what are the health effects from exposure to carbon monoxide?
TRANSCRIPT
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CARBON MONOXIDE: LESSON TWO
What are the Health Effects from Exposure to Carbon Monoxide?
LESSON SUMMARY
Carbon monoxide (CO) is an odorless, tasteless, colorless and nonirritating gas that is impossible to detect by an exposed person. CO is produced by the incomplete combustion of carbon-‐based fuels, including gas, wood, oil and coal. Exposure to CO is the leading cause of fatal poisonings in the United States and many other countries. When inhaled, CO is readily absorbed from the lungs into the bloodstream, where it binds tightly to hemoglobin in the place of oxygen.
CORE UNDERSTANDING/OBJECTIVES
By the end of this lesson, students will have a basic understanding of the physiological mechanisms underlying CO toxicity. For specific learning and standards addressed, please see pages 30 and 31.
MATERIALS INCORPORATION OF TECHNOLOGY
Computer and/or projector with video capabilities
INDIAN EDUCATION FOR ALL
Fires utilizing carbon-‐based fuels, such as wood, produce carbon monoxide as a dangerous byproduct when the combustion is incomplete. Fire was important for the survival of early Native American tribes. The traditional teepees were well designed with sophisticated airflow patterns, enabling fires to be contained within the shelter while minimizing carbon monoxide exposure. However, fire was used for purposes other than just heat and cooking. According to the historian Henry Lewis, Native Americans used fire to aid in hunting, crop management, insect collection, warfare and many other activities. Today, fire is used to heat rocks used in sweat lodges. Use of fire in these enclosed spaces can pose a risk of CO poisoning.1
ENGAGE
Grade Level: 9 – 12
Subject(s) Addressed: Science, Biology Class Time: 1 Period
Inquiry Category: Guided
Project an image of the human circulatory system (An example image is shown in the page 2 sidebar). Distribute 3 x 5 index cards or have students take out a half sheet of paper. Have students number 1 through 6 on one side of the card or paper. Ask students the following questions and instruct them to record their answers: 1) What color is oxygenated blood? 2) What makes oxygenated blood this color? 3) What color is deoxygenated blood? 4) What makes deoxygenated blood this color? 5) What is the color of blood in arteries? 6) What is the color of blood in veins? When students are finished recording their answers, the teacher may collect the cards/paper and tally the responses on the board. Discuss responses to gauge student ideas and misconceptions but do not give value to their answers at this point. Let students know that you will revisit these questions at the end of the lesson.
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VOCABULARY
Copies of blank student vocabulary banks (see page 5) can be distributed for completion as either a classroom or homework assignment.
EXPLORE
Carbon monoxide exposure is one of the leading causes of accidental death due to poisoning in the U.S. The toxic effects of carbon monoxide are primarily caused by the formation of carboxyhemoglobin within the red blood cells. When CO and hemoglobin bind to form carboxyhemoglobin, the oxygen-‐carrying capacity of the blood is reduced resulting in hypoxia of the tissues. In the presence of carbon monoxide, the affinity of hemoglobin for oxygen is reduced—compounding the effects of carboxyhemoglobin formation. Additionally, carbon monoxide exposure causes immunological and inflammatory changes increasing the adverse effects observed in the victim.
Have students watch the short video (http://bit.ly/1Z7Zv2J) showing the effects carbon dioxide, oxygen, and carbon monoxide have on the blood. The teacher can distribute “Lab 1: What Are the Effects of Different Gases on the Color of Blood?” (see pages 7-‐10) for students to complete during the video.
*Note: There will be prompts throughout the video for the teacher to pause the video, allowing time for students to record their observations and answers.
EXPLAIN
Subsequent to watching the video, have students break into small groups and discuss possible explanations for their observations during the video. Then come back together for a whole group discussion on possible explanations from each group accounting for the differences in the color changes of the blood.
ELABORATE
After completing the other activities, revisit the six engage questions from the beginning of the lesson and discuss the differences between oxygenated and deoxygenated blood and how the normal respiratory cycle of the body is disrupted by exposure to carbon monoxide.
1) What color is oxygenated blood? Oxygenated blood is bright red.
2) What makes oxygenated blood this color? Red blood cells contain an iron-‐containing protein (metalloprotein) called hemoglobin that is primarily responsible for the color of blood. Each hemoglobin molecules has four heme groups and the interaction of these groups with compounds, such as oxygen, determine the color of the blood. When the heme groups combine with oxygen (i.e., blood is oxygenated), a bright red color is exhibited.
3) What color is deoxygenated blood? Deoxygenated blood is dark red.
"Blutkreislauf". Licensed under Creative Commons Attribution-‐Share Alike 2.5 via Wikimedia Commons -‐ http://commons.wikimedia.org/wiki/File:Blutkreislauf.png#mediaviewer/File:Blutkreislauf.png
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4) What makes deoxygenated blood this color? The teacher may guide students to think about where a phlebotomist draws blood from (i.e., veins) and have them explain the color of the blood when it is drawn. Similar to oxygen, carbon dioxide is responsible for the dark red color exhibited by the heme groups contained in the hemoglobin molecules. Carbaminohemoglobin has a blue hue to it, resulting in a darker red color of venous blood compared to arterial blood.
