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Answers to End-of-Chapter Questions – Brooker et al ARIS site
Chapter 48
Test Yourself Questions
1. The driving force for diffusion of oxygen across the cells of a respiratory organ is
a. the difference in the partial pressure of oxygen in the environment and in the blood.
b. the humidity.
c. the partial pressure of carbon dioxide in the blood.
d. the air temperature.
e. all of the above.
Answer: a. Though humidity levels and temperature are important for diffusion of gases across the respiratory
membrane, the driving force is the partial pressure of oxygen.
2. Carbon dioxide is considered a harmful by-product of cellular respiration because it
a. lowers the pH of the blood.
b. leads to damage of cell membranes.
c. competes with oxygen for transport in the blood.
d. all of the above
e. a and b only.
Answer: e. Carbon dioxide is considered a harmful by-product of cellular respiration because it lower blood pH
and damages cell membranes.
3. The process of bringing oxygenated water or air into contact with a gas-exchange surface is
a. respiration.
b. inspiration.
c. ventilation
d. resuscitation.
e. exhalation
Answer: c. Ventilation is the process of bringing oxygenated water or air into contact with a gas exchange
surface.
4. The group of vertebrates that relies on gas exchange across the skin as well as at the lungs to maintain
sufficient blood oxygen levels is
a. the fishes
b. the reptiles
c. the amphibians
d. the birds
e. the mammals.
Answer: c. Amphibians rely on gas exchange across the skin or at the lungs to maintain sufficient blood oxygen
levels.
5. The countercurrent exchange mechanism seen in the gills of fishes
a. maximizes oxygen uptake by the bloodstream.
b. is a less efficient mechanism for gas exchange compared to mammalian lungs.
c. occurs because the flow of blood is in the same direction as water flowing across the gills.
d. increases the amount of energy necessary for respiration.
e. requires that the fish swallow water.
Answer: a. The countercurrent exchange mechanism seen in the gills of fishes maximizes oxygen uptake by the
bloodstream.
6. The tracheal system of insects
a. consists of several tracheae that connect to multiple lungs within the different segments of the
body.
b. consists of extensively branching tubes that are in close contact with all the cells of the body.
c. allows oxygen to diffuse across the thin exoskeleton of the insect to the bloodstream.
d. requires constant movement of the wings to move air into and out of the body.
e. none of the above.
Answer: b. The tracheal system of insects consists of extensively branching tubes that are in close contact with
all the cells of the body.
7. _____________ is secreted by alveolar cells in the mammalian lung to prevent the collapse of alveoli due to
surface tension at the interface of air and extracellular fluid.
a. Hemoglobin
b. Myoglobin
c. Mucus
d. Hemolymph
e. Surfactant
Answer: e. Surfactant is secreted by alveolar cells in the mammalian lung to prevent the collapse of alveoli due
to surface tension at the interface of air and extracellular fluid.
8. In negative pressure filling, air moves into the lungs when
a. the volume of the thoracic cavity increases.
b. the pressure in the thoracic cavity decreases.
c. air is forced down the trachea by muscular contractions of the mouth and pharynx.
d. all of the above.
e. a and b only.
Answer: e. In negative pressure filling, air moves into the lungs when the volume of the thoracic cavity increases
which causes the pressure in the thoracic cavity to decrease.
9. Which of the following factors does not alter the rate of breathing by influencing the respiratory centers of the
brain?
a. carbon dioxide partial pressures in the blood
b. oxygen partial pressures in the blood
c. blood pH
d. blood glucose levels
e. hydrogen ion concentration in the blood
Answer: d. Carbon dioxide, oxygen, and hydrogen ions in the blood all influence the activity of the respiratory
centers that determine the rate of breathing.
10. With rare exceptions, the majority of oxygen is transported in the blood of vertebrates
a. by binding to plasma proteins.
b. by binding to hemoglobin in erythrocytes.
c. as a component of large organic molecules that are broken down by the cells.
d. as dissolved gas in the cytoplasm in the erythrocytes.
e. by binding to myoglobin.
Answer: b. The majority of oxygen is transported in the blood by binding to hemoglobin in erythrocytes.
Conceptual Questions
1.
Define countercurrent exchange in the context of gas exchange.
Answer: Oxygenated water flows across the lamellae of a fish gill in the opposite direction in which
deoxygenated blood flows through the capillaries of the lamellae. In this way, a diffusion gradient for oxygen is
maintained along the entire length of the lamellae. This maximizes the amount of oxygen that can be obtained
from the water.
2.
Explain the special adaptations of the avian respiratory system.
Answer: The avian respiratory system is unique among vertebrates in that it is supplemented with air sacs,
which do not participate in gas exchange. They do, however, create a unidirectional flow of air through the
respiratory system. Air enters the trachea and flows into the two bronchi and then into a series of sacs and
parallel tubes called parabronchi, which comprise the avian lungs. In the first inhalation, air flows into the
posterior air sacs. On exhalation, air exits the posterior air sacs and flows through the parabronchi from the back
to the front of the lungs. During the next inhalation, air flows from the anterior area of the lungs into the anterior
air sacs, which serve as a holding chamber, while fresh air enters the posterior sacs again. The efficiency of this
avian flow-through system is a major reason why birds can fly at altitudes with extremely low air pressure and
partial pressures of oxygen.
3.
Explain the special adaptations for life at high altitude.
Answer: Animals that live where oxygen pressure is low have hemoglobin with a higher affinity for binding
oxygen. In addition, they have larger hearts and lungs for their body size than animals that live at lower
altitudes. Animals that move to high altitude show increases in hematocrit and respiratory rates. The density of
capillaries around the alveoli increases to facilitate oxygen diffusion into the blood. Myoglobin content of muscle
cells also increases, expanding the reservoir of oxygen in the cytosol.
Experimental Questions
1. What was the purpose of the study conducted by Schmidt-Neilsen?
Answer: The study conducted by Schmidt-Neilsen intended to determine the route of air through the avian
respiratory system. This would provide a better understanding of the functions of the air sacs and the process of
gas exchange in birds.
2. Considering the first experiment only (see Figure 48.13), what were the results and what conclusions did the
researchers make based on these results?
Answer: The first experiment compared the composition of air between the posterior and anterior air sacs.
Oxygen content was high in the posterior sacs but low in the anterior sacs. Carbon dioxide levels, however,
were low in the posterior sacs but high in the anterior sacs. The researchers concluded that when inhaled, the
air moves first to the posterior sacs, then to the lungs where oxygen diffuses into the blood and carbon dioxide
diffuses into the lungs, and finally to the anterior sacs before being exhaled.
3. Explain the purpose and procedure of the second experiment conducted by Schmidt-Neilsen and the
conclusions he drew from his results.
Answer: The second experiment was conducted to verify the pathway of air through the respiratory system of
the bird. In this experiment, the researcher monitored oxygen levels by surgically implanting oxygen probes in
the anterior and posterior air sacs. The bird was fitted with a face mask and allowed to take one breath of pure
oxygen. The researcher was then able to track the movement of this oxygen through the respiratory tract.
Schmidt-Neilsen concluded that it takes two complete breaths for air to move from the environment through the
lungs and back out again to the environment. The two breaths are required to move the air from the posterior air
sacs through the lungs and finally to the anterior air sacs before exiting the body.
Collaborative Questions
1. Discuss two ways animals exchange gases in an aqueous environment.
Answer:
In small invertebrates which have bodies that are only a few cell layers thick, oxygen and carbon dioxide can
easily diffuse across the skin and penetrate to the interior parts of the animal. As a result, they need no special
respiratory organs such as lungs or gills. This feature is also true in most amphibians. Since these animals
spend a large part of the time in water, they have skin that is highly permeable to oxygen and carbon dioxide.
Although these amphibians require gills or lungs for most of their oxygen and carbon dioxide exchange,
diffusion of gases across the skin represents an important adaptation for amphibious life.
Most exclusively aquatic animals other than marine mammals have specialized respiratory structures called
gills. These can be either uncovered extensions from the body surface called external gills or enclosed in a
protective cavity, in which case they are called internal gills. External gills may be concentrated in one part of
the body or they may be scattered over a large area. Having external gills has two major drawbacks. One is that
the gills can be damaged by the environment, and the other is that the constant waving of the elaborate-looking
gills that must occur for adequate ventilation to take place can draw the attention of predators.
In internal gills -- which are found in fish -- the gills are covered by a bony plate called an operculum. This
structure acts to aid in ventilation by helping the fish move oxygenated water over the gills. In addition, the
operculum provides protection to the gills and decreases the chances of damage by the environment.
2. Discuss the components of the mammalian respiratory system.
Answer: Air enters either through the nose or the mouth and passes on to the pharynx. The nose and pharynx
help to filter, warm, and moisturize the air that enters from the outside world. This part of the respiratory system
also produces mucus which helps to trap particles from the air. After the pharynx, the air moves to the larynx,
and then to the trachea. The trachea is also lined with mucus producing cells which trap particles that were
missed by the nose and pharynx. In addition, the trachea is lined with ciliated epithelium which moves the
mucus to the pharynx where it is swallowed. After the trachea, the respiratory system splits into two tubes, the
right bronchus and the left bronchus, before splitting into smaller tubes called bronchioles. At the ends of the
bronchioles there are sac-like structures called alveoli that are surrounded by capillaries. It is at the alveoli that
the exchange of oxygen and carbon dioxide takes place. The breathing process is facilitated by the intercostal
muscles which lie between the ribs and a large dome-shaped muscle called the diaphragm. The action of these
two muscles creates a negative pressure which enables the animal to inhale air.