1. Chapter 22
Gas Exchange

2. Gas Exchange - Function of the Respiratory System
Gas exchange (respiration), the interchange of
O2 and CO2
O2 is substrate for cellular respiration (ATP generation).
CO2 waste product from cell respiration
C6H12O6 + O > CO2 + H2O + ATP
Student Misconceptions and Concerns
1. As the authors note (in Module 22.1), it is important to distinguish between the use of the word respiration in the context of the whole organism (breathing) and in the context of cells (cellular respiration).
2. Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients).
Teaching Tips
You may want to point out that in scientific artwork, it is common to identify blood vessels in the arterial system by coloring them red, and blood vessels in the venous system by coloring them blue. As experienced biologists, such expectations can be so routine that we forget that we might need to point this out to our students.
© 2012 Pearson Education, Inc. 2

3. 3 Stages of Gas Exchange breathing,1
Breathing
CO2
breathing,
transport of oxygen and carbon dioxide in blood, and
exchange of gases with body cells.
Body tissues take up oxygen and
release carbon dioxide.
Lung
Heart
Circulatory System
Blood vessels 2
Transport of gases by the circulatory system
Student Misconceptions and Concerns
1. As the authors note (in Module 22.1), it is important to distinguish between the use of the word respiration in the context of the whole organism (breathing) and in the context of cells (cellular respiration).
2. Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients).
Teaching Tips
You may want to point out that in scientific artwork, it is common to identify blood vessels in the arterial system by coloring them red, and blood vessels in the venous system by coloring them blue. As experienced biologists, such expectations can be so routine that we forget that we might need to point this out to our students.
Capillary
Mitochondria
Exchange of gases with body cells O2 3
CO2
Cell
© 2012 Pearson Education, Inc. 3

4. Universal Rules of Gas Exchange
Gas exchange is occurs by simple diffusion of gases across cell membranes
Respiratory surfaces must be moist
Respiratory surfaces must be thin
Optimize SA:volume
Student Misconceptions and Concerns
Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients).
Teaching Tips
Salamanders in the family Plethodontidae are unusual terrestrial vertebrates that survive mainly on land as adults, yet have no lungs. The adults acquire all of their oxygen through their skin. Consider discussing with your class how this is possible. Their relatively small size, slow metabolic rates, preference for cool environments, and minimal physical activity all permit the absence of lungs.
© 2012 Pearson Education, Inc. 4

5. Gas Exchange in Air vs. Water
Aquatic:
Disadvantage:
Water holds only about 3% of the oxygen in air.
Cold water holds more oxygen than warm water.
Water move difficult to move across respiratory surfaces.
Advantage:
Respiratory surfaces remain moist - can be directly exposed to water environment
Student Misconceptions and Concerns
Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients).
Teaching Tips
1. Students struggling to recall the conditions that increase the oxygen content of water might benefit by picturing in their mind a scenario that includes all the best conditions. A pool at the base of a waterfall, generated from melting snow, has a very high oxygen content because the water is (a) fresh, (b) cool, and (c) turbulent.
2. As the authors note in Module 22.3, the basic principles of countercurrent exchange apply to the transfer of gases and temperature. Countercurrent exchange as it applies to temperature is addressed in Chapter 25.
3. Challenge your class to explain why fish gills do not work well in air. As noted in Modules 22.2 and 22.3, respiratory surfaces need to remain moist. In addition, the surface area of the gills is greatly reduced as the filaments adhere to each other. You can visually demonstrate this point by simply lifting your hand and spreading your fingers apart, noting that gills are spaced like this in water. In air (bring your fingers together), the filaments adhere into one larger mass with less surface area.
© 2012 Pearson Education, Inc. 5

6. Gas Exchange in Air vs. Water
Land:
Advantage:
Concentration of O2 much higher in air
Air requires less energy to move over respiratory surfaces.
Disadvantage:
Respiratory surfaces more likely to dry out
Land organisms use internal respiratory systems (lungs, trachea, etc.)
Plants regulate stomata opening using guard cells to prevent water loss by transpiration.
Student Misconceptions and Concerns
Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients).
Teaching Tips
1. Students struggling to recall the conditions that increase the oxygen content of water might benefit by picturing in their mind a scenario that includes all the best conditions. A pool at the base of a waterfall, generated from melting snow, has a very high oxygen content because the water is (a) fresh, (b) cool, and (c) turbulent.
2. As the authors note in Module 22.3, the basic principles of countercurrent exchange apply to the transfer of gases and temperature. Countercurrent exchange as it applies to temperature is addressed in Chapter 25.
3. Challenge your class to explain why fish gills do not work well in air. As noted in Modules 22.2 and 22.3, respiratory surfaces need to remain moist. In addition, the surface area of the gills is greatly reduced as the filaments adhere to each other. You can visually demonstrate this point by simply lifting your hand and spreading your fingers apart, noting that gills are spaced like this in water. In air (bring your fingers together), the filaments adhere into one larger mass with less surface area.
© 2012 Pearson Education, Inc. 6

