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. (2)

  ● 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. (2)

  ● Not all glucose reabsorbed at proximal convoluted tubule

  ● As glucose carrier / cotransporter proteins are saturated /

  working at maximum rate