Section E

• Diffusion


  The movement of particles from high concentration to low concentration
• Diffusion is the movement of particles from high concentration to low concentration
• Diffusion is a passive process that does not require energy
• As temperature increases


  The rate of diffusion increases
• As concentration gradient increases


  The rate of diffusion increases
• As surface area to volume ratio increases

  The rate of diffusion increases
• As distance decreases


  The rate of diffusion increases
• Substances that can diffuse in/out of cells


  • O₂, CO₂, CH₃OH, H₂O, amino acids, fatty acids + glycerol, glucose, water
• Single-celled organisms rely on diffusion to get nutrients and get rid of waste products
• Adaptations of single-celled organisms to speed up diffusion

  • Larger surface area
• There is a limit to how big single-celled organisms can grow due to the surface area to volume ratio
• Plants don't have the same limit on size as animal cells due to diffusion
• Experiment to investigate the effect of temperature on the rate of diffusion of ammonia


  1. Place cotton wool with ammonia in one end of tube

  2. Measure time for universal indicator paper at different distances to change colour

  3. Repeat at different temperatures
• The number of drops of ammonia should be controlled in the experiment
• To investigate the effect of concentration on the rate of diffusion, the concentration of ammonia could be changed instead of the temperature
• Osmosis


  The movement of water molecules from an area of high water potential to an area of low water potential through a semipermeable membrane
• Diffusion


  The movement of particles from high concentration to low concentration
• Types of solutions


  • Hypotonic
  • Hypertonic
  • Isotonic
• Hypotonic solution


  Dilute solution / high water potential
• Hypertonic solution


  Concentrated solution / low water potential
• Isotonic solution


  Equal concentration inside and outside, equal water potential
• Plasmolysed cell


  Cell body shrinks and pulls away from cell
• Flaccid cell


  In between / normal
• Turgid cell


  Cell swells but generally retains shape
• Crenation


  Cells shrink and shrivel
• Lysis


  Cells swell and burst
• Seaweeds contain iodine at concentrations many times higher than in sea water
• Active transport requires energy released by respiration
• Active transport


  • Transports large or charged particles
  • Active process (energy needed)
  • Requires a protein in the membrane
  • Moves from low to high concentration
• Osmosis is the movement of water molecules from an area of high water potential to an area of low water potential through a semi-permeable membrane
• Water moves into the cell by osmosis from high water potential to low water potential across a semi-permeable membrane
• Cell loses water plasmolysed by osmosis from high water potential to low water potential across a semi-permeable membrane
• Potatoes floated at 80-100% because they are less dense compared to the solution
• Potatoes sink at 0-60% because they are more dense compared to the solution