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.
72 exam-style questions on OCR GCSE Biology 1.2 What happens in cells (and what do cells need)?, covering 1.2.1 Structure of DNA, 1.2.2 Nucleotides and complementary bases, 1.2.3 Protein synthesis, 1.2.4 DNA structure and the proteins made, 1.2.5 Investigating enzymatic reactions, and 1.2.6 Mechanism of enzyme action. Each one has a worked solution and a mark scheme showing where the marks go.