Partial pressure reflects the relative amount of gas in a mixture and is measured in millimeters of mercury (mm Hg). Llamas are native to the Andes Mountains in South America. The partial pressure of O2 (abbreviated PO₂) in the atmosphere where llamas live is about half of the PO₂ at sea level. As a result, the PO₂ in the lungs of llamas is about 50 mm Hg, whereas that in human lungs at sea level is about 100 mm Hg. A dissociation curve for hemoglobin shows the percentage of saturation (the amount of O2 bound to hemoglobin) at increasing values of PO₂ As you see in the graph below, the dissociation curves for llama and human hemoglobin differ. Compare these two curves and explain how the hemoglobin of llamas is an adaptation to living where the air is 'thin.'
Ch. 22 Gas Exchange
Taylor, Simon, Dickey, Hogan10th EditionCampbell Biology: Concepts & ConnectionsISBN: 9780136538783Not the one you use?Change textbook
Chapter 22, Problem 16
E-cigarettes pose a dilemma for public health officials. Because e-cigarettes produce fewer toxic chemicals than regular cigarettes, they may be a safer alternative for people who want to quit smoking but still crave nicotine. On the other hand, e-cigarettes may encourage nicotine addiction among teenagers. Evaluate the scientific evidence. Are e-cigarettes an effective aid for quitting cigarettes? What evidence supports the assertion that e-cigarettes are especially harmful to adolescents? The Centers for Disease Control website is a good place to start. cdc.gov/tobacco/basic_information/e-cigarettes/
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Step 1: Define the problem and identify the key questions. The problem involves evaluating the scientific evidence regarding the effectiveness of e-cigarettes as a smoking cessation aid and their potential harm to adolescents. The key questions are: (1) Are e-cigarettes effective for quitting smoking? (2) What evidence supports their harm to adolescents?
Step 2: Research the effectiveness of e-cigarettes for smoking cessation. Look for studies comparing the success rates of quitting smoking among individuals using e-cigarettes versus other methods (e.g., nicotine replacement therapy or behavioral interventions). Pay attention to sample size, study design (e.g., randomized controlled trials), and statistical significance.
Step 3: Investigate the impact of e-cigarettes on adolescents. Examine studies that explore the prevalence of e-cigarette use among teenagers, the likelihood of transitioning to regular cigarettes, and the effects of nicotine on adolescent brain development. Focus on evidence showing how nicotine affects cognitive function, memory, and addiction pathways in developing brains.
Step 4: Analyze the chemical composition of e-cigarettes. Compare the toxic chemicals produced by e-cigarettes versus regular cigarettes. Highlight the reduced levels of harmful substances in e-cigarettes but also note the presence of nicotine and other potentially harmful compounds (e.g., flavoring agents or heavy metals).
Step 5: Synthesize the findings and evaluate the trade-offs. Summarize the evidence supporting e-cigarettes as a safer alternative for adult smokers trying to quit, while emphasizing the risks they pose to adolescents. Discuss the importance of public health policies that balance harm reduction for smokers with prevention strategies for youth.

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Nicotine Addiction
Nicotine is a highly addictive substance found in tobacco products, including e-cigarettes. Understanding how nicotine affects the brain is crucial, as it stimulates the release of neurotransmitters like dopamine, leading to feelings of pleasure and reinforcing the desire to continue using the substance. This addiction can be particularly concerning for adolescents, whose brains are still developing, making them more susceptible to the addictive properties of nicotine.
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Public Health Implications
Public health officials must weigh the benefits and risks of e-cigarettes as smoking cessation tools against their potential to create new health issues, particularly among youth. While e-cigarettes may reduce exposure to harmful chemicals compared to traditional cigarettes, their increasing popularity among teenagers raises concerns about long-term health effects and the possibility of initiating nicotine addiction in a new generation.
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Scientific Evidence and Research
Evaluating the effectiveness of e-cigarettes as a smoking cessation aid requires a thorough examination of scientific studies and data. Research often includes clinical trials, surveys, and longitudinal studies that assess both the success rates of quitting smoking with e-cigarettes and the potential health risks associated with their use, especially in adolescents. Understanding the quality and findings of this evidence is essential for making informed public health decisions.
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Scientific Method
Related Practice
Textbook Question
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Textbook Question
Mountain climbers often spend weeks adjusting to the lower partial pressure of oxygen at high altitudes before and during their ascent of high peaks. During that time, their bodies begin to produce more red blood cells. Some runners and cyclists prepare for competition by training at high altitudes or by sleeping in a tent in which PO₂ is kept artificially low. Explain why this training strategy may improve an athlete's performance.
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Textbook Question
One of the many mutant opponents that the movie monster Godzilla contends with is Mothra, a giant mothlike creature with a wingspan of 7–8 m. Science fiction creatures like these can be critiqued on the grounds of biomechanical and physiological principles. Focusing on the principles of gas exchange that you learned about in this chapter, what problems would Mothra face? Why do you think truly giant insects are improbable?
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