RP11 - Production of a dilution series

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. (2)

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. (2)

Answer 4

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