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LAB GUIDE
BIOLOGY 8TH GRADE
NATHALY ECHEVERRY
TESTING BIOMOLECULES IN FOOD
This document is the guide that provides a theoretical framework for the laboratory, and it describes the activities to be
carried out before, during, and after the lab practice. A thorough reading and the complete completion of all learning
activities are required. A quiz will be conducted before the practice begins to ensure that you have thoroughly read
the guide.
Understanding goal:
Students will explore the world of genetics through hands-on activities and visual learning
Comprehension goal:
To explore key processes in molecular biology, such as DNA replication, transcription, and translation, in order to
analyze how genetic information is transferred and expressed at the molecular level
Introduction:
All living things are made up of biomolecules. These are special molecules that help cells to function, grow, and survive.
The four main types of biomolecules are: Carbohydrates – These are the body's main source of energy. Foods like
bread, rice, and fruits contain carbohydrates. They also help build important structures in plants and animals. Lipids
(Fats) – These store energy and make up cell membranes. Butter, oils, and nuts contain lipids. They also help protect
organs and keep the body warm and help form cell membranes, which protect cells. Proteins – These are essential for
growth, repair, and many body functions. Proteins are found in meat, eggs, and soy. They also work as enzymes, helping
chemical reactions happen in the body, proteins are made of smaller parts called amino acids, and their arrangement
affects their function. Nucleic Acids (DNA & RNA) – These carry genetic information that determines how an organism
looks and functions. DNA and RNA are found in all living cells and help make proteins. DNA is shaped like a twisted
ladder so it can store lots of information in a small space (Adapted from Britannica Kids, 2023).
In biology laboratories, we use chemical reagents to identify the presence of different biomolecules in food. A reagent is
a substance that, when it comes into contact with specific compounds, produces a color change or another visible
reaction. In this lab experiment, we will use three main reagents: Lugol's iodine, which turns dark blue or black in the
presence of starches (complex carbohydrates); Benedict's solution, which changes to orange or red when it detects
simple sugars like glucose; and Biuret reagent, which turns violet if proteins are present in the sample. These reagents
will help us determine which biomolecules are found in different types of food and better understand their importance in
nutrition and bodily functions (Nelson and Cox, 2000).
Objective: To test common food items to identify the presence of carbohydrates, proteins, and lipids, linking the results to
the structure and function of biomolecules.
Research Question: _______________________________________________________________________________
Hypothesis: _____________________________________________________________________________________
Materials:
Each group will need to bring materials together. You do not need to bring all the food samples listed, just two different
options for each type of biomolecule (complex carbohydrates, simple sugars, proteins). Here is a list of suggested food
samples your group can choose from.
Bread, portion of cooked rice, potato, banana, corn.
Apple juice, honey, soda, milk.
Row egg whites, cheese, yogurt, cooked chicken, soy.
Additionally, you will need one small knife and a cutting board (for food preparation).
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Methodology:
1. Preparation of food samples:
Solid foods (bread, potato, cheese, etc.) should be mashed or cut into very small pieces.
Liquids (milk, juice, honey) should be used as they are. If the food is too thick (e.g., yogurt), mix with a small amount of
distilled water.
Starch-rich foods (such as rice) should be mixed with a little distilled water to make a suspension.
Protein foods (e.g., egg whites, chicken) should be finely chopped or mixed with water for better reaction visibility.
2. Biomolecule’s test:
1. Starch Test (Iodine Solution):
1. Label a test tube for each food sample.
2. Place 2 mL of each sample in its corresponding test tube.
3. Add 2-3 drops of iodine solution to each test tube.
4. Observe any color change:
o Positive result: Blue-black color indicates the presence of starch.
o Negative result: No color change (iodine remains yellow-brown).
2. Simple Sugars Test (Benedict’s Solution):
1. Label a test tube for each sample.
2. Place 2 mL of each sample into its corresponding test tube.
3. Add 10 drops of Benedict’s solution to each test tube and gently mix.
4. Place the test tubes in a hot water bath (around 80°C) for 5 minutes.
5. Observe color changes:
o Positive result: Green, yellow, orange, or brick-red indicates the presence of simple sugars (red = high
concentration).
o Negative result: Solution remains blue.
