Transport in and out of cells 

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  • Transport in and out of cells
    • Diffusion
      • Diffusion - the net movement of particles from a high concentration to a low concentration
      • Examples
        • Oxygen and carbon dioxide diffuses during the gas exchange in lungs, gills and plant leaves
        • Urea diffuses from cells into the blood plasma for excretion by the kidney
        • Digested food molecules are diffused from the small intestine into blood
      • Factors affecting diffusion
        • Concentration gradient
        • Temperature
        • Surface area
    • Osmosis
      • Osmosis - the diffusion of water from a dilute solution to a concentrated solution across a partially permeable membrane
      • Required Practical
        • Method:       Cut potato cylinders and measure mass. Place cylinders in different concentrations of sugar solution. Leave. Remove the cylinders, dry and measure mass
        • Variables: Independent  - the concentration of sugar solution. Dependant  - the change in mass    Control - temperature, time cylinders are left and volume of solution
    • Active transport
      • Active transport - the movement of particles from a low concentration to a high concentration, using energy
      • Energy from respiration is needed in active transport because the process works against a concentration gradient
      • Examples
        • Mineral ions can be absorbed into root hair cells from a very dilute solution in soil
        • Sugar molecules can be absorbed from low concentration in the gut into the blood, which has a high concentration

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