Deck 48: Gas Exchange

Question 1

Breathing provides the body with the oxygen required to support the energy metabolism of all cells and also eliminates _______, one of the waste products of cell metabolism.

A) carbon dioxide
B) carbon monoxide
C) carbon tetrachloride
D) calcium carbonate
E) carbonic acid

Answer 1

A

Question 2

Which statement about insect respiration is true?

A) Spiracles are the air tubes that carry the respiratory gases.
B) Because O₂ diffuses more quickly in water than in air, the respiratory system of aquatic insects is highly efficient.
C) Air capillaries are sparsely distributed throughout insects' flight muscles.
D) Many larval insects have external lungs.
E) The insect tracheal system brings air to all tissues in the body.

Answer 2

E

Question 3

Aquatic animals that lack an internal system for transporting O₂

A) often have thick bodies.
B) are always large.
C) may have a thick body built around a central cavity through which water circulates.
D) have cells that are all close to the respiratory medium.
E) have lungs that project outward into the water.

Answer 3

D

Question 4

One reason rapid gas exchange can be accomplished more easily in air than in water is that

A) the O₂ content of water is higher than that of air.
B) the CO₂ content of water is higher than that of air.
C) O₂ diffuses more rapidly in water than in air.
D) water is more dense and viscous than air.
E) more energy is required to move air than to move water.

Question 5

Gas exchange in animals always involves

A) lungs.
B) breathing movements.
C) neural control.
D) diffusion between internal body fluids and the outside medium.
E) active transport of gases.

Question 6

Oxygen can be exchanged more easily in air than in water in part because

A) the oxygen content of air is lower than that of water.
B) oxygen diffuses more slowly in water than in air.
C) water is less dense than air, so more energy is required to move it.
D) as water warms, the concentration of oxygen in the water increases.
E) as water warms, the partial pressure of oxygen in the water increases.

Question 7

The respiratory system of insects consists of

A) branched air tubes called spiracles that supply blood capillaries.
B) branched air tubes called tracheae and tracheoles that end in air capillaries.
C) branching gill systems that end in openings called tracheae.
D) branching gill systems that end in openings called tracheoles.
E) extensive layers of gas exchange tissue just under the exoskeleton.

Question 8

Which is a response of a fish to the rise in water temperature due to global warming?

A) Increased metabolic rate
B) Decreased blood flow
C) Decreased O₂ consumption
D) Decreased expenditure of energy for breathing
E) Decreased body temperature

Question 9

If a planet were discovered where the atmospheric pressure was 2,000 mm Hg at sea level and the air was 15% O₂, the partial pressure of its O₂ at sea level would be

A) 15%.
B) 30%.
C) 15 mm Hg.
D) 133 mm Hg.
E) 300 mm Hg.

Question 10

Refer to the figure showing various gas exchange systems.Recall that Fick's law of diffusion is Q = DA(P₁ - P₂)/L. The term D in the equation for Fick's law of diffusion depends in part on the _______, indicating that this term is higher for the diffusion of O₂ in the organism(s) shown in _______.

A) medium; A and B because O₂ diffuses faster in water than in air
B) medium; C and D because O₂ diffuses faster in air than in water
C) area across which the gas is diffusing; C because it has the largest surface area for exchange of respiratory gases
D) the path length for diffusion; D because every cell is next to an air capillary
E) partial pressure of the gas that is diffusing; A and B because the partial pressure of O₂ is higher in water than in air

Question 11

By being aquatic, _______ are in a double bind, because their demand for oxygen increases as the temperature of their water environment increases, but the oxygen content of water declines with increasing water temperatures.

A) seals
B) fish
C) whales
D) aquatic birds
E) alligators

Question 12

Humans often have difficulty breathing at high elevations primarily because the _______ than it is at low elevations.

A) percentage of O₂ in the air is lower
B) temperature is lower
C) barometric pressure is higher
D) partial pressure of O₂ is lower
E) air is drier

Question 13

Small insects may take a bubble of air underwater when they dive.The bubble can serve as an air tank for some time because

A) as CO₂ increases, the bubble inflates.
B) as O₂ is consumed, air pressure in the bubble decreases.
C) as O₂ is consumed, more O₂ diffuses into the bubble.
D) the partial pressure of nitrogen remains constant.
E) for each O₂ molecule used, a CO₂ molecule replaces it.

Question 14

Which is a reason that diffusion of CO₂ from an animal is less problematic than diffusion of O₂ into an animal?

A) CO₂ is less soluble in water than O₂ is.
B) Cellular respiration produces less CO₂ than the O₂ that is consumed.
C) The CO₂ content of air is higher than the O₂ content.
D) The atmospheric partial pressure of CO₂ is negligible compared to the atmospheric partial pressure of O₂.
E) There is less of a concentration gradient between the cell and the atmosphere for CO₂ than for O₂.

Question 15

Atmospheric pressure at sea level is 760 mm Hg, and oxygen makes up 20.9% of this air when the air is dry.Scientists at a Mount Everest base camp measured the atmospheric pressure there as 400 mm Hg.When the air is dry, the partial pressure of oxygen at this base camp is approximately _______ mm Hg.

A) 21
B) 40
C) 84
D) 160
E) 400

Question 16

External gills, tracheae, and lungs share which set of characteristics?

A) They are parts of gas exchange systems, they exchange both CO₂ and O₂, and they increase surface area for diffusion.
B) They are used by water breathers, their functioning is based on countercurrent exchange, and they make use of negative pressure for breathing.
C) They exchange only O₂, they are associated with a circulatory system, and they are found in vertebrates.
D) They are found in insects, they employ positive-pressure pumping, and their functioning is based on crosscurrent flow.
E) They are parts of gas exchange systems, they exchange both CO₂ and O₂, and they decrease surface area for diffusion.

Question 17

The rate at which a gas diffuses between two locations _______ between those locations.

A) is unrelated to the distance
B) is positively related to the distance
C) is the square root of the distance
D) is negatively related to the distance
E) increases as the distance increases

Question 18

Refer to the figure showing a variety of animals. Which organism requires ventilation of its respiratory surfaces with a medium containing O₂, but does not require perfusion of its respiratory surfaces with blood?

A) A
B) B
C) C
D) D
E) E

Question 19

The movement of O₂ and CO₂ between the blood in the tissue capillaries and the cells in tissues depends most directly upon

A) active transport of O₂ and CO₂.
B) total atmospheric (barometric) pressure differences across the cell membranes.
C) diffusion of O₂ and CO₂ down a concentration gradient.
D) diffusion of O₂ and CO₂ down a partial pressure gradient.
E) osmosis across cell membranes.

Question 20

Which statement about respiratory adaptations is true?

A) Respiratory surfaces in all animals require ventilation.
B) External gills are found only in invertebrates.
C) Most fishes ventilate their gills by swimming almost constantly with their mouths open.
D) In fish, water flows unidirectionally into the mouth, over the gills, and out from under the opercular flaps.
E) Desiccation of the respiratory surface is more likely to occur in gills than in lungs.

Question 21

Which feature characterizes the lungs of mammals?

A) Air sacs
B) Tidal ventilation
C) Complete emptying in exhalation
D) Crosscurrent air flow
E) Countercurrent air flow

Question 22

Refer to the figure showing a countercurrent exchanger from a fish gill. The values in the figure represent percent saturation of O₂.Based on the information provided, which statement is true?

A) Fluid flowing through A represents water and B represents blood.
B) Fluid flowing through B represents water and A represents blood.
C) The change in O₂ levels is accomplished by transfer of hemoglobin from tube A to tube B.
D) The change in O₂ levels is accomplished by transfer of hemoglobin from tube B to tube A.
E) The direction of flow in both tubes is from left to right.

Question 23

In the respiratory cycle of birds, air flows through the trachea, to the bronchi, and then

A) into the parabronchi.
B) back through the trachea.
C) to the air capillaries.
D) into the posterior air sacs.
E) into the anterior air sacs.

Question 24

Which of the following represents the correct air pathway during inhalation in humans?

A) Pharynx $\rightarrow$ trachea $\rightarrow$ bronchi $\rightarrow$ larynx $\rightarrow$ alveoli
B) Larynx $\rightarrow$ trachea $\rightarrow$ pharynx $\rightarrow$ bronchi $\rightarrow$ alveoli
C) Trachea $\rightarrow$ larynx $\rightarrow$ pharynx $\rightarrow$ bronchi $\rightarrow$ alveoli
D) Trachea $\rightarrow$ larynx $\rightarrow$ pharynx $\rightarrow$ alveoli $\rightarrow$ bronchi
E) Pharynx $\rightarrow$ larynx $\rightarrow$ trachea $\rightarrow$ bronchi $\rightarrow$ alveoli

Question 25

Refer to the figure showing the respiratory system in birds. In the respiratory cycle of birds, air flows

A) through the trachea, to the bronchi, to the posterior air sacs, and then into the parabronchi.
B) through the bronchi, to the trachea, to the parabronchi, and then into the posterior air sacs.
C) through the trachea, to the parabronchi, to the bronchi, and then into the posterior air sacs.
D) through the trachea, to the parabronchi, to the posterior air sacs, and then into the bronchi.
E) through the trachea, to the posterior air sacs, to the parabronchi, and then to the parabronchi.

Question 26

The delicate gills of fishes are protected by _______ and supported by _______.

A) opercular flaps; gill arches
B) opercular flaps; gill filaments
C) gill filaments; gill arches
D) opercular flaps; a diaphragm
E) gill arches; a diaphragm

Question 27

The rate of gas exchange in mammals is maximized by

A) a large residual volume in the lungs.
B) the opening of the larynx (voice box) into the trachea.
C) an enormous surface area for gas exchange.
D) the animals' small increase in size during inhalation.
E) the production of mucus and surfactants.

Question 28

Which statement about the structure of the fish gill is true?

A) Efferent vessels bring blood to the gills, whereas afferent vessels take blood away from the gills.
B) Exchange of respiratory gases occurs within the lamellae of the gill filaments.
C) The efferent and afferent vessels are the countercurrent flow system of the gill.
D) The lamellae are further subdivided into gill filaments.
E) The opercular flaps open to take in water from outside into the gill chamber.

Question 29

Refer to the graph showing a spirometer tracing. Which term is paired correctly with its location on the spirometer tracing?

A) 1 - Inspiratory reserve volume
B) 2 - Tidal volume
C) 3 - Vital capacity
D) 4 - Residual volume
E) 5 - Total lung capacity

Question 30

Tidal breathing decreases the efficiency of gas exchange in organisms such as mammals for a number of reasons.Which is not one of those reasons?

A) The absence of countercurrent gas exchange
B) The existence of dead space in the airways
C) The residual volume of the lungs
D) A short diffusion path length
E) The limit in the O₂ concentration gradient between air and blood

Question 31

Air flows into the lungs of mammals during inhalation because the

A) pressure in the lungs falls below atmospheric pressure.
B) volume of the lungs decreases.
C) pressure in the lungs rises above atmospheric pressure.
D) diaphragm moves upward toward the lungs.
E) internal intercostal muscles contract.

Question 32

Refer to the figure. This figure could represent a blood capillary in a(n) _______.Blood at A has come most recently from the _______; blood at B is going most directly to the _______.

A) fish; heart; body
B) bird; body; heart
C) rabbit; heart; heart
D) insect; spiracle; air sac
E) human; heart; body

Question 33

Refer to the graph showing a spirometer tracing. Suppose that you have been resting on the couch while watching a 30-minute TV show; you test your airflow with a spirometer and record the tracing shown in the graph.From this, you see that while you are breathing normally without added effort, you are moving approximately _______ of air into your lungs when you breathe in (inhale) and approximately _______ of air out of your lungs when you breathe out (exhale).

A) less than a half liter; more than a half liter
B) more than a half liter; less than a half liter
C) slightly more than a half liter; slightly more than a half liter
D) slightly more than a liter; less than a liter
E) slightly more than a liter; slightly more than a liter

Question 34

Bird and fish respiratory systems are similar in that both

A) employ a countercurrent exchanger.
B) have air sacs.
C) function by means of unidirectional flow of the environmental medium over the gas exchange membranes.
D) consist of infoldings of the body.
E) include a trachea that branches into paired bronchi.

Question 35

Both bird and mammal lungs

A) require two cycles of inhalation and exhalation in order for a breath of air to be expelled.
B) contain alveoli at the terminal ends.
C) have an anatomical dead space.
D) exchange O₂ and CO₂ with blood in capillaries.
E) have a unidirectional flow of air moving through them.

Question 36

In the equation below, which quantity represents the volume of your normal breath? Total lung capacity = residual volume + expiratory reserve volume + inspiratory reserve volume + tidal volume

A) Total lung capacity
B) Residual volume
C) Expiratory reserve volume
D) Inspiratory reserve volume
E) Tidal volume

Question 37

Which is not an adaptation seen in fish gills?

A) A countercurrent exchange system
B) Bidirectional ventilation of the gills
C) Morphological features that increase the surface area available for gas exchange
D) Morphological features that decrease the path length for diffusion of the respiratory gases
E) Morphological features that maximize the efficiency of O₂ extraction

Question 38

Refer to the figure showing the respiratory system in birds. Based on the figure, which statement about the air sacs of birds is true?

A) Most air enters the lungs having by-passed the air sacs.
B) They are primarily unpaired.
C) They provide an extra gas exchange surface.
D) Air flows from the posterior air sacs into the lungs.
E) Only the posterior air sacs are connected to the lungs.

Question 39

Which structure is the site of gas exchange in the lungs?

A) Alveoli
B) Bronchi
C) Bronchioles
D) Trachea
E) Larynx

Question 40

A patient who has chronic obstructive pulmonary disease from having been a smoker for a number of years is tested for lung volume.It is determined that the patient's tidal volume is 0.6 liters, his inspiratory reserve volume is 2.6 liters, his expiratory reserve volume is 1 liter, and his residual volume is 3.2 liters.Prior to smoking, this man's tidal volume was 0.5 liters, his inspiratory reserve volume was 3.1 liters, his expiratory reserve volume was 1.2 liters and his residual volume was 1.2 liters.These numbers indicate that

A) the vital capacity of this patient has not been altered.
B) the vital capacity of this patient has increased since he started smoking.
C) the total lung volume of this patient is 50% less than when he started smoking.
D) the increased total lung volume of this patient improves his ability to extract oxygen from the air he breathes.
E) the increased residual volume of this patient decreases the patient's respiratory ability.

Question 41

In humans, the process of exhalation is brought about in large part by

A) the contraction of external intercostal muscles.
B) elastic recoil of the lung tissues.
C) contraction of the diaphragm.
D) complete collapse of the lung tissue.
E) lowering of pressure in the thoracic cavity.

Question 42

Refer to the graph showing several different O₂-binding/dissociation curves for hemoglobin. Curve _______ would most likely represent a human fetus, curve _______ would most likely represent an adult human with blood at pH 7.2, and curve _______ would most likely represent a human with blood at pH 7.4.

A) A; B; C
B) A; C; B
C) B; A; C
D) B; C; A
E) C; B; A

Question 43

If a new air pollutant were to destroy the surfactant in people's lungs, one likely result would be

A) decreased surface tension of the fluid lining their alveoli.
B) increased uptake of CO₂ from the environment.
C) increased effort needed to breathe.
D) decreased levels of hydrogen bonding in the fluid of their alveoli.
E) decreased amounts of CO₂ carried in their blood.

Question 44

If the O₂-binding/dissociation curves were plotted for the following molecules, which curve would be to the left of all the others?

A) Fetal human hemoglobin
B) Adult human hemoglobin in a person exercising heavily
C) Adult human hemoglobin in a person at rest
D) Myoglobin
E) Adult human hemoglobin in a person exercising at high altitudes

Question 45

Which statement about the binding of oxygen by hemoglobin is true?

A) The percentage of completely O₂-saturated hemoglobin decreases as PO₂ increases.
B) The O₂-binding/dissociation curve is U-shaped.
C) Over the full length of the O₂-binding/dissociation curve, O₂ dissociation-association is rapid.
D) A very low PO₂ is required for all four hemoglobin subunits to bind to O₂.
E) Once one subunit of hemoglobin binds to O₂, the affinity of the remaining subunits for their O₂ increases until three O₂ are bound.

Question 46

Which statement about the mechanics of ventilation in humans is true?

A) If the pleural cavity is punctured, the lung will overinflate.
B) As the diaphragm contracts, air is expelled from the respiratory system.
C) As the diaphragm contracts, pressure within the pleural cavity increases.
D) Less energy is expended during the exhalation phase than during the inhalation phase.
E) There is a slight positive pressure within the pleural cavity between breaths.

Question 47

Refer to the figure. The black arrows in part A show the direction of movement of the thoracic cavity and diaphragm.The process shown in part A is represented by the portion of the graph labeled _______, which corresponds to _______.

A) B; exhalation
B) B; contraction of internal intercostal muscles
C) C; inhalation
D) C; contraction of external intercostal muscles
E) C; exhalation

Question 48

Refer to the graph showing several different O₂-binding/dissociation curves for hemoglobin. Curve _______ would most likely represent a normal adult human, curve _______ would most likely represent an adult human exposed to high altitude, and curve _______ would most likely represent a human fetus.

A) A; B; C
B) A; C; B
C) B; A; C
D) B; C; A
E) C; B; A

Question 49

Surfactant produced by cells lining the alveoli serves to

A) increase surface tension.
B) increase stretching of the alveolar walls.
C) directly assist muscular movements of breathing.
D) reduce cohesion of surface molecules.
E) reduce ciliary movement.

Question 50

Smokers tend to cough frequently because coughing

A) releases the tar that fills numerous alveoli.
B) is a response to histamine that is released when smoke narrows the airway.
C) clears the mucus, which the paralyzed cilia can no longer do.
D) assists in release of surfactant, which is inhibited by smoking.
E) assists the diaphragm in contracting, improving exhalation.

Question 51

When you are lying on the couch, resting, the blood going from your heart to your lungs is approximately _______ % saturated with oxygen.When you are running fast on a treadmill, _______.

A) 0; your active muscles extract most of the oxygen bound to hemoglobin
B) 25; your active muscles extract all the oxygen that is bound to hemoglobin
C) 50; the partial pressure of oxygen in your active muscles is high, causing most bound oxygen to be released from hemoglobin in these tissues
D) 75; the lower partial pressure of oxygen in your active muscles causes hemoglobin to release more bound oxygen to these tissues
E) 100; the partial pressure of oxygen in your blood falls below 40 mm Hg

Question 52

Which statement about the transport of respiratory gases by the blood in humans is true?

A) The amount of O₂ that can be dissolved directly in plasma is sufficient to support the resting metabolism.
B) By binding O₂, hemoglobin prevents an O₂ concentration gradient from forming between the blood and the tissues.
C) Internal perfusion of the gas exchange surfaces is dependent on blood flow.
D) Each hemoglobin molecule can carry a maximum of two O₂ molecules.
E) Molecules of O₂ are associated with the polypeptide subunits of hemoglobin.

Question 53

Each molecule of hemoglobin, when fully saturated, carries _______ molecule(s) of oxygen.

A) 1
B) 2
C) 4
D) 20
E) nearly 100

Question 54

If the thoracic wall is punctured, air leaking in will cause the lung to collapse.Thus in the normal, intact thoracic cavity,

A) lung expansion is passive.
B) air pressure is the same as it is on the outside.
C) a slight negative pressure in the pleural cavity keeps the alveoli partly inflated.
D) inhalation decreases the volume of the thoracic cavity.
E) increasing the volume of the thoracic cavity decreases the tension between the pleural membranes lining the thoracic cavity.

Question 55

The alveoli of the lungs do not contain air with 20.9% O₂ (i.e., the percentage in dry air) because

A) we normally do not ventilate our lungs at a high enough rate.
B) the lungs have too many alveoli to ventilate.
C) there is dead space in the trachea, bronchi, and lungs.
D) the trachea and bronchi are too small in volume to contain this amount of O₂.
E) some O₂ has been exchanged before reaching the alveoli.

Question 56

In humans, the lower (posterior) side of the thoracic cavity is defined by the

A) diaphragm.
B) esophagus.
C) stomach.
D) ribs.
E) intercostal muscles.

Question 57

The lungs expand during an inhalation because

A) the diaphragm contracts upward.
B) the shoulder girdle moves upward.
C) the volume of the thoracic cavity increases.
D) lung tissue actively stretches.
E) the lung tissue rebounds from exhalation.

Question 58

Which part of the blood is most efficient at carrying oxygen?

A) Blood plasma solution
B) Blood plasma proteins
C) Blood platelets
D) Membrane molecules of red blood cells
E) Hemoglobin molecules of red blood cells

Question 59

One of the most serious effects of cigarette smoking on the lungs is the

A) removal of mucus from the airways.
B) immobilization of cilia lining the airways.
C) speeding of airflow through the airways.
D) increase in surfactant action that it causes.
E) increase in the surface area of alveoli that it induces.

Question 60

Which statement about surfactants is true?

A) Lung surfactant is a sticky substance similar to mucus.
B) Surfactants increase the cohesive forces between water molecules.
C) Certain cells in the diaphragm produce surfactants to increase its elasticity.
D) Increased surface tension caused by surfactants reduces the amount of effort required to inflate the lungs.
E) Premature infants suffer respiratory distress syndrome if natural surfactants are not present within the lungs.

Question 61

Carbon monoxide (CO)

A) binds to hemoglobin with a lower affinity than O₂ does.
B) may accumulate in a closed space through incomplete combustion by faulty furnaces or burning charcoal.
C) exposure is not hazardous to health.
D) increases hemoglobin's affinity for O₂.
E) is similar to CO₂ in the manner in which it is carried in the blood.

Question 62

The Bohr effect describes the

A) outward movement of Cl^- from a blood cell in exchange for HCO₃^- moving into the cell.
B) leftward shift of hemoglobin's O₂-binding/dissociation curve when temperature rises.
C) rightward shift of hemoglobin's O₂-binding/dissociation curve when pH rises.
D) rightward shift of hemoglobin's O₂-binding/dissociation curve when pH falls.
E) leftward shift of hemoglobin's O₂-binding/dissociation curve when BPG increases.

Question 63

Which is a benefit provided by fetal hemoglobin?

A) It occurs in higher density in red blood cells than adult hemoglobin does.
B) It releases O₂ at a lower partial pressure than adult hemoglobin does.
C) In the placenta, O₂ diffuses from fetal hemoglobin to adult hemoglobin.
D) At low O₂ pressures, it is less likely to pick up oxygen than adult hemoglobin is.
E) It transfers O₂ from adult hemoglobin to the fetus.

Question 64

If the O₂-binding/dissociation curves were plotted for the following types of hemoglobin at the pH levels indicated, which curve would be to the right of all the others?

A) Fetal human hemoglobin at pH 7.6
B) Adult human hemoglobin at pH 7.6
C) Adult human hemoglobin at pH 7.2
D) Fetal human hemoglobin at pH 7.2
E) Adult human hemoglobin at pH 7.2 in a person at a high altitude

Question 65

In acidic tissues, hemoglobin releases _______ it does in less acidic environments.

A) more O₂ than
B) less O₂ than
C) more CO₂ than
D) less CO₂ than
E) the same amount of O₂ and CO₂ as

Question 66

The presence of CO₂ in blood will lower blood pH because CO₂ combines with _______ to form _______.The rate of the reaction is increased by _______.

A) H₂O; H⁺ and HCO₃^-; carbonic anhydrase
B) H₂O; only HCO₃^-; carbonic anhydrase
C) H₂O; only H⁺; carbonic ions
D) H⁺; HCO₃^-; oxyhemoglobin
E) H₂O; H⁺ and HCO₃^-; fetal hemoglobin

Question 67

In which of these PO₂ environments would hemoglobin release its O₂ most readily?

A) 30 mm Hg
B) 50 mm Hg
C) 70 mm Hg
D) 90 mm Hg
E) 110 mm Hg

Question 68

Which statement about myoglobin is true?

A) The lead-containing ring structure of the myoglobin molecule can bind to O₂.
B) It is found in muscle cells.
C) It has a lower affinity for O₂ than hemoglobin does.
D) Diving mammals have lower concentrations of myoglobin in their muscles.
E) Skeletal muscles are all similar in their myoglobin content.

Question 69

Refer to the figure. This capillary could be in a(n) _______.This is apparent because _______.

A) human intestine; carbon dioxide is diffusing from the tissue labeled 1 into the plasma of the capillary
B) human intestine; CO₂ is binding with hemoglobin and remaining in the red blood cell
C) human lung; the enzyme present at label 2 is catalyzing the reaction in which carbon dioxide and water are combined to form bicarbonate
D) human lung; the reaction at label 2 is being catalyzed by the enzyme called carbon dioxide hydrase
E) insect air sac; bicarbonate ions are entering the plasma in exchange for chloride ions

Question 70

Refer to the figure showing the hemoglobin-oxygen binding/dissociation curve. Which statement about hemoglobin's O₂-binding/dissociation curve is true?

A) At rest, our body's hemoglobin activity can be illustrated by only the upper one-fourth of its O₂-binding/dissociation curve.
B) A smaller decrease in PO₂ is required for hemoglobin to drop from 100 to 75% saturation than for hemoglobin to drop from 75 to 50% saturation.
C) Our blood normally carries a small reserve of O₂.
D) The steepest part of the O₂-binding/dissociation curve results in a small release of O₂ for a large drop in PO₂.
E) The PO₂ of our blood drops well below 40 mm Hg during light exertion.

Question 71

Carbonic anhydrase is an enzyme in red blood cells that catalyzes a reaction between CO₂ and

A) HCO₃^-.
B) H₂CO₃.
C) hemoglobin.
D) O₂.
E) water.

Question 72

Breathing rhythm is generated in the _______ and modified by neurons either in or above the _______.

A) medulla; pons
B) medulla; spinal cord
C) spinal cord; pons
D) spinal cord; cerebellum
E) cerebellum; medulla

Question 73

If the O₂-binding/dissociation curves were plotted for adult hemoglobin under the following conditions, which curve would be to the right of all the others?

A) pH 7.6, little 2,3-bisphosphoglyceric acid
B) pH 7.6, much 2,3-bisphosphoglyceric acid
C) pH 7.2, little 2,3-bisphosphoglyceric acid
D) pH 7.2, much 2,3-bisphosphoglyceric acid
E) pH 7.4, little 2,3-bisphosphoglyceric acid

Question 74

Hemoglobin delivers O₂ to body cells from the red blood cells

A) until the hemoglobin is depleted of O₂.
B) until the partial pressures of O₂ in the two different cells are equivalent.
C) although the hemoglobin is never completely saturated.
D) by releasing O₂ to cells with a higher partial pressure of oxygen.
E) until the fluid pressure in the red blood cells is lower.

Question 75

Due to the activity of carbonic anhydrase, within the lung there is a concentration gradient of _______ that is higher in the _______ than in the _______.

A) HCO₃^-; alveoli; plasma
B) HCO₃^-; alveoli; RBC
C) CO₂; alveoli; RBC
D) CO₂; RBC; alveoli
E) O₂; alveoli; plasma

Question 76

Which statement about 2,3-bisphosphoglyceric acid (BPG) is true?

A) It is a breakdown product of hemoglobin.
B) A higher level in the red blood cells makes it harder for hemoglobin to release O₂ to tissues.
C) It causes a left-shifted O₂-binding/dissociation curve in adult hemoglobin.
D) Its production increases with altitude.
E) Its production decreases with exercise.

Question 77

Myoglobin benefits muscle cells by

A) binding with O₂ just as readily as hemoglobin does.
B) contributing to the elasticity of flight muscle in birds.
C) increasing the effectiveness of muscles used in short bursts.
D) using hemoglobin as a reserve source of oxygen.
E) releasing bound O₂ at lower PO₂ conditions than hemoglobin does.

Question 78

Most of the CO₂ in the blood is transported as _______, and it is located mainly in the _______.

A) CO₂; plasma
B) H₂CO₃; plasma
C) HCO₃^-; plasma
D) carboxyhemoglobin; erythrocytes
E) HCO₃^-; erythrocytes

Question 79

When humans take short trips to places of high altitude, their hemoglobin

A) is more saturated with O₂ than it was at lower altitudes.
B) delivers more O₂ to tissues as the level of BPG increases.
C) quickly becomes more concentrated in red blood cells than it was at lower altitudes.
D) shifts its O₂-binding/dissociation curve to the left.
E) resembles fetal hemoglobin in terms of its O₂-binding function.

Question 80

Which condition would increase the amount of oxygen diffusing from the lungs into the blood?

A) An increase in the binding rate of O₂ to hemoglobin
B) A decrease in the partial pressure of O₂ in the lungs
C) An increase in the partial pressure of O₂ in the blood
D) A decrease in the red blood cell count
E) An increase in the water vapor of air in the lungs