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The Making of the Fittest:
Got Lactase?
The Co-evolution of Genes and Culture

HANDS-ON
STUDENT HANDOUT

MILK—HOW SWEET IS IT?
INTRODUCTION
In the film, The Making of the Fittest: Got Lactase? The Co-Evolution of Genes and Culture, Dr
...
Spencer Wells is able to digest lactose, the main sugar in milk, by having him rapidly drink a liter of milk and then
measuring glucose levels in his blood
...
These two simpler
sugars are absorbed from the intestine into the bloodstream
...


Not all human adults, however, produce lactase—in fact, most people worldwide don’t
...
When lactose-intolerant individuals drink milk, the lactose passes undigested through
the small intestine into the large intestine and may cause gas, bloating, and sometimes diarrhea
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In this activity, you will test glucose levels in four “patient” samples to determine whether they are lactase persistent or
nonpersistent
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Swallow did in the film, you will measure glucose in samples of milk
to which you will add fluids that represent the contents of the small intestines of the four patients
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BioInteractive
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1
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2
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Use a graduated cylinder to measure 5 mL of Patient #1 intestinal
fluid and pour it into the Patient #1 cup
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Use a clean (i
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, rinsed in water) graduated cylinder to measure 5 mL of
Patient #2 intestinal fluid and pour it into the Patient #2 cup
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(e) Label a medicine cup “Negative Control” and add to it 5 mL of water
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(h) Label six medicine cups “Milk” and add 5 mL of milk to each one
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Remove the two pages at the end of this document and place them on your desk
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The Glucose Test Strips Chart is where you will place the wet glucose reagent test strips
after you use them
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Milk–How Sweet Is It?
www
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org

Page 2 of 8

The Making of the Fittest:
Got Lactase?
The Co-evoluti on of Genes and Culture

HANDS-ON
STUDENT HANDOUT

Determining baseline (time 0) glucose levels
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Use six glucose test strips to test the baseline (i
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, before the experiment) glucose levels of the intestinal fluids of
the four patients and the two controls
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(b) Lay the strip on the Glucose Test Strips Chart on the section labeled Patient #1, 0 min
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(This time may vary depending on the instructions for the
particular brand of glucose test strips you are using
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,
in the row for Patient #1
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The test is time-sensitive
and waiting longer will affect the accuracy of your measurement
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Each time write your results in the “time 0” column
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Determining whether lactase is present in your samples
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If you are working with a partner, decide who will do what
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It will take too long to do all the steps for
one sample before moving to the next one
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Alternatively, you can do all the samples simultaneously and one person
dips in the glucose test strips at the appropriate times and the other person records the results after 30 seconds
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For each sample, you will carry out the following steps:
(a) Add 5 mL of milk to the Patient #1 cup and gently stir with a plastic rod
...
)
(b) Start your timer immediately – you need to take more measurements at 2 minutes and at 7 minutes after adding
milk to your sample!
(c) At time 2 minutes dip the glucose test strip in the mixture in the Patient #1 cup, lay the strip down on the
Glucose Test Strips Chart in the Patient #1 2 min
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Record the glucose
concentration on the Lactase Data Table in the column labeled “Glucose levels (mg/dL),” 2 min
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(d) Repeat the step above at the 7 minute time
point
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Be sure
to use a different stirring rod for each sample
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The colors of the test
strips will vary
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BioInteractive
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When you were measuring patients’ samples, why did you have to use a clean graduated cylinder each time?
To avoid contamination
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2
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Lactose  Glucose + Galactose
enzyme

3
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What is the source of lactose? The source of lactose in this experiment is milk
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What is the name of the enzyme that digests lactose into glucose and galactose? The name of the enzyme that
digests lactose into the glucose and galactose is lactase

c
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d
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The graph should show the results of the 0, 2-, and
7-minute glucose test for all your samples, including the controls
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LACTASE DATA GRAPH
Baseline

2 Minutes

7 Minutes

30
25
20
15
7 Minutes

10

2 Minutes

5

Baseline

0
Patient # 1

Patient # 2

Negative Control

Postive Control

Milk–How Sweet Is It?
www
...
org

Page 4 of 8

The Making of the Fittest:
Got Lactase?
The Co-evoluti on of Genes and Culture
4
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Which patient(s) appear to be lactase persistent (lactose tolerant)? Patient # 1 appears to be
persistent
b
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Glucose level was increased which indicates that the intestinal fluid contains enough
lactase to breakdown lactose into glucose and galactose
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a
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Describe the evidence supporting this claim
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This shows that the intestinal fluid did not contain lactase
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a
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When water is added to the milk, it serves as a negative control because water
does not contain any lactase, so it should not produce any glucose when
combined with milk
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Explain why it was necessary to measure glucose levels in a sample of milk to which 5 mL of lactase solution was
added (the positive control)
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Why do you need both negative and positive controls?
The two controls, positive and negative, detect different potential errors
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If the negative control had resulted in the data shown in the graph below, what would you conclude? Provide
two possible explanations to account for these results
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Milk–How Sweet Is It?
www
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org

Page 5 of 8

The Making of the Fittest:
Got Lactase?
The Co-evoluti on of Genes and Culture

HANDS-ON
STUDENT HANDOUT

7

Instead of measuring glucose levels in the milk, identify another compound you could have measured the levels of
to determine whether lactase was active
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8
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Explain why in the film Dr
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In this experiment, simulated intestinal fluid was used whereas the lactase has an
immediate contact with the lactose which quickly breaks down into glucose and
galactose
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a
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In addition to carbohydrates, which include lactose, list the other
nutrients present
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b
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Explain why it is possible for them to digest the proteins in milk even though they lack the
lactase enzyme
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Lactase only digests lactase
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c
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It is
composed of glucose and fructose
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Digesting sucrose requires enzymes other than lactase
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Individuals who are lactose
intolerant only lack in enzyme lactase but can still produce enzyme digesting
sucrose
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A milk allergy is the result of an immune reaction to one or more of the components of milk, such as the protein
casein
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Milk allergy is an insusceptible reaction which includes the creation of antibodies
explicit to substances in milk
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The symptoms of
milk allergy and lactose intolerant are different
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Milk–How Sweet Is It?
www
...
org

Page 6 of 8

The Making of the Fittest:
Got Lactase?
The Co-evolution of Genes and Culture

HANDS-ON
STUDENT HANDOUT

LACTASE DATA TABLE

Samples

0 minutes (baseline)

2 minutes

7 minutes

Glucose levels

Glucose levels

Glucose levels

(mg/dL)

(mg/dL)

(mg/dL)

Patient
#1

18
...
2

27
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5

22
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7

LOW

LOW

1
...
7

Negative LOW
Control

Positive
Control

LOW

Milk–How Sweet Is It?
www
...
org

Page 7 of 8



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