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Content Benchmark L.8.B.5
Students know disease can result from defects in body systems or from damage caused by
infection. E/S
Disease is defined as an unnatural or abnormal condition of the body as a result of a homeostatic
imbalance caused by an infection or congenital genetic disorder (from www.dictionary.com).
Homeostasis literally translates to “a state of being the same.” This is a slightly misleading
translation because homeostasis is a dynamic process where the internal conditions of the body
are most often oscillating around a set point. When the mechanisms that maintain homeostatic
conditions are disrupted by either environmental or genetic defects, the result is a disease state.
Figure 1. Body Temperature Homeostasis.
(From http://faculty.etsu.edu/currie/images/homeostasis1.JPG)
Sickle cell anemia is a congenital genetic defect that is caused by a single base pair substitution
at the DNA level. The disorder is caused by problems during the process where the DNA
message (from the mRNA) is used as a template to create a sequence of amino acids that
eventually become proteins. With sickle cell anemia, the point mutation in the DNA impacts the
folding of the proteins. A person with two sickle cell genes produces abnormal hemoglobin
which results in the red blood cells having sickle shape instead of the typical “donut shape”
(biconcave sphere). The sickled cells cause problems with limited oxygen carrying capacity and
have the potential to create “clogs” in the smaller blood vessels.
Figure 2. Normal Red Blood Cells (right) and a Sickled Red Blood Cell (left).
(From http://www.defiers.com/scd.html)
For more information on sickle cell anemia and genetic mutations, see MS TIPS Benchmark
L.8.A.2
Sickle cell anemia is only one example of a genetic defect/mutation causing an imbalance of
homeostasis. In this instance, the cells of the body do not receive adequate oxygen and nutrient
supply. The body attempts to correct the imbalance in a variety of ways including an increase in
both respiratory and heart rates. Due to the clogged vessels and the reduced oxygen carrying
capacity of the red blood cells, the homeostatic imbalance cannot correct itself, and it could
eventually lead to very serious complications and even death. Other examples of diseases caused
by genetic mutations are cystic fibrosis, hemophilia, Marfan syndrome, and Huntington’s
disease.
For more information on genetic disorders, visit the Your Genes, Your Health website which
provides detailed information about the genetic disorders listed above. To access the site, go to
http://www.ygyh.org/.
Diabetes is another example of a disease resulting from a homeostatic imbalance that can be
attributed to either a genetic predisposition or potentially a viral infection
(http://www.umm.edu/endocrin/diabmel.htm). In a normal healthy individual, blood glucose
(blood sugar) levels are tightly controlled by the person’s endocrine system. When blood
glucose levels rise, insulin is released to increase cellular uptake and usage of the sugar. When
glucose levels fall, the liver releases the stored glucose. In diabetes, a person’s blood sugar will
rise beyond the normal limits and stay that way. These persistently high levels of blood glucose
result in health problems such as kidney failure, high blood pressure, and even heart problems.
There are two basic types of diabetes, Type I and Type II.
Figure 3. Illustration of Type 1 Diabetes.
(From http://www.ghi.com/WebMD/topics/Type1.jpg)
Type 1 diabetes is believed to have either a genetic predisposition or a viral cause. The viral
cause is a result of the body’s immune system attacking the insulin receptors because they
resemble a virus that the body has already combated. With adult onset diabetes, or type 2
diabetes, some environmental cue causes a person’s insulin receptors to become less sensitive
and therefore have an impact on the uptake of glucose out of the blood and into the cells.
Some viruses or bacteria can cause health concerns both in the short term and potentially long
term if left untreated. The body responds by issuing an immune response. This immune
response is how the body deals with both viral and bacterial infections. What we think of, as the
“disease” is actually the body’s response to the infection. In an effort to prevent the spread of
the micro-organism, the body will first activate non-specific defenses that will hopefully prevent
the spread, and set the stage for the body’s specific killers to take action against the invader.
For example, when you contract the flu or a cold, your body will respond by creating excess
mucus causing you to be “stuffy” this prevents the spread of the pathogen (foreign substance)
and allows the body time to create its “army of soldiers” or lymphocytes. In addition to the
excessive production of mucus, the body may also increase its core temperature. This rise in
body temperature (fever) is also a defense mechanism to cause potential damage to the foreign
particles (viruses or bacteria).
