To study how cells obtain the respiratory substrate glucose from nutrient polymers, a student incubates a starch suspension with amylase. To confirm that the starch has been successfully hydrolyzed into reducing sugars before cellular uptake, the student tests a sample of the reaction mixture.
Which reagent, experimental condition, and positive observation correctly identify the presence of these reducing sugars?
Biuret reagent, incubated at 37∘C37^\circ\text{C}37∘C for 5 minutes, resulting in a lilac color.
Benedict's reagent, heated in a boiling water bath for 5 minutes, resulting in a brick-red precipitate.
Iodine in potassium iodide solution, kept at room temperature, resulting in a blue-black color.
Ethanol followed by an equal volume of water, shaken at room temperature, resulting in a cloudy emulsion.