Complete the following concept map to review some of the concepts of gas exchange.

Label the parts of the human respiratory system.

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When you hold your breath, which of the following first leads to the urge to breathe?

a. Falling CO₂

b. Falling O₂

c. Falling pH of the blood

d. Rising pH of the blood

Countercurrent gas exchange in the gills of a fish

a. Maintains a gradient that enhances diffusion.

b. Enables the fish to obtain oxygen without swimming.

c. Means that blood and water flow at different rates.

d. Allows O₂ to diffuse against its partial pressure gradient.

When you inhale, the diaphragm

a. Relaxes and moves upward.

b. Relaxes and moves downward.

c. Contracts and moves upward.

d. Contracts and moves downward.

In which of the following organisms does oxygen diffuse directly across a respiratory surface to cells, without being carried by the blood?

a. A grasshopper

b. A whale

c. An earthworm

d. A mouse

What is the function of the cilia in the trachea and bronchi?

a. To sweep air into and out of the lungs

b. To increase the surface area for gas exchange

c. To dislodge food that may have slipped past the epiglottis

d. To sweep mucus with trapped particles up and out of the respiratory tract

What do the alveoli of mammalian lungs, the gill filaments of fish, and the tracheal tubes of insects have in common?

a. Use of a circulatory system to transport gases

b. Respiratory surfaces that are infoldings of the body wall

c. Countercurrent exchange

d. A large, moist surface area for gas exchange

What is the primary feedback used by the brain to control breathing?

a. Heart rate

b. Partial pressure of O₂

c. Blood pH, which indicates O₂ level

d. Blood pH, which indicates CO₂ level

Trace the path of an oxygen molecule in its journey from the air to a muscle cell in your arm, naming all the structures involved along the way.

Carbon monoxide (CO) is a colorless, odorless gas found in furnace and automobile engine exhaust and cigarette smoke. CO binds to hemoglobin 210 times more tightly than does O₂. CO also binds with an electron transport protein and disrupts cellular respiration. Explain why CO is such a deadly gas.

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 P_O₂) in the atmosphere where llamas live is about half of the P_O₂ 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 P_O₂ 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.'

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 P_O₂ is kept artificially low. Explain why this training strategy may improve an athlete's performance.

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/