5) What is the color of blood in arteries? Arterial blood, or oxygenated blood, is bright red in color (see #3 above). 6) What is the color of blood in veins? Venous blood, or deoxygenated blood is dark red in color. Veins close to the surface of the skin appear blue because of the light scattering properties of the skin, not the color of venous blood. End the discussion by addressing the differences in the binding of carbon monoxide versus oxygen to hemoglobin and why this is an important human health subject. Note that while hemoglobin easily exchanges oxygen for carbon dioxide—as observed by the changes in the color of blood—carbon monoxide binds much tighter and prevents the hemoglobin molecule from subsequently binding to oxygen. Additionally, the follow discussion topics may be used to deepen learning: • What are the similarities and/or differences between carbon monoxide
exposure and sickle-‐cell anemia? • What are the pros/cons of the meat packing industry’s current use of carbon
monoxide to preserve the bright red color of meat? • Are some individuals more or less susceptible to the effects of carbon
monoxide poisoning (i.e. smokers versus nonsmokers, elderly, children, etc.)?
• Why do you think it is important for health professionals to understand chemistry?
• Why do sketches of the circulatory system often depict blood as either red or blue?
• How might an individual be exposed to carbon monoxide around their home and how can these exposures be prevented?
EVALUATE
Use the discussions as an opportunity for informal assessment. The lab worksheet provides opportunity for formal assessment. For additional formal assessment, distribute “Comprehension 1: What are the Health Effects of Carbon Monoxide?” and the accompanying guiding questions (pages 15-‐21). Have students complete this as homework.
For further explanation of O2/CO2 transport in the blood, show students the following video (“Hemoglobin moves O2 and CO2”) from Khan Academy: http://bit.ly/1nJxmha
Notes:
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Carbon Monoxide Health Effects – Vocabulary
Ligand: Cooperative Binding:
Hemoglobin: Oxygen:
Carbon Dioxide: Oxyhemoglobin:
Carboxyhemoglobin:
Pulmonary Respiration:
Hypoxia:
Chemical Affinity:
Sickle-‐cell Anemia:
Mendelian Genetics:
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Carbon Monoxide Health Effects – Vocabulary
Ligand: A ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. In biology, ligands include substrates, inhibitors, activators, and neurotransmitters. Cooperative Binding: (biochemistry) A type of chemical binding in which a macromolecule’s affinity for its ligand changes with the amount of ligand already bound.
Hemoglobin: An iron containing protein in red blood cells that transports oxygen. Oxygen: A colorless, odorless, combustible gas that is the life-‐supporting component of air.
Carbon Dioxide: A naturally occurring chemical compound composed of two oxygen atoms each covalently double bonded to a single carbon atom. It is a colorless, odorless, incombustible gas that is present in the atmosphere and formed during respiration. Oxyhemoglobin: A compound formed when oxygen binds with the heme groups of a hemoglobin molecule.
Carboxyhemoglobin: A stable complex that forms from carbon monoxide and the hemoglobin in red blood cells when carbon monoxide is inhaled or produced in normal metabolism. Formation of large quantities can hinder delivery of oxygen to the body.
Pulmonary Respiration: The transport of oxygen from the outside air to the cells within tissues and the transport of carbon dioxide in the opposite direction.
Hypoxia: A condition in which the oxygen supply to a tissue falls below physiologically necessary levels despite adequate perfusion of the tissue by blood.
Chemical Affinity: An attractive force between two substances that causes them to chemically combine.
Sickle-‐cell Anemia: A genetic disorder in which the body makes abnormal hemoglobin causing the red blood cells to form a sickle-‐shape rather than the normal disk-‐like shape.
Mendelian Genetics: The basic laws of inheritance as described by Gregor Mendel, a nineteenth-‐century Austrian monk who conducted hybridization experiments using garden peas.
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LAB 1: WHAT ARE THE EFFECTS OF DIFFERENT GASES ON THE COLOR OF BLOOD?
Question: What is the importance of an experimental control?
Make some observations: Describe any differences between the control sample and the sample treated with O2 (tube #1).
Describe any differences between the control sample and the sample treated with CO2 (tube #2).
Describe any differences between the sample treated with O2 (tube #1) and the sample treated with CO2 (tube #2).
Question: Why do you think the blood treated with O2 looks different from the blood treated with CO2?
Make some predictions (CO2 + O2): Do you think there will be a difference in the color of the blood first treated with CO2 and then with O2 when compared to the control blood or the samples treated with CO2 or O2 alone? Why or why not? Here are all the options: Blood + CO2 + O2: Blood + CO2 only: Blood + O2 only:
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Make an Observation: Describe any differences between the samples treated with CO2 and O2 alone compared to the sample treated first with CO2 followed by O2. Did your predictions match these results? Can you explain what is happening to cause the change to the color of the blood?
Make a prediction about CO Exposure: We’re going to compare the blood we previously examined to blood treated with CO. Do you expect any differences? Why or why not? Here are all the options: Blood + CO2 only: Blood + O2 only: Blood + CO only:
Make an observation: Describe any differences between the previous samples and the blood treated with CO.
Question: Did your predictions match the actual results? Can you explain what is happening to cause the change in the color of the blood?
Make another prediction about CO exposure: We’re going to compare CO treated blood with blood that has also been treated with CO2 or O2. Based on what you have already observed, do you think you will see any differences in the blood that has been first treated with CO compared to blood treated with CO and then with CO2? What about blood first treated with CO and then O2? Why or why not? Here are all the options: Blood + CO + CO2: Blood + CO + O2:
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Make an observation: Describe the differences observed between samples treated with CO, CO + CO2, and CO + O2.
