Download Case Study: Lactose Intolerance READ THE FOLLOWING

Case Study: Lactose Intolerance READ THE FOLLOWING SCENARIO:
Scott: Hi, Jack. You ready for lab today?
Jack:
No, I’m not feeling good. I didn’t study until last night. That’s when I started feeling sick.
Scott: What happened?
Jack:
You know I moved out of my parents’ house recently. I didn’t feel like cooking last night,
so I ate a lot of cereal. I had almost a quart of milk. A short time after , I started feeling ill.
Scott: What are you going to do?
Jack:
I’m going to see my doctor. Now, I have to talk to my professor about that.
Jack goes, talks to his professor and comes back to get his belongings before he leaves.
Scott: Are you leaving?
Jack: Yes, but I have to make up the lab sometime this week with another professor. I don’t
know how I can find the time for that because I’m working all the time I’m not at school. Bye.
At the Doctor’s Office:
Doctor: What can I do for you Jack?
Jack:
I’m not feeling good. My stomach hurts and I have cramps, gas, and diarrhea.
Doctor: When did these symptoms start?
Jack:
Last night after eating cereal with and milk.
Doctor: Have you experience such symptoms before?
Jack:
Oh yes, two weeks ago after eating ice cream.
Doctor: Do these episodes seem associated with certain types of food?
Jack:
When I eat large portions of dairy products, I experience some of the symptoms I’m
having right now. But Doc, it’s strange because I don’t feel any discomfort when I eat a small tub of
yogurt for lunch or have milk in my coffee.
Doctor: Well Jack, my hypothesis is that you might be lactose intolerant. But first, before we
get to any conclusion, I need you to do two tests. Based on the results of these tests, I’ll be able to
falsify or support my hypothesis.
Jack:
You know Doc, I just started Gen Biology class at college and we studied that lactose is a
disaccharide made of two smaller sugar molecules called glucose and galactose, but what is this
lactose intolerance thing?
Doctor: Lactose is the sugar found in milk. Our small intestine secretes an enzyme called
lactase to break down lactose to the two sugars you mentioned, glucose and galactose. Some
people lack this enzyme and as a result of that, lactose doesn’t get digested. So, lactose moves
with the undigested food from the small to the large intestine where it draws water into the large
intestine, causing diarrhea. Also, the bacteria in the large intestine break down lactose and
produce gases such as hydrogen, carbon dioxide, and methane. Lactose intolerance is not usually
an all-or-nothing condition: the reduction in lactase production, and hence, the amount of lactose
that can be tolerated varies from person to person. The more lactose you consume, the more
severe the symptoms are.
Jack:
Doc, Would you explain how the tests you’ve recommended determine if I’m a lactose
intolerant or not?
Doctor: You’ll come to the clinic’s laboratory once a week for two weeks. In the first week,
you’ll drink one liter of lactose solution containing 50g of lactose. This is the equivalent of one quart
of milk. The lab technician will make you breathe into a machine every hour over the following five
hours in order to measure the concentration of hydrogen gas produced by your intestine. A week
later, you’ll do a similar test but with a smaller amount of lactose; that is, you’ll drink 250ml of an
aqueous solution containing 12g of lactose (that would be equivalent to one cup of milk), and
hydrogen gas will be monitored as in the first test.
Jack:
How do you know if I’m lactose intolerant or not?
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Doctor: I’ll analyze the concentration of hydrogen gas in your breath over a period of 5 hours.
You’ll be classified as lactose intolerant if the hydrogen concentration in your breath increases by
more than 10 ppm (parts per million) per hour.
Jack: Thank you, Doc. I’ll make an appointment to have these tests done, and since I feel a
bit better knowing what might have caused my discomfort.
