CAIE A-Level Biology AS 2.1.2 Iodine Test for Starch Questions

Glucose is used in the synthesis of amylose. Glucose is first converted to glucose 1-phosphate (G 1-P).

Starch phosphorylase is an intracellular enzyme that can catalyse the synthesis of amylose from G 1-P, which is the substrate for the reaction:

n= a large number
Students used a colorimeter to investigate the progress of the reaction.
The students made a reaction mixture containing $0.01 \mathrm{~mol} \mathrm{dm}^{-3} \mathrm{G}$ 1-P in a buffer solution at pH6.0. A very small quantity of amylose was added to initiate the reaction.

A solution of starch phosphorylase was added to the reaction mixture and samples were taken at 1-minute intervals. Each sample was added to a dilute iodine solution, stirred and then poured into a cuvette. The absorbance of each solution was recorded.

The results of the investigation are shown in Fig. 2.1.

Explain why the absorbance increases, as shown in Fig. 2.1.