Questions: Did your prediction match the actual results? Can you explain what is happening to cause the change in the color of blood?
Can you predict what the possible consequences might be to your cells’ energy-‐producing abilities if you are exposed to carbon monoxide?
Make some observations: Describe the overall differences in color between all of the blood samples. Here are the options: Control: Control + O2 only: Control + CO2 only: Control + CO2 + O2: Control + O2 + CO2: Control + CO only: Control + CO + CO2: Control + CO + O2:
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Question: Why does the color change when the blood has been exposed to both CO2 and O2, but remains the same after exposure to CO? Can you explain what is happening?
Question:
Based on the observations made in this video, can you draw any conclusions about the binding strength between hemoglobin and O2 compared to hemoglobin and CO? Explain.
Bonus Questions: Can you explain why a person suffering from carbon monoxide exposure often has cherry-‐colored skin? What do you think exposure to carbon monoxide does to your ability to generate energy from the food you eat? This experiment is missing an example of blood that has been treated with CO2, followed by CO. Can you predict the color of blood that has been treated in that way?
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LAB 1: WHAT ARE THE EFFECTS OF DIFFERENT GASES ON THE COLOR OF BLOOD? TEACHER KEY
Question: What is the importance of an experimental control?
The control provides a standard for comparison for the experimental results. In the case of this experiment, how would we be able to recognize changes in blood color if we did not know what standard blood looks like?
Make some observations: Describe any differences between the control sample and the sample treated with O2 (tube #1). The sample treated with O2 is brighter red than the control sample.
Describe any differences between the control sample and the sample treated with CO2 (tube #2). The sample treated with CO2 is darker red than the control sample.
Describe any differences between the sample treated with O2 (tube #1) and the sample treated with CO2 (tube #2).
The sample treated with O2 is bright red while the sample treated with CO2 is dark red.
Question: Why do you think the blood treated with O2 looks different from the blood treated with CO2?
Student answers will vary but they should be able to explain that the light absorbing/reflecting properties of the blood must change somehow when blood is saturated with oxygen versus carbon dioxide.
Make some predictions (CO2 + O2): Do you think there will be a difference in the color of the blood first treated with CO2 and then with O2 when compared to the control blood or the samples treated with CO2 or O2 alone? Why or why not? Here are all the options: Blood + CO2 + O2: Blood + CO2 only: Blood + O2 only:
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Student answers will vary as they are not yet familiar with hemoglobin’s bonding affinity for different gases. They may predict that the color of hemoglobin treated with CO2 then O2 will be some intermediate form of dark and bright red rather than the actual bright red that will result.
Make an Observation: Describe any differences between the samples treated with CO2 and O2 alone compared to the sample treated first with CO2 followed by O2. Did your predictions match these results? Can you explain what is happening to cause the change to the color of the blood?
The blood sample treated with CO2 then O2 was bright red like the sample that was treated only with O2.
Make a prediction about CO Exposure: We’re going to compare the blood we previously examined to blood treated with CO. Do you expect any differences? Why or why not? Here are all the options: Blood + CO2 only: Blood + O2 only: Blood + CO only:
Students will likely predict that, since CO is a chemically distinct compound, it will produce a different blood color than the samples treated with CO2, O2, or CO2 then O2.
Make an observation: Describe any differences between the previous samples and the blood treated with CO. The blood sample treated with CO was bright red color very similar to the sample treated with O2.
Question: Did your predictions match the actual results? Can you explain what is happening to cause the change in the color of the blood?
Make another prediction about CO exposure: We’re going to compare CO treated blood with blood that has also been treated with CO2 or O2. Based on what you have already observed, do you think you will see any differences in the blood that has been first treated with CO compared to blood treated with CO and then with CO2? What about blood first treated with CO and then O2? Why or why not? Here are all the options: Blood + CO + CO2:
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Blood + CO + O2:
Student answers will vary. They may predict that, since the CO treated blood had a similar color to the O2 treated blood, the outcome will be similar to the result of blood treated with CO2 then O2. They may also predict that gas used in the second treatment (because O2 was used second in the CO2 then O2 trial and the resulting blood color was the bright red associated with O2) in this case CO2, will dictate the blood color causing the sample to be dark red.
Make an observation: Describe the differences observed between samples treated with CO, CO + CO2, and CO + O2.
There are no obvious differences between the samples.
Questions: Did your prediction match the actual results? Can you explain what is happening to cause the change in the color of blood?
The actual blood color of the sample treated with CO then CO2 was bright red similar to the color of the sample treated with only CO. This indicates that the hemoglobin has a higher chemical affinity for CO than CO2. The resulting carboxyhemoglobin complex is likely more stable than the hemoglobin complex formed with CO2.
Can you predict what the possible consequences might be to your cells’ energy-‐producing abilities if you are exposed to carbon monoxide?
The cells will experience oxygen depletion, which will inhibit their ability to convert food energy into cellular energy via cellular respiration. Therefore, the energy-‐producing ability of the cells will decrease.
Make some observations: Describe the overall differences in color between all of the blood samples. Here are the options: Control: Control + O2 only: Control + CO2 only: Control + CO2 + O2: Control + O2 + CO2:
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Control + CO only: Control + CO + CO2: Control + CO + O2:
Question: Why does the color change when the blood has been exposed to both CO2 and O2, but remains the same after exposure to CO? Can you explain what is happening?
