Sarah Craig
AP Bio Student - Mrs. McConnell Period 1
Testing for Reducing Sugars in Glucose, Sucrose, Starch, and Water Using Bendict’s Reagant
The Effect of Benedict’s Reagant on the Color of Glucose, Sucrose, Starch, Water, and Unknown Substances
In this lab, Benedict’s reagent was used to determine whether or not reducing sugars were present in various substances, including water, glucose, sucrose, starch, and two unknowns. This was done by putting each substance in a test tube, adding the reagent to the test tube, and observing the initial color of the resulting solution. Then, the test tubes were heated in boiling water for three minutes, and their final color was recorded. Water, sucrose, starch, and unknown one showed no change in color while glucose changed from blue to a cloudy brown/yellow color and the second unknown to a light milky blue (indicating that some type of precipitate was formed).
Benedict’s reagent was used as an indicator to determine the presence of reducing sugars. A reagent is a chemical which, when applied to other chemicals, produce reactions which give the observer important information. Benedict’s reagent causes a change in color or the formation of a precipitate if a reducing sugar is present. Benedict’s reagent is a compound made with copper sulfate that can detect the presence reducing sugars, like glucose, which contain aldehyde groups that may be oxidized to form carboxylic acids. When reducing sugars are present, the color of the solution of Benedict’s and another substance may change or a precipitate could be formed.
In this experiment, glucose was the positive control because glucose is a well-known reducing sugar. Its resulting color was a cloudy brown/yellow. Because the solution was cloudy, it can be assumed a precipitate was formed. The negative control in this experiment was water, which shouldn’t contain any reducing sugars. The final and initial color of water and Benedict’s reagent was blue. Both the positive and negative controls yielded the expected result, therefore the validity of this experiment was affirmed.
While Benedict’s reagent is useful in the classroom to distinguish between substances that contain reducing sugars and ones that don’t, it also has many practical applications in the real world. One of these applications includes diagnosing people with diabetes. Benedict’s reagent is often added to women’s urine while they are pregnant to test for an abundance of fructose. If the test comes back positive, this is an indicator for gestational diabetes. However, the presence of fructose in urine may be caused by a variety of factors rather than gestational diabetes, and further testing must take place if it is detected. Benedict’s reagent is the most cost effective form of screening, though, so it is the most popular form of initial screening for gestational diabetes.
After careful evaluation of the results, it was determined that glucose and the second unknown were the only substances that contained reducing sugars. The final color of the glucose was a cloudy brown/yellow and the final color of the second unknown was a light milky blue, thus a precipitate was formed. The first unknown, on the other hand, did not contain a reducing sugar because it did not change color after it was heated in the boiling water. This unknown could have been anything from water to a sugar that was not a reducing sugar dissolved in water. The second unknown produced a precipitate, but it was not as obvious as the precipitate produced by the glucose. Therefore, the concentration of reducing sugars was not as high as pure glucose. It could have contained a substance that has glucose or fructose in it, such as a mixture of fruit juices.
Testing for Starch in Water, Glucose, Sucrose, and Starch Using Iodine
The Effect of Iodine on the Color of Water, Glucose, Sucrose, Starch, and Two Unknowns
*#6 a little bit lighter than the rest
In this experiment, iodine was used to determine whether or not starch was present in water, glucose, sucrose, starch, and two unknowns. This was done by filling each individual test tube with a different substance and then adding iodine to it. The initial color for each substance with iodine added to it was amber. After the test tube was swirled around a bit and allowed to sit for a couple of minutes, all of the final colors differed from the initial color. The final colors of water, glucose, sucrose, and the second unknown were all a clear yellow while starch and the first unknown were a dark blue.
Iodine was used in this experiment as an indicator of starch. Natural starches are made up of a mixture of amylose and amylopectin. Iodine is able to detect amylose. If amylose is detected, then a dark blue is formed because it seeps into the long, coiled polymer chains of glucose units. If amylose is not detected, then the color of the iodine mixture will remain either yellow or orange.
When testing for starch, there were both a positive and negative control. The positive control would be the starch itself, which yielded the expected result of having a final color of dark blue. The negative control was the water, which yielded the expected result of having a yellow final color. These controls added validity to the experiment because they yielded the expected result.
Iodine as an indicator for starch has many practical applications. Back before there were sophisticated technologies to transfer encrypted messages, people would often use “invisible ink.” This invisible ink was merely lemon juice. They would use lemon juice to write a message on a piece of paper. The message was then passed along to the intended receiver. The receiver would then coat the paper in a thin layer of iodine and water. The paper would then turn a dark blue or purple except where the sender had written with the lemon juice. The iodine would turn the paper purple because it had detected the starch in the paper, but the lemon juice would prevent it from turning purple where it was applied.
While it was impossible to tell what the unknowns exactly were, it was determined that the first unknown contained starch because it turned dark blue while the second one did not because it turned a clear yellow when iodine was added. The first unknown could be a wheat grain or some resistant starch (fiber) dissolved into water because those substances do not contain reducing sugars but do contain starch. The second unknown did not contain starch, therefore it could not be a wheat grain, contain potatoes (which have a lot of glucose, a reducing sugar), or a resistant starch.
Using Iodine to Observe Potato Underneath a Microscope
Note: both of these drawings are at 100x magnification
Because iodine turns purple when it comes in contact with starches, it acts as a stain when viewing potato underneath a microscope. Without iodine, the vacuoles and cell walls are visible, but not definitively. With the iodine stain, the cell walls were clearly visible along with the nucleus and the vacuoles.
A close up image of a potato cell stained with iodine. The cell takes up practically all of the image.
