1 SUB-UNIT 1.2: TRANSPORT ACROSS MEMBRANES

2 Learning Outcomes By the end of the topic, you should be able to -define diffusion describe examples of substances which enter and leave the cell by diffusion, discuss the importance of diffusion to cells. state that osmosis is a ‘special case’ of diffusion of water explain osmotic effects in plant and animal cells discuss the effects of placing plant and animal cells in hypertonic, hypotonic and isotonic solutions. explain the meaning of the terms plasmolysed, turgid and flaccid.

3 Cells and Diffusion As the ammonium hydroxide (an alkali) moves through it turns the pH paper blue. This demonstrates that the gas is spreading out from a region of high to low concentration.

4 Importance of diffusiondissolved food oxygen nucleus cell membrane cytoplasm carbon dioxide Human cheek cell

5 Importance of diffusionThe cell membrane freely allows oxygen to diffuse into the cell. high high high low Oxygen moves from a high concentration to a low concentration. low high low high low high high

6 Importance of diffusionThe cell membrane freely allows carbon dioxide to diffuse out of the cell. low Carbon dioxide moves from a high concentration to a low concentration. low low high high low low high high low low

7 Diffusion in ParameciumA unicellular animal has only _____ cell. The animal is constantly respiring. This means that it is using up ________ and producing _________ __________. The concentration of oxygen inside the unicellular animal is _______ than the concentration in the water outside. Oxygen therefore diffuses _____ the cell to allow continued respiration. one oxygen carbon dioxide less into

8 Diffusion in ParameciumHigher concentration of oxygen outside cell Lower concentration of oxygen oxygen CO2 Lower concentration of CO2 outside cell Higher concentration of CO2

9 Diffusion in ParameciumAt the same time the cell is making CO2. The CO2 concentration becomes greater _______ the cell than in the water _________. As a result CO2 diffuses _____ the cell. If it wasn’t for diffusion unicellular organisms wouldn’t get any oxygen or be able to get rid of waste CO2. inside outside out of

10 Diffusion in Amoeba Food vacuole containing soluble fooddiffusion of food

11 Diffusion in Amoeba Amoeba get their food by phagocytosis The food becomes enclosed in a food vacuole and digestive enzymes break it down into small soluble products. The dissolved food then moves by diffusion from a _____ concentration (inside the food vacuole) to a _____ concentration (in the cytoplasm) ______ a concentration gradient. Therefore diffusion allows all parts of the cell to get food. high low down

12 Importance in Multicellular Organismsoxygen carbon dioxide

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14 Diffusion in multicellular animalsBlood returning to the lungs from cells has a higher CO2 concentration and lower oxygen concentration than the air in the lungs. CO2 diffuses from the _____ into the ________ and oxygen diffuses from the ________ into the ________. Diffusion is also essential for dissolved food (e.g. ___________ and __________ _______ ) moving from the blood to respiring cell. Urea also moves in the opposite direction by diffusion. lungs blood lungs blood glucose amino acids

15 lung cells High O2 conc O2 Low CO2 conc O2 O2 Low O2 conc CO2High CO2 conc cells CO2

16 Diffusion in Green PlantsGreen plants need diffusion to get the raw materials needed for photosynthesis ( ___________ ________ and _________) CO2 diffuses from the air, through the stomata and into the air spaces in the leaf. Water moves from the soil into the roots, then enters the xylem and then enters the leaf cells. carbon dioxide water

17 Importance of diffusionWater molecules are also free to move in and out of the cell. However a cell needs to have some control which substances can enter and leave the cell. If not, then it could gain substances it doesn’t need or even lose substances it does need due to diffusion.

18 Cell Membrane Cell membrane with pores = SELECTIVELY PERMEABLEwater molecules small area of cell enlarged Oxygen molecules Carbon dioxide molecules Glucose molecules Starch/salt molecules

19 Model Cell experiment You will need to set up: Methoda length of visking tubing a boiling tube a test tube rack a filter funnel a paper towel a plastic syringe, a dropper a dimple tray stopclock starch and glucose solution Iodine solution Benedict’s solution water bath Method 1. Fill tubing with starch and glucose solution 2. Wash and dry bag 3. Place in boiling tube 4. Immediately test sample of water for glucose and starch 5. Test every 4 minutes

20 Importance of diffusionLarge molecules like starch cannot pass through the cell membrane. Molecules of soluble food e.g. glucose can pass through. The membrane is selectively permeable.

