San Beda College Alabang
8 Don Manolo Blvd., Alabang Hills Village,
Muntinlupa City, 1770
INTEGRATED BASIC EDUCATION DEPARTMENT (K-12)
LABORATORY ACTIVITY #2: TESTING THE PRESENCE OF BIOMOLECULES
Date
Viray, Yanna; Villegas, Herman;
Dec 8, 2022
Submitted
Lopez, Charlize
STEM12 - B
Grade &
Topic
Lesson #6 - Biomolecules
Section:
Name:
Objective of the Laboratory Activity:
●
Test the presence of biomolecules such as carbohydrates, proteins, and lipid in each food
samples.
Key Concepts
● Carbohydrates and lipids are composed of the same chemical elements but in different
proportions. Both are used as energy sources for cell metabolism.
● Each gram of carbohydrates stores 4 calories of energy, whereas each gram of lipid stores 9
calories. Therefore, lipid serves as a more compact way to store energy since it contains more
energy per gram than carbohydrates.
● Proteins have many roles in cells and cell communication.
General Instructions:
1. Read and follow the given instructions on each laboratory activity.
2. Remember and follow the laboratory safety rules and precautions all the time.
3. Submit the accomplished laboratory sheet by uploading your file in PDF format using the file
name format (S12-section_LA2_SURNAME)
Laboratory Task
Key Ideas
ACTIVITY 1: TESTING CARBOHYDRATES
Perform chemical tests to identify the presence of sugars and starch in
the food samples.
● Carbohydrates are the body's most important and readily available
energy source.
● Forms of carbohydrates:
1. Simple sugars (simple carbohydrates), such as fructose,
glucose, and lactose, are found in nutritious whole fruits.
2. Starches (complex carbohydrates), found in foods such as
starchy vegetables, grains, rice, bread, and cereals
METHOD 1: SIMPLE SUGAR
Materials needed
Alcohol lamp, test tube holder, 3 test tubes with stoppers, Iodine solution,
Benedict's solution, corn starch, water, 2 food products (Note: Choose
from white/brown cooked rice, fruits/vegetable, and milk products).
Indicator
● The Benedict’s Solution provides a test for the presence of simple
sugars.
● If sugar is present, Benedict’s Solution will turn color (shades of
yellow, orange, brown).
● If the color upon heating is changed into green, then there would
be 0.1 to 0.5% sugar in the solution.
● If it changes color to yellow, then 0.5 to 1% sugar is present.
● If it changes to orange, then it means that 1 to 1.5% sugar is
present.
● If the color changes to red, then 1.5 to 2.0 percent sugar is
present.
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●
And if the color changes to brick red, it means that more than 2%
sugar is present in the solution.
Procedures
1. Place the foods in separate test tubes.
- if the food is liquid, pour enough to just cover the bottom of the
glass.
- If the food is solid (e.g., banana, apple, potato chips), crush a
small amount and add enough water to cover the bottom of the
tube.
2. Add 10 drops of Benedict’s Solution to each test tube.
3. Observe each test tube at room temperature.
4. Then, light up the alcohol lamp to heat each test tube
simultaneously.
5. Using the test tube holder, hold the test tube at an angle above the
flame and point it away from yourself and others.
Laboratory Setup (Draw or attach a captured image of the setup and its result)
Observations
Complete the chart below using the food your group has compiled.
FOOD
1. Rice
2. Grapes
. 3. Starch
Materials needed
Procedures
Indicator
DESCRIPTION OF
ANY
CHANGE(S) BEFORE
HEATING
DESCRIPTION OF
ANY
CHANGE(S) AFTER
HEATING
CONCLUSION: ARE
SIMPLE
SUGARS PRESENT?
White in color with a slimy yet
No changes happened.
No simple sugars were present.
pulpy appearance.
Light Green in color, watery texture Brick Red in color but it retains its Simple sugars have more than 2%
with grape pulps.
texture.
present.
White in color, watery texture. Blue and green in color but it
retains its texture.
Simple sugars have at least 0.1
to 0.5% present.
METHOD 2: STARCH
Test tube holder, 3 test tubes, 3 food products (Note: Use the same food
items in Method 1), and Iodine solution
1. Place a sample of each food into the test tube. Test similar amounts of
each food.
2. Place a few drops of iodine solution on each food.
3. Make observations immediately.
4. Wait a few more minutes and note any other changes.
● When drops of iodine solution are applied to food containing
starch, the solution will turn dark blue, purple, or blackish.
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Laboratory Setup (Draw or attach a captured image of the setup and its result)
Observations
Complete the chart below using the food your group has compiled.
FOOD
DESCRIPTION
BEFORE TESTING
DESCRIPTION
AFTER TESTING
CONCLUSION: ARE
COMPLEX
SUGARS PRESENT?
Blackish-White pulpy liquid
solid.
The sugars are present in Rice.
1. Rice
White in color with a slimy yet
pulpy appearance.
2. Grapes
Light Green in color, watery texture Purple in color with a watery
with grape pulps.
texture.
The sugars are present in Grapes.
3. Starch
White in color, watery texture. Black in color with the same
texture.
The sugars are present in starch.
Questions and Analysis
1. What color changes did you observe after adding the iodine and benedict solutions to each
food product?
- We observed that the colors retained their color before adding the Iodine and/or the
benedict solutions. Once the solutions were added to each test tube, the colors slowly
turned into a darkish color compared to their previous colors.
2. What difference did you observe between the results in Method 1 and Method 2 of the
experiment?