The color change must be dependent on the gas that has the higher chemical affinity for bonding to hemoglobin. Therefore, hemoglobin must have a higher chemical affinity for bonding with O2 and CO than bonding with CO2.
Question:
Based on the observations made in this video, can you draw any conclusions about the binding strength between hemoglobin and O2 compared to hemoglobin and CO? Explain.
Because blood treated with O2 or CO results in a similar bright red color, it is difficult to form any conclusions about the chemical affinity hemoglobin has for O2 versus hemoglobin’s chemical affinity for CO.
Bonus Questions: Can you explain why a person suffering from carbon monoxide exposure often has cherry-‐colored skin?
Normally, there is equilibrium between the darker colored blood that is saturated with CO2 and the bright red colored blood that is saturated with O2. However, because CO saturated blood is also bright red and it also lowers the amount of CO2 saturated blood in the system, overall the system is brighter in color. This change is reflected in the cherry red color observed in the skin of victims.
What do you think exposure to carbon monoxide does to your ability to generate energy from the food you eat?
It would be significantly reduced because the lack of oxygen would prevent cellular respiration from efficiently converting glucose into ATP.
This experiment is missing an example of blood that has been treated with CO2, followed by CO. Can you predict the color of blood that has been treated in that way?
It would most likely be a bright cherry red color.
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COMPREHENSION 1
What are the Health Effects from Exposure to Carbon Monoxide?
WHAT IS CARBON MONOXIDE?
Carbon monoxide is a colorless, odorless, tasteless, highly poisonous gas that is slightly less dense than air and is formed from the incomplete combustion of carbon or a carbon-‐containing material such as gasoline. In addition, carbon monoxide is produced in low levels through the metabolic processes of animals. In the atmosphere, carbon monoxide is short-‐lived and plays a role in the formation of ozone. Chemically, carbon monoxide consists of one carbon and one oxygen atom that are connected by a triple bond.
WHAT IS HEMOGLOBIN?
Hemogloblin is the red protein found in the blood of animals that is responsible for the delivery of oxygen from the lungs to the rest of the body and for returning carbon dioxide to the lungs to be exhaled. In adults, hemoglobin is formed by the connection of four globulin chains. In the center of each globulin molecule is a heme complex, which contains iron. It is the iron found in the heme complex that enables the transport of oxygen and carbon dioxide through the blood. Iron is also the component of hemoglobin that results in the red color of blood. The presence of hemoglobin in the blood increases its oxygen-‐carrying capacity seventy-‐fold more than if oxygen was simply dissolved in the blood. This is because each molecule of hemoglobin is able to carry 4 molecules of oxygen.
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WHAT IS CARBOXYHEMOGLOBIN?
Carboxyhemoglobin is a stable compound that is formed through interaction of carbon monoxide and hemoglobin. Formation of carboxyhemoglobin can occur following the production of carbon monoxide from normal metabolic processes or from exposure through external sources. Carboxyhemoglobin formation results in an inability of the hemoglobin to carry oxygen from the lungs to the rest of the body.
WHAT IS THE RELATIONSHIP BETWEEN CARBON MONOXIDE EXPOSURE AND HYPOXIA?
Exposure to carbon monoxide prevents delivery of oxygen from the lungs to the body tissues via two mechanisms. First, formation of carboxyhemoglobin prevents oxygen from binding to the hemoglobin, reducing the oxygen carrying capacity of the blood. This is due to the high affinity of hemoglobin for carbon monoxide, which is much higher than for oxygen (by a factor of approximately 240:1). Furthermore, the presence of carboxyhemoglobin in the blood shifts the oxygen-‐hemoglobin dissociation curve to the left. A shift in the dissociation curve means that the remaining oxygen-‐carrying hemoglobin cannot “deliver” the oxygen to the body tissues as easily as before carbon monoxide exposure. So, the blood cannot carry as much oxygen and it is more difficult to deliver the oxygen that it does carry. As a result, the tissues are starved for oxygen and become hypoxic.
WHAT IS THE OXYGEN-‐HEMOGLOBIN DISSOCIATION CURVE?
The oxygen-‐hemoglobin dissociation curve is simply a graph depicting the percent saturation of hemoglobin at differing partial pressures of oxygen. At high partial pressures of oxygen, such as that found in the lungs, hemoglobin binds to oxygen to form oxyhemoglobin. As the blood travels to the many tissues of the body the oxygen
dissociates—leaving hemoglobin free to return to the lungs. The oxygen-‐hemoglobin
0 10 20 30 40 50 60 70 80 90 100
0 10
20
30
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50
60
70
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100 Oxyhemoglobin (%
Saturation)
PO2 (mmHg)
Hypothetical Oxygen-‐Hemoglobin Dissocation Curve
Exercise
Normal Conditions
Carbon Monoxide
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dissociation curve is a sigmoidal shape due to the cooperative binding properties of oxygen to the four polypeptides of hemoglobin. This means that hemoglobin’s affinity for oxygen increases after it has bound its first oxygen molecule. Therefore, hemoglobin is most attracted to oxygen when three of its four polypeptide chains have already bound to oxygen. Also, there are various factors that can cause the curve to shift to the left or right. For example, carbon monoxide causes the curve to shift to the left (see figure above). This leftward shift indicates that the hemoglobin has an increased affinity for oxygen, however the oxygen is bound more tightly and cannot dissociate as easily to be deposited in the tissues. In contrast, a shift to the right increases the oxygen delivered to the tissues when it is most needed, such as during exercise.
HOW DOES NORMAL PULMONARY RESPIRATION WORK?
