A Level Biology Practice Exam

What is the purpose of the biuret test?

1. To identify carbohydrates in a solution

2. To test for the presence of lipids

3. To detect proteins by forming violet colored complexes with copper ions

4. To measure the acidity of a solution

The correct answer is: To detect proteins by forming violet colored complexes with copper ions

The purpose of the biuret test is indeed to detect proteins in a solution by forming violet-colored complexes with copper ions. When protein is present, the peptide bonds in proteins interact with the copper ions (Cu²⁺) in the biuret reagent, leading to a color change that indicates the presence of proteins. This reaction is specific to peptide bonds and thus serves as a reliable method for identifying proteins in various samples. Other options do not apply in this context: the biuret test does not identify carbohydrates, test for lipids, or measure the acidity of a solution. Each of those processes would require different specific tests or reagents tailored to detect those particular macromolecules or properties.