Required Practical 11

Question 1

Describe how a calibration curve could be produced for glucose.

Answer 1

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.

Question 2

Describe how the concentration of glucose in an unknown ‘urine’ sample can be identified using a calibration curve.

Answer 2

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.

Question 3

Give examples of variables that should be controlled.

Answer 3

• Volume of sample used.
• Volume of Benedict’s solution.
• Temperature of water bath.
• Time samples were heated for in water bath.

Question 4

Explain why a high blood glucose concentration can cause glucose to be present in the urine of a diabetic person.

Answer 4

• Not all glucose reabsorbed at proximal convoluted tubule.
• As glucose carrier / cotransporter proteins are saturated / working a maximum rate.