- We noticed that the differences between the two methods are in the samples’ colors.
Method 1 had warmer colors aside from green while method 2 had more cooler colors.
3. Which among the food samples mainly contain simple sugars and starch?
- In our opinion, the food sample that have both simple sugars and starch present is the rice.
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Laboratory Task
Materials needed
Procedures
ACTIVITY 2: TESTING PROTEINS
Test the presence of proteins in selected food
Meat (Note: Choose from chicken, beef, pork, or fish), milk, tofu, water, 4
test tubes, test tube rack, and biuret reagent (Solution A and Solution B)
1. Put the same amount of each food sample in 2 test tubes.
2. For the meat, add some water and try to squash it.
3. Half-fill the test tube with water (controlled).
4. Add about 2mL of Biuret reagent (Solution A and Solution B)
ineach test tube.
5. Then, light up the alcohol lamp to heat each test tube
simultaneously.
6. Using the test tube holder, hold the test tube at an angle above the
flame and point it away from yourself and others.
7. Observe and note the color changes. Then, record your
observations.
A purple or pink change in color indicates the presence of proteins in
the sample.
Laboratory Setup (Draw or attach a captured image of the setup and its result)
Indicator
Observations
Complete the chart below using the food your group has compiled.
FOOD
1. Pork
2. Tofu
3. Water
DESCRIPTION
BEFORE TESTING
DESCRIPTION
AFTER TESTING
CONCLUSION: ARE
PROTEINS
PRESENT?
Light Brown in color with a muddy Dark Purple in color but retains its Due to the color changing to Dark
yet pulpy texture.
textures.
Purple, proteins are present.
Due to the color changing to
Beige in color with a muddy
Purple in color but retains its
Purple, proteins are present.
texture.
textures.
Clear
White murky liquid with a
grimy texture.
Neither Pink nor Purple were
present in the liquid, therefore it
does not contain any proteins.
Questions and Analysis
1. How many test tubes show a color change? What does each test tube show?
- There are two out of three test tubes that show a color change. The test tube with pork turned
from a Light brown color to a dark purple color while the test tube with the tofu turned from a
beige color to a purple color.
2. Was there a change when you mixed water with the Biuret reagent? Why?
- No there were no changes in the water since there are no proteins present in the water.
3. Which among the food samples contains more proteins?
- In our observations, it would be the pork as it has the darkest purple color.
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Laboratory Task
Key Ideas
Materials needed
Procedures
ACTIVITY 3: TESTING LIPIDS
Test the presence of lipids in selected food through an Ethanol Emulsion
test.
Ethanol Emulsion Test is a food test that determines the presence of a
broad group of naturally occurring compounds known as lipids.
2 food samples (Note: Choose from peanut butter, avocado, burger, milk,
butter, oil, or fried french fries), mortar and pestle, distilled water, spatula,
and 2 test tubes
For solid sample:
1. Crush the food sample and place in a dry test tube.
2. Add ethanol to about 2mL above the level of the sample and shake
thoroughly.
3. Allow the solid to settle (about 3 min) to allow the lipid to be
extracted.
4. Decant the ethanol into another test tube.
5. Add 2mL of deionized water to the second test tube
6. Make observations.
For the liquid sample:
1. Add a few drops of the liquid food sample to a dry test tube.
2. Add 2mL ethanol and shake it thoroughly
3. Add 2mL of deionized water.
4. Make observations.
●
Indicator
●
Lipids are not present if the solution remains colorless and no
emulsion is formed.
Lipids are present if a layer of cloudy white suspension forms at
the top of the solution.
Laboratory Setup (Draw or attach a captured image of the setup and its result)
NONE
Observations
Complete the chart below using the food your group has compiled.
COLORLESS
FOOD
1. Oil
2. Milk
LAYER OF
CLOUDY WHITE
SUSPENSION
The oil stayed at the top layer of the The oil had a cloudy white
ethanol. It remained colorless
suspension after putting water in
the mixed solution.
The milk had a cloudy white
The milk and the ethanol are
suspension after putting water in
mixed together.
the mixed solution.
CONCLUSION: ARE
LIPIDS
PRESENT?
Lipids are present because the oil
had a cloudy white suspension after
putting water.
Lipids are present because the milk
had a cloudy white suspension after
putting water.
Questions and Analysis
1. Which among the food samples contain lipids?
- Both of the food samples contain lipids.
2. What kind of lipid-rich foods should be taken in moderation? Why?
- In our opinion, it would be the oil sample. Oil consists of high levels of fats which is really
detrimental to a person’s health when consumed more than the average consumption rate.
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References:
●
●
●
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Aryal, S. (2019, August 15). Benedict’s Test- Principle, Composition, Preparation, Procedure
and Result Interpretation. Microbiology Info.
https://microbiologyinfo.com/benedicts-test-principle-composition-preparation-procedure-and-r
esult-interpretation/
Brilliant Biology Student. (2015). Food Tests - Ethanol Emulsion Tests. Brilliant Biology
Student. http://brilliantbiologystudent.weebly.com/ethanol-emulsion-test-for-lipids.html
Evangelista, L. T. (2017). General Biology 1 for Senior High School. C&E Publishing, Inc. 839
EDSA, South Triangle Quezon city, Philippines.
Kingsborough Community College. The Science of Nutrition Laboratory Science 70.
https://www.kbcc.cuny.edu/academicdepartments/physci/documents/labmanuals/sci70/Sugars
_starch.pdf
That in all things, may God be glorified!
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