Performance Benchmark L.12.B.3
Students know disease disrupts the equilibrium that exists in a healthy organism. E/S
Homeostasis, or the regulation of an organism’s internal environment is necessary to
maintain conditions suitable for life. The internal equilibrium of the body is the ultimate
gauge of its proper function. Homeostasis involves the maintenance of a consistent range
in the concentration of certain molecules in the body. Disruption of homeostasis in the
body systems can make an organism susceptible to disease and possibly lead to death.
Body temperature and hormone levels are examples of mechanisms that are regulated by
the body to maintain homeostasis. Homeostasis encompasses many body processes. We
probably think of maintaining a constant body temperature, but homeostasis also includes
water balance, which is influenced by the amount of water in the external environment
and whether it is fresh or salt water. Water balance is regulated through such things as
thirst and urination. Other factors which are under regulation include internal salt
concentration, pH (Despite the fact that cellular respiration creates CO2 which dissolves
in our blood to make carbonic acid, the pH of our blood is buffered at 7.4 or we would
die.), nutrients and various chemicals (regulated by factors like blood sugar level,
feelings of hunger, or cravings for certain foods). Homeostasis is controlled by feedback
loops (positive and negative), most of which are negative feedback loops. An example of
a positive feedback loop (this particular one is not involved in homeostasis) is the process
of giving birth to a baby. Labor contractions push the baby against the cervix causing the
cervix to dilate. This, in turn, triggers the production of oxytocin, a hormone which
triggers stronger contractions. A negative feedback loop works in the opposite direction
from what it is trying to accomplish. An example of a negative feedback loop involved in
homeostasis is maintenance of body temperature. As a person’s body gets too hot, he
begins to sweat in an attempt to lower the temperature. If someone’s body is too cool, he
will begin to shiver in an attempt to increase the temperature.
The systems of the body cooperate in maintaining homeostasis, that is, the relative
constancy of the internal environment despite external environmental changes. The
circulatory system is critical to the internal environment in that tissue fluid is nourished
and purified by the movement of small molecules across capillary walls. The digestive
system contributes nutrients to the blood, while the excretory system removes wastes.
The respiratory system takes in oxygen and excretes carbon dioxide. Oxygen is used
during cellular respiration and carbon dioxide is a waste product of cellular respiration.
The nervous and endocrine systems exert the ultimate control over homeostasis because
they coordinate the functions of the body's systems. Main examples of homeostasis in
mammals are as follows:



The regulation of the amounts of water and minerals in the body. This is known as
osmoregulation. This happens primarily in the kidneys.
The removal of metabolic waste. This is known as excretion. This is done by the
excretory organs such as the kidneys and lungs.
The regulation of body temperature. This is mainly done by the skin.
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
The regulation of blood glucose level. This is mainly done by the liver and the
insulin and glucagon secreted by the pancreas in the body.
These hormones associated with the regulation of blood glucose are considered
antagonistic because their actions have opposite effects; an increase in glucose
concentration following glucagon secretion is counteracted by an insulin secretion.
