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Question Video: Recalling the Biological Molecule That Sudan IV Indicator Tests For Biology

Which biological molecules can Sudan IV indicator be used to test for the presence of?

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Video Transcript

Which biological molecules can Sudan IV indicator be used to test for the presence of? (A) Proteins, (B) lipids, (C) carbohydrates, (D) nucleic acids, or (E) fibers.

Sudan IV is a red dye. The Sudan indicator test begins by taking a sample of food and, if it is a solid, making it liquid by crushing it with a pestle and mortar and mixing it with water. The sample is then placed in a test tube, and a few drops of the indicator are added. The test tube is then gently swirled so that the dye and sample mix. And finally, the test tube is placed in a rack and the results are observed.

In an indicator test, we are looking for a color change. In this case, if an orange-red layer floats to the top of the sample solution, this would be a positive result. If the solution does not change color, that would suggest a negative result.

But what biological molecule does Sudan IV test for? Sudan IV will only bind to nonpolar molecules. That is, molecules without a charge. These molecules are also not soluble in water. Proteins and carbohydrates are two examples of charged, polar molecules. The most reliably nonpolar class of molecules are the fats and oils, or lipids.

So the correct answer to this question is (B). The Sudan IV test indicates the presence of lipids.

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