3. Protein Test (Biuret Solution):
1. Label a test tube for each food sample.
2. Place 2 mL of each sample in its corresponding test tube.
3. Add 2 mL of Biuret solution to each test tube.
4. Gently shake the test tubes to mix.
5. Observe color changes:
o Positive result: Purple or violet color indicates the presence of proteins.
o Negative result: Solution remains light blue.
Create a flowchart or graphic organizer to represent the methodology:
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Results:
Presence
of
Tested Biomolecu- Final Color/
Food Sample Reagent Used Initial Color Biomolec
le Reaction
ule
(Yes/No)
[In this space, the student must provide a written description of the results obtained]
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Analysis of results: [In this space, students must analyze the obtained results, compare them, and draw conclusions in
light of their hypothesis and research question. It is important for students to investigate the explanation of their results
based on the literature and provide at least two sources of reference]
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____________________________________________________________________________________
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How do these biomolecules contribute to human nutrition?
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Conclusions: [A brief explanation of the results obtained and their relationship with the hypothesis, objectives,
implications, and limitations is provided].
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Bibliography:
Nelson, D. L., & Cox, M. M. (2000). Lehninger Principles of Biochemistry (8th ed.). W. H. Freeman.
Rogers K., (2023). Biomolecules. Britannica
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Needs Improve- Incomplete (25%
Criteria Excellent (Full Points) Good (75%) Points
ment (50%) or Less)
Clearly stated, specific,
Research and relevant to the experi- Clearly stated and Question is vague Missing or poorly
Question (0.2 ment. Demonstrates relevant but lacks or not fully relevant formulated ques- ___ / 0.2
pts) strong understanding of some specificity. to the experiment. tion.
the topic.
Well-defined, testable, and
Missing or does
logically connected to the Testable and rele- Hypothesis is un-
Hypothesis (0.3 not relate to the
research question. Inclu- vant but lacks clear or not fully ___ / 0.3
pts) research ques-
des reasoning based on strong reasoning. testable.
tion.
prior knowledge.
Flowchart is clear, de-
Flowchart is mostly Flowchart is in- Missing or does
Methodology tailed, and accurately rep-
clear and follows complete, difficult not represent the
(Flowchart) (1.0 resents the experimental ___ / 1.0
logical order but to follow, or miss- methodology ac-
pts) steps. Logical sequence
lacks some details. ing key steps. curately.
and proper formatting.
Observations and
Clearly recorded observa- Results are vague,
data are recorded
Results (1.0 tions and data. Well-orga- incomplete, or lack Missing or largely
but could be more ___ / 1.0
pts) nized with appropriate use proper organiza- incorrect results.
detailed or struc-
of tables or charts. tion.
tured.
Thoroughly interprets re-
Provides a reason- Analysis is superfi-
sults, compares findings, Missing or does
able analysis and cial, with little con-
Analysis (1.5 and connects them to the not provide mean-
some comparison, nection to the hy- ___ / 1.5
pts) hypothesis and research ingful interpreta-
but lacks depth or pothesis or litera-
question. Includes referen- tion.
external references. ture.
ces to scientific literature.
Clearly summarizes find- Summarizes find-
Conclusion is
ings, linking them to the ings and mentions
weak, with minimal Missing or pro-
Conclusion (0.5 hypothesis, objectives, hypothesis but
connection to the vides a poor sum- ___ / 0.5
pts) and real-world implica- lacks depth in dis-
hypothesis or im- mary of findings.
tions. Mentions limitations cussing implications
plications.
and future research. or limitations.
At least one rele-
At least two relevant
vant source is cited, Sources are un-
References (0.2 sources are properly cited, No references in-
but not well inte- clear, irrelevant, or ___ / 0.2
pts) supporting the analysis cluded.
grated into the dis- improperly cited.
and discussion.
cussion.
Quiz (0.3)
1. _____________________________________________________________________________________
2. _____________________________________________________________________________________
3. _____________________________________________________________________________________
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