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.