Pulmonary respiration is the process by which we breathe in air through the lungs, transport oxygen throughout the body and finally exhale the waste products, primarily carbon dioxide. The breathing movement, which involves both inspiration and expiration, is an active process that primarily uses the contraction of the diaphragm to create a negative pressure in the upper chest cavity, which expands the lungs and draws in air. Conversely, exhalation occurs when the diaphragm relaxes. During periods of forced inhalation or exhalation (such as blowing up a balloon), the intercostal muscles are used to augment the functions of the diaphragm. Once oxygen is inhaled, it binds to hemoglobin within the blood and is carried throughout the body through a series of vessels that get progressively smaller. The smallest of these vessels, the capillaries, branch out into all areas of the body, supplying the organs, glands, and other tissues with a constant supply of oxygen. This oxygen is used by cells in the process of cellular respiration, which converts larger molecules of glucose from the food we ingest into usable energy in the form of ATP. Carbon dioxide is a by-‐product of cellular respiration that enters the blood stream and is carried by hemoglobin back to the lungs where it is exhaled. The water created in cellular respiration leaves the body via perspiration or urine. The following is the formula for cellular respiration:
C6H12O6 (glucose) +6CO2 ! 6CO2 + 6H2O + Energy (ATP)
The exchange of oxygen and carbon dioxide between the blood and the cells of the body is due to differences in the partial pressure of arterial (oxygen rich) and venous (carbon dioxide rich, or oxygen poor) blood.
WHAT ARE THE SYMPTOMS OF CARBON MONOXIDE EXPOSURE?
According to the Centers for Disease Control and Prevention (CDC), the most common symptoms of carbon monoxide exposure include: headache, dizziness, weakness, nausea, vomiting, chest pain, and confusion.
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High levels of CO inhalation can cause loss of consciousness and death. Furthermore, one can die from CO poisoning before ever experiencing symptoms. These symptoms are similar to those observed in individuals suffering from oxygen deprivation because both situations are caused by a lack of oxygen being delivered to the various tissues in the body.
WHAT ROLE DOES GENETICS PLAY IN THE FUNCTIONING OF HEMOGLOBIN?
Some people carry a gene that encodes for an abnormal hemoglobin molecule that forms a sickle shape rather than the disc-‐shape of normal hemoglobin. The sickle-‐cell trait is recessive so people with two copies of this gene (i.e., one from each parent) have the disease called sickle-‐cell anemia. If only one copy of the gene is carried, then the person is known as a carrier of the sickle-‐cell trait, but does not have sickle-‐cell anemia. The inheritance pattern for sickle-‐cell anemia follows typical Mendelian genetics, which means that if only one parent is a carrier of the sickle-‐cell gene then only half the of the offspring will likely be carriers of the gene; whereas if both parents are carriers of the sickle-‐cell gene then every pregnancy has a 25% probability of a normal child, 50% probability of a child who carries the gene but is without the disease, and a 25% probability of a child suffering from sickle-‐cell anemia. In addition, children with sickle-‐cell anemia have been found to have higher levels of carboxyhemoglobin than their normal counterparts. The sickle cell gene has a higher incidence in certain segments of the population. In the United States, 7-‐9% of individuals of sub-‐Saharan African descent are found to carry the trait and approximately 1 out of 500 of these African Americans are afflicted with the disease.
WHAT ARE THE PRIMARY SOURCES FOR CARBON MONOXIDE IN THE ENVIRONMENT?
In the home, the combustion of fuel for heating and cooking is the primary source of carbon monoxide. An improperly maintained or blocked chimney or furnace can allow carbon monoxide to enter the home. Similarly, carbon monoxide can enter the home from the garage when a car, lawn mower or other engine is in operation. Gas stoves and ranges can also be a significant source of carbon monoxide if they are not operated correctly.
In the ambient environment, motor vehicles produce about 60 percent of carbon monoxide nationwide; in cities, it may be as high as 95 percent. Other sources include industrial processes, non-‐transportation fuel combustion, and wildfires.
Tobacco smoke and the resulting second hand smoke are also a significant source of carbon monoxide. Blood carbon monoxide levels are ten times higher in smokers than in nonsmokers. Although smokers do not generally suffer from true carbon monoxide poisoning, their hemoglobin’s ability to transport and release oxygen is still adversely affected causing the heart to work harder in order to move adequate oxygen to the tissues.
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WHAT ARE THE BEST PREVENTIVE MEASURES FOR PREVENTING CO POISONING?
The CDC recommends the following to prevent CO exposure and poisoning:
• Call a qualified technician to check your heating system, water heater and any other gas, oil, or coal burning appliances. Do this on a yearly basis.
• Do not use portable flameless chemical heaters (catalytic) indoors. Although these heaters do not have a flame, they burn gas and can cause CO to build up inside your home, cabin, or camper
• If you smell an odor from your gas refrigerator's cooling unit have an expert service it. An odor from the cooling unit of your gas refrigerator can mean you have a defect in the cooling unit. It could also be giving off CO.
• When purchasing gas equipment, buy only equipment carrying the seal of a national testing agency, such as the CSA Group.
• Install a battery-‐operated or battery back-‐up CO detector in your home and check or replace the battery when you change the time on your clocks each spring and fall.
Additional measures to prevent CO exposure and poisoning:
• Don't use a generator, charcoal grill, camp stove, or other gasoline or charcoal-‐burning device inside your home, basement, garage, or near a window.