Figure 4. The adenovirus is a virus normally associate with respiratory infections.
(From http://www.flupatrol.com/2007/05/01/genetics-of-infectious-diseases/)
Treatment for these two sources of disease is quite different. A bacterial infection occurs when a
bacterial cell invades your body, finds a safe place, and then starts to rapidly divide. Most often,
a bacterial infection is a result of the bacterial cells getting past your surface barriers such as
your skin when you have a cut or scrape. Once in, the bacteria start to divide and can lead to an
infection. Most of the time, your body successfully fends off the bacteria and you may not even
notice any problems. Sometimes, though, the bacteria replicates itself fast enough that it
outpaces your defense systems, this is when you go to the physician’s office and receive a
prescription for antibiotics. Antibiotics are used only for bacterial infections as they interfere
with functions that only bacteria perform. Antibiotic resistance is a relatively recent problem
resulting from the over prescription of antibiotics. Due to the over use of commonly prescribed
antibiotics, resistant strands of bacteria known as “super bugs” have evolved.
For more information on antibiotic resistant strands of bacteria, view the CDC’s website at
http://www.cdcfoundation.org/healththreats/AntibioticResistance.aspx.
There are many examples of diseases caused by bacteria. E. coli infection is one we often hear
about in the news. E. coli is short for Escherichia coli which is the name for a specific type of
bacteria that infects our gastrointestinal tract causing irritation that results in severe diarrhea and
vomiting. The diarrhea and vomiting are our body’s way of attempting to rid the body of the
bacteria.
Viruses, while also capable of infecting the body, are vastly different than bacteria, and cannot
be treated with antibiotics. As mentioned above, diseases such as the common cold, flu, or even
chicken pox are caused by viruses. While scientists are researching ways of combating viruses,
in most cases your physician will just suggest that you let the virus “run its course” allowing
your body’s immune system to combat the invader.
Some diseases such as malaria can be caused by pathogenic (disease causing) eukaryotes. In
such diseases, the human body plays host to part or all of another organism’s life cycle. While
you are infected with such a parasite, your body’s immune system, while attempting to combat
the organism, is outpaced by the growth. In addition, because the parasite infects living cells,
once the parasite has invaded the cell, the immune system cannot combat the problem without
causing destruction to it’s own cells. Malaria is a disease that is typically contracted in tropical
areas of the world as the vector is the mosquito. A vector is an organism that carries a disease
causing pathogen. Organisms found in the family Plasmodium are parasitic protists that utilize
humans and other animals as a source of energy and a safe place to replicate themselves. When
the Plasmodium eggs are injected by a mosquito into a human they find a safe place in the
human’s liver. It is there that the parasite begins replicating itself using the liver as a source of
nutrients and energy. Once it has reached a certain population size, it needs to find another host
so the parasites enter the blood stream. Once in the blood stream these organisms cause a whole
host of problems due to the fact that the feed off of and destroy a person’s red blood cells.
However, if the parasite is floating in the blood stream, another mosquito can pick it up when
biting the infected host. This initiates a whole new cycle as can be seen in Figure 5.
Figure 5. Plasmodium Life Cycle.
(From http://encarta.msn.com/media_461541582/life_cycle_of_the_malaria_parasite.html)
Fungi are multicelled organisms that also have the potential to cause disease. A good example of
this is the fungus that causes Athlete’s Foot. Dermatophytes are a classification of fungi that like
to grow in warm and damp places. When a person comes into contact with the fungus, it
attaches itself to the skin, and uses it as a source of nutrients. While the symptoms may not be
life threatening, the fungus will eventually infect farther than just the epidermis, and can cause
painful ulcerations or sores. This breach of the body’s outer defenses can open the individual up
to other more serious infections.
Figure 6. Dermatophyte: Multicellular fungus that causes Athlete’s Foot.
(From http://www.michigan.gov/mdch/0,1607,7-132-2945_5103_31554-96303--,00.html)
In summary, the above examples have been used to illustrate the ideas that the source of a
disease may be one of several different causes. However, each one of these sources results in an
imbalance in the normal everyday operating procedures of the body. We call this a homeostatic
imbalance.
