Osmosis and Diffusion

• What is osmosis?


  Osmosis is the movement of water molecules from an area of high water concentration to an area or lower water concentration through a partially pereable membrane
• Diluted


  Made thinner or weaker by adding water
• What has to be controlled in the cells?

  The water concentration
• What is lysis?


  Animal cells do not have a cell wall and burst if too much water goes in
• What do plant cells rely on to stop lysis?

  Plant cells rely on osmosis for support
• What is a turgid cell?


  - A turgid cell is full of water molecules

  - They are plump and firm
• What happens if a cell is placed in diluted water?

  The cells swells and bursts
• What happens if a cell is put in a concentrated salt solution?

  The cells shrink and shrivel
• When is a cell normal?


  When the cell is the the same concentration of solution
• When is a cell turgid


  When the cell is in a diluted solution
• When is a cell flaccid?

  When the cell is in a more concentrated solution
• What is a cell plasmolysed?


  When the cell is in a higher concentration and the cytoplasm is pulling away from the cell wall
• Isotonic


  Water leaves the cell as the same rate that it goes in
• Hypotonic


  Water enters the cell and it swells
• Hypertonic


  Water leaves the cell and it shrinks
• Percentage change in mass equation

  Percentage change in mass = (Change in mass/Starting mass) x 100
• What is active transport?


  - Substances move form a lower concentration to a higher concentration

  - The energy needed for active transport is an enzyme called ATP

  - Moving from a lower to higher concentration = against the concentration gradient

  - Particles pass through a protein carrier in the cell membrane
• What are the uses of active transport?


  - Moving mineral ions from the soil into the plants root hair cells

  - Glucose molecules may be absorbed from the low concentration in the small intestines into the blood
• What is diffusion?


  Diffusion is the movement of particles from a higher concentration to a lower concentration
• Is diffusion passive or not?

  Its passive
• What does passive mean?


  It does not require energy
• Where does diffusion happen?


  - Diffusion happens into and out of cells

  - The particles need to be small enough to fit through the cell mebrane
• What particles can be diffused?


  - Glucose

  - Water

  - Oxygen
• What are the factors that effect diffusion?


  - Surface area

  - Temperature

  - Distance

  - Concentration
• How does surface area effect the rate of diffusion?

  The bigger the surface area to volume ratio the faster diffusion occurs
• Surface area for diffusion practical


  - 3 sugar cubes that are (1 is 2x2cm, 1 is 1.1cm, 1 is 0.5x0.5cm)

  - Put each cube is a different beaker with the same concentration of 25 cm*3 of Hydrochloric acid

  - Time how long it takes for the acid to change the colour of each block
• What is the equilibrium?

  Equilibrium is reached when the reactions occur at exactly the same rate in both directions
• How does tempreture effect diffusion?

  The higher the temperature the faster the rate of diffusion
• How does distance effect the rate of diffusion?


  - The shorter the distance the particles have to move the faster the rate of diffusion

  - This is why cell membrane are thin to there is a shorter diffusion pathway
• How does the concentration effect diffusion?

  The bigger the difference in concentration the faster diffusion will occur
• Examples of diffusion


  Alveoli:

  - Oxygen diffuses form the alveoli into the red blood cells

  - Carbon dioxide diffuses out of the plasma into the alveoli

  
  

  Villi:

  - Small food molecules diffuse from the small intestine into the blood

  - The small intestine had finger-like projections called villi

  - The villi increase the surface area and therefore increase the surface are of diffusion
• What substances are transported using diffusion?


  - Carbon dioxide

  - Oxygen

  - Water

  - Food substances

  - Waste

  - ect
• What substances are transported using osmosis?

  Water
• What substances are transported in active transport?


  - Mineral ions into plant roots.

  - Glucose from the gut into intestinal cells, from where it moves into the blood
• Osmosis in a non-living thing


  - Dialysis tubing (sometimes referred to as visking tubing) is a non-living partially permeable membrane made from cellulose

  - Pores in this membrane are small enough to prevent the passage of large molecules (such as sucrose) but allow smaller molecules (such as glucose and water) to pass through by diffusion and osmosis

  
  

  This can be demonstrated by:

  - Filling a section of dialysis tubing with concentrated sucrose solution

  - Suspending the tubing in a boiling tube of water for a set period of time

  - Noting whether the water level outside the tubing decreases as water moves into the tubing via osmosis

  - Water moves from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane