Neco Model Questions Vol1 2023 Biology Question 3

A group of students investigated the rate of starch hydrolysis by amylase in three different food samples (boiled potato, raw banana and cooked rice). 5 g of each sample was homogenised in 50 mL distilled water. 10 mL of the homogenate was mixed with 10 mL of a standard amylase solution (0.5 U mL⁻¹) and incubated at 37 °C. At 0, 5, 10 and 15 min aliquots (2 mL) were withdrawn, the reaction was stopped by adding 1 mL of 0.5 M HCl and the remaining starch was quantified by the iodine colour‑reaction. Absorbance (A) of each aliquot was measured at 620 nm. The data obtained are shown in the table below. | Sample | Time (min) | Absorbance (A) | |-----------------|------------|----------------| | Boiled potato | 0 | 0.800 | | | 5 | 0.500 | | | 10 | 0.300 | | | 15 | 0.150 | | Raw banana | 0 | 0.750 | | | 5 | 0.620 | | | 10 | 0.520 | | | 15 | 0.460 | | Cooked rice | 0 | 0.820 | | | 5 | 0.600 | | | 10 | 0.380 | | | 15 | 0.200 | Assume that absorbance is directly proportional to the concentration of starch present and that the absorbance at time 0 represents 100 % starch remaining for each sample.