Molecules of Life Lab – SHORT FORM REPORT
State Standard 1.h: Students know most macromolecules in cells and organisms are synthesized from a small collection of simple
precursors.
------------------------------------------------------------------------Useful Background Information---------------------------------------------Many of the special characteristics of living things
for living things. These simple sugars include glucose and
come from the molecules that make them up. Life on Earth is
fructose. Carbohydrates containing two monosaccharides are
based on the element carbon, and carbon-containing
called disaccharides. An example is sucrose, table sugar.
compounds are called organic compounds. There are four
Polysaccharides are carbohydrates made up of 100 – 1000
major classes of macromolecules found in living things,
monosaccharides and store energy.
carbohydrates, lipids, proteins, and nucleic acids.
In this laboratory you will conduct tests that reveal
The Lugol’s iodine chemical test and the Benedicts
the presence of the functional groups specific to one of the
chemical test will be used in this lab. The Lugol’s iodine
four major types of macromolecules: carbohydrates. The
changes color when it is mixed with the polysaccharide,
three of other classes of large molecules, lipids, nucleic acids,
starch. Lugol’s iodine does NOT react with monosaccharides
and proteins will not be covered in this laboratory.
like glucose. The Benedict’s chemical changes color when it
Carbohydrates are organic compounds containing
is mixed with monosaccharides like glucose. But, for the color
carbon, hydrogen, and oxygen. The ratio of hydrogen to
change to take place, the mixture must be heated. Benedict’s
oxygen is the same as found in water (2 to1). The simplest
chemical does not react with polysaccharides like starch.
carbohydrates, the monosaccharides, are a source of energy
------------------------------------------------------------------------------------------------------------------------------------------------------------Purpose:
To conduct and interpret qualitative color tests that reveals the presence of different types of carbohydrates – monosaccharides
and polysaccharides.
Hypotheses:
If the unknown substance __________ color when the Lugol’s iodine was added, then the unknown substance contains ______.
If the unknown substance __________ color when the Benedict’s solution is added and heated, then the unknown substance
contains _______.
Procedure:
PART A: TESTING KNOWN SUBSTANCES FOR CARBOHYDRATES
1.
1.
2.
3.
4.
Lugol’s Test for Starch*
Label 3 test tubes: starch, glucose, and water.
Place 1 ml of the appropriate substance to each test tube.
Add 1 ml of Lugol’s solution (iodine) to each test tube.
Record the initial and final color of the Lugol’s solution.
2.
1.
2.
3.
4.
5.
6.
Benedict’s Test for Simple Sugars*
Label 3 test tubes: starch, glucose, and water.
Place 1 ml of the appropriate substance to each test tube.
Add 1 ml of Benedict’s solution to each test tube.
Record the initial color of the Benedict’s solution.
Heat the test tubes in a hot water bath for 5 minutes.
Record the results.
PART B: TESTING UNKNOWN SOLUTIONS FOR CARBOHDRATES*
1.
1.
2.
3.
4.
Using Lugol’s to Test Unknown substance*
Label 2 test tubes: unknown substance, and water.
Place 1 ml of the appropriate substance to each test tube.
Add 1 ml of Lugol’s solution (iodine) to each test tube.
Record the initial and final color of the Lugol’s solution.
2.
1.
2.
3.
4.
5.
6.
Using Benedict’s to Test Unknown substance*
Label 2 test tubes: unknown substance, and water.
Place 1 ml of the appropriate substance to each test tube.
Add 1 ml of Benedict’s solution to each test tube.
Record the initial color of the Benedict’s solution.
Heat the test tubes in a hot water bath for 5 minutes.
Record the results.
Rather than Copy
down the procedure
you will make 2
Figure diagrams to
illustrate the
Procedure
Figure 1: Lab set up
Lugol’s test for starch
Figure 2: lab set up
Benedict’s Test for
simple sugars
Data/Results:
Table 1: Color change of known substances
Substance
Lugol’s Iodine
Initial Color of
Final Color of
Chemical Indicator
Chemical Indicator
Starch
Glucose
Water
Table 2: Color change of unknown substance and control (water)
Substance
Lugol’s Iodine
Initial Color of
Final Color of
Chemical Indicator
Chemical Indicator
Unknown
Water
Benedict’s
Initial Color of
Final Color of
Chemical Indicator
Chemical Indicator
Benedict’s
Initial Color of
Final Color of
Chemical Indicator
Chemical Indicator
Conclusion:




Must include the following
Topic sentence: re-word the purpose so that it is a topic sentence for the conclusion
How does the color data collected show what…
o Lugol’s iodine tests for
o Benedicts solution tests for
(Part A of the lab)
What happened to the unknown solution’s color compared to water’s color for the
o Lugol’s test  explain how that supports or rejects the Lugol’s hypothesis
o Benedict’s test  explain how that supports or rejects the Benedict’s hypothesis
What was in the unknown solution? How do you know?