Name: ___________________________________________ Period ___________ Date
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Tests for Biological Molecules (Organic Compounds)
pasta
rice
Food items:
milk
corn starch
egg whites
potato
mayo
oil
granulated sugar
water
beans
Background:
1. Which of the above food items do you think contains polysaccharides/starch?
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2. Which of the above food items do you think contains lipids?
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3. Which of the above food items do you think contains proteins?
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Nutrient
Type of test
Negative Test
Positive Test
Polysaccharides (aka starches)
Iodine
Amber/brown
Blue-black
Lipids
Brown paper
No change once dry
Translucent, semi-transparent
Protein
Biuret reagent
Blue
Lavender-violet
Procedure: (NOTE: at each lab station, you will be testing a different food item). The procedure at
each station is as follows. Please be sure to read the procedure carefully and to follow all steps.
1.
2.
3.
4.
5.
6.
Put a small amount for the food item into each of the two dixie cups (dixie cup A and dixie
cup B) at the station
Rub a small amount of the food item onto the brown paper bag, rubbing it in completely
and leave to dry (these are all common household items so you may use your fingers).
add 5-7 drops of biuret solution into dixie cup A
add 5-7 drops of iodine solution into dixie cup B.
Record your result in your table.
You will rotate to the next lab station when you hear instructions to do so. At the end of
the lab period you may return to any lab station to complete any unfinished test.
Data Table:
Food Item
Biuret, Protein
+ Purple
- Blue
Iodine, Starch
+ Purple/Black
- Brown/Orange
Brown Bag, Lipids
+ Translucent
- Dry/no change
Water (control), no
organic biological
molecules
egg whites
rice
beans
corn starch
potato
mayo
milk
oil
sugar
pasta
1.
What was used to test for the presence of polysaccharides?
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2. How can you tell by using this test that a substance contains polysaccharides?
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3. Which items do contain polysaccharides?
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4. What was used to test for the presence of lipids?
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5. How can you tell by using this test that a substance contains lipids?
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6. Which items contain lipids?
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7. What was used to test for the presence of proteins?
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8. How can you tell by using this test that a substance contains protein?
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9.
Which items contain proteins?
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Name: _____________________________________Period ___________ Date _____________
Tests for Biological Molecules (Organic Compounds)
Extension Questions: Answer each question in complete, full sentences.
1. Biuret reagent will turn the skin purplish-brown. Explain why this occurs.
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2. Why might there not a simple positive/negative test for the presence of nucleic acids?
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3. Draw a line to match the monomer of the left with the macromolecule on the right.
Fatty acid and glycerol
Protein
Monosaccharide
Lipid
Nucleotide
Nucleic acid
Amino acid
Carbohydrate
4. Draw a line to match the monomer on the left with the polymer on the right
Fatty acid and glycerol
DNA
Nucleotide
Triglyceride
Amino acid
Starch
Glucose
Enzyme
5. Draw a line to match the polymer on the left with the macromolecule on the right
Cholesterol
Polysaccharide
DNA
Lipid
Enzyme
Nucleic Acid
Cellulose
Protein
6. How are monomers related to polymers? Cite examples from questions 3-5 to assist you.
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Figure 1
Figure 2
7. In figures 1 and 2 above what process is occurring that is creating the lipid and the disaccharide?
When our body needs additional energy it uses the carbohydrates source first as a “quick” energy,
instead of the fat molecule, why do you think our bodies use the carbohydrate molecules first?
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