• Don't run a car or truck inside a garage attached to your house, even if you leave the door open.
• Don't burn anything in a stove or fireplace that isn't vented.
• Don't heat your house with a gas oven.
Notes:
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CO Health Effects Comprehension 1 Guiding Questions
1. What is the primary biological function of hemoglobin? 2. What is cooperative binding?
3. What properties make carbon monoxide of particular concern to public health officials?
4. What happens to the oxygen-‐carrying capacity of blood after carbon monoxide exposure? Why?
5. In your own words, what is carboxyhemoglobin and why is it important?
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6. Examine the Oxyhemoglobin Dissociation Curve. Explain the shifts from the normal conditions curve demonstrated by the carbon monoxide and exercise curves.
7. What are the symptoms of carbon monoxide exposure and why do they make sense given the mechanism of action of carbon monoxide poisoning?
8. What is the relationship between pulmonary and cellular respiration? 9. Describe how carbon monoxide exposure interferes with normal respiration, and how that in
turn interferes with cellular respiration
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CO Health Effects: Guiding Questions Teacher Key
1. What is the primary biological function of hemoglobin? The primary function of hemoglobin is the transport of oxygen from the lungs to the tissues of the body
and removal of carbon dioxide via the lungs. 2. What is cooperative binding?
In biochemistry, cooperative binding is a term used to describe the binding property of a macromolecule that exhibits a changing affinity for its ligand depending on the amount already bound. For example, hemoglobin’s affinity for oxygen increases after it has bound one or more oxygen molecules.
3. What properties make carbon monoxide of particular concern to public health officials?
Carbon monoxide is a tasteless, odorless, colorless gas that can be lethal at very low concentrations. In addition, carbon monoxide is produced from common appliances and machines used in and around many households. Because carbon monoxide is difficult to detect and the onset of symptoms occurs rapidly, there is a high risk of illness or even death before one has become aware of exposure to carbon monoxide.
4. What happens to the oxygen-‐carrying capacity of blood after carbon monoxide exposure? Why?
In the presence of carbon monoxide, the oxygen carrying capacity of blood is reduced because of an inability of hemoglobin to properly bind with oxygen. Normally, when hemoglobin binds with oxygen it undergoes a conformational change that allows it to bind more oxygen at an increasing rate. However, when carbon monoxide binds to hemoglobin, the conformational change prevents further binding of oxygen and also makes it more difficult for the hemoglobin to release oxygen to the tissues for delivery.
5. In your own words, what is carboxyhemoglobin and why is it important?
Carboxyhemoglobin is formed when hemoglobin is exposed to carbon monoxide. When hemoglobin reacts with carbon monoxide to form carboxyhemoglobin its oxygen-‐carrying capacity is diminished. As a consequence, the body is deprived of adequate oxygen.
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6. Examine the Oxyhemoglobin Dissociation Curve. Explain the shifts from the normal conditions curve demonstrated by the carbon monoxide and exercise curves.
The cooperative binding between carbon monoxide and hemoglobin increases hemoglobin’s affinity for oxygen causing the hemoglobin to be more saturated with oxygen while at the same time making it more difficult for the oxygen to dissociate from the hemoglobin. The exercise curve shows that the oxygen saturation level decreases at a given partial pressure compared to the normal curve because the oxygen more readily dissociates from the hemoglobin where it is released into the tissues. This accommodates the increased oxygen demand associated with exercise.
7. What are the symptoms of carbon monoxide exposure and why do they make sense given the mechanism of action of carbon monoxide poisoning?
Symptoms of carbon monoxide poisoning include headache, dizziness, weakness, nausea, vomiting, chest pain, and confusion. The symptoms of carbon monoxide poisoning are very similar to those experienced during oxygen deprivation. This is due to a diminished ability of hemoglobin to deliver oxygen to the brain and other vital organs.
8. What is the relationship between pulmonary and cellular respiration? In pulmonary respiration, oxygen is brought into the lungs and transferred to the blood stream where it
is carried by hemoglobin to the cells of the body. Once oxygen has reached the cells, it is then used for cellular respiration, which creates usable energy in the form of ATP from glucose molecules.
9. Describe how carbon monoxide exposure interferes with normal respiration, and how that in
turn interferes with cellular respiration
During normal respiration, the hemoglobin component of blood binds with oxygen and then delivers it to the body, accepting carbon dioxide in return for oxygen. However, in the presence of carbon monoxide, the ability of hemoglobin to bind with oxygen or carbon dioxide is diminished—preventing the blood from delivering adequate amounts of oxygen to the body. Therefore, even though the victim may be breathing in sufficient oxygen, they may by suffering from hypoxia because of an inability of the blood to deliver the oxygen throughout the body. With no oxygen being delivered to the cells of the body, the process of cellular respiration is inhibited.
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CO Health Effects: Evaluation Questions
For questions 1-‐5, place the letter of the best answer in the space before the question.
_____1. What is the name of the condition where oxygen levels in the tissues fall below physiologically required levels?
A. asphyxiation B. pulmonary embolism C. carboxyhemoglobin D. hypoxia
_____2. Which of the following gases will make blood a dark red color?
A. oxygen B. carbon monoxide C. carbon dioxide D. all will make blood dark red
_____3. The heme-‐ in hemoglobin refers to the presence of _____ metal in hemoglobin.
A. calcium B. copper C. iron D. magnesium
_____4. Carbon monoxide can only be reliably detected by technological instrumentation.
A. true B. false
_____5. Hemoglobin has the highest bonding affinity for
A. oxygen B. carbon monoxide C. carbon dioxide D. there is equal affinity for each
Answer the following questions completely and concisely using complete sentences.
