chapter 13 diffusion and osmosis

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Chapter 13 Diffusion and Osmosis. Diffusion & Osmosis. Draw a spider diagram about what you know about movement of substances in & out of the cell. Syllabus -- Objectives. Define the term: Selectively permeable Explain the role of selectively permeable membranes. - PowerPoint PPT Presentation


  • Chapter 13Diffusion and Osmosis

  • Diffusion & OsmosisDraw a spider diagram about what you know about movement of substances in & out of the cell

  • Syllabus -- ObjectivesDefine the term: Selectively permeableExplain the role of selectively permeable membranes.Define the terms: osmosis & diffusionGive examples of diffusion and osmosis.Define the term: turgor.Explain turgidity in plant cells.Describe the application of high salt or sugar concentration in food preservation.

  • Selective permeability of membranesAll cell membranes (biological membranes) are similar in structure.The cell membrane (plasma membrane) around a cell works the same as membranes around organelles eg. Mitochondria & nucleus.

  • Movement in cells takes place through membranes

    All the membranes in a cell act in the same wayMitochondrial membranesCell MembranesChloroplast membranesNuclear membranes

  • New VocabularySelectively permeable: A selectively permeable membrane allows some but not all substances to pass through. E.g. cell membrane

    Permeable: A permeable membrane allows all substances through e.g. cell wall is fully permeable.

    Impermeable: An impermeable membrane does not allow substances to pass through.

  • Biological membranes are semi-permeable. Other membranes e.g. cellophane, visking tubing & dialysis tubing are semi permeable (selectively permeable)

    These membranes allow small molecules such as water, oxygen and carbon dioxide to pass through freely.

  • They do not allow large molecules e.g. protein, sugars and salts to pass through easily. Cells have specialised mechanisms in their membranes to allow these substances e.g. proteins, sugars & salts through when necessary.

  • DialysisDialysis is used on patients whose kidneys do not work properly. The dialysis membrane in the machine is used to filter the persons blood and remove substances e.g. salts, water and urea.

  • MovementSubstances move in and out of cells in 2 ways1. DiffusionMovement of molecules from a region of higher concentration to a region of lower concentration. This method does not require energy. 2. Active TransportMovement of molecules from a less crowded to a more crowded area WITH the use of energy. Molecules are carried" into or out of the cell using some of the cell's energy.

  • Learning checkWhat type of movement in cells requires energy?What type of movement in cells does not require energy?Diffusion is the movement of substances from an area of ....... concentration to an area of ......... concentrationName 3 different types of membranes

  • PermeabilityMembranes can be:

    Permeable let everything in and out e.g. cell wallSemi Permeable - let some things in and out e.g. cell membraneImpermeable let nothing in and out e.g. wall of cork cells

  • Diffusion in everyday lifeSmell of perfumeBread bakingFood colouring in waterSugar in tea

  • Diffusion in a LeafIn photosynthesis Carbon dioxide gas diffuses into leaf and oxygen gas diffuses out

    Carbon dioxide


  • Learning CheckWhat type of permeability allows free movement of substances?What type of permeability allows some movement of substances?What type of permeability allows no movement of substances?Can you name a few common examples of diffusion?

  • New Vocabulary

  • OsmosisOsmosis is the movement of water across a semi-permeable membrane from a region of high water concentration to a region of low water concentration

  • Solvent: A solvent is a liquid that dissolves other substances e.g. water

    Solute: A solute is a substance that has been dissolved e.g. sugar & salt

    Solution: The mixture of the solvent and solute is a solution. E.g. salty water

  • Osmosis is a special type of diffusion that does not require energy

    Osmosis is passive (no energy required)

  • Experiment to Demonstrate OsmosisResults Table T/B pg 134

    Sucrose SolutionDistilled WaterTurgid (fullness) at startTurgid (fullness) at endMass at start (g)24.1g24.0gMass at end of Activity (g)29.5g24.0g

  • If pure water is separated from salt water by a membrane the following occurs:The water molecules move randomly in both directionsThe salt molecules cannot move out so more water moves in to the salt solutionWhat you have is water moving from where there is a high concentration of water to where there is a lower concentration of water this is osmosis

  • Learning CheckWhat is osmosis?Does osmosis require energy?

  • Osmosis and Animal CellsAnimal cells are only enclosed by a membraneIf an animal cell is surrounded by a solution that is the same concentration as the cytoplasm in the cell water will move in and out at the same rate and the cell will remain intact.

  • Many animals that live in the sea have cytoplasm with a similar concentration to sea water. If this didnt happen the fish would swell up or shrivel up.It is the function of our kidneys to make sure the fluid in our bodies that surrounds our cells (plasma) has a stable concentration.

  • Animal cells in a less concentrated solutionIf an animal cell is in a solution that is less concentrated than its cytoplasm (i.e. if there is more water outside than inside the cell) the water from outside will move into the cell and may cause it to burst or die.

  • Amoebas (microscopic animal cells)

  • Amoeba Amoeba is a microscopic animalthat lives in fresh water or sea water.Amoeba has a special organelle called a contractile vacuole When amoeba absorbs water through its cell membrane it sends it to the contractile vacuole.

  • When the contractile vacuole is full of water it bursts onto the surface of the amoeba like a pimple releasing its water.If amoeba did not have a contractile vacuole it would not be able to get rid of the absorbed water and would swell up and burst.

  • Animal Cells in a more concentrated solutionIf animal cells are in a solution that is more concentrated than their cytoplasm (i.e. if there is more water in their cytoplasm than in the solution outside) then the water may leave the animal cell and the cells shrivel up and may die.

  • Shrivelled Animal Cells Normal cellsSwollen cellsRed blood cells (animal cells)

  • Learning checkWhat surrounds an animal cell?How does water move in and out of an animal cell?What will happen to animal cells in a very dilute (watery) solution?What will happen to animal cells in a very concentrated solution?

  • Osmosis and Plant CellsPlant cells have a membrane which is surrounded by a cell wallCell walls are fully permeable and will allow all substances in and out of the cellIf a plant cell is surrounded by a less concentrated solution then water from outside will move into the cytoplasm and vacuole of plant cellsThis is how roots absorb water by osmosis

  • Water entering roots by osmosisThe water outside is less concentrated than the water in the cytoplasm

  • TurgorWhen the outside water enters the plant cell the vacuole becomes bigger and the cytoplasm swellsThis causes the membrane to be pushed out towards the cell wallWhen cells are fully swelled like this with the membranes pushing against the cell wall they are described as Turgid.

  • Turgid Cells

  • Plant Cells in solutions of different concentration

  • Turgor pressureThis turgor pressure gives plants their strengthIf plants did not have this they would be wilted (dead)Plants that dont have wood such as lettuce and house plants rely on turgor pressure for strength

  • Plant cells

  • Plant cells in a more concentrated solutionIf plant cells are surrounded by a more concentrated solution (for example if plant cells were surrounded by salt water) the water inside the cell would move out to the more concentrated solution outside and the cell will shrivel up (flacid cell)

  • Turgid plant cell & flacid plant cell

  • Wilted Plant, b) normal plant, c) plant with too much water

  • Learning CheckWhat surrounds the membrane of a plant cell?Can this structure control what moves in and out of cells?How does water enter roots of a plant?What is meant by a turgid cell?How could you identify a turgid cell?

  • PlasmolysisWhen this happens the cell wall stays intact but the membrane shrivels up away from itThis is called PlasmolysisCells in this condition are called plasmolysed cells we can look at this easily by placing a layer of red onion cells in salt water

  • Normal plant cell and plasmolysed plant cell

  • Plasmolysed Plant CellsPond weed (Elodea)

  • Plasmolysed red onion cells

  • Food PreservationWhy might you need to preserve foods?

    Can you name any food preservation methods?

  • Osmosis and Food PreservationBacteria and Fungi are the most common causes of food spoilageBoth these cells are enclosed by a membraneIf a food is placed in a sugary or salty solution then any bacteria or fungi present will lose the water in their cells to the more concentrated solution outside

  • When this happens the cells will shrivel and die and the food will not become contaminated with loads of bacteria and fungi.These types of preservation can keep food fresh for long periods of time.

  • Prevents and delay microbial decomposition and damage from mechanical causes, insects and rodentsEnsures more interesting and nutritionally adequate family mealsEnsure a safer food intake

    Food Preservation

  • Commonly used in meat and fish and less in fruits and vegetablesIn some foods, salting is combined with other