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Starch is a nutrient in food - Edexcel - GCSE Biology - Question 7 - 2019 - Paper 1
Question 7
Starch is a nutrient in food. Starch is a source of energy. (a) Name the enzyme that breaks down starch. (b) Enzymes from different parts of the digestive system w... show full transcript
Worked Solution & Example Answer:Starch is a nutrient in food - Edexcel - GCSE Biology - Question 7 - 2019 - Paper 1
Step 1
Step 2
Give one reason why the contents of both test tubes were blue-black at the beginning of the investigation.
Answer
At the beginning of the investigation, both test tubes contained starch and iodine solution. The iodine turns blue-black in the presence of starch, thus both solutions appeared blue-black.
Step 3
Explain the results of this investigation after ten minutes.
Answer
After ten minutes, test tube 1 showed an orange color, indicating that the starch was broken down by the amylase from the mouth to maltose or glucose. Test tube 2 remained blue-black, suggesting that the acid environment in the stomach inhibited the action of any amylase present, preventing the breakdown of starch.
Step 4
Devise a method to compare the energy content of two foods using this equipment.
Answer
To compare the energy content of two foods using the given equipment, follow these steps:
- Measure a specific mass (e.g., 5 grams) of each food item.
- Place one food sample in the boiling test tube filled with water, ensuring that the water is at a consistent starting temperature.
- Heat the food item until it completely combusts. Record the temperature of the water before and after combustion.
- Repeat the process for the second food sample.
- Calculate the energy released by using the formula: Energy (in joules) = mass of water (g) × specific heat capacity (4.18 J/g°C) × temperature change (°C).
- To control variables, ensure that the mass of food, the volume of water, and the boiling time are kept constant for both trials.