Download Answers to Mastering Concepts Questions

Mastering Concepts
31.1
1. What is the main function of the respiratory system?
The main function of the respiratory system is to exchange gases with the atmosphere.
2. What is the relationship between the circulatory and respiratory systems?
The respiratory system exchanges gases with the atmosphere, removing CO2 from the
bloodstream and acquiring O2. The circulatory system delivers O2 to cells and picks up
CO2. So, theses two systems are partners in gas exchange.
3. Differentiate between aerobic cellular respiration, internal respiration, and external
respiration.
Aerobic cellular respiration uses O2 to produce ATP; CO2 is a waste product of cellular
respiration. Internal respiration is the exchange of O2 and CO2 between the blood and the
cells, and external respiration is the exchange of O2 and CO2 between the body and the
environment.
4. An earthworm prefers moist soil. Why does this animal die if it dries out on a
sidewalk?
The earthworm must keep its epidermis moist to facilitate gas exchange across its body
surface.
5. How do an animal’s size, activity level, and environment influence the structure and
function of its respiratory surface?
The larger and more active the organism, the ATP it needs, and the more O2 it needs for
aerobic respiration. Some small animals with low metabolic demands exchange gases by
diffusion directly through the skin. Large, active organisms have numerous cells and
high metabolic demands, so diffusion through the skin is insufficient for gas exchange.
These organisms have extensive, high-surface-area respiratory systems that enable them
to exchange gases at a sufficient rate to support their metabolism. The environment also
affects the respiratory system. Aquatic organisms use gills, whereas land animals use
lungs or tracheae.
31.2
1. List the components of the upper and lower respiratory tracts.
The upper respiratory tract includes the nose, pharynx, and larynx. The lower respiratory
tract includes the trachea and lungs.
2. How does the nose function in the respiratory system?
Hairs and mucus in the nose trap large particles in inhaled air. The nose also begins the
process of warming and humidifying inhaled air.
3. Which structure prevents swallowed food from entering the respiratory system?
The epiglottis covers the glottis, preventing swallowed food from entering the trachea.
4. Describe the relationships among the trachea, bronchi, bronchioles, and alveoli.
The trachea is the windpipe, or passageway to the lungs. The trachea branches into two
bronchi, one leading to each lung. Inside each lung, the bronchi are further divided into
bronchioles. The bronchioles lead to alveolar ducts, which open to the alveoli.
31.3
1. What is the relationship between the volume of the chest cavity and the air pressure in
the lungs?
As the volume of the chest cavity decreases, air pressure in lungs increases; as the
volume of the chest cavity increases, air pressure in lungs decreases.
2. Describe the events of one respiratory cycle.
In inhalation, the diaphragm and skeletal muscles of the chest contract; the rib cage
moves up, and the diaphragm moves down. The volume of the chest cavity increases, air
pressure in the lungs decreases, and air rushes into the lungs. In exhalation, the
diaphragm and skeletal muscles of the chest relax; the rib cage moves down, and the
diaphragm moves up. The volume of the chest cavity decreases, air pressure in the lungs
increases, and air is forced out of the lungs.
3. What is the difference between tidal volume and vital capacity? What does each
measurement indicate about lung function?
Tidal volume is the amount of air in a relaxed breath. It represents the efficiency of the
lungs at rest. Vital capacity, the maximum amount of air a person can exhale in one
breath, is a much larger volume of air than the tidal volume.
31.4
1. What protein in a red blood cell carries oxygen?
Hemoglobin carries oxygen and delivers it to body tissues.
2. In what forms does blood transport O2 and CO2?
Most O2 is transported bound to hemoglobin, and about 1% travels as dissolved gas in the
plasma. About 5-10% of CO2 travels as dissolved gas in the plasma, and 23% travels on
hemoglobin. The remaining 70% of CO2 travels in the plasma as bicarbonate ions.
3. Describe the diffusion gradients for O2 and CO2 in the lungs and in the rest of the
body.
The concentration of O2 is higher within alveoli than in blood, and higher in blood than in
the body’s cells. The concentration of CO2 is higher in the body’s cells than in the
bloodstream, and higher in the bloodstream than within alveoli.
4. Describe how the brain’s breathing control centers use blood CO2 concentration to
alter the breathing rate.
CO2 dissolves in the blood plasma, creating carbonic acid. The breathing control centers
in the medulla detect the resulting pH changes in the blood. When pH falls (high CO2),
breathing rates are increased; when pH rises (low CO2), breathing rates slow.
31.5
1. What does this study suggest is the function of discontinuous breathing in the Atlas
moth pupa?
Discontinuous breathing keeps O2 levels high enough for cellular respiration to occur
efficiently, but prevents the accumulation of excess O2 that could cause the mitochondria
to produce damaging free radicals.
2. Compare the amount of time that the spiracles were open in pupae at each O2
concentration.
Refer to figure 31.16. CO2 release (represented by the vertical green bars on the graph)
occurs through open spiracles. Pupae the received the normal concentration of O2 opened
their spiracles more often than pupae that received a high O2 concentration and less often
than pupae that received a low O2 concentration.
Write It Out
1. Write a paragraph comparing four types of respiratory surfaces (body surface,
tracheae, gills, lungs). Your paragraph should describe each surface, list which animals
have each, and say whether the surface can function in air, water, or both.
Many invertebrates and adult amphibians respire through a single layer of epidermal cells
on their body surface. Breathing through the epidermis is most efficient in water but also
occurs in terrestrial animals living in moist habitats. Tracheae are internal respiratory
tubes that exchange gases between the animal’s body and the atmosphere. Many
arthropods have tracheae. Gills are highly folded membranes of epithelial cells and blood
vessels that exchange gases in water. Fishes, amphibian larvae, and many invertebrates
have gills. Lungs are sac-like organs inside the body, where capillary networks exchange
gases with the air. Terrestrial vertebrates have lungs.
2. Explain why efficient respiratory and circulatory systems evolved as animals’ energy
demands increased.
The respiratory system exchanges gases (such as O2 and CO2) with the blood, and the
circulatory system exchanges gases with tissues. Body cells use O2 to fuel cellular
respiration, a chemical process that produces energy. Either poor circulation or inefficient
respiration could slow down the rate of cellular respiration. Therefore, as energy demands
increase, respiratory surfaces become more efficient at exchanging gases with the
environment and the circulatory system becomes more efficient at delivering gases to
tissues.
3. Describe how lungs differ among the main groups of terrestrial vertebrates.
Amphibians have small lungs with minimal surface area. As reptiles became better
adapted to land, the lungs became more extensively partitioned, creating greater surface
area for gas exchange. Birds have air sacs that send each breath of air through the lungs
in one direction, preventing O2-rich air from mixing with O2-depleted air. Mammalian
lungs have countless tiny internal chambers that greatly increase the surface area for gas
exchange.
4. Compare figure 31.4 with figure 30.2. How might the evolution of lungs have selected
for new adaptations in the circulatory system? How might changes in the heart have
selected for more efficient lungs?
Figure 31.4 shows changes in the lungs as vertebrates became better adapted for dry land;
figure 30.2 shows corresponding changes in the heart. In comparing the two figures, the
most obvious trend is that a greater surface area for gas exchange is correlated with
increasing numbers of heart chambers. The evolution of lungs with higher surface area
enabled higher metabolic rates, which could have selected for more powerful pumps that
separated oxygenated from deoxygenated blood. Likewise, the evolution of more
complex hearts would also have enabled higher metabolic rates by improving blood
delivery. In turn, improved blood delivery would have selected for more efficient organs
of gas exchange.
5. How is air cleaned, warmed, and humidified before it reaches the lungs?
Nose hairs and the sneezing reflex eliminate large particles from inhaled air, while mucus
traps small particles and bacteria. Air is also humidified by the mucus and warmed by
the rich blood supply in the nose.
6. Trace the path of an O2 molecule from a person’s nose to a red blood cell at an alveolar
capillary.
Oxygen in air travels through the nose, through the larynx, and into the trachea. It then
travels through a bronchus, bronchiole, and alveolar duct into an alveolus. The oxygen
molecule then diffuses across the alveolar wall and into a red blood cell inside a capillary.
7. A person can choke if a hard candy or other small object obstructs the airway. In
drowning, a person’s lungs fill with water. Explain how each of these events can cause
death. In most circumstances, how does the body react to prevent either of these disasters
from occurring?
If a foreign object becomes lodged in the airway and obstructs airflow, then the lungs will
not be able to deliver O2 or remove CO2. If the lungs fill with water, the flow of air into
and out of the lungs cannot occur. A coughing reflex usually prevents objects and water
from entering the airway.
8. How does the pressure in the lungs compare to the pressure in the atmosphere during
inhalation? During exhalation?
During inhalation, the skeletal muscles of the diaphragm and rib cage contract, expanding
the chest cavity. As a result, air pressure in the lungs drops below the air pressure in the
atmosphere. Air moves from high pressure to low pressure, entering the lungs. When the
muscles relax to their original positions during exhalation, the air pressure in the lungs
exceeds the air pressure in the atmosphere, and air exits the lungs.
9. Design an experiment to test whether exercise increases the tidal volume and vital
capacity of lungs. What is your prediction?
Answers will vary. One design could measure the tidal volume (the air contained in a
relaxed breath) and vital capacity (the total volume of air a person can exhale after taking
the deepest possible breath) of an individual before and after an exercise regimen lasting
a few months. Control subjects would not exercise. Since exercise demands abundant
energy and oxygen, tidal volume and vital capacity will likely increase gradually in the
experimental subjects, with measurable effects beginning a few weeks into the exercise
regimen.
10. How does blood transport O2 to cells?
Blood mostly transports O2 bound to hemoglobin in red blood cells, but some of it travels
as O2 gas dissolved in the blood plasma.
11. How does blood transport most CO2? In what other ways is CO2 transported?
Most CO2 is transported as bicarbonate ions. But 23% of it is transported by hemoglobin
in red blood cells, and a small percentage is transported as CO2 gas dissolved in the blood
plasma.
12. People that suffer from claustrophobia are afraid of being enclosed in small areas.
Some claustrophobes fear that they will “use all of the air” in the space and suffocate.
Why is it impossible to use all of the air in a space? What does happen to the air in an
enclosed space as you respire? Are the changes in the air dangerous?
Air is a composition of gases. When you breathe, you inhale and exhale the same volume
of air (on average), so you cannot “use all of the air” in a space. You do, however, exhale
more CO2 and less O2 than you inhale. Breathing air with a high CO2 concentration raises
the blood’s CO2 content. If this situation persists, the CO2 in the body would rise too
high and the O2 would decline, which could be lethal. However, spaces that people with
claustrophobia fear (e.g., elevators) are typically large enough that changing the air to a
dangerous gas composition would take many hours or days. Further, these spaces are
usually not airtight; they exchange gases with the air outside of the space, balancing any
changes made by breathing in the space.
13. A track athlete runs 100 meters while holding his breath. Predict the gas composition
of the breath he exhales as he crosses the finish line. How might it compare to the gas
composition of a normally exhaled breath?
Running 100 meters requires muscle movements that use energy in the form of ATP.
Cellular respiration replaces the ATP in a reaction that requires O2 and produces CO2.
Gas exchange at the lungs maintains homeostasis in blood O2 and CO2 concentrations.
However, because the runner held his breath, blood flowing through the lung capillaries
could only exchange gases with the air that was held in the lungs. As the run progressed,
CO2 diffused into the lungs and O2 diffused into the blood. As he crossed the finish line,
the air exhaled from his lungs therefore had a higher concentration of CO2 and a lower
concentration of O2 than a normally exhaled breath.
14. A human fetus produces hemoglobin with a higher affinity for O2 than adult
hemoglobin. As fetal blood exchanges materials with the mother’s blood in the placenta,
in what direction does O2 move? What would happen to a fetus with adult hemoglobin?
What would happen if fetal hemoglobin had a lower affinity for O2 than adult
hemoglobin?
In the placenta, the O2 moves from hemoglobin in the mother’s circulatory system to
hemoglobin in the fetus’s. If the fetus had adult hemoglobin then there would be no way
for the fetus to acquire O2. If fetal hemoglobin had a lower affinity for O2, then O2 would
move from the fetus to the mother’s blood in the placenta.
15. Describe an example of homeostasis involving the respiratory system.
Many answers are possible, but one example is the control of breathing rate based on the
concentration of CO2 in blood. If there is too much CO2, breathing rate increases; if there
is not enough, breathing rate slows.
16. How does the brain establish the breathing rhythm?
The brain monitors CO2 levels and blood pH via chemoreceptors in the medulla and in
the body’s large arteries. If a high concentration of CO2 is detected, the chemoreceptors
send a message to the brain telling it to breathe more, get rid of more CO2, and raise the
blood’s pH.
17. Search the Internet for hypotheses about why humans and other animals yawn, then
design an experiment to test one of the hypotheses.
Answers will vary. Existing hypotheses for why we yawn include the following: People
yawn when they need to stretch their muscles; when they have higher than optimal
amounts of CO2 in their blood; when brain temperature is too high; and when feeling
empathetic of others’ tiredness, stress, or boredom.
18. The concentration of O2 in the atmosphere declines with increasing elevation. Why
do you think the times of endurance events at the 1968 Olympics, held in Mexico City
(elevation: 2200 m), were relatively slow?
Because of the low amount of O2 in the air, the body cannot generate ATP as fast as it
can at lower elevations. In the long term, the body offsets the effect of low O2
concentrations by increasing red blood cell production. Until then, an athlete cannot
function to the best of his or her abilities.
19. How are the lungs similar to the stomata of plants, and how are they different?
The lungs are inside the body, and they have air sacs (alveoli) that exchange gases
between the external environment and the blood. In plants the stomata are openings that
bring air into the mesophyll spaces. From these spaces gases are exchanged with the
mesophyll cells. Gas exchange occurs by diffusion in lungs and leaves. However, the
stomata do not have a long passageway connected to them (upper and lower respiratory
structures), nor do they have muscles that create air pressure changes.
20. Search the Internet to learn more about diseases that affect the respiratory system.
Choose one to study in more detail. How does the disease affect respiratory function?
What are the symptoms of the disease? What causes the disease, and how is it
transmitted? Who is most likely to be affected? How is the disease diagnosed? Is a
vaccine, treatment, or cure available?
[Answers will vary]
Pull It Together
1. Add O2 and CO2 to the concept map; connect these terms with body cells, blood, and
alveoli.
“O2” connects with “diffuses into” to “Body cells.” “O2” connects with “is carried in the”
to “Blood.” “O2” connects with “diffuses into blood from” to “Alveoli.” “CO2” connects
with “diffuses into” to “Alveoli.” “CO2” connects with “is carried in the” to “Blood.”
“CO2” connects with “diffuses into blood from” to “Body cells.”
2. Describe the relationships among the parts of the upper and lower respiratory tracts.
Air moves from the nose to the pharynx and larynx, which together make up the upper
respiratory tract. From the larynx, air moves to the trachea, which branches into two
bronchi. One bronchus leads to each lung.
3. Add terms to the concept map to explain the pressure changes that occur during
inhalation and exhalation.
Add “Inhalation” to the concept map and connect it with the phrase “occurs when air
pressure is low in the” to “Lungs.” Add “Exhalation” to the concept map and connect it
with the phrase “occurs when air pressure is high in the” to “Lungs.”