As you recall, the color of blood is largely determined by the type of hemoglobin-‐blood gas complex and the manner in which that complex absorbs light. Examine the data in the table below relating blood color to gas exposure then use the data to answer questions 6-‐8 below:
Table 1: Blood Color Compared To Gas Exposure
Gas Blood Color
Oxygen Bright red
Carbon monoxide Bright red
Carbon dioxide Dark red
Carbon dioxide then oxygen Bright red
Carbon monoxide the carbon dioxide Bright red
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6. Based on the data, does hemoglobin have a higher bonding affinity for carbon monoxide or carbon dioxide? Explain.
7. Examine the data where blood is exposed to carbon dioxide then oxygen. Predict the result if the situation was reversed; the blood exposed to oxygen then carbon dioxide.
8. Predict the result if a blood sample was exposed to oxygen then carbon monoxide. Would you be able to predict which gas has a higher bonding affinity to hemoglobin based on your predicted result? Explain.
Use the Oxygen-‐Hemoglobin Dissociation Curve to answer questions 9-‐10.
0 10 20 30 40 50 60 70 80 90 100
0 10
20
30
40
50
60
70
80
90
100
Oxyhemoglobin (%
Saturation)
PO2 (mmHg)
Hypothetical Oxygen-‐Hemoglobin Dissocation Curve
Exercise
Normal Conditions
Carbon Monoxide
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9. Explain the curve labeled normal conditions as it relates to movement of oxygen from the lungs to the other tissues of the body.
10. Examine the curve labeled carbon monoxide. It is clear that this curve represents oxyhemoglobin that is more saturated with oxygen at the same oxygen partial pressure than the oxyhemoglobin under normal conditions. Explain how the carbon monoxide curve can lead to hypoxia even though it is more highly saturated with oxygen.
11. Why does carbon monoxide exposure have similar symptoms to suffocation?
12. Why should a house that has gas appliances or is heated by a combustion processes, gas furnace or wood burning stove/fireplace, have a carbon monoxide detector?
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CO Health Effects: Evaluation Questions Teacher Key
For questions 1-‐5, place the letter of the best answer in the space before the question.
_____1. What is the name of the condition where oxygen levels in the tissues fall below physiologically required levels?
A. asphyxiation B. pulmonary embolism C. carboxyhemoglobin D. hypoxia
_____2. Which of the following gases will make blood a dark red color?
A. oxygen B. carbon monoxide C. carbon dioxide D. all will make blood dark red
_____3. The heme-‐ in hemoglobin refers to the presence of _____ metal in hemoglobin.
A. calcium B. copper C. iron D. magnesium
_____4. Carbon monoxide can only be reliably detected by technological instrumentation.
A. true B. false
_____5. Hemoglobin has the highest bonding affinity for
A. oxygen B. carbon monoxide C. carbon dioxide D. there is equal affinity for each
Answer the following questions completely and concisely using complete sentences.
As you recall, the color of blood is largely determined by the type of hemoglobin-‐blood gas complex and the manner in which that complex absorbs light. Examine the data in the table below relating blood color to gas exposure then use the data to answer questions 6-‐8 below:
Table 1: Blood Color Compared To Gas Exposure
Gas Blood Color
Oxygen Bright red
Carbon monoxide Bright red
Carbon dioxide Dark red
Carbon dioxide then oxygen Bright red
Carbon monoxide the carbon dioxide Bright red
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13. Based on the data, does hemoglobin have a higher bonding affinity for carbon monoxide or carbon dioxide? Explain. When blood is exposed to carbon monoxide then carbon dioxide, the blood is bright red indicating that the hemoglobin is bonding to the carbon monoxide. If hemoglobin had a higher bonding affinity for carbon dioxide, then the carbon dioxide should replace the carbon monoxide in the hemoglobin-‐blood gas complex resulting in a dark red blood color.
14. Examine the data where blood is exposed to carbon dioxide then oxygen. Predict the result if the situation was reversed; the blood exposed to oxygen then carbon dioxide. The blood should remain a bright red color. The results from the carbon monoxide then carbon dioxide exposure demonstrate that the order of exposure is unimportant. The gas with the highest bonding affinity to the hemoglobin will determine the blood color.
15. Predict the result if a blood sample was exposed to oxygen then carbon monoxide. Would you be able to predict which gas has a higher bonding affinity to hemoglobin based on your predicted result? Explain. Both gases turn blood a bright red color making it impossible to use blood color to predict which gas, oxygen or carbon monoxide, has a higher bonding affinity to the hemoglobin.
Use the Oxygen-‐Hemoglobin Dissociation Curve to answer questions 9-‐10.
0 10 20 30 40 50 60 70 80 90 100
0 10
20
30
40
50
60
70
80
90
100
Oxyhemoglobin (%
Saturation)
PO2 (mmHg)
Hypothetical Oxygen-‐Hemoglobin Dissocation Curve
Exercise
Normal Conditions
Carbon Monoxide
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16. Explain the curve labeled normal conditions as it relates to movement of oxygen from the lungs to the other tissues of the body. The normal conditions curve shows that when the partial pressure of oxygen is highest, which would be in the lungs, the oxygen saturation of hemoglobin is also at its peak. As the blood moves away from the lungs, the partial pressure of the oxygen decreases allowing the oxygen to dissociate and diffuse into the tissues.