Jack’s Test Results
Hydrogen Concentration (ppm)
Time
(hr)
50g lactose
12g lactose
0
0
0
1
44
1
2
50
2
3
43
2
4
38
2
5
32
2
The idea of this case study has been
articulated from the following sites:
http://www.middlesex.mass.edu/carneg
ie/PDFs/klein.pdf
http://www.tititudorancea.com/z/lactose
_intolerance.htm
Case Study Experiment: Application of the Scientific Method
BSC1010C is probably your first college science course so it is important for you to
understand how scientists know what they know. Scientists are like detectives. They investigate
an event and gathering clues through their observations. Then they try to determine the cause of
what they have observed. It is the “how” they determine the cause that is important. They use a
logical strategy called the scientific method.
The Problem Statement
The scientific method is a highly organized plan that is used to answer why something
happens the way it does. The scientific method calls this question a problem statement. We all
have questions about life, but the important difference is that the scientific method’s problem
statement is always measurable.
Exercise: Write a problem statement for your current case study:
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The Hypotheses
The second major difference between how you solve a problem and how a scientist does is how
possible outcomes are predicted. Your answer could be an “educated guess”, but scientists make
a “measurable prediction” to answer the problem statement.
Exercise: Write a hypothesis for your current case study.
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The Experiment: Now the scientist will design an experiment to test these hypotheses. The most
critical characteristic of the experiment is that it can be duplicated. Other scientists must be able to
conduct the same experiment and expect to come up with the same answers. Otherwise the
results are meaningless. Therefore, the experiment is always written in great detail so that anyone
can replicate the experiment exactly as it was performed.
A well-designed experiment has three important parts: a control, an independent variable, and a
dependent variable.
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A control provides a baseline upon which you can compare your results from the
experiment. The control forms one of the two groups in any experiment. The other group is the
experimental group. In the experimental group, all variables that might affect the results are kept
constant (or controlled) so that only one variable is tested.
Exercise: What would be the control group?
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Exercise: What would be the experimental group?
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The independent variable is what the scientist changes in the experiment. Think of it as “I control
the independent variable.” There is only one independent variable in each experiment.
Exercise: What is the independent variable in your case study?
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The dependent variable is what changes or varies with the independent variable. This provides
the data/findings/results for the experiment.
Exercise: What is the dependent variable?
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Both the independent and dependent variables are measured in metric measurements or scientific
notation. (For instance, if they involve temperature, it is expressed in C.)
Results/Findings/Data
The results of the experiment, called data, are shown visually in either a table or a graph. This visual
comparison must have a clear descriptive title which allows anyone to quickly see what happened.
Graphs are the preferred way of showing results and many of your lab exercises will use a line
graph. Graphs have two axes, the X, or horizontal axis, and the Y, or vertical axis. The
independent variable is placed on the X axis and the dependent variable on the Y axis.
Exercise: For the graph below make a title for your case study and label the axes with variables.
Title:
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Results are plotted on the graph as data points. Although these data points can be “raw data,”
usually the experiment is run several times and the mean (average) is plotted. Repetition of the
experiment increases the validity of the data collected and the conclusions drawn.
Exercise: Plot the results for your case study on the above graph
Analysis of Results/Findings/Data: The data collected seldom leads to a single outcome…the
same result. There is always variation in the data. Statistics is a tool that helps the scientist
examine this variability and make a statement about the data collected. The other function of
analysis is to look at existing scientific theories and laws to determine if these results can be
explained by what scientists currently know.
Conclusion: The conclusion is a simple statement referring back to the hypothesis. Either the
findings support or fail to support the hypothesis. Conclusions never discuss right or wrong, true
or false. In fact, scientists never “prove” anything, they only support or fail to support a hypothesis.
Exercise: Discuss your conclusion for this case study.
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Exercise: Does it support or fail to support your hypothesis? Why?
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Scientific Theories and Laws: If an experiment is conducted numerous times by many scientists
and the conclusions are always the same, a theory is formed. Again, this doesn’t say that the
theory is “true” or “correct”…just supported by a lot of research. If the theory continues to be
supported by further research, it will eventually become a scientific law.
In the history of science there are many examples of theories and laws, which were once widely
supported and have subsequently been cast aside in light of more experiments. This is probably
the most difficult concept for students to grasp; that science and our knowledge is constantly
evolving and what was a theory or law today may change in the future as a result of more
experiments.
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