A-LevelBiologyBiological molecules9700/12 · May/June 2010 · 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
A: sample 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
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