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Content Benchmark L.12.B.3
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Life Science
Structure of Life
Organisms and Their Environment
Diversity of Life
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Nature of Science (NOS)
Life Science
Earth Science
Physical Science

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.
• 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

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

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 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

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.
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

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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 or

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. 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

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

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

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Content Benchmark L.12.B.3

Students know disease disrupts the equilibrium that exists in a healthy organism. E/S

Sample Test Questions

1st Item Specification: Evaluate how a disease disrupts the homeostasis of an organism.

Depth of Knowledge Level 1

  1. The process by which organisms maintain a stable internal environment is called
    1. homeostasis.
    2. disease.
    3. equilibrium.
    4. immunity.
  1. The most common way bacteria cause disease is by
    1. releasing toxins.
    2. engulfing healthy cells.
    3. entering healthy cells.
    4. absorbing hormones.
  1. The main purpose of a fever is to
    1. slow the growth of pathogens.
    2. cause unhealthy cells to die.
    3. return the body to homeostasis.
    4. prompt an immune response.
  1. Viruses disrupt normal cell functions by
    1. releasing toxins into the cell.
    2. using the cell machinery to replicate viruses.
    3. engulfing the cells as a food source.
    4. replicating outside the cell to attack it.

Depth of Knowledge Level 2

  1. Use the graph below to answer the following question. The graph shows the number of antibodies in the blood over a period of time.

(From Holt ExamView)

What is the best reason why Response II is greater than Response I?

  1. More bacteria entered at point 2 than at point 1.
  2. Memory cells were produced during Response I.
  3. Antibodies from Response I still remained in the blood.
  4. Macrophages increased their production of antibodies.
2nd Item Specification: Describe ways that an imbalance in one organ system affects the entire organism.

Depth of Knowledge Level 1

  1. Which body systems may be affected by the influenza virus?
    1. Only the digestive system
    2. Only the muscular system
    3. The immune and muscular systems
    4. The immune, digestive and muscular systems
  1. An autoimmune disease can affect the entire body because, an autoimmune disease causes the immune system to attack
    1. beneficial bacteria.
    2. beneficial viruses.
    3. the body’s own cells.
    4. any foreign substance to the body.

Depth of Knowledge Level 2

  1. A disease that attacks and destroys lung tissue would most likely affect the entire body because it could interfere with
    1. cellular respiration in the cells.
    2. photosynthesis in the cells.
    3. glycolysis in the cells.
    4. anaerobic respiration in the cells.
  1. Botulism is a disease that paralyzes the muscles in the body. This disease is usually fatal because it
    1. paralyzes the muscles used to breathe.
    2. paralyzes the muscles that aid in digestion.
    3. damages all the muscle cells of the immune system.
    4. destroys the muscle cells of the cardiovascular system.

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Content Benchmark L.12.B.3

Students known genetic information passed from parents to offspring is coded in the DNA molecule. E/S

Answers to Sample Test Questions

  1. A, DOK Level 1
  2. A, DOK Level 1
  3. A, DOK Level 1
  4. B, DOK Level 1
  5. B, DOK Level 2
  6. D, DOK Level 1
  7. C, DOK Level 1
  8. A, DOK Level 2
  9. A, DOK Level 2

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Content 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

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

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

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