Starch is a nutrient in food - Edexcel - GCSE Biology - Question 7 - 2019 - Paper 1

At the beginning of the investigation, both test tubes contained starch and iodine solution, which reacted to form the blue-black color.

After ten minutes, test tube 1 shows a color change to orange, indicating that starch has been broken down by amylase from the mouth. Test tube 2 remains blue-black, suggesting that the conditions in the stomach, such as acidity, inhibited the activity of the enzyme, preventing starch breakdown.

To compare the energy content of two foods using the provided equipment, follow these steps:

1. Preparation of Food Samples: Cut equal-sized pieces of the two food samples to ensure a fair test.

2. Setup: Place each food sample on a mounted needle and ensure they are positioned in a boiling tube containing a known volume of water.

3. Ignition: Light each food sample using a controlled flame, ensuring that both samples are ignited at the same time.

4. Temperature Measurement: Use the thermometer to measure the initial temperature of the water before igniting the samples. After a set burning time, measure the final temperature of the water.

5. Energy Calculation: Calculate the energy released by each sample using the formula: $ext{Energy} = ext{mass of water} imes ext{specific heat capacity} imes ext{temperature change}$

6. Controls: To control variables:

   • Use the same volume of water for each experiment.
   • Conduct the tests in the same location to minimize heat loss to the environment.
   • Ensure the food samples are of the same mass.
   • Repeat the experiment multiple times for accuracy.