A Level Biology Practice Exam

What indicates the presence of lipids in the emulsion test?

1. A clear solution

2. A change in color

3. A white emulsion

4. A brown precipitate

The correct answer is: A white emulsion

In the emulsion test, the presence of lipids is indicated by the formation of a white emulsion. When lipids are mixed with water and an appropriate solvent, such as ethanol, they can form small droplets that create a suspension. This suspension scatters light, resulting in a cloudy or white appearance. The white emulsion signifies that lipids are present in the solution, as they do not dissolve well in water and thus form a distinct emulsion when they are mixed. In this context, options that imply no presence of lipids, such as a clear solution, or incorrect colors like a brown precipitate, do not denote lipid presence effectively. The change in color alone is not specific enough to indicate lipids, as it could pertain to various other substances, while a clear solution would suggest the absence of lipids entirely.