Testing for DNA in Water, DNA, and RNA Using Dische Diphenylamine
The Effect of Dische Diphenylamine on Water, DNA, RNA, and Two Unknowns
In this experiment, dische diphenylamine was used to determine whether or not water, DNA, RNA, and two unknowns contained DNA. This was done by filling individual test tubes with different solutions and adding dische diphenylamine to them. They were allowed to sit for a few minutes, and the final color was then recorded. All of the solutions resulted in a clear final color except for the DNA and the second unknown.
Dische diphenyline is a reagant that causes deoxyribose, a component in DNA, to bond with diphenylamine. This bonding creates a blue color. Therefore, water, RNA, and the second unknown do not contain DNA while the DNA and the first unknown did.
When testing for DNA, there were both positive and negative controls. The positive control was the DNA, which yielded a final color of blue, the expected result. The negative control was the water, which had a clear final color, also the expected result. This added validity to the experiment because it affirmed that the Dische diphenylamine was able to identify the presence and the absence of DNA accurately.
Dische diphenylamine is used to detect for DNA in substances. If one wanted to isolate DNA from something, and they wanted to know if they had done so correctly, they could use Dische diphenylamine. Because Dische diphenylamine turns a darker color blue when there is more DNA present, one can determine the concentration of DNA in a particular substance. If there was no other way to determine whether the DNA was properly isolated, then Dische diphenylamine would be added to a sample and observed underneath a microscope to check for nuances in the change of color.
From this experiment, it was determined that the first unknown contained DNA while the second unknown didn’t. This meant that the first unknown was made up of a substance that either living or once alive. This could mean it was a plant, like some type of fruit, or that it contained an animal product, like milk or eggs. The second unknown must have been some type of nonliving substance. It tested positive for reducing sugars, so it could have been a reducing sugar mixed with water.
Testing for Proteins in Water, Honey, Vegetable Oil, and Egg Whites Using Biuret Reagent
The Effect of Biuret Reagent on Water, Honey, Vegetable Oil, and Egg White
In this experiment, biuret reagent was used to determine whether or not water, honey, vegetable oil, and egg whites contained protein. Water and the first unknown had the same initial and final color while honey turned an olive green, vegetable oil stayed the same color but developed a foam on top, and the egg white and second unknown had a violet final color.
The biuret reagent is made up of copper sulfate and potassium hydroxide. Peptides that contain more than three amino acids or amido groups react with the copper sulfate. This reaction creates a pink to a violet color. With this in mind, the only substances that contained proteins were the egg whites and the first unknown.
In this experiment, the positive control was the egg white. It is a well-known fact that egg whites contain protein; many athletes eat them in order to build up their muscles. This control yielded the expected result, which was a final color of violet. The negative control in this situation was water, which yielded a final color of cyan, indicating that it did not contain protein. Because the controls yielded the expected results, they added validity to the experiment.
The biuret test is useful for many applications, including medical testing. One can use the biuret test to gauge the total protein in one’s blood. Blood is extracted from the body and then given a biuret test. If the total protein is high, the patient may be subject to inflammation, and it is possible that they have contracted cancer. If the total protein is low, then the patient may have a protein deficiency or liver disease.
It was concluded from this experiment that the first unknown did not contain protein while the second one did. Because the second unknown was determined not to have DNA, it would have to be made up of some nonliving substance containing protein. Research on this subject determined that the unknown itself could be some kind of protein because there are few nonliving things with proteins (viruses, for example), and it wouldn’t be feasible for some of these things to be an unknown in this particular experiment. The first unknown, on the other hand, was determined not to have protein. This did not provide any more information on its identity, but it further ruled out the possibility of it being an animal product because animal products often contain protein.
Testing for Lipids in Water, Honey, Oil, and Egg White Using a Brown Bag
Determining the Presence of Lipids in Water, Honey, Oil, Egg, and Two Unknowns Using a Brown Bag
Determining the Presence of Lipids in Water, Honey, Oil, Egg, and Two Unknowns Using a Brown Bag
In this experiment, a brown bag was used to determine whether or not lipids were present in water, honey, oil, egg white, and two unknowns. This was done by placing a small amount of each substance on the paper bag and waiting for them to dry. If the paper bag was translucent after the substance had completed drying, then there were lipids present. From this experiment, it was determined that the only substance with lipids present was the oil.
The brown paper bag is translucent when lipids are applied to it because light is transmitted through fat by refraction. On the other hand, when light hits a regular brown bag a part of it is absorbed, a part is reflected, and a part is scattered. The fat cuts down on the amount of light that is scattered, and instead refracts it through the brown paper bag. Thus, the paper bag looks transparent.
The controls in this experiment were water and oil. The water was the negative control, and it was not translucent after the brown bag was dry. It yielded the expected result. Also, the oil was the positive control. It was the only substance that made the brown bag transparent, so it yielded the expected result. These findings added validity because they complied with the expected results.
This lipid test is not utilized to determine the fat content of most foods in real life simply because it is not accurate. However, if there were a situation in which one had no access to nutritional information and no other way of testing, it could be determined with this test whether or not food possessed fat. This test is performed in real life all the time, though. When one buys doughnuts or muffins in a brown paper bag, the bag becomes greasy and often translucent. The same holds true for fries and other fast food items. This is why muffins and doughnuts are wrapped in wax paper and then placed into a brown paper bag.
It was determined from this experiment that neither unknown one nor unknown two contained lipids. The first unknown contained DNA, so it would most likely be a plant product because animal products often contain fat. (With the exception of egg whites, which was shown not to contain lipids in this experiment.) The second unknown did not contain lipids as well, but no further conclusions can be drawn upon its identity.
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