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

Both test tubes contained starch, which reacts with iodine to form a blue-black color.

After ten minutes, test tube 1 showed an orange color, indicating that the starch was broken down by the amylase from the mouth. In contrast, test tube 2 remained blue-black, suggesting that the liquid from the stomach did not effectively digest the starch, possibly due to the acidic conditions that inhibit amylase activity.

To compare the energy content of two foods:

1. Gather materials: Use two identical food samples, a boiling tube for each sample, water, and a thermometer.
2. Preparation: Measure a fixed volume of water (e.g., 100 ml) into each boiling tube.
3. Setup: Mount the needle to hold each food sample above the flame without directly touching the flame.
4. Burn the food: Ignite one sample and allow it to burn under the boiling tube until it is completely consumed, simultaneously measuring the temperature change in the water with a thermometer.
5. Record data: Document the initial and final temperatures of the water.
6. Repeat for the second food sample: Perform the same steps with the second food sample.
7. Control variables: Ensure both samples are of equal mass and type of food, and conduct the experiment in identical environmental conditions to ensure comparability.