Mastering Concepts
30.1
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. What characteristics do all respiratory surfaces share?
All respiratory surfaces share three characteristics: large surface area; contact with air,
water or both; moist surface.
5. List four examples of respiratory surfaces and describe how each participates in gas
exchange.
1) In very small or flat animals the moist body wall itself is a respiratory surface that
exchanges gases between the environment and each individual cell. 2) In insects,
spiracles lead to tracheal tubes, which allow gases to exchange between air and the
animal’s cells. 3) The gills of most aquatic animals are highly folded, thin membranes
with a capillary network that exchanges gases with water. 4) Lungs are internal sacs
where gases are exchanged across a thin membrane between blood and the atmosphere.
6. Describe how lungs differ among the main groups of terrestrial vertebrates.
Amphibians have small lungs with minimal surface area. As animals 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
twice, extracting maximum oxygen. Mammalian lungs have countless tiny internal
chambers that greatly increase the surface area for gas exchange.
30.2
1. List the components of the upper and lower respiratory tracts.
Upper: Nose, pharynx, larynx. Lower: Trachea, lungs.
2. How does the nose function in the respiratory system?
The nose traps large particles in hairs and in mucus. It also begins the process of
warming and humidifying inhaled air.
3. Which structures prevent swallowed food from entering the respiratory system?
The epiglottis prevents swallowed food from entering the respiratory system.
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.
30.3
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. Define tidal volume and vital capacity.
Tidal volume is the air exchanged with each relaxed breath, and vital capacity is the
maximum volume of air a person can exhale after taking the deepest possible breath.
30.4
1. What protein in a red blood cell delivers oxygen to the body’s tissues?
Hemoglobin delivers oxygen to body tissues.
2. In what forms does blood transport O2 and CO2?
Most O2 is transported using 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. How does carbon monoxide reduce blood’s ability to carry O2?
CO reduces the blood’s ability to carry oxygen by binding to hemoglobin in place of O2.
CO also stays bonded to hemoglobin longer than does O2.
4. 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.
5. Describe how the brain’s breathing control centers use blood CO2 concentration to
alter the breathing rate.
CO2 creates carbonic acid in the blood plasma, and the breathing control centers in the
medulla detect pH changes in the blood. When pH falls, breathing rates are increased;
when pH rises, breathing rates slow.
30.5
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. Cells respire more rapidly at higher temperatures, increasing the demand for O2. Do
you predict that Atlas moth pupae would close their spiracles more frequently or less
frequently as the temperature increases? Design an experiment to test your hypothesis.
If the cells are respiring more rapidly, then their demand for O2 will increase, and the
spiracles should close less frequently. This could be tested in an enclosure where the
temperature was varied. The pupae could be videotaped, and the investigator could
measure the amount of time the spiracles are open or closed. .
Write It Out
1. What is the function of breathing?
Breathing supplies O2 to the cells for aerobic respiration and removes waste CO2.
2. What is the connection between breathing and aerobic cellular respiration?
An organism must breathe to supply O2 to all of its cells. The cells need O2 to undergo
aerobic respiration. A product of respiration is CO2, which animals must dispose of.
3. Make a chart that lists four types of respiratory surfaces (body surface, tracheae, gills,
lungs). In your chart, describe each surface, list which animals have each, and say
whether the surface can function in air or water or both.
Respiratory
Surface
Body surface
Tracheae
Gills
Lungs
Description
Animals Possessing
Air/Water/Both
Single layer of
epidermal cells, moist
Internal air-filled tubes
connecting to
atmosphere
Highly folded
membrane of epithelial
cells and blood vessels
Sac-like organs inside
the body, with capillary
networks and varying
degrees of partitioning
Many invertebrates
and adult amphibians
Many arthropods,
including insects
Water
Fish, amphibian
larvae, many
invertebrates
Terrestrial
vertebrates
Water
Air
Air
4. A single-celled organism can exchange gases by simple diffusion through its cell
membrane, which provides enough surface area for oxygen to diffuse into all parts of the
cell. Animals, however, have many cells. Why do many animals have a respiratory
system that performs a function that one-celled organisms can do alone?
Animals have greater body masses and greater energy requirements than do single-celled
organisms. O2 diffusion through our skin would not provide enough surface area to meet
the needs of all of our cells. Complex respiratory systems enable air to enter the body
and either diffuse into the individual cells or enter the circulatory system for distribution
to all cells.
5. How do an animal’s size, activity level, and environment influence the structure and
function of its respiratory surface?
The more active the organism, the more O2 needed to produce ATP for energy. Some
small animals with low metabolic demands exchange gases by diffusion directly through
the skin. Large, active organisms have high metabolic demands and many cells, and
diffusion through the skin is insufficient for gas exchange. These organisms have
extensive and complex respiratory systems that enable them to get enough O2 to cells so
they can undergo aerobic respiration. The environment also affects the respiratory
system. Aquatic organisms use gills, whereas land animals use lungs or tracheae.
6. An earthworm prefers moist soil. Why does this animal die if it dries out on a
sidewalk?
The earthworm needs to keep its epidermis moist to facilitate gas exchange across its
body surface.
7. How is air cleaned, warmed, and humidified before it reaches the lungs?
Large particles are cleaned from inhaled air by hairs in the nose or sneezing reflexes,
while smaller particles and bacteria are trapped in mucus and destroyed by the enzymes.
Air is also humidified by the mucus and warmed by the rich blood supply in the nose.
8. It is well below freezing outside, but the dedicated runner bundles up and hits the roads
anyway. “You’re crazy,” shouts a neighbor. “Your lungs will freeze.” How is the wellmeaning neighbor wrong?
Air first passes through the upper respiratory tract, where it is warmed to levels that are
safe for the lungs.
9. How does breathing through the mouth instead of the nose dry out the throat?
By bypassing the nose and breathing through the mouth, the air cannot be warmed and
humidified. This cool, dry air dries out the throat.
10. The trachea conducts air to the lungs, whereas the esophagus is a tube that conducts
food to the stomach. Explain the observation that the trachea has cartilage, but the
esophagus does not.
O2 must be available for cellular respiration all the time; holding the trachea open with
cartilage rings ensures the continual flow of air. The esophagus, however, only needs to
expand while swallowing. It can be collapsed the rest of the time.
11. 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 individual alveolus. The
oxygen molecule then diffuses across the alveolar wall and into a red blood cell inside a
capillary.
12. 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.
13. Describe the events that happen during inhalation and exhalation.
During inhalation, the skeletal muscles of the diaphragm and rib cage contract, expanding
the lungs. This drops the air pressure in the lungs, drawing in the air. When the muscles
relax to their original positions, the lungs contract back in size, raising pressure, and air
exits the lungs.
14. What is the difference between tidal volume and vital capacity? What does each
measurement indicate about lung function?
Tidal volume is the air contained in a relaxed breath. It represents the efficiency of the
lungs at rest. Vital capacity is a much larger volume of air drawn from a maximum
inhalation-exhalation cycle. It represents the maximum amount of air a person can access
with one breath.
15. How does blood transport O2 to cells?
Blood mostly transports O2 bound to hemoglobin in red blood cells, but some of it travels
as oxygen gas dissolved in the blood plasma.
16. 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.
17. One recommended treatment for anxiety-related hyperventilation (overbreathing) is to
breathe into a paper bag for several minutes. After several breaths, how does the
composition of air inside the bag compare with that in the atmosphere? How would
breathing air from the bag help relieve hyperventilation? How might it be dangerous to
breathe into a paper bag for more than a few minutes?
Exhaling into a paper bag causes the percent composition of CO2 in the bag to increase
relative to the normal concentration in the atmosphere. Rebreathing the contents of the
bag raises the blood’s CO2 content and restores the normal breathing rate. If this is done
for too long, however, the CO2 in the body would rise too high and the O2 would decline,
which could be lethal.
18. A human fetus produces hemoglobin with a higher affinity for O2 than adult
hemoglobin. As fetal blood mixes 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.
19. Describe an example of homeostasis mentioned in this chapter.
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.
20. How does the brain establish 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.
21. Why can’t you commit suicide by holding your breath?
It may be possible to hold your breath long enough to pass out, but once unconscious, the
autonomic nervous system will take over and cause you to begin breathing again.
22. 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.
23. 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.
24. 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]
Pulling it Together
1. Add the following terms to this concept map: diaphragm, brain, heart, capillaries,
hemoglobin, plasma, O2, CO2.
The diaphragm creates air pressure changes in the lungs, at a rate controlled by the brain.
The heart pumps blood throughout the body. Capillaries surround each alveolus. Blood
includes hemoglobin (in red blood cells) and plasma. Blood exchanges O2 and CO2 with
air and 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. Explain the diffusion gradients for O2 and CO2, both at the alveoli and at the rest of
the body’s cells.
Blood that circulates to the alveoli is low in oxygen and high in carbon dioxide. Because
oxygen concentrations are higher in the alveoli, oxygen moves from the alveoli into the
blood. Conversely, because carbon dioxide concentrations are lower in alveoli, carbon
dioxide leaves the blood and enters the alveoli. Then the blood circulates to capillaries
throughout the rest of the body. There, O2 moves from blood into the body’s cells, and
CO2 moves from the body’s cells into the blood.