Microscopy Results

Organic Molecules

Exercise A

The review on pages 41-42 is very informative and the illustrations help to convey the structure of mono/disaccharides. Table 5A-1 should look similar to the following:

Benedict's tests for mono or disaccharides and it changes from blue to green to yellow to reddish-orange, depending upon the amount of sugar.
Lugol's tests for the presence of polysaccharides such as starch.

	Benedict's Test		Lugol's Test
Tube	Original Color Before Boiling	Color After Boiling	Original Color Before Adding Lugol's	Color After Adding Lugol's
1. Water	blue	blue	yellow	yellow
2. Starch	blue	blue	yellow	blue-black
3. Glucose	blue	red precipitate	yellow	yellow
4. Maltose	blue	red precipitate	yellow	yellow
5. Sucrose	blue	blue	yellow	yellow
6. Onion	blue	blue	yellow	blue-black
7. Potato	blue	blue	yellow	blue-black
8. Milk	blue	red precipitate	yellow	yellow

Some notes about the table:

Starch may have reacted due to the heating in the water bath. This is because the high temperature can break the bonds in the chain of sugar and release individual monosaccharides into solution. It is these molecules that react with the Benedict's reagent.
If maltose reacted in the Lugol's Test it is a false-positive.
The potato slices may not have reacted in Lugol's because the sugars are still stored within the slice and are therefore inaccessible to the Lugol's solution.

Exercise B

The test for lipids involved two parts. I'm going to skip over the "grease spot" discussion because I'm sure most of us have spilt oil from some sort of food onto your clothes before. I know I have. Anyways, the Sudan IV test uses a red dye to help identify non-polar substances in a polar and non-polar solution. It's important to remember that there is no reaction occurring here! The dye is simply dissolving in non-polar liquids and allowing you to see them separate from polar solutions. Granted, it is sometimes hard to distinguish the presence of the dye if the mixture is dominently polar, but it still may form small "pockets" in non-polar liquids.

Exercise C

Testing for the presence of amino acids was also two part. The first part introduced the Biuret Reagent. This solution changes from blue to violet in the presence of proteins. While other colors may show up in some solutions, the only color you should be concerned about is violet. The results should look as follows:

Substance	Color After 2 Minutes	Protein Present (+) or Absent (-)
1. Distilled Water	blue	-
2. Egg albumin	violet	+
3. Potato Starch	blue	-
4. Glucose	blue	-
5. Amino Acids	blue	-

Since Biuret Reagent only tests for the presence of proteins and not free amino acids, we should not see a positive result for the last substance.

The last part of this exercise utilized Ninhydrin to test for the presence of free amino acids. With Ninhydrin, a purple or yellow color is indicative of a positive result (the presence of amino acids). However, and this is important to distinguish, yellow denotes the presence of an amino acid with a ring structure. So while either color tells you that there are amino acids, yellow should further inform you that a ring structure is present (such as in proline). Refer to page 49 for an illustration of an amino acid with a ring structure.

Exercise D

Omitted