A student mixed 10 cm³ of starch solution with 5 cm³ of amylase solution and kept the tube in a water bath at 25°C - Edexcel - GCSE Biology - Question 6 - 2020 - Paper 1

1. The temperature of the water bath must be kept constant to ensure reliable enzyme activity.
2. The concentration of the starch solution and the amylase solution must remain consistent across trials to ensure valid comparisons.

The tube with distilled water was included as a control to demonstrate that any change observed in starch or glucose detection was due to the action of amylase and not due to other variables.

1. Prepare several test tubes with starch solution and add amylase solution to each test tube.
2. Use buffer solutions at different pH levels (e.g., 5, 6, 7, 8) for each test tube.
3. Place all test tubes in a water bath at a consistent temperature of 25°C.
4. At regular intervals, test the solutions for starch presence using iodine.
5. The optimum pH is identified by the test tube where starch is completely broken down the fastest, showing a change in iodine color.

Amylase is not produced in the stomach because it requires a neutral to slightly alkaline pH to function effectively. The acidic environment in the stomach (pH around 1.5-3.5) denatures amylase, rendering it inactive. Thus, digestion of starch primarily occurs in the mouth and then in the small intestine.