Required Practical 11

• Describe how a calibration curve could be produced for glucose:

  1)Use distilled water and a glucose solution of known concentration to produce a dilution series (of glucose solutions of known concentrations)

  2)Heat a set volume of each solution with a set volume of Benedict’s solution

  3)Measure absorbance (of light) of each solution using a colorimeter

  4)Plot a graph of absorbance (y axis) against concentration of glucose solution (x axis) and draw a line / curve of best fit
• Describe how the concentration of glucose in an unknown ‘urine’ sample can be identified using a calibration curve:

  1)Perform Benedict’s test on sample using same volumes of solutions used in producing calibration curve

  2)Measure absorbance using a colorimeter

  3)Absorbance value for ‘urine’ sample read off calibration curve to find associated glucose concentration
• Give examples of variables that should be controlled:

  ● Volume of sample used

  ● Volume of Benedict’s solution

  ● Temperature of water bath

  ● Time samples were heated for in water bath
• Explain why a high blood glucose concentration can cause glucose to be present in the urine of a diabetic person:

  ● Not all glucose reabsorbed at proximal convoluted tubule

  ● As glucose carrier / cotransporter proteins are saturated / working at maximum rate