Hands-On Lab
Identifying Organic Nutrients
Timing: one 90-minute class session
Objective(s):
Students will use chemical indicators to test unknown substances for the presence of certain organic
molecules (glucose, starches, proteins, and lipids). They will make predictions about known/control
substances and compare their results from the unknown substances with those from their control
substances.
Safety Precautions: Students should wear closed-toe shoes, gloves, a lab apron, and safety goggles.
Remind students not to eat or drink anything in the lab, including the experiment materials. Students
should report any broken glass or chemical spills immediately and should not try to clean these up by
themselves. Familiarize yourself with the hazards posed by all the reagents used in this lesson by
reading the appropriate MSDS sheets. Be sure to communicate any hazards to your students.
Materials:
Per group of 3–4 students:
• dropper bottle of of Benedict’s solution
• dropper bottle of IKI (Iodine Potassium Iodine solution)
• dropper bottle of Biuret’s reagent
• dropper bottle of Sudan IV
• ethanol
• eye dropper
• test tubes, approximately 24
• test tube racks, 4
• hot water bath
• distilled water
• 25 mL graduate cylinder
• marker for labeling test tubes
• stopwatch or timer
• four unknown nutrient samples, one of each: glucose (labeled A), starch (labeled B), protein
(labeled C), lipid (labeled D)
• clearly labeled positive and negative nutrient samples, one of each liquefied nutrient samples
containing: glucose, starch, lipid, and protein
• disposable gloves, one pair per student
• lab apron, one per student
• safety goggles, one pair per student
Teacher Preparation:
Once the nutrient indicator chemicals are obtained, materials can be prepared in a day prior to the lab.
Make sure to obtain positive and negative control samples for each test. These controls can overlap.
For instance, the lipid control can serve as a positive control for the lipid test and a negative control for
the protein, starch, and sugar tests. Also make sure to obtain known and unknown samples that are as
pure as possible. You may choose food samples from home (such as flour, pasta, oil, corn syrup, and
meat; just make sure they’ve been sufficiently mashed or liquefied. Alternatively, you might choose to
use laboratory-grade chemicals such as glucose, cellulose, laboratory grade amino acids, etc.) Prepare
a copy of the student investigation sheet for each student.
Procedure:
The Hands-On Labs include both Directed and Guided Inquiry approaches. If your students are new
to the investigational methods being used in the Hands-On Lab, it is recommended that the Directed
Inquiry approach be used to provide scaffolding that will ensure student safety and support the success
of their investigations. Often, the Directed Inquiry approach involves modeling the basic laboratory
techniques and methods to be used in the activity. A discussion of each step in the investigative
process will also be included. In some cases, students may then be asked to create a procedure based
on the one modeled for them. This may involve changing specific variables or adjusting the procedure
to determine the effect on the outcome.
You may choose to use the Guided Inquiry path on its own or after completing the Directed Inquiry
activity. During Guided Inquiry, students are allowed to conduct the investigations more independently.
They will be given opportunities to formulate their own questions, develop their own procedures, and/or
manipulate variables of their own choosing. It may be necessary to provide additional materials and
supplies for students using Guided Inquiry. It will also be important to set clear limits on students’
activities to ensure their safety and the relevance of their inquiry experience to the content you are
teaching.
Directed Inquiry
Engage students in a discussion about the different nutrient macromolecules (make sure to mention
that the class of macromolecules that will not be addressed in this lab are the nucleic acids). Students
should be able to name and classify the major organic nutrients according to their basic chemical
composition and characteristics, as well as their functional roles in living cells. Review this material by
providing students with specific characteristics and/or functions of the different macromolecules and
asking students to identify and hold up for display the corresponding macromolecule on an individual
white board or sticky note. It may be helpful to also have the information on the board so that students
are able to use it as a reference throughout the lab. Remind students about the difference between
organic and inorganic molecules.
In this lab, students will work in groups of three or four to test unknown nutrient samples for the
presence of simple sugars (monosaccharides; some disaccharides), starches, lipids, or proteins. For
each test, students should make a prediction about what colors they will observe after testing their
positive and negative control food samples. They will compare the results of their test samples with the
positive and negative control nutrient samples. Make sure that students use a marker to label every test
tube that they use, denoting the contents of the tube. Hand out or copy onto the board the following
table, noting that each test will take approximately three to five minutes for colors to develop:
Read the steps aloud for each test, using one lab group’s materials to model each step.
Simple sugars test using Benedict’s solution:
1. Label four test tubes A1, B1, C1, D1.
2. Add 5 mL of distilled water to the test tubes.
3. To each test tube, add 1 mL of a different unknown nutrient sample, making sure the test tube
labels coordinate with the nutrient sample labels.
4. Add 20 drops of Benedict's solution to each test tube.
5. Label two more test tubes, one with “positive” and one with “negative.” Add 20 drops of
Benedict's solution to each of the test tubes: one containing a positive and one containing a
negative glucose control nutrient sample.
6. Place the test tubes in a hot water bath for 10 minutes.
7. Record the observations/results in a data chart.
Complex carbohydrate test using IKI (iodine potassium iodine) solution:
1. Label four test tubes A2, B2, C2, D2.
2. Add 5 mL of distilled water to the test tubes.
3. To each test tube, add 1 mL of a different unknown nutrient sample, making sure the test tube
labels coordinate with the nutrient sample labels.
4. Add 20 drops of IKI solution to each test tube.
5. Label two more test tubes, one with “positive” and one with “negative.” Add 20 drops of IKI
solution to each of the test tubes: one containing a positive and one containing a negative
starch control nutrient sample.
6. Record the observations/results in a data chart.
Protein (amino acid) test using Biuret solution:
1. Label four test tubes A3, B3, C3, D3.
2. Add 5 mL of distilled water to the test tubes.
3. To each test tube, add 1 mL of a different unknown nutrient sample, making sure the test tube
labels coordinate with the nutrient sample labels.
4. Add 20 drops of Biuret solution to each test tube.
5. Label two more test tubes, one with “positive” and one with “negative”. Add 20 drops of Biuret
solution to each of the test tubes: one containing a positive and one containing a negative
protein control nutrient sample.
6. Record the observations/results in a data chart.
Lipid test using Sudan IV solution:
1. Label four test tubes A4, B4, C4, D4.
2. Add 5 mL of distilled water to the test tubes.
3. To each test tube, add 1 mL of a different unknown nutrient sample, making sure the test tube
labels coordinate with the nutrient sample labels.
4. Add 20 drops of Sudan IV solution to each test tube.
5. Label two more test tubes, one with “positive” and one with “negative”. Add 20 drops of Sudan
IV solution to each of the test tubes: one containing a positive and one containing a negative
lipid control nutrient sample.
6. Record the observations/results in a data chart.
*Note: students may need to add a few drops of ethanol to their water + nutrient sample solutions if the
Sudan IV test did not work. The same number of drops should be added to each test tube.
Allow lab group to review their results and determine the identities of the four unknown nutrient
samples. Have a student from each group record their results on the board. For example, they might
write, “Nutrient A was a protein, Nutrient B was a carbohydrate, etc.”
Reveal the identities of the four unknown nutrient samples. Students will analyze any discrepancies in
results as they answer the Conclusion/Analysis questions.
Guided Inquiry
For a guided inquiry, explain to students that they will be investigating the contents of different unknown
solutions that contain nutrient molecules, either simple sugars, complex carbohydrates, proteins, or
lipids. They may design their experiments based on their knowledge of the procedures and materials
used in this lab. Depending on available time and resources, you may wish to provide students with a
chart of indicator results like the one from the Directed Inquiry, or you may instruct students to research
the use and results of the indicators. Provide students with some guiding questions to help them focus
their inquiry:
1. What are the four main types of organic nutrient macromolecules?
2. What chemical indicator is used to determine the presence of each of the following molecules:
simple sugars, starches, proteins, and lipids?
3. What, specifically, does each indicator react with?
4. What color results do you predict each indicator to yield from each of the positive and negative
control tests?
5. What will be your independent variable, dependent variable, constants, and control for each
test?