17. Examine the curve labeled carbon monoxide. It is clear that this curve represents oxyhemoglobin that is more saturated with oxygen at the same oxygen partial pressure than the oxyhemoglobin under normal conditions. Explain how the carbon monoxide curve can lead to hypoxia even though it is more highly saturated with oxygen. The cooperative binding properties of carbon monoxide with hemoglobin causes an increased affinity between the hemoglobin and oxygen. This more tightly bound oxygen does not dissociate as easily. Therefore, even though the hemoglobin is more highly saturated with oxygen, the oxygen is not as readily released into the tissues.
18. Why does carbon monoxide exposure have similar symptoms to suffocation? Both carbon monoxide exposure and suffocation cause hypoxia. As stated in #10 above, carbon monoxide exposure causes hypoxia by not readily allowing hemoglobin to release oxygen to the tissues. Suffocation causes hypoxia by not allowing oxygen to enter the lungs. In both cases, the oxygen supplies to the tissues falls below physiological necessary levels.
19. Why should a house that has gas appliances or is heated by a combustion processes, gas furnace or wood burning stove/fireplace, have a carbon monoxide detector? Gas appliances or combustion heating will produce carbon monoxide as a result of incomplete combustion. If the appliances are not properly vented and the house is closed, carbon monoxide levels will increase in the house. Since carbon dioxide is colorless, odorless, and tasteless, it is impossible to detect without technological instrumentation.
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Carbon Monoxide Lesson 2: Specific Learning Objectives and Standards Specific Learning Objectives Upon completion of this lesson, students will be able to:
• understand the basic exchange of oxygen and carbon dioxide in the blood.
• explain how oxygen is used in the body (i.e. cellular respiration) and why it is critical to life.
• describe how oxygen, carbon dioxide, and carbon monoxide each bind differently to the hemoglobin in red blood cells.
• summarize the symptoms of carbon monoxide poisoning and explain why ingestion of carbon monoxide is dangerous (i.e. prevents delivery of oxygen to tissues within the body for use in cellular respiration).
• identify sources of carbon monoxide in the home.
NEXT GENERATION SCIENCE STANDARDS Students who demonstrate understanding can:
HS-‐LS1-‐2 Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.
HS-‐LS1-‐7 Use a model to illustrate that cellular respiration is a chemical process whereby the bonds of food molecules and oxygen molecules are broken and the bonds in new compounds are formed resulting in net transfer of energy.
MONTANA STATE SCIENCE STANDARDS A proficient student will (upon graduation):
Science Content Standard 1: Students, through the inquiry process, demonstrate the ability to design, conduct, evaluate, and communicate the results and form reasonable conclusions of scientific investigations.
1.2 select and use appropriate tools including technology to make measurements (in metric units), gather, process and analyze data from scientific investigations using appropriate mathematical analysis, error analysis and graphical representation.
1.3 review evidence, communicate and defend results, and recognize that the results of a scientific investigation are always open to revision by further investigations. (e.g. through graphical representation or charts)
Science Content Standard 3: Students, through the inquiry process, demonstrate knowledge of characteristics, structures and function of living things, the process and diversity of life, and how living organisms interact with each other and their environment.
3.2 describe and explain complex processes involved in energy use in cell maintenance, growth, repair, and development.
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ALASKA STATE SCIENCE STANDARDS
SA1 Students develop an understanding of the processes of science used to investigate problems, design and conduct repeatable scientific investigations, and defend scientific arguments.
[10] SA1.1 The student demonstrates an understanding of the processes of science by asking questions, predicting, observing, describing, measuring, classifying, making generalizations, analyzing data, developing models, inferring, and communicating.
[11] SA1.1 The student demonstrates an understanding of the process of science by recognizing and analyzing multiple explanations and models, using this information to revise student’s own explanation or model if necessary.
SC2 Students develop an understanding of the structure, function, behavior, development, life cycles, and diversity of living organisms.
[10] SC2.1 The student demonstrates an understanding of the structure, function, behavior, development, life cycles, and diversity of living organisms by describing the structure function relationship (i.e. joints, lungs).
[10] SC2.3 The student demonstrates an understanding of the structure, function, behavior, development, life cycles, and diversity of living organisms by describing the functions of organs of major systems (i.e. respiratory, digestive, circulatory, reproductive, nervous, musculoskeletal, and excretory).
[10] SC2.4 The student demonstrates an understanding of the structure, function, behavior, development, life cycles, and diversity of living organisms by tracing the pathways of digestive, circulatory, and excretory systems.
IDAHO STATE STANDARDS Biology:
Goal 1.2 Understand Concepts and Processes of Evidence, Models, and Explanations
9-‐10.B.1.2.1 Use observations and data as evidence on which to base scientific explanations.
9-‐10.B.1.2.3 Develop scientific explanations based on knowledge, logic and analysis.
Goal 1.6 Understand Scientific Inquiry and Develop Critical Thinking Skills
9-‐10.B.1.6.4 Formulate scientific explanations and models using logic and evidence.
Goal 3.2 Understand the Relationship between Mater and Energy in Living Systems
9-‐10.B.3.2.4 Describe cellular respiration and the synthesis of macromolecules.
Goal 3.3 Understand the Cell is the Basis of Form and Function for All Living Things
9-‐10.B.3.3.2 Explain cell functions involving chemical reactions.