Under the Scope: Biological Molecules


Biological macromolecules are polymers that have been proven and most definitely essential in sustaining Life. But thinking of how scientists determine and notice their presence is a question to ordinary people. On this laboratory work, the researchers knew that there are many tests that are used but they focused on five major tests that are used inside a science laboratory with which each of which determines the physical presence of major biological macromolecules that corresponds to their given reagents. With the five substances that are always present in our typical kitchen, the researchers found out that, on every test, there is a significant chemical change that happens to the samples. The samples then will change in color if they are either positive or not in each of the five test. This is to see if the sample is having the possible Biological Macromolecules in a certain test. The researchers then found out that some of the samples change in color with the added reagents with respect to the test performed, thus finding out the biological macromolecules that are present in each of the five samples.

Keywords: Biomolecules, proteins, lipids, starch, carbohydrates, sugars


Biological Macromolecules are naturally occurring substance of large molecular weight. These are the molecule that is present in living organisms which includes large macromolecules such as proteins, carbohydrates, lipids, and DNA. These types of large molecules were the basis in finding the biomolecules of every substance.

The first that was performed during the lab activity is the Benedict’s solution is used to detect presence of reducing sugar that a substance has, when it is conducted or performed. The best example for this test is when a person has or he/she was diagnosed having Diabetes, it can be seen in the urine of a person and by conducting some medical tests. It can also use for food testing. The second test is the Iodine solution is used to test for the presence of starch this test has been proven through the process of healing wounds. Iodine is applied to the skin to kill germs and bacteria of a human. The third test is the Ninhydrin solution, used to test for the presence of amino acids not proteins this explains that amines including amino acids react with Ninhydrin to give a coloured product of a substance. Next test is the Sudan IV test for lipids is used for staining of lipids, triglycerides, proteins on frozen paraffin sections which separate the substance from paraffin waxes. The last of them, the Fehling’s test solution, is a chemical reagent used to differentiate between water soluble carbohydrate and ketone functional group this solution separates substance from the reagent Fehling. Through these following tests we can indicate and identify different biological macromolecules of a certain substance.



These are the materials that are necessary to perform the test includes the following: test tube, for the containment of the samples and observing them change color at the same time; test tube rack, for test tube safety and order; test tube holder, for clasping the tube when hot; Medicine Droppers/pipettes, for a controlled and careful transfer of the samples or reagents; beakers, for the containment of the reagents; hot plate, the one thing this is needed is for the benedicts test for sugars in which the samples are heated; Starch solution, corn syrup (50 mL), egg albumin (2), cooking oil (50 mL), will serve as the sample to be tested by the reagents; Lugol’s iodine, Benedict’s solution, Fehling’s reagent, Ninhydrin reagent, Sudan IV reagent, serves as the testing agents if the samples are positive of bio-macromolecules.


          For the procedure in performing the test, the first thing to do is to gather all the materials given above. There are five tests that were performed in order to discover the biological molecules that are present in each of the samples. Label the test tubes with the corresponding samples that are meant for them to contain. Make sure that the samples do not mix with each other to secure a reliable result. For every test, the test tube should be cleansed and therefore no foreign chemical that is present in every test.

Benedict’s test for sugars

  • For the Benedict’s test for sugars, transfer 5 mL of the test samples into the test tube and make sure it is labeled. Add 10mL of the Benedict’s reagent to each test tube and then shake moderately. Heat the test tube in a boiling water bath for five minutes. Use a tong in transferring the test tubes in the test tube rack. Record any change in color.

Iodine test for Starch

  • Transfer 3 mL of the samples to their designated test tubes. Add ~10 drops of Lugol’s Iodine to each of the test tube and shake. Record any change in color.

Ninhydrin test for proteins

  • Transfer 5 mL of the test samples to their designated test tubes. Add 2 mL of the Ninhydrin reagent to each test tube and shake carefully. Heat the test tube in a boiling water bath for five minutes. Use a tong in transferring the test tubes in the test tube rack. Record any change in color.

Fehling’s test for aldehydes

  • Transfer 5 mL of the test samples into their designated test tubes and label them. Add 2.5 mL of Fehling’s reagent to each of the test samples and shake. Set aside for any color changes.

Sudan IV test for lipids

  • For the Sudan IV test, transfer 3 mL of each of the samples to the test tube. Add ~10 drops of Sudan IV to each of the samples. Mix and let them be set aside. Add 2 mL of H2O (water) to each test tube. Record the color change and separation of layers.


Iodine Test for Starch – positive will appear Blue, Purple or Black. Starch solution is found out to be positive.

Fehling’s Test for aldehydes/reducing sugars – positive will appear green or red. Corn syrup made a green pigment so it positive in the test.

Sudan IV Test for lipids – positive will let the solution sink. Cooking oil is found out that it is. It is then positive for having lipids.

Ninhydrin test for proteins – positive signs will appear to be deep blue or purple called Ruhemann’s purple. It is, as seen, found out that egg albumin is positive and has proteins.

Benedict’s test for Sugars – Benedict’s test could also be used as an alternative for Fehling’s test.


Guide Questions:

Enumerate the different types of Biological macromolecules and their functions. Provide example for each.

  • Distilled water

Biomolecule/s: NONE

  • Glucose Solution/corn syrup


– contains varying amount of maltose and a high amount of oligosaccharides

– High-fructose corn syrup


– Major uses in commercially prepared foods as a thickener, a sweetener as an ingredient that retains moisture and remains the freshness of the food.

High fructose corn syrup:

– 24% water, the rest are sugar

– 55% fructose, 45% glucose HFCS (high fructose corn syrup) used in sodas

  • Starch Solution:

– Chains of glucose which consist of 4 glucose equal to starch + 4 water molecules

Function: energy storage

Examples: potatoes – pure starch, pasta, bread, crackers

  • Albumin:

Biomolecule/s: -protein as a blood plasma

Example: -serum albumin is the most abundant blood plasma protein

  • Cooking Oil:


– Lipid/saturated fat

Function: long term storage of energy

Examples: Olive oil, Palm oil, Soybean oil, grape sea oil, sesame oil.

Hypothesize why you got the results for all the tests you did for each test substance.

  • Iodine test detects the presence of starch. In here the starch is positive, the rest turns negative. Starch is a real starch.
  • In Sudan IV test for lipids, the cooking oil has lipids so it will turn positive.
  • In Benedict’s test for sugars, the corn syrup has sugars so it would appear positive in the test.
  • Ninhydrin test indicates the presence of Proteins; egg albumin turns out to be positive. It contains proteins.
  • Fehling test is for aldehyde group and reducing sugar. Test for this indicates that corn syrup is positive.

What are the limitations of these tests?

In Benedict’s test for Sugars, it will detect reducing sugars such as glucose, fructose, and maltose, but it will not detect sucrose unless it has been inverted to the monosaccharides.

In Iodine test for Starch, however, the intensity of the color decreases with increasing temperature and with the presence of water-miscible organic solvents, such as ethanol. Also, the test cannot be done at very low pH values due to the hydrolysis of the starch under these conditions.

Ninhydrin for proteins is a chemical used to detect for ammonia or primary and secondary amines.

The Sudan IV test will test positivity for lipids. The test procedure involves adding a few drops of Sudan IV to the test solution. Sudan IV is a dye that will stain lipids.

Alkaline solution used to test for the presence of aldehydes or other compounds that contain the aldehyde functional group, -CHO.


The researchers had found out major and noticeable color changes in each of the samples at a given reagent.

After conducting several test. The students was able to arrive at these conclusion based on the findings of the study. “Amylose in starch is responsible for the formation of a deep blue color in the presence of iodine.” In order to know the result in Iodine’s test. The students tried this test to know the effects. The Iodine solution changed to blue-black which means that the starch is present. On the other hand, the iodine with cooking oil mixed.

Benedict’s solution is used to test for simple sugars, such as glucose. It is a clear blue solution. In the presence of simple sugars, the blue solution changed from the original blue color to green, yellow, and brick-red, depending on the amount of sugar. The substance to be tested is heated with Benedict’s solution; formation of a brick-red precipitate indicates presence of the aldehyde group.

Fehling’s test is the alternative for the Benedict’s test. However it is less popular as it less sensitive and requires that the reagents. But with the same results it appears that the corn syrup has the positive result.

In Sudan IV the solution will sink and then cooking oil is found to be having that kind of interaction with the Sudan IV reagent so it has lipids as per Sudan IV test’s purpose.

In Ninhydrin test for proteins since positive signs will make a certain sample to show the colors of Ruhemann’s purple, the egg albumin turns out to be on the line so it definitely is positive and contains proteins.


The reagents were not thoroughly removed from the individual test tubes. The samples were not visually inspected for vials for damage, discoloration or contaminations. Prepare the reagents according to instruction –Inspect equipment and electrical connections for integrity.

Literature Cited

Sybil P. Parker et al, 1997. McGraw Hill: Dictionary of Bioscience. 11 West 19th Street, NY: McGraw Hill Companies Inc.