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Carbohydrates- Final Lab Report
Introduction
Carbohydrates are very important for the survival of humans. One of their main jobs is
storing energy as glycogen in our liver, which is broken into glucose when our body needs to use
it as an energy source. Carbohydrates are the simplest biomolecules to break down in our body,
which makes them our primary energy source, even though they do not give us the most energy
overall. Plants produce their own glucose, while animals must eat plant material to get
carbohydrates. The formula for a basic carbohydrate is CH20, having one carbon atom, two
hydrogen atoms, and one oxygen atom.
The simplest carbohydrate is a monosaccharide, which is also called a single sugar.
Monosaccharides can further be broken down for the number of carbon atoms they have, trioses
have 3, pentoses have 5, and hexoses have 6. A monosaccharide can have up to 10 carbon atoms.
Two monosaccharides can form a disaccharide with a dehydration reaction, which is when a
water molecule(H20) is lost. Sucrose, lactose, and maltose are some examples of disaccharides,
each having 12 carbon atoms. When disaccharides are broken down into their simpler sugars,
they are then used for energy. If a sugar has a free aldehyde or ketone group, it is known as a
reducing sugar. If monosaccharides form long chains, the chains are known as polysaccharides,
which can be branched or unbranched. One of the most common polysaccharides is starch.
Polysaccharides are stored in our liver and muscles to be converted to energy when need.
Unbranched polysaccharides consist of the same glycosidic bonds throughout the chain, while
branched polysaccharides have different glycosidic bonds throughout the chain. A glycosidic
bond is a covalent bond that puts 2 sugar molecules together.
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There are 3 different tests used to test sugars. The first is Benedict’s test, which will test
to see if a sugar is reducing. In Benedict’s test, you add Benedict’s solution to your sample and
look for a color change, then after, you boil the solution and look at the final color change, which
will tell you if it is a reducing sugar or not. In order to be a reducing sugar, a carbohydrate must
contain a free aldehyde or ketone group. The color will change if Benedict’s solution is heated
with a reactive sugar. If the solution is blue or green after being boiled it will be a non-reducing
sugar, but if the solution is red after being boiled it will be a reducing sugar. The second test is
Barfoed’s test, which will test to see if you have a monosaccharide. Similar to Benedict’s, in
Barfoed’s you add Barfoed’s solution to your sample and look for a color change and then boil
the solution to see the final color change. The end color will tell you if you have a
monosaccharide. The reagent has copper ions that react with the free aldehyde or ketone groups,
but only monosaccharides will be able to reduce the ions because of the acidity of the solution.
After boiling, monosaccharides will be red, and if you do not have a monosaccharide it will be
blue. The final test is Lugol’s test, which will test to see if you have a branched or unbranched
polysaccharide, or no polysaccharide at all. In Lugol’s you will add iodine and note any color
changes. When iodine is dissolved in water with the presence of potassium iodide, I2KI is
formed. Highly branched polysaccharides react with I2KI less intensely than unbranched
polysaccharides. If the color is blue it will not be a polysaccharide, brown will be a branched
polysaccharide, and black will be an unbranched polysaccharide. If the solution is brown or
black, you will have to boil the sample to see if it can be reversed.
During the assay, we tested many different substances to see if they were reducing sugars,
monosaccharides, and polysaccharides. Powdered milk contains lactose which is known to be a
reducing sugar, not a monosaccharide, and no polysaccharide. If unknown A, being powdered
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milk, is assayed throughout the experiment, then powdered milk will produce a reducing sugar,
not a monosaccharide, and an unbranched polysaccharide.
Materials and Methods
“BIO 1510 Laboratory Manual Second Edition” (Department of Biological
Sciences, Wayne State University)
The unknowns being tested are water, glucose, fructose, galactose, maltose, lactose,
sucrose, glycogen, starch, unknown A (powdered milk), Unknown B (potato flake).
Results
Benedict’s test
Sample
Original Color
Color Before Boiling Color After Boiling
Water
Clear
Blue
Blue
Glucose
Clear
Blue
Red
Fructose
Clear
Blue
Red
Galactose
Clear
Blue
Red
Maltose
Clear
Blue
Red
Lactose
Clear
Blue
Red
Sucrose
Clear
Blue
Blue
Glycogen
Clear
Blue
Blue
Starch
Clear
Blue
Blue
Powdered Milk
Clear
Blue
Green
Potato Flake
Clear
Blue
Green
Water, sucrose, glycogen, and starch were blue after being boiled. Glucose, fructose,
galactose, maltose, and lactose were red after boiling. Powdered milk and potato flake were
green after boiling.
Barfoed’s test
Sample
Water
Glucose
Fructose
Galactose
Maltose
Lactose
Original Color
Clear
Clear
Clear
Clear
Clear
Clear
Color Before Boiling
Blue
Blue
Blue
Blue
Blue
Blue
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Color After Boiling
Blue
Red
Red
Red
Blue
Blue
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Sucrose
Clear
Blue
Blue
Glycogen
Clear
Blue
Blue
Starch
Clear
Blue
Blue
Powdered Milk
Clear
Blue
Blue
Potato Flake
Clear
Blue
Blue
Water, maltose, lactose, sucrose, glycogen, starch, powdered milk, and potato flake were
blue after being boiled. Glucose, fructose, and galactose were red after being boiled.
Lugol’s test
Sample
Original Color
Color Before Boiling Color After Boiling
Water
Clear
Orange
---Glucose
Clear
Yellow
---Fructose
Clear
Orange
---Galactose
Clear
Yellow
---Maltose
Clear
Orange
---Lactose
Clear
Orange
---Sucrose
Clear
Orange
---Glycogen
Clear
Brown
Yellow/Orange
Starch
Clear
Black
Black
Powdered Milk
Clear
Orange
---Potato Flake
Clear
Orange
---Water, fructose, maltose, lactose, sucrose, powdered milk, and potato flake were orange
after adding iodine and did not need to be boiled. Glucose and galactose were yellow after
adding iodine and did not need to be boiled. Glycogen was brown after adding iodine and after
being boiled it turned orange. Starch was black after adding iodine and after being boiled it
stayed black.
Discussion
The three tests indicated that their different colors after boiling indicated characteristics
about the sample. For Benedicts test, if the final color after boiling was blue, the sample was a
non-reducing sugar, having zero traces of being a reducing sugar. If the color was green, it has
some traces of being a reducing sugar. If the color was yellow or orange, it has moderate traces
of being a reducing sugar. Lastly, for Benedict’s test, if the final color after boiling was red, the
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sample had large amount of traces for being a reducing sugar. For Barfoed's test, if the final color
after boiling was blue, the sample was not a monosaccharide. Also, for Barfoed's test, if the final
color after boiling had any trace of red precipitate, the sample was a monosaccharide. For
Lugol’s test, if the final color was orange or yellow, the sample was not a polysaccharide. Also
for Lugol’s test, if the final color was brown, the sample was a branched polysaccharide, being
glycogen. Lastly, for Lugol’s test, if the final color was black, the sample was an unbranched
polysaccharide, being starch.
The results of the experiment showed that my prediction was correct in some aspects.
Since powdered milk contains lactose, which is known to be a reducing sugar, powdered milk
would also be a reducing sugar. Both lactose and powdered milk had the same results for
Benedict’s test, a red color after being boiled. This means that they are both, in fact, reducing
sugars. I predicted that powdered milk would not give you a monosaccharide when tested with
Barfoed’s. I predicted this because powdered milk is a mixed solution, making me believe that it
would contain more than one sugar molecule, making it a disaccharide or a polysaccharide. The
results for powdered milk when tested with Barfoed’s was blue, meaning it is not a
monosaccharide, making my prediction correct. This test also lined up with the results for
lactose, which is found in powdered milk. My final prediction was that powdered milk would be
an unbranched polysaccharide considering powdered milk should be made up different sugar
molecules. This prediction was wrong. In Lugol’s test, powdered milk was orange, meaning it
was not a polysaccharide. The results for lactose and powdered milk were the same for each test.
This is logical because lactose is the most predominant carbohydrate in powdered milk.
Diabetes is when the immune system attacks its own pancreas, affecting the production of
insulin. Insulin serves a big role in helping glucose throughout your body. After eating, food is
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Taylor Fiore 6
turned into glucose, which will be used for energy. After food is turned into glucose, the pancreas
is supposed to release insulin. Insulin is used for getting glucose into the cells, so you can use the
energy. Without insulin, the glucose cannot get into the cell and the sugar will build up in the
blood. Having too much glucose built up in your bloodstream can cause many problems if not
dealt with. People that have diabetes should stay away from starches. Starches are unbranched
polysaccharides, which are long chains of monosaccharides. Diabetics should avoid starches
because they are made up of many sugars molecules. All of these sugar molecules would result
in an increased amount of glucose in your blood. This assay would be helpful to diabetics
because it shows which sugar molecules would be the easiest to break down. Since
monosaccharides are simple sugars, they will be the easiest to break down and have the least
amount of glucose in them.
References
Department of Biological Sciences, Wayne State University. BIO 15 Laboratory Manual. 2nd
edition Macmillan Learning curriculum solutions
Healthline. “A Guide to Healthy Low-Carb Eating with Diabetes”
https://www.healthline.com/nutrition/low-carb-diet-for-diabetes#section1
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