A-LevelBiologyBiological moleculesMay/June 2010Paper 1 Q261 Mark
A student tested four samples of food, A, B, C and D, for the presence of • lipids • protein • reducing sugars • starch One of the food samples, milk, was found to contain lipid, protein and reducing sugar. Which of the food samples, shown in the results below, is milk?
Asample A: adding biuret reagent: lilac; adding iodine in potassium iodide solution: orange; boiling with Benedict's solution: orange precipitate; mixing with ethanol and adding to water: milky emulsion
Bsample B: adding biuret reagent: lilac; adding iodine in potassium iodide solution: blue-black; boiling with Benedict's solution: blue; mixing with ethanol and adding to water: milky emulsion
Csample C: adding biuret reagent: pale blue; adding iodine in potassium iodide solution: blue-black; boiling with Benedict's solution: orange precipitate; mixing with ethanol and adding to water: clear
Dsample D: adding biuret reagent: pale blue; adding iodine in potassium iodide solution: orange; boiling with Benedict's solution: blue; mixing with ethanol and adding to water: clear
✓ Correct Answer
The correct answer is A. This question tests the candidate's understanding of biological molecules within the Biologysyllabus. The examiner's mark scheme requires...
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
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