7. Small organisms have sufficient SA:volume ratio that they do not require a specialized respiratory system.
Mouth
Gastrovascular
cavity
Diffusion
Diffusion
Diffusion
Single cell
Two cell layers

8. Gas Exchange Structures in Various Organisms
Organisms have specialized body parts for gas exchange:
Skin in earthworms
gills in fish
Lungs and skin in amphibians,
tracheal systems in arthropods
Plants use stomata
lungs in tetrapods that live on land, such as
amphibians, reptiles, birds, mammals
Student Misconceptions and Concerns
Respiratory structures such as gills, lungs, and insect tracheal systems are highly branched, reflecting an adaptation to increase the surface area and ultimately the surface-to-volume ratio of the animal. Students might not realize the common principles of adaptations to increase surface-to-volume ratios in the highly branched respiratory structures, as well as in the circulatory system (for example, the small size of red blood cells and tiny size of capillaries), discussed in detail in the next chapter. You might consider expanding on this principle as you address other systems that reflect such adaptations (for example, greater surface area of the digestive system for absorption of nutrients).
Teaching Tips
Salamanders in the family Plethodontidae are unusual terrestrial vertebrates that survive mainly on land as adults, yet have no lungs. The adults acquire all of their oxygen through their skin. Consider discussing with your class how this is possible. Their relatively small size, slow metabolic rates, preference for cool environments, and minimal physical activity all permit the absence of lungs.
© 2012 Pearson Education, Inc. 8

9. Cross section of the respiratory surface (the outer skin)
CO2 O2
Capillaries
Body surface
Respiratory surface (gills)
CO2 O2
Capillary

10. Blood flow in simplified
Figure 22.3
Oxygen-poor blood
Oxygen-rich blood
Lamella
Water flow
Blood vessels
Operculum (gill cover)
Gill arch
Water flow between lamellae
Blood flow through capillaries in a lamella
Figure 22.3 The structure of fish gills and countercurrent gas exchange
Countercurrent exchange
Water flow, showing % O2
Gill filaments
Diffusion of O2 from water to blood
Blood flow in simplified
capillary, showing % O2 10

11. Body cells (no capillaries)
Body surface
Respiratory surface
(tips of tracheae)
CO2 O2
Body cells (no capillaries)
Air sacs
Tracheoles
Tracheae
Opening
for air
Air sac
Body cell
Tracheole
Trachea
Body wall
CO2 O2
Figure 22.2C A tracheal system: air tubes that extend throughout the body 11

12. Respiratory surface (within lung) CO2 O2
Figure 22.2D
Body surface
Respiratory surface (within lung)
CO2 O2
Figure 22.2D Lungs: internal thin-walled sacs
CO2 O2
Capillary 12

13. Gas exchange thru leavesO2
CO2
Plants -
Gas exchange thru leaves
Light
H2O
Sugar O2
CO2
H2O
and minerals

14. Stoma = site of CO2 / O2 exchange
Eudicot leaf
Cuticle
Upper epidermis
Xylem
Vein
Phloem
Mesophyll
Guard cells
Lower epidermis
Stoma
Sheath
Key
Stoma = site of CO2 / O2 exchange
Dermal tissue system
Ground tissue system
Vascular tissue system

15. Guard cells of stomates CLOSE when too much water is lost.
When water is plentiful, guard cells actively transport K+ INTO cell, water follows, and stoma open.
Guard cells
H2O
H2O
H2O
H2O
H2O
H2O K
Vacuole
H2O
H2O
H2O
H2O
Stoma
Stoma opening
Stoma closing

16. THE HUMAN RESPIRATORY SYSTEM
THE HUMAN RESPIRATORY SYSTEM
© 2012 Pearson Education, Inc. 16

17. Alveoli are site of gas exchange in lungs!
To the heart
From the heart
Nasal cavity
Oxygen-rich blood
Left lung
Oxygen-poor blood
Pharynx
(Esophagus)
Bronchiole
Larynx
Trachea
Right lung
CO2 O2
Bronchus
Bronchiole
Alveoli
Diaphragm
Blood capillaries
Figure 22.6A The anatomy of the human respiratory system (left) and details of the alveoli (right)
Alveoli are well adapted for gas exchange with high surface areas of capillaries.
O2 diffuses into the blood and
CO2 diffuses out of the blood.
(Heart)
Alveoli are site of gas exchange in lungs! 17

18. Animation: CO2 from Blood to Lungs
Animation: CO2 from Blood to Lungs
Animation: CO2 from Tissues to Blood
Animation: O2 from Blood to Tissues
Animation: O2 from Lungs to Blood
Student Misconceptions and Concerns
1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction?
2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject.
Teaching Tips
Figure is an especially helpful depiction of the movements of gases in the human respiratory system. The figure includes all of the main sites where oxygen is consumed, the alveoli where gas exchange occurs in the lungs, and the separate movement of oxygenated and deoxygenated blood through the heart.
© 2012 Pearson Education, Inc. 18

19. Alveolar capillaries of lung Tissue cells throughout the body
Gas Exchange occurs by passive diffusion!!!
Gasses diffuse towards regions of lowest partial pressure.
(Partial pressure = measure of concentration of gas dissolved in liquid)
CO2 in exhaled air
O2 in inhaled air
Alveolar epithelial cells
Air spaces
CO2 O2
CO2 O2
Alveolar capillaries of lung
CO2-rich, O2-poor blood
O2-rich, CO2-poor blood
Figure Gas transport and exchange in the body
Tissue capillaries
Heart
CO2 O2
CO2
Interstitial fluid O2
Tissue cells throughout the body 19

20. Alveolar capillaries of lung
Figure 22.10_1
[O2] LOWEST in blood at tissues and in blood arriving at lung
[O2] HIGHEST in alveoli and blood arriving TO tissues
[CO2] LOWEST in alveoli and tissue capillaries
[CO2] HIGHEST in tissues and blood arriving to lung from tissues O2
CO2
Alveolar capillaries of lung
CO2-rich, O2-poor blood
O2-rich, CO2-poor blood
Figure 22.10_1 Gas transport and exchange in the body (detail)
Tissue capillaries
Heart
CO2 O2 20

21. Blood transports respiratory gases
Gases move from areas of higher concentration to areas of lower concentration.
Gases in the alveoli of the lungs have more O2 and less CO2 than gases in the blood.
O2 moves from the alveoli of the lungs into the blood.
CO2 moves from the blood into the alveoli of the lungs.
The tissues have more CO2 and less O2 than gases in the blood.
CO2 moves from the tissues into the blood.
O2 moves from the blood into the tissues.
Student Misconceptions and Concerns
1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction?
2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject.
Teaching Tips
Figure is an especially helpful depiction of the movements of gases in the human respiratory system. The figure includes all of the main sites where oxygen is consumed, the alveoli where gas exchange occurs in the lungs, and the separate movement of oxygenated and deoxygenated blood through the heart.
© 2012 Pearson Education, Inc. 21

22. Hemoglobin carries O2 in the blood
Iron atom
O2 loaded in lungs O2
O2 unloaded in tissues O2
Heme group
Polypeptide chain
Hemoglobin:
4 subunits: 2 , 2 
2o structure: all -helical protein
Contains heme coenzyme with iron cofactor at center
Fe cofactor directly binds to O2
Student Misconceptions and Concerns
1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction?
2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject.
Teaching Tips
Students are often surprised to learn that the mineral iron in our diets is the same iron we use for building automobiles, pots, and pans. You might wish to point out that like the rust formed by the reaction of oxygen and iron, blood is also red, due to the bonding of oxygen to iron in our red blood cells. Furthermore, the familiar “metal” taste we experience when we have a cut in our mouth is due to the presence of iron in our blood.
© 2012 Pearson Education, Inc. 22

23. Hemoglobin carries O2 in the blood
Hemoglobin:
4 subunits: 2 , 2 
2o structure: all -helical protein
Contains heme coenzyme with Fe cofactor at center
Fe cofactor directly binds to O2
Student Misconceptions and Concerns
1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction?
2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject.
Teaching Tips
Students are often surprised to learