Enzymes: explain question

A student carries out an experiment to investigate the specificity of amylase. They add 1 cm³ of amylase solution to two test tubes: one containing 5 cm³ of starch solution and the other containing 5 cm³ of cellulose solution. The mixtures are incubated at 37 °C. Every minute, a sample is removed and tested with iodine solution in a colorimeter. The results show that the absorbance of the starch-containing mixture decreases over time, whereas the absorbance of the cellulose-containing mixture remains constant. Explain why amylase only catalyses the breakdown of starch, and not cellulose. In your answer, describe the features of the active site that contribute to enzyme specificity and outline how the lock‑and‑key and induced‑fit models help to explain this.