21 The Cell Membrane

22 Structure of cell membrane

23 Structure of cell membraneFluid Mosaic model – Composed of protein and lipid molecules Surface proteins – give support - carry molecules across membrane - enzymes to speed up reactions Channel proteins – allow small molecules to pass through membrane Phospoholipid bilayer – molecules can move and swap places

24 Relative water concentrationsWater concentration - compares concentration of solutions Higher solute concentration Lower solute concentration Lower water concentration Higher water concentration hypotonic Solution A is _________________ to solution B Solution B is _________________ to solution A hypertonic

25 More concentrations More concentrations hypotonicHigher solute concentration Higher water concentration Lower water concentration Lower solute concentration hypotonic Solution X is _________________ to solution Y Solution Y is _________________ to solution X hypertonic

26 hypertonic = less waterLower solute concentration Higher solute concentration Higher water concentration Lower water concentration HYPOTONIC HYPERTONIC hypotonic = more water hypertonic = less water

27 Osmosis is a special kind of diffusion, where:Water molecules move from a region of high water concentration to a region of low water concentration across a selectively permeable membrane. Let’s take a look

28 High water concentration Low water concentrationSelectively permeable membrane Sucrose molecules High water concentration Low water concentration Water molecules Inside the cell Outside the cell

29 Selectively permeable membraneSucrose molecules Water molecules are small enough to pass across the selectively permeable membrane Water molecules Inside the cell Outside the cell

30 Water molecules passing into the cellSelectively permeable membrane Water molecules passing into the cell Inside the cell Outside the cell

31 Selectively permeable membraneSucrose molecules Osmosis continues until the water molecules are evenly spread inside and outside of the cell Water molecules Inside the cell Outside the cell

32 SELECTIVELY PERMEABLE MEMBRANESolute molecules are too large to pass through the pores of the membrane Net movement of small water molecules PURE WATER SOLUTION (SOLVENT IS WATER)

33 Osmosis Diffusion of water through cell membranesDiffuses from an area of high water concentration [HWC] to an area of low water concentration [LWC] The difference in concentration between the areas is called the concentration gradient

34 Osmosis Set up test tubes shown Weigh dried cylindersCylinder of potato water Salt solution Weigh dried cylinders Leave for 30 minutes Dry then re-weigh

35 Molecular Model of OsmosisModel cell A 0.5M sucrose solution 0.1 M sucrose solution

36 Molecular Model of OsmosisModel cell B 0.5M sucrose solution Model cell B 0.5M sucrose solution

37 Molecular Model of OsmosisModel Cell C 0.5M sucrose solution 1.0M sucrose solution

38 Direction of Osmosis? 1 High water concentrationLow water concentration (100% water) 2 10% sucrose solution (90% water) distilled water (90% water) (80% water) 3 10% sucrose solution 20% sucrose solution (100% water) (99.5% water) 4 distilled water 0.5% sucrose solution (90% water) (99% water) 5 10% starch solution 1% starch solution (100% water) 6 animal cell distilled water

39 Animal cells in water

40 Plant cells in water turgid plasmolysed

41 Animal Cells Plant Cells In distilled water, an animal cell will gainwater & burst In strong salt/sugar solution, an animal cell will lose water & shrink Animal Cells In distilled water, plant cells gain water & become swollen (turgid) Plant Cells In strong salt/sugar solution, plant cells lose water, the cytoplasm & vacuole shrink in from the cell wall – cell becomes plasmolysed

42 The animal cell does not.So why does the animal cell burst in distilled water when the plant cell does not? The plant cell has a rigid cell wall that helps the plant cell keep its shape. The animal cell does not.

43 Unicellular animals Contractile vacuole with canals to collect waterWhen water passes in, vacuole expands then bursts when full When one vacuole is emptying, the other is filling This is osmoregulation

44 Osmosis and Energy ProductionThe world's first test plant to harness osmotic power, a new emission-free source of energy, opened recently in Norway. Near Oslo, the facility will exploit the energy produced when fresh water meets seawater. 44

45 Fresh water and salt water is guided into two separate chambers, divided by an selectively permeable membrane. The fresh water moves by osmosis towards the seawater. The flow puts pressure on the seawater side, and that pressure can be used to drive a turbine, producing electricity.

46 Problems…….. The plant at Oslo produces 2 kilowatts of electricity – enough to run a coffee machine!! Very Expensive to build But Huge potential with further research.

47 Active Transport

48 low concentration high concentration energy from respirationACTIVE TRANSPORT low concentration high concentration PLASMA MEMBRANE …..releases them on the other side Carrier protein takes up particles on one side of the plasma membrane and ………. energy from respiration low concentration gradient high

49 It takes energy to move molecules against their concentration gradient.

50 Active Transport is….. The movement of molecules against aconcentration gradient, this means from a low concentration to a high concentration. Energy is needed for active transport. Carrier proteins pump molecules e.g. into the cell in order to maintain a high concentration inside the cell or out of the cell in order to maintain a low concentration in the cell.

51 Active transport in High conc. of A inside cellLow conc. of A outside cell Plasma membrane protein Active transport in

52 Animation: How the Sodium Potassium Pump WorksNerve Cells: Sodium ions are actively transported out of the cell and potassium ions transported into the cell.

53 Cells in our thyroid gland actively uptake iodineCells in our thyroid gland actively uptake iodine. They use it to make hormones.

54 More oxygen Less oxygen More respiration Less respirationMore energy produced Less energy produced More active transport of molecules Less active transport of molecules

55 Hyperlink: Summary of Diffusion, Osmosis, Active TransportMembrane Transport