Content Benchmark L.8.B.5
Students know disease can result from defects in body systems or from damage caused by
infection. E/S
Common misconceptions associated with this benchmark.
1. Students often incorrectly believe that viruses are the same as bacteria and that they
can both be treated with antibiotics.
In fact, viruses and bacteria can cause disease, but they are not the same. Viruses are
merely protein shells containing some type of genetic material and maybe a few proteins
that help it move into the target cell. In contrast, bacteria are single-celled organisms that
can cause disease, but are also very beneficial. Antibiotics are designed to aid in the
destruction of bacteria and are therefore useful in treating bacterial infections. Antibiotics
cannot be utilized to treat viral infections.
Information about this misconception can be found by reading the linked article
http://pediatrics.aappublications.org/cgi/content/full/111/2/231.
2. Students incorrectly believe that they can contract the cold or flu by being out in the
cold.
The idea that being in inclement weather one day and contracting a cold the next day is a
misconception that is relatively persistent. Colds or the flu are caused by viruses
disrupting the normal working of the cell and our bodies try to combat the disease by
instituting immune defense systems such as increasing the core body temperature or
causing an increase in mucus production to prevent the spread.
For more information on this misconception, visit
http://www.kittivisianlife.com/articles/03-2007/rain-and-the-common-cold
Content Benchmark L.8.B.5
Students know disease can result from defects in body systems or from damage caused by
infection. E/S
Sample Test Questions
Questions and answers to follow on separate document
Content Benchmark L.8.B.5
Students know disease can result from defects in body systems or from damage caused by
infection. E/S
Answers to Sample Test Questions
Questions and answers to follow on separate document
Content Benchmark L.8.B.5
Students know disease can result from defects in body systems or from damage caused by
infection. E/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. Lesson Plans for Middle School Teachers
The National Science Digital Library (NSDL) has an incredible web site filled with activities
to help students differentiate between viruses and bacteria. The “What’s Making You Sick”
website is designed to facilitate discussions about viruses and bacteria, and helps aid middle
school students in understanding the differences.
The website is available at http://msteacher.org/epubs/science/science4/lessons.aspx
There are also other websites that also help students understand the causes of diseases. The
following website is one that delves into how viruses cause disease.
To access the website, go to http://library.thinkquest.org/23054/gather/index.shtml
2. Homeostasis: It’s All a Matter of Balance
To help students understand concepts of homeostasis, there is a great inquiry activity that has
students create their own experiments to test their body’s homeostasis.
To download this PDF lesson, go to
http://www.the-aps.org/education/k12curric/activities/pdfs/slifstein.PDF
3. Howard Hughes Medical Institute: Blazing a Genetic Trail
To help students understand the concepts of genetics and disease, the Howard Hughes
Medical Institute has put together a great website with lots of different information about the
human genome and the human genome project. This is a valuable web resource for both this
benchmark, and many others dealing with genetics.
The HHMI website is available at http://www.hhmi.org/genetictrail/
4. How Does an Infectious Disease Spread? HIV Simulation
This website provides an infectious disease simulation using phenolphthalein and a diluted
base. The activity gives the students a dramatic visual of how quickly any infectious disease
can spread through a population by exchanging “body fluids”.
The lesson can be access at http://seplessons.ucsf.edu/node/226
5. BAM! Body and Mind
The Center for Disease Control and Prevention has a website to inform students about the
importance of a healthy lifestyle. The website contains a variety of activities and simulations
that are informative and maintain the interest of a middle school student.
To access the website, go to http://www.bam.gov/sub_diseases/index.html
6. Infectious Disease: Causes and Prevention
In this activity, students take on the role as “Mysterious Disease Detectives” as they try to
determine the cause of a disease. The lesson contains informational sheets that the students
use to solve the mystery and provides an opportunity for the students to discuss their results
with the other sleuths in the classroom.
To download this PDF lesson, click on http://etd.library.pitt.edu/ETD/available/etd04102006-203036/unrestricted/DownieAppendixD3.pdf