BIOLOGY Lab2 – Organic molecules
Date: 19/12/13
Thaksaporn (May)
Warattaya (Mook)
Kanyapat (Nuey)
Kantisa (Milk)
Parima (Kaew)
Natarpakul (Tammy)
Purpose:
To test different organic molecules of foods by using various chemicals such as Benedict’s
reagent, iodine solution, Biuret’s reagent, and absolute ethanol to find sugars, starch, protein, and
lipids in each sample and identify what are positive and negative controls and the content of three
unknown samples.
Hypothesis:
I think if we put Benedict’s reagent, iodine solution and Biuret’s reagent in each test tube of
water, the color will not change. But if we put Benedict’s reagent in other test tubes, the test tubes that
contain sugars will change color from blue to green, yellow, orange or red. If we put iodine solution in
other test tubes, the test tubes that contain starch will change color from brown to black-blue. If we
put Biuret’s reagent in other test tubes, the test tubes that contain protein will change color from blue
to purple. And if we put absolute ethanol in the tube that contains lipids, it will turn the solution white
with homogenous mixture.
Procedure:
Procedures (Carbohydrates and proteins)
1) Fill 300ml of water into the 500ml beaker with a magnetic stirrer. Place the beaker on the hot
plate.
2) Turn on the hot plate and the stirrer to the instructed levels.
3) Make labels on provided marking tape to be placed on the outside of each test tube. Use the
chart below for abbreviation.
4) Apply the label on each test tube. And arrange the test tube on the rack according the Table.
5) Put on protective gloves and a goggle.
6) Adding approximately 1cm of each sample according to the label.
6.1In total you should have 3 tubes of each of the following samples
- Water >>> negative controls
- Glucose solution (Monosaccharide) >>> positive controls for Benedict’s solution
- Starch solution (Polysaccharide) >>> positive controls for Iodine solution
- Gelatin solution - ---(Protein) >>> positive controls for Biuret solution
- Diluted milk
- 3-4 pieces of diced onion + water
- 3-4 pieces of diced potato + water
- Unknown1
- Unknown2
- Unknown3
7) In ROW1: Add 5 drops of Biuret solution into each of the sample.
7.1 Gently swirls the test tube around.
7.2 Observe and take note any the color changes in the result section.
8) In ROW2: Add 5 drops of Iodine solution into each of the sample.
8.1 Gently swirls the test tube around.
8.2 Observe and take note any the color changes in the result section.
9) In ROW3: Add 5 drops of Benedict’s solution into each of the sample.
9.1 Gently swirls the test tube around.
9.2 Use the beaker tong to transfer the test tube one at a time into the boiling water in the
beaker for around 3-5 minutes.
9.3 Observe and take note any the color changes in the result section.
10) Turn of the hot plate and stirrer.
11) Continue to the next part of the experiment.
Procedures (Oils)
1) Collect two test tubes labeled A&B from your instructor.
2) Unscrew the cap of the tube
3) Add approximately the same amount of absolute ethanol into each tube.
4) Screw the cap back on tightly.
5) Shake each tube vigorously. Observe the change and record the findings in the results
section.
6) Call your instructor to show you the brown-paper test and record the findings in the results
section.
Result:
Organic Molecules Test Data Table
Contents
Abbreviation
Testing
Reagents
Water
Glucose
solution
Starch
solution
Gelation
solution
Diluted
milk
Onion+
water
Potato+
water
Unknown
1
Unknown
2
Unknown
3
W
GL
ST
GE
DM
ON
PO
U1
U2
U3
Row1
Benedict’s
solution
No
Change
Orange
+
No
Change
Light
purple
Yellow
+
Light
yellow
+
Light
yellow
+
Light
purple
Orange
+
No
Change
Row2
Iodine
solution
No
Change
No
Change
Black
blue
+
No
Change
No
Change
No
Change
Black in
potato
stuff
+
No
Change
No
Change
No
Change
Row3
Biuret
solution
No
Change
No
Change
No
Change
Light
purple
+
Cloudy
purple
+
Light
yellow
Light
gray
Light
purple
+
No
Change
No
Change
“+” is positive result
Emulsification Test Data Table
Emulsification Test
Tube
With Ethanol
Without Ethanol
A (oil)
White opaque
+
Yellow (No change)
B (water)
No change
No change
“+” is positive result
Conclusion:
The negative and the positive controls display the correct color. For testing sugars, the
contents which contain sugar will show the positive controls and the color of that samples will turn
from blue color to display green, yellow, orange, and red color such as glucose solution displays
orange color, diluted milk displays yellow color, onion water displays light yellow color, potato water
displays translucent yellow color, and the unknown2 tube displays orange color. The other samples
display light blue color (no change) and light purple color. For testing starch, the contents which
contain starch will show the positive controls and the color of that samples will turn from yellowishbrown to display blue-black color such as starch solution and potato stuff. The other samples display
light yellow color (no change). For testing protein, the contents which contain protein will show the
positive controls and the color of that samples will turn from blue to display purple color such as
gelation solution, diluted milk, and the unknown1 tube. The other samples display blue color (no
change), light yellow, and light gray. For testing lipids, the tube which contains lipids will show the
positive control and turn the solution white with homogenous mixture when absolute ethanol is
added such as the test tube A with ethanol that displays white opaque color. Meanwhile, the others
display yellow color (no change) and no changed color.
Questions:
1. Does potato store glucose as starch? How do you know from your results?
Yes, it does because when plants synthesize they will produce glucoses, which plants will use them
as energy. Potato has to store these energies to use for next time so they will store them as
polysaccharide such the starch. Potato stores these glucoses as starch. According to the results, potato
displays the changing color in only the potato stuff. When we dropped iodine into the test tube the
color of only the potato stuff turns to black, it shows that potato contains starch and the starch was
stored in the potato obviously so potato is a good source of energy for human.
2. Does onion store glucose as starch? How do you know from your results?
No, it doesn’t. Onion does not contain starch because when we dropped iodine for test starch in an
onion, the onion has no any change that shows us onion doesn’t contain any starch but from the
results the onion contains sugar instead of starch. To explain this, I have to search in google and find
that mostly plants will store the energy as starch but there are some types of plants that will store the
energy as sugar and oil. So I think that onion is the type of plants that stores energy as sugar instead of
starch.
3. What sugar is most likely present in the diluted milk?
The sugar that is most likely present in the diluted milk is lactose, a disaccharide sugar. Milk is
probably the most nutritionally complete food that can be found in nature. Whole milk contains
vitamins (principally thiamine, riboflavin, pantothenic acid, and vitamins A, D, and K), minerals
(calcium, potassium, sodium, phosphorus, and trace metals), proteins (which include all the essential
amino acids), carbohydrates (chiefly lactose), and lipids (fats). When the fats and the proteins have
been removed from milk, the carbohydrates remain, the main carbohydrate in milk is lactose.
4. Even though, gelatin is made from protein, it changed color to purple after heating with
Benedict’s solution?
Gelatin is made from protein, but contains high amounts of sugar so if you test it with Benedict, the
results will be positive.
5. A test tube contains starch, a digestive enzyme for starch, and water. The biuret test is
negative showing no change. However, after 30 minutes, the Benedict’s test is positive. What
substance is present? How do you know?
At first when it is tested, starch is only present so the results will be negative. However, when time
passed the digestive enzyme will digest the starch, which gives you sugar, so the test will become
positive after about 30 minutes.
6. How would you test an unknown solution for each of the following: a. Sugars: It can be tested use Benedict’s reagent. Boil the solution and the color will change in a
range of green to red depending on the concentration.
b. Fat: You can test fat by dropping the substance with an eye-dropper on any kind of paper, if the
paper doesn’t get crinkled and doesn’t evaporate, it means that the substance contains fat.
c. Starch: You need iodine to test for starch. Drop around drops in to the substance, if it contains
starch the color will turn to dark blue.
d. Protein: Biuret reagent is used to test for the presence of proteins and will change for blue to
purple if the test is positive.