Have students work in their lab groups to develop a procedure and method for recording data. Students
should seek your approval prior to starting on the experiments. Help them test their questions and
predictions by making sure they use a logical progression of experiments. For instance, make sure that
they make use of the negative and positive control samples whenever using an indicator solution to test
an unknown sample.
Analysis and Conclusions:
In order to help students analyze and interpret their results, consider discussing some or all of the
following questions or assigning them as homework:
1. How did your predictions for each of the known positive and negative control samples compare
with the test results from those samples? Answers will vary.
2. Why was it important to have both a positive and negative control sample? It was important to
use both positive and negative controls so that one can be confident that the indicator does
successfully indicate the presence of the desired molecule and does not accidently indicate the
presence of the desired molecule when it is not actually present. This avoids both false positive
and false negative results.
3. What sources of error might have been present in your lab group’s experiments or your
classmate’s experiments? The food solutions that were used may not have been concentrated
or pure enough or sufficiently broken down and liquefied.
4. If you were given a sample of an unknown food, how would you go about analyzing it to
determine what it is composed of? Sample answer: I would make several test solutions using
the food and test each with one of the reagents used in this experiment. In that way, I could
determine what the food does and does not contain.
5. What results would you expect to get if you tested whole milk, and why? Sample answer: Whole
milk contains lipids, protein, and sugar, so I would expect positive result when I tested it with the
appropriate reagents.
Inquiry and Nature of Science Skills in this Lab:
• Identify Questions
o Develop a question that:
 Asks a question about a specific science concept or process
o Recognize and develop testable questions that
 Require the changing of one variable at a time
 Can be answered with a science investigation or observational study.
o Develop predictions/hypotheses that:
 State what may happen in an investigation based on prior knowledge or
experience (prediction)
• Design Investigations
o Practice Lab Safety By:
 Following lab safety procedures
 Recognizing safety equipment and materials and knowing their proper use
 Incorporating laboratory safety practices into the investigation design
o Design and conduct investigations using:
 Fair test - changing only one variable at a time makes comparisons valid
 Independent variable - the one variable the investigator chooses to change
 Dependent variables - what changes as a result of, or in response to, the change
in the independent variable
 Control (control group) - used for comparison in which the independent variable
is not changed
• Gather Data
o Use tools and the SI (metric) system to accurately measure:
 Volume
 Temperature
o Chooses appropriate tools to conduct an investigation
 Glassware
 Pipette
 Test tube
 Hot plate
 Other laboratory equipment
o Uses senses to observe
 Seeing (color)
o Uses the appropriate format to record data
 Writing (journal, worksheet, electronic text)
• Interpret Data
o Sorts and classifies using scientific reasoning
 Objects, substances and organisms by characteristic
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 Apply a classification scheme to objects, substances or organisms
o Identifies and interprets patterns
 Repeating physical or data pattern
 Based on an analysis of data collected during an investigation
Evaluate Evidence
o Drawing and supporting a conclusion by
 Comparing results to hypothesis
 Answer the testable question
Communication in science:
o Participating in critiquing/peer review by:
 Evaluating data for accuracy
Patterns and Systems
o Systems
 Physical and biological systems tend to change until they reach equilibrium and
remain that way unless their surroundings change.
 A system usually has some properties that are different from those of its parts but
appear because of the interaction of those parts.
o Patterns and Change
 Some events can be predicted with certainty, such as sunrise and sunset, and
some cannot, such as storms.
 Some small changes can be detected by taking measurements.
 Some changes are very slow and some are very fast and that some of these
changes may be hard to see and/or record.
 Certain things change in some ways and stay the same in others, such as in their
color, size, and weight.
Scientific Investigation
o Scientific Investigation:
 Scientific investigation begins with a testable question
 Scientific investigation results in things we know and things we don't know.
 Hypotheses are valuable, even if they turn out not to be true, because they lead
to further investigation.
 Scientific investigations lead to the development of scientific explanations.
o Scientific Data and Outcomes
 It is important in science to keep honest, clear, and accurate records.
 Arguments and conclusions are invalid if based on very small samples of data,
biased samples, or samples for which there was no control sample.