The objective of this macromolecules lab was to identify the presence any of the major macromolecules in various every day food items. The three macromolecules that this lab was carried out for were carbohydrates, lipids, and proteins. There were five different experiments conducted and each of those experiments had one factor in common, they all had the same controls. The controls in this lab activity were already set for the lab activity. The controls were the distilled water and the baking soda solution. These controls were certainly crucial to the lab because they were the basis to what the results of each experiment should have been.
Distilled water was an effective control because it is made of H2O molecules therefore it is impossible for it to contain any of the macromolecules. Baking soda is a control because it is made of NaHco3 molecules therefore it does not contain any macromolecules. Because baking soda and water do not contain any of the macromolecules which the lab tries to identify in each solution, both solutions will give negative results for all tests. If any other results were found, it would mean that the solution being tested contains any of the three macromolecules.
To begin, two tests were conducted to detect any presence of carbohydrates in specific substances. The tests were the Benedict Reagent Test and the Lugol’s Test (Appendix 3). In the Benedict’s Reagent test, fructose, glucose, and sucrose gave positive reactions as they changed from blue to one of the colours given in Appendix 1. Fructose and glucose gave that gave them a sugar concentration of approximately 1. 5-2. 0%. Sucrose changed to a slightly green colour giving it between 0. 5-1. 5% on the sugar concentration scale. Starch and the unknown substance remained mostly blue but some very subtle hange was noticed, therefore they each had approximately 0-0. 5% sugar concentration. Most of the results of the tests made sense.
Benedict’s reagent is used to test for glucose and not for sucrose because it only tests for monosaccharides and some disaccharides which excludes sucrose. The result obtained may have been a source of error which will be discussed later. Because glucose and fructose are monosaccharide and are reducing sugars, they did have a positive reaction. Reducing sugars are sugars that reduce Cu2+ to Cu+ which is why they turn orange in Benedict’ reagent.
Sucrose is a non-reducing sug gar therefore no change is observed (Hunt, 2009). Starch and the unknown gave no reactions because they are not reducing sugars or monosaccharides. In the Lugol’s test, the only substances that gave a reaction were starch and the unknown. (Appendix 3). Starch’s reaction was expected because it is a polysaccharide and this test only identifies polysaccharides (Senese, 2010). It turned a deep opaque black because of the lodine in the Lugol’s solution. The unknown reacted differently compared to the other sugars.
It did not turn black indicating polysaccharides nor did it take the colour of mono/ oligosaccharides. It seemed to have formed a precipitate in the centre but the rest of the solution was like the monosaccharide or oligosaccharide reactions. Overall, the results made sense. Secondly, two tests were conducted also conducted to identify foods with lipids. In the Sudan IV test there was a variety of reactions (Appendix 4). If lipids were present the Sudan IV would stain them reddish-orange. Both vegetable oil and whipping cream showed positive signs of lipids.
On the other hand, skim milk showed negative results in the test. There was no change in the colour of the solution. Unlike the other, the unknown solution did not give a definite result. There was some foam occurring but no colour change was noticed. In the brown paper test, vegetable oil resulted in a high degree of translucency which was expected because oil is in its name which is a form of lipids followed by whipping cream. The unknown also gave somewhat positive results in this test though not as much as the vegetable oil. Skim milk on the brown paper resulted in a negative reaction for lipids.
Therefore, vegetable oil, whipping cream, and the unknown contained some degree of lipids while skim milk had little to no lipids present. The observations stated in Appendix 4 make sense because vegetable oil and whipping cream contain lipids which is why they got positive results in the Sudan IV which stains lipids reddish-orange. Whipping cream contains lipids because it is made from dairy products which usually contain lipids. Vegetable oil is made from plant seed oils which are storages of unsaturated fats in seeds, therefore creating a lipid content in the vegetable oil (Gunnars, 2013).
The reason why skim milk showed mixed or even negative results for lipids is because “by law, skim milk can have no more than 0. 2 percent milk fat” (Sheehan, n. d. ). If this was whole or at least 1 percent milk, there would have been a much more noticeable reaction in both of the lipid test. The unknown substance’s reaction seemed to show positive signs of a lipid presence. Using the results of the other known solutions, it can be deduced that the unknown substance contains low amounts of lipids but slightly more lipids than skim milk.
In the final experiment which was identifying proteins, there were no results that were out of the ordinary. The Biuret solution is used to test for proteins because “the Biuret test is based on the ability of Cu (II) ions to form a violet-coloured chelate complex with peptide bonds (-CONH- groups) in alkaline conditions. Lone electron pairs from 4 nitrogen atoms in the peptide bond coordinate a copper (II) ion to form the chelate complex. Because the chelate complex absorbs light at 540nm, the colour of the tested solution turns violet.
The colour depends on the concentration of proteins (n. . , 2015). All substances tested resulted in a protein concentration of Violet + + or over. (Refer to Appendix 5 for details). The skim milk which tested negative for lipids earlier, showed a large amount of protein in this test. Overall, all of the results seem accurate. Albumin is a a common protein found in the blood, providing the protein that the body needs to grow and repair (Swartzendruber, n. d. ). Gelatin and milk is also known to contain proteins. Even though skim milk has less fat than normal milk, it still has a similar amount of proteins.
Therefore, according to research, these results make sense. This lab was very successful although there were a few minor sources of error. Firstly, there was a source of error when testing sucrose for a carbohydrate presence using Benedict’s Regent. According to Dr. Hunt, the sucrose solution should have remained blue but instead the sucrose turned teal in colour. This could be a result of mixing different solutions by accident. Fortunately, this was a very minor issue which was unfortunately over looked. The next source of error happened while the Sudan IV test was being conducted.
The unknown solution produced a precipitate when the Lugol’s solution was added. This may have been due to the fact that the spot plate used had traces of other chemicals in it from the many labs it may have been used for. This could have resulted in the precipitate’s formation. The final source of error also happened when testing for carbohydrates. The hot plate was not 80 degrees Celsius at all times as it was very difficult to keep it at a constant 80 degrees. This may have been due to the hot plate being faulty which could have resulted in the inconsistent heating it provided.
These errors can be easily avoided. In conclusion, this lab went swimmingly but there are a couple of ways that it could be improved. More time could have been given to the students to do the lab more thoroughly. The students needed to rush to each test which is also a potential source of error. An extra fifteen minutes of time would have sufficed. Having a better and cleaner equipment would have been very beneficial. If the hot plate was not malfunctioning and if the spot plate was as clean as possible, the tests would have been much more pure and accurate.
The identity of the unknown substance is still unknown. It seems like it has a very little amount of all macromolecules but it is mostly protein. Macromolecules are essential for cells to function and in turn, for the body to function as a whole. A balanced diet of all three macromolecules would help maintain a healthy lifestyle. Carbohydrates give quick energy to the body which can help with metabolism and helps break down fatty acids. Fruits and vegetables are a great source of carbohydrates. Lipids are used as a backup energy storage but having just enough fat can be beneficial to the body.
Lipids are used as insulation so the body does not lose too much heat. They have some physiologic energy values as well. Finally, proteins help in the muscle building process because they help repair and strengthen muscles after a workout. They are present in milk, meat, eggs, poultry and fish. Proteins also have a large part in the immune system. It maintains muscle health and proper white blood cell count. This is why drinking juices filled with protein strengthens your immune systems. Overall, this was a fun and educational lab.