Blogging My Biology Class 20080915 Lab

Biology, Eighth Edition, by Campbell & Reece, et al.

Biology, Eighth Edition, by Campbell & Reece, et al.

My notes and thoughts from Biology 111 Lab, for Monday, September 15, 2008. The entire series can be found here.

In this lab, we learned to use reagents to test for the presence of proteins, starch, and sugars, using distilled water as a negative control.

Since distilled water should be straight H2O and nothing else, each time we did a test, we could see what the reagent did in solution without the presence of whatever it was we were testing for.

We worked in groups, and our group consisted of four students.

A. In the first experiment, we tested for the presence of proteins with Biuret reagent, a highly corrosive blue/purply substance. Our Lab Manual and Doc each warned us about its potential hazards, safety precautions, and what to do if we got it on our skin.

We marked four test tubes at the 1 cm level.

1) Test tube 1 we filled to the mark with distilled water. We then added about 5 drops of Biuret reagent. The water turned light blue. This was our negative control to which we could compare the other tubes when the Biuret reagent was added.

Lab continues, below the fold.

2) Test tube 2 we filled to the mark with Albumin solution. We then added about 5 drops of Biuret reagent. The solution turned a purple color, indicating the presence of proteins.

3) Test tube 3 we filled to the mark with Pepsin solution. We then added about 5 drops of Biuret reagent. The solution turned a pinkish/purple color, indicating the presence of peptides.

4) Test tube 4 we filled to the mark with Starch solution. We then added about 5 drops of Biuret reagent. The solution turned a light blue color, indicating the absence of proteins and peptides.

B. In the second experiment, we tested for the presence of starch with iodine.

We marked five test tubes at the 1 cm level.

1) Test tube 1 we filled to the mark with distilled water. We then added about 5 drops of iodine solution. The water turned orange. This was our negative control to which we could compare the other tubes when the idodine solution was added.

2) Test tube 2 we filled to the mark with 1% starch solution. We then added about 5 drops of iodine. The solution turned a black color, indicating the presence of starch (duh). This was our positive control to which we could compare the other tubes when the iodine solution was added.

3) Test tube 3 we filled to the mark with onion juice that we extracted by mortar and pestle. We then added about 5 drops of iodine solution. The solution turned an orange color, indicating the absence of starch.

4) Test tube 4 we filled to the mark with potato juice that we extracted by mortar and pestle. We then added about 5 drops of iodine solution. The solution turned a black color, indicating the presence of starch.

5) Test tube 5 we filled to the mark with glucose solution. We then added about 5 drops of iodine solution. The solution turned an orange color, indicating the absence of starch.

C. In the third experiment, we tested for sugars (monosaccharides, specifically) with Benedict’s reagent and heat.

We marked five test tubes at the 1 cm level.

1) Test tube 1 we filled to the mark with distilled water. We then added about 5 drops of Benedict’s reagent and heated in a boiling water bath for 10 minutes. The solution turned a very pale light blue.

2) Test tube 2 we filled to the mark with glucose solution. We then added about 5 drops of Benedict’s reagent and heated in a boiling water bath for 10 minutes. The solution turned a pumpkin orange color, indicating a high concentration of monosaccharides.

3) Test tube 3 we filled to the mark with onion juice. We then added about 5 drops of Benedict’s reagent and heated in a boiling water bath for 10 minutes. The solution turned a yellow/orange color, indicating a moderate concentration of monosaccharides.

4) Test tube 4 we filled to the mark with potato juice. We then added about 5 drops of Benedict’s reagent and heated in a boiling water bath for 10 minutes. The solution turned a green color, indicating a low concentration of monosaccharides.

5) Test tube 5 we filled to the mark with starch suspension. We then added about 5 drops of Benedict’s reagent and heated in a boiling water bath for 10 minutes. The solution turned a very pale light blue, indicating the absence of monosaccharides.

D. In the fourth experiment, we tested for starch, with 1% Amylase solution, Benedict’s reagent, and heat. The point was to show that starch contains sugar. (Amylase ends in -ase, and as we remember from our earlier lecture, that means it’s an enzyme that breaks down sugar through the process of hydrolysis. In this case, amylase breaks down starch to disassociative maltose. Presumably, the heat pushes the hydrolysis of maltose into glucose?)

We marked two test tubes at the 2 cm, 4 cm, and 6 cm levels.

1) Test tube 1 we filled to the 2 cm mark with distilled water and to the 4 cm mark with 1% amylase. We then corked and shook the tube, and waited 30 minutes. At the end of 30 minutes, we noted the color of the solution and added 5 drops of Benedict’s reagent and heated for 10 minutes. The solution did not change color.

2) Test tube 2 we filled to the 2 cm mark with starch suspension and to the 4 cm mark with 1% amylase. We then corked and shook the tube, and waited 30 minutes. At the end of 30 minutes, we noted the color of the solution and added 5 drops of Benedict’s reagent and heated for 10 minutes. The solution turned a green color, indicating the presence of a low concentration of monosaccharides.

E. In the fifth experiment, we experimented with the emulsification of lipids using Sudan IV.

We marked two test tubes, the first at the 3 cm and 4 cm levels, and the second at the 2 cm, 3 cm, and 4 cm levels.

1) Test tube 1 we filled to the 3 cm mark with distilled water and the 4 cm mark with vegetable oil. We then shook the tube and observed the behavior of the liquid, watching it separate and not become a solution.

2) Test tube 2 we filled to the 2 cm mark with water, to the 3 cm mark with vegetable oil, and to the 4 cm mark with Sudan IV. We then shook the tube and observed the behavior of the liquid, watching it take much longer to separate. The Sudan IV seemed to retard the separation process quite a bit.

We then discussed the results of our testing, and the lab ended.

From whence came the art:

The first image is of our textbook, Biology, Eighth Edition, by Campbell & Reese et al.

Other images by me and are licensed under the Creative Commons Attribution- NonCommercial- Share Alike 3.0 License.

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