To learn more about how the body maintains the internal environment in relation to its
external environment go to
http://www.mhhe.com/biosci/genbio/maderbiology/supp/homeo.html
http://www.biology-online.org/4/1_physiological_homeostasis.htm
http://www.biology-online.org/4/2_water_homeostasis.htm
http://www.biology-online.org/4/3_blood_sugar.htm
The overall effect of a disruption in the body’s internal environment is disease. Disease is
a change that disrupts homeostasis in the body. Heart disease is the leading cause of death
in the United States and is a major cause of disability. Almost 700,000 people die of heart
disease in the United States annually. That is about 29% of all U.S. deaths. Heart disease
and strokes are common cardiovascular diseases. They are the third and first top cause of
death for both genders. The most common heart disease in the United States is coronary
heart disease, which often appears as a heart attack. Cancer is the second leading cause of
death in the United States. Cancer refers to any one of a large number of diseases
characterized by the development of abnormal cells that divide uncontrollably and have
the ability to infiltrate and destroy normal body tissue. Cancer can spread throughout
your body. Cancer doesn't discriminate when it comes to race, sex or age — anyone can
get cancer. The American Cancer Society estimates that half the men and one-third of the
women in the United States will develop cancer in their lifetimes. The American Cancer
Society estimates that about 1.4 million new cases of cancer are expected in 2007, and
about 560,000 people will die of the disease. To learn more about the leading causes of
death in the United States go to
http://www.nutritionstreet.com/7deadlydiseases.shtml
Disease-producing agents such as bacteria, protozoans, fungi, viruses and other parasites
are called pathogens. The main sources of pathogens are soil, contaminated water, and
infected people or animals. Any disease caused by the presence of pathogens in the body
is called an infectious disease. One-half of all human diseases are infectious. Not all
diseases are caused by pathogens. Some diseases can be inherited, such as sickle cell
anemia or be due to body aging (wear and tear) like osteoarthritis. Pathogens can be
transmitted in four main ways. The first way is through direct contact, for example
STD’s and influenza are easily spread through contact. The second way is through food
or drink contamination which can result in poisoning, Salmonella, Botulism and E-coli
are some common examples of food contamination. Some disease-causing germs travel
through the air in particles considerably smaller than droplets. These tiny particles remain
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suspended in the air for extended periods of time and can be carried by air currents. If
you breathe in an airborne virus, bacterium or other germ, you may become infected.
Tuberculosis and SARS are two infectious diseases usually spread through the air, in both
particle and droplet forms. The final way that someone is susceptible to disease is
through intermediate organisms (vectors), for example, malaria which is spread by
mosquitoes.
Diseases can be classified into two categories, endemic and epidemic. Endemic diseases
are diseases that are constantly present in a population like “the common cold”. Epidemic
disease occurs when many people in a given area are afflicted with the same disease in a
short period of time. A very prominent epidemic occurred when people became infected
with polio in the 1950’s. There are more common diseases that affect us in today’s world
to which polio has fallen into the shadows of, and that is the common flu virus. Seasonal
(or common) flu is a respiratory illness that can be transmitted person to person. Most
people have some immunity, and a vaccine is available. Avian (or bird) flu (AI) is caused
by influenza viruses that occur naturally among wild birds. Low pathogenic AI is
common in birds and causes few problems. H5N1 is highly pathogenic, deadly to
domestic fowl, and can be transmitted from birds to humans. There is no human
immunity and no vaccine is available. At the time of this writing H5N1 does not seem to
spread easily from person to person. Pandemic flu is virulent human flu that causes a
global outbreak, or pandemic, of serious illness. Because there is little natural immunity
to that “pandemic” strain of flu virus, the disease can spread easily from person to person.
The influenza pandemic of 1918-1919 killed more people than the Great War, known
today as World War I, at somewhere between 20 and 40 million people. It has been cited
as the most devastating epidemic in recorded world history. More people died of
influenza in a single year than in four-years of the Black Death, or Bubonic Plague, from
1347 to 1351. Known as "Spanish Flu" or "La Grippe" the influenza of 1918-1919 was a
global disaster.
To learn more about disease go to
http://www.sirinet.net/~jgjohnso/immune.html
Carriers are people who harbor a disease without showing any signs, yet they can pass the
disease on to others. Until 1876 it was quite difficult to determine the cause of a disease,
in that year Robert Koch provided definitive proof of the germ theory by isolating the
cause of anthrax and showing it to be a bacterium. From this came the development of
Koch's Postulates, a set of rules for the assignment of a microbe as the cause of a disease.
1. The specific organism should be shown to be present in all cases of animals suffering
from a specific disease, but should not be found in healthy animals.
2. The specific microorganism should be isolated from the diseased animal and grown in
pure culture on artificial laboratory media.
3. This freshly isolated microorganism, when inoculated into a healthy non-immune
laboratory animal, should cause the same disease seen in the original animal.
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4. The microorganism should be re-isolated in pure culture from the experimental
infection.
This is his most famous contribution to science and it is a testament to the utility of these
postulates that they are stilled used today to discover the cause of new emerging diseases.
Koch went on to apply these principles in the study of many other diseases including
tuberculosis, cholera and sleeping sickness. It should be pointed out that Koch’s
postulates cannot be applied to all diseases. Also, it is not always possible to obtain a
disease-causing microbe in pure culture. Koch developed the tools for obtaining pure
cultures to attack the problem of disease. Advances in science often come from
innovations in the available technology. Robert Koch was an important microbiologist
because his pioneering work in the isolation and characterization of bacterial diseases
helped to identify the causes of many of the maladies plaguing humanity. Further work
by other scientists then began the long road to conquering them.
To learn more about a specific disease associated with humans go to
http://www.cdc.gov/az.do
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Performance Benchmark L.12.B.3
Students know disease disrupts the equilibrium that exists in a healthy organism. E/S
Common misconceptions associated with this benchmark
1. Students incorrectly think cold weather and rain can cause a person to get a cold
or flu.
This question has probably been asked since the first time the flu made someone sick.
After all, cold and flu season occurs when the weather is cold. No matter how many times
your mother and grandmother told you not to go out in the cold because you would catch
a cold or the flu, it just doesn’t work that way.
The truth is that the flu and the common cold are caused by viruses. People get sick more
often in the winter because they are exposed to each other more in the winter than in the
summer. When it is cold outside, people tend to stay inside and are more likely to spread
germs to one another. Also, because school is in session, kids are around each other all
day and are “not afraid” to share their germs. With so many people in such close contact,
the likelihood of passing germs is much higher when it is cold outside than when it is
warm and people are outdoors. The viruses that cause flu are found in the nose and throat
and are sprayed into the air when an infected person sneezes, coughs or talks. It is the
close proximity of people to one another that is the leading factor of the spread of the flu
virus or common cold.
In tropical areas, where it does not get cold, the common cold and flu season generally
occurs during the rainy season. But again, these illnesses are not caused by the rain. They
are just more prevalent because people come in closer contact with each other than they
do during the dry season.
For further information regarding confusion about cold weather being linked to the
common cold and flu visit http://health.howstuffworks.com/question38.htm or
http://www.alka-seltzer.com/asp/asp_coldflu_faq.html#q2
2. Students erroneously think that AIDS can be spread through casual contact with
an HIV infected individual
Because the worldwide spread of HIV has had such a great effect on millions of people, a
number of misconceptions have arisen surrounding the disease known as AIDS. You
cannot become infected with HIV through day-to-day contact in social settings, schools
or in the workplace. You cannot be infected by shaking someone's hand, by hugging or
"dry" kissing someone, by using the same toilet or drinking from the same glass as an
HIV-infected person, or by being exposed to coughing or sneezing by an infected person.
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HIV is transmitted through direct contact with the blood or body fluid of someone who is
infected with the virus. That contact usually comes from sharing needles or by having
unprotected sex with an infected person. A nursing infant could get HIV from a mother
who is infected.
For further information regarding the HIV virus visit
http://kidshealth.org/parent/infections/bacterial_viral/hiv.html
3. Students incorrectly believe viruses are made from or are the same as bacteria.
Viruses are tiny structures that can only reproduce inside a living cell. They range in size
from 20 to 250 nanometers (one nanometer is one billionth of a meter). Outside of a
living cell, a virus is dormant, but once inside, it takes over the resources of the host cell
and begins the production of more virus particles. Viruses are more similar to robots, than
to animal life.
Bacteria are one-celled living organisms. The average bacterium is 1,000 nanometers
long. (If a bacterium were human size, a typical virus particle would be the size of a tiny
mouse. If an average virus were the size of a human, a bacterium would be the size of a
building over ten stories tall.) All bacteria are surrounded by a cell wall. They can
reproduce independently, and inhabit virtually every environment on earth, including
soil, water, hot springs, ice packs, and the bodies of plants and animals. Bacteria cause
diseases such as pneumonia, meningitis, botulism, cholera, anthrax, and diphtheria.
For further information regarding the differences between viruses and bacteria visit
http://www.mansfieldct.org/schools/mms/staff/hand/Immunebacteriavsviruses.htm
4. Students tend to inaccurately believe that all bacteria are harmful.
Most bacteria are harmless to humans. In fact, many are quite beneficial. The bacteria in
the environment are essential for the breakdown of organic waste and the recycling of
elements in the biosphere. Bacteria that normally live in humans can prevent infections
and produce substances we need, such as vitamin K. Bacteria in the stomachs of cows
and sheep are what enable them to digest grass. Bacteria are also essential to the
production of yogurt, cheese, and pickles. However, some bacteria cause infections in
humans. In fact, they are a devastating cause of human disease. E. coli, a type of bacteria
found in our digestive tract, helps to turn our food into sugars and processed vitamins.
Unfortunately, certain types (called strains) of E. coli can get from the intestines into the
blood. This is a rare illness, but it can cause a very serious infection. One very bad strain
of E. coli was found in fresh spinach in 2006 within the state of Nevada.
To learn more about types of bacteria that are harmful to humans visit
http://www.cubanology.com/Articles/Virus_vs_Bacteria.htm.
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Performance Benchmark L.12.B.3
Students know disease disrupts the equilibrium that exists in a healthy organism. E/S
Sample Test Questions
1. HIV can be transmitted
a. By the transfer of body fluids containing HIV
b. By drinking from the same glass of an HIV infected person
c. By shaking someone’s hand that is infected with HIV
d. By using the same restroom facilities as someone who has HIV
2. A pathogen is an agent that is
a. beneficial to humans.
b. harmful only to plants.
c. harmful to living things.
d. nearly extinct.
3. Refer to the illustration below. Which structure is found outside the cell
after the cell is infected?
a. Structure 1
b. Structure 2
c. Structure 3
d. Structure 4
4. Which of the following is a viral disease of humans?
a. Anthrax
b. Meningitis
c. Tuberculosis
d. Hepatitis
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5. An infectious disease is one that is caused by
a. Heredity or inheriting parental traits
b. Materials in the environment
c. Pathogens
d. Hemophilia
6. An example of an infectious disease that is spread by viruses in the air is
a. Athlete’s foot
b. Tuberculosis
c. Influenza
d. Tetanus
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Performance Benchmark L.12.B.3
Students know disease disrupts the equilibrium that exists in a healthy organism. E/S
Answers to Sample Test Questions
1. (a)
2. (c)
3. (a)
4. (d)
5. (c)
6. (c)
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Performance Benchmark L.12.B.3
Students know disease disrupts the equilibrium that exists in a healthy organism. 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. Travel Brochure of the Body Systems
Access Excellence, a web based site from the National Health Museum, has produced a
“Travel Brochure of the Body Systems.” The curriculum content and lesson plan present
a journey through the human body. Each system is looked at in detail and students are
responsible as groups (consultants to an Ad agency) to complete a travel brochure
showing the major areas of the human body. Along the way students illustrate the various
anatomical structures associated with each system and answer the many objectives
accompanying each system.
The lesson can be found at
http://www.accessexcellence.org/AE/ATG/data/released/0285-FayeCascio/
2. Parasites and Disease
The National Geographic Xpeditions Program has provided a collection of lessons
covering the various issues involving disease and health. Each lesson not only provides a
detailed list of the materials, time requirements, and connections to other curriculums, but
also the student objectives that are covered throughout the duration of the lesson.
The following is a link to a specific lesson dealing with parasites and how they are a
vector for disease
http://www.nationalgeographic.com/xpeditions/lessons/18/g912/parasites.html
3. STD Web and HIV Transmission Game
The activities addressed in either of the web sites listed below allow students the
opportunity to witness first hand how quickly STD’s, specifically HIV, can be spread
from human to human. The lessons stage a hypothetical scenario (class activity) of the
spread of an STD and opens up discussion on preventative measures that can be taken to
prevent the transmission.
The following are direct links to the activities relating to transmission of disease
http://www.pecentral.org/lessonideas/ViewLesson.asp?ID=1231
http://www.advocatesforyouth.org/lessonplans/hivtransmission.htm
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