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Investigating Macromolecules and their Properties

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There are many nutrients that are present in an organism that provides it energy in order to grow and reproduce. Some nutrients are required in larger amounts compared to others. These nutrients, that are required in larger amounts, are known as macromolecules. Identifying and distinguishing these macromolecules can be beneficial to scientists. Knowing these macromolecules and how they are shaped can help scientists and doctors create healthy diet systems, and discover many diseases that are caused by their deficiencies. With advanced technologies, scientists are constantly trying to develop new ways to identify these molecules.

Macromolecules are made up of large and complex organic molecules. They are grouped in four different categories. These are carbohydrates, lipids, proteins, and nucleic acids. In this investigation, we will identify different macromolecules and their properties.


Identify and determine the different types of solutions (sugar, protein, starch, and triglyceride) and their properties.


The Biuret reagent (KNaC4H4O6�4H2O) is made up of potassium hydroxide (KOH) and copper (II) sulfate (CuSO4). This blue reagent turns violet in the presence of proteins, and turns pink when combined with short-chain polypeptides (which are simplest form of proteins). Since proteins are made up of amino acids, and amino acids react with Biuret reagent, one of our solutions which would be a protein will turn either pink or violet depending on the complexity and concentration of the protein. (MadSci Network).

Benedict’s solution is a chemical reagent used to identify monosaccharides (simplest form of carbohydrates, also known as simple sugars). It is prepared from sodium carbonate, sodium citrate and copper (II) sulfate. The solution changes its color according to the concentration of monosaccharides present. It will change into different colors starting from blue (with no monosaccharides present), then green, then yellow, then orange, then red, and then brick red or brown (with high concentration of monosaccharides present). Since sugar contains monosacharides, it will change its color. What color will it change to, would be determined by the concentration of sugar that we will add. (Wikipedia)

Iodine solution is prepared by dissolving iodine in an aqueous solution of potassium iodide. It turns into deep blue-black color in the presence of starch. Since one of our beakers will contain starch, it will turn blue-black. (Wikipedia)

Lipids have certain properties that distinguish them from other macromolecules. Lipids do not dissolve in water and instead form a new layer on top of the water. Some substances dissolve lipids in higher amounts compared to other substances. Brown paper is such a substance. It absorbs lipids in high amounts but absorbs only small portions of other substances. Triglyceride is a form of lipid and will be absorbed by the brown paper. (Biology Web)


Manipulated variable is the variable that the experimenter decides to change to see whether there is or there isn’t an effect on the experiment. The manipulated variable for this experiment is the different kinds of reagents which are used to classify between solutions.

The responding variable is the variable that will change as a result of the change in the manipulated variable. It may also be observed and or measured to determine the quantity or quality of change. In our case, the responding variables will be the color change or the absorption rate. The reagents would react differently to different solutions and would in turn be able to give us result which would help us in distinguishing and classifying these solutions. This will also allow us to identify different properties of these solutions.

Several variables which could affect the dependent variable were controlled. This includes the amount of each type of reagent added. In this case, the compounds in a test tube will be 30 ml and reagents will be 5 drops. Note that even though we are measuring qualitative data, controlling the amount of substance added would be still important. All the materials will be washed before using. The size and the thickness of the brown paper will be same i.e. 4 * 4 inch. Time is controlled for the process of hot water bath only. The sizes of the test tubes would be same as well. In this case they would be 100ml. We will also add water as the 5th compound and make it into a controlled variable so that we can easily compare our results after.


We would test four unknown compounds in this experiment and would test one known compound which would give us negative results for all the experiments. This known compound would be water and this would serve as a controlled variable for us to compare with. We would perform four different tests on all five of the substances to prove our hypothesis. We know that all these compounds are either lipids (triglyceride), proteins, carbohydrates (sugar), starches, or water. In this experiment we will use four different tests to identify the different substances. We would perform iodine test to prove which of the substances, is starch (since iodine turns dark blue-black in the presence of starch). We would perform Biuret reagent test to prove which of the substances, is a protein (since Biuret reagent changes its color to pink in the presence of proteins). We will carry out the Benedict’s Solution test to prove which of the substances, is sugar (since Benedict’s solution turns its color in the presence of carbohydrates). Finally we would perform the brown paper test to prove which of the substances, is a lipid. The substance that would be absorbed the most by the brown paper, and would allow the most amount of light to pass through, would be the lipid. Note: some substances might give a positive result for more than one test. In this case, we would use our knowledge to distinguish between them.

Material required:

> Lab aprons

> Safety goggles

> 15-100ml calibrated test tubes (or 5 but wash it thoroughly)

> 100ml of solution 1

> 100ml of solution 2

> 100ml of solution 3

> 100ml of solution 4

> 100ml of distilled water

> Biuret Reagent

> Iodine solution

> Benedict’s solution

> Test tube holders

> Test tube tongs

> Eye droppers

> Graduated cylinders

> Tape and a marker for labeling

> Hot water bath apparatus – heating plate, water, and a beaker

> Five 4 * 4 inch brown papers


1. Clean all the test tube, graduated cylinders, eye droppers and funnels before starting the experiment.

2. Mark the four unknown solutions as solution#1, solution#2, solution#3, and solution#4.

3. Add water as the fifth solution to keep it as a controlled variable. Mark water as #5.

4. Measure 25ml of Solution #1 and place it into a test tube. Label this test tube as “#1”.

5. Measure 25ml of solution #2 and place it into another test tube. Label this test tube as “#2”.

6. Measure 25ml of solution #3 and place it into another test tube. Label this test tube “#3”.

7. Measure 25ml of solution #4 and place it into another test tube. Label this test tube “#4”.

8. Measure 25ml of distilled water and place it into another test tube. Label this test tube as “#5”.

9. Add 5 drops of Biuret solution in all the test tubes. Observe any changes and record your findings.

10. Obtain another set of test tubes (or use the same ones but make sure to wash them thoroughly). Repeat steps 4 to 8.

11. Add 5 drops of Iodine solution into each of the test tubes. Observe any changes and record your findings.

12. Repeat step 10.

13. Now add 5 drops of Benedict’s solution in each of the test tubes. Place all the test tubes containing the Benedict’s solution in a beaker. Now place the beaker on a heating plate and increase the temperature to about 100�C. Leave the test tubes for 10-12 minutes. Observe any changes and record your findings.

14. Now place 5 pieces of brown paper on the test area.

15. Place three drops of solution#1, three drops of solution#2, three drops of solution#3, three drops of solution#4, and three drops of distilled water on each separate brown paper. Leave it for few minutes.

16. Now hold the brown paper towards the light to see which of the substances make the brown paper most see-through.

17. Observe any changes and record your observations.


All experimenters would wear safety goggles and aprons. Experimenters should know about their diseases and allergies and should report to the teacher before hand in order to avoid any accidents. After the experiment, experimenters should carefully dispose the chemicals in the waste bucket rather than in the drain.

Observations (Qualitative):







Biuret Reagent

Remained blue

Turned green on the top

Turned orange

Turned dark pink

Remained blue

Benedict’s solution

Remained blue

Turned green

Turned cloudy orange

Turned orange

Remained blue


Turned dark blue-black

Turned orange

Turned yellowish orange

Turned orange

Turned light orange

Brown paper

The spot created was transparent

The spot created was very transparent

The spot created was not transparent

The spot created was a bit transparent

The spot created was a bit transparent


After observing the test tubes and the results we got from it, we identified the unknown solutions. The following results from the experiment were recorded. Solution # 4 was protein solution. Biuret reagent reacts with amino acids to either turn into pink or violet (depending on the concentration and the complexity of the protein) and proteins are made up of amino acids. When the Biuret reagent was added to solution # 4 it turned pink. From this we can conclude that Solution # 4 was protein solution.

Benedict’s solution is a chemical reagent used to identify monosaccharides. The solution changes its color according to the concentration of monosaccharides present. It will change into different colors starting from blue (with no monosaccharides present), then green, then yellow, then orange, then red, and then brick red or brown (with high concentration of monosaccharides present). In case of Benedict’s Solution, Solution # 1 and water remained blue so we can say that they do not contain monosaccharides, where as solution # 2 turned green so it contains a small amount of monosaccharides. When Benedict’s reagent was added to Solution # 4 it changed into oranges transparent color. But if you look at Solution # 3 you will see that the solution changed into cloudy orange color and was about to change into red color. From this we can infer that Solution # 3 is Sugar solution.

The Iodine solution transformed Solution #1 to a blackish-blue liquid. Iodine is a starch indicator so basically iodine solutions turn into Blackish blue in the presence of starch. From this we can conclude that Solution # 1 was starch.

When the brown paper test is conducted it should absorb and dissolve the lipid containing compound. When we held this test, we observed that it was not possible to see through Solution # 3 because of absence of lipids whereas Solutions # 4 and water were translucent. But when Solution # 1 and 2 were compared, we realized that Solution # 2 was the most transparent and we could easily see the light through it. So we can say that Solution # 2 was triglyceride (it is made up of lipids).

Solution # 1 was starch

Solution # 2 was triglyceride

Solution # 3 was sugar

Solution # 4 was protein


Although we had the fixed amount of compounds in the procedure, we didn’t use that amount because of time deficiency. The amount was estimated for the compounds but we measured the amount of reagent added. Due to the lack of the time and the inefficiency of the amount added, we could have made small mistakes, but when the results were compared with the hypothesis, they were all correct.

The sizes of the test tubes were not the same. Even though we mentioned this as our controlled variable, we did not keep it controlled in the experiment. This was due to the materials that we were provided with. Also the test tubes we were provided with contained soap contamination which might have caused an error in our results.



http://www.madsci.org/posts/archives/2004-12/1102321490.Gb.r.html http://www.geocities.com/auburngirl71/macromolecules.htm http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20101/Bio%20101%20Laboratory/Chemical%20Composition%20of%20Cells/Chemical%20Composition%20of%20Cells.htm

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