Diffusion food c

• Equipment

  • 6 Petri dishes, with lids, containing solidified agar jelly, at least 5 mm deep
  • 6 concentrations of red or blue food colouring between 20% and 70%
  • 5 mm cork borer
  • Cocktail stick
  • 1 cm³ graduated syringe
  • 30 cm ruler with millimetre divisions
  • Marker pen
• Cutting out discs in agar jelly

  1. Use a 5 mm cork borer to cut out

  2. Three evenly spaced discs in the agar jelly
• Removing discs


  1. Remove the discs with a cocktail stick to leave wells in the jelly

  2. Discard the discs
• Adding food colouring solution

  Use the 1 cm³ syringe to add 0.1 cm³ of a 20% concentration of food colouring solution to each of the wells
• Labelling Petri dish


  1. Place a lid on the Petri dish

  2. Label it with the correct concentration using the marker pen
• Repeating steps 1 to 4

  Repeat steps 1 to 4 for the other five Petri dishes with five different concentrations of food colouring
• Leaving Petri dishes


  Leave the Petri dishes undisturbed at room temperature for 24 hours
• Measuring distance of food colouring diffusion


  Measure the distances the food colouring has diffused for the three wells on each Petri dish
• Calculating mean distance and plotting graph

  1. Calculate the mean distance for each concentration

  2. Plot a graph of distance travelled by the food colouring against concentration
• Cv for wells

  Wells must be cut to same size
• choose evenly spaced concentrations
• you could include error bars in your graph
• Why should you cover the top of the dish with a lid

  To stop the food colouring solution being lost by evaporation