RBC shrink.
  24. 24. RBC are placed in a dilute sugar solution 3. RBC take up water . What happens? RBC swell and finally burst.
  25. 25. Osmosis in plant cellsIn a weak solution In a concentratedwater will enter solution the cellthe cell and fill the loses water andvacuole. The cell goes flaccidmembrane will because thepush against the vacuole becomescell wall making flaccid and thethe cell very cytoplasm stopsinflexible. It is said pushing againstthat cells in this the cell wall. Thisstate are turgid. state is called plasmolysis. 4.9
  26. 26. What happens to PLANT cells?Cell in dilute Cell in same Cell in Cell in a much solution concentrated concentrated becomes: concentration solution solution of solution. becomes: becomes: TURGID FLACCID PLASMOLYSED
  27. 27. Summary: What happens to cells when placed in a solution which is :
  28. 28. Explain why red blood cells burst indistilled water but plant cells do not. Rigid cell wall in plants prevents bursting.
  29. 29. What happens to the cytoplasm in a plasmolysed cell?It is pulled away from the cell wall. A plant wilts when cells are plasmolysed. Is the plant dead in this wilted sate?
  30. 30. Lose water Gains waterTURGID PLASMOLYSED
  32. 32. Stomata are: OPEN when CLOSED whenguard cells are: guard cells are: FLACCIDTURGID
  33. 33. Soil became flooded with seawater. The plant wilted.However, the plant recovered after it rained. Explain. Wilted: Plant recovered: cells lost water cells absorbed water by osmosis. by osmosis.
  34. 34. To demonstrate osmosis in non-living material.Visking tubing / dialysistubing / cellulose tubing
  35. 35. To demonstrate osmosis in living tissue.
  36. 36. What do you expect to happen?Strong sucrose Distilled watersolution in bag. in beaker. Bag membrane Water enters bag by osmosis.
  37. 37. Explain the result of this experiment: 1. Starch is placed inside a bag. 2. The bag is put in a tube containing iodine solution and left for one hour. Iodine molecules diffused into the bag. Bag is selectively permeable.
  38. 38. Explain the results of this experiment Salty water Distilled water1. Slice your potato into 5 mm slices. 2. Place one slice in distilled water and one in salty water.Distilled 3. After 30 minutes, you water can bend the slice of potato in salty water easily. Salty water
  39. 39. Two pieces of celery were for left for 4 hours as shown: Distilled Salty water water Explain the result.
  40. 40. What has happened? Pins mark level of water.Set up apparatus. Result after 1 hour.
  41. 41. Why does water enter an amoeba? An amoeba is more concentrated than thesurrounding water. Water enters by osmosis.H2O
  42. 42. Why doesn’t an amoeba burst like a RBC? Contractile vacuole releases excess water. 2 Excess water enters 1 Water enters contractile vacuole. due to osmosis. 7 The cycle is repeated. 3 Contractile vacuole swells. 6 Contractile vacuole bursts and expels water. 4 Contractile vacuole moves to edge of cell.
  43. 43. Salting: Is a way to preserve meat.
  44. 44. Explain why there is no need to place jam in a refrigerator. Bacteria DIE Dilute Bacteria die as theylose water by osmosis. Concentrated
  45. 45. Have a sore throat? Use a salt gargle. WHY is this effective against bacteria? Bacteria die as they lose water by osmosis.
  46. 46. Name the process: Oxygen moves out from a stoma: diffusion Water enters a root hair / amoeba: osmosis
  47. 47. Name the process: Glucose absorbed by small active transport intestine:
  48. 48. Is when substances cross the cell membraneagainst a concentration gradient, usingenergy and carriers in the membrane.
  49. 49. Large molecules and ions pass through proteins in the cell membrane proteins
  50. 50. ATP: Adenosine Triphosphate ATP is the molecule that supplies ENERGY
  51. 51. Fig. 4 Active transport. AGAINST a concentration gradient
  52. 52. How do Osmosis & Diffusion occur? DOWN a concentration gradient Low High conc. conc. AGAINST a concentration gradient
  53. 53. Question: [MAY, 2009] Paper 2Paramecium lives in stagnant water. During aninvestigation about the average time taken by acontractile vacuole to fill up and empty, it wasfound that the contractile vacuoles fill up andempty every 60 seconds when placed in watercompared to 180 seconds when placed in 0.3% saltconcentration. Explain. (4)
  54. 54. Question: [MAY, 2009] Paper 2More water enters a Paramecium living inwater than when is a salt solution. Waterenters the cell by osmosis from a dilute to amore concentrated salt solution. The moreconcentrated the external solution is, the lesswater that enters.
  55. 55. Question: [APRIL, 2010] Paper 2Explain ONE benefit of each of the followingfeatures in the parasitic mode of life of aparasite living in the gut of its host:a) body surface covered with microvilli; (1) To increase the surface area for absorption of food
  56. 56. Question: [APRIL, 2010] Paper 2b) long and thin body; (1) For a large surface area for absorption of food (Accept allows food to flow past so that the parasite is not washed away/decrease in diffusion distance)c) body wall has active transport systems. (1) For uptake of food molecules even against a concentration gradient.
  57. 57. Question: [APRIL, 2010] Paper 1Fresh cherries are fleshy and juicy. Candiedcherries are prepared by placing fresh cherries in avery strong sugar solution. Explain why candiedcherries lose their fleshy juicy texture. (2)
  58. 58. Question: [APRIL, 2010] Paper 1Water moves out of the cherries by osmosis.Cherry cells are dilute when compared to thesurrounding solution. Water follows itsconcentration gradient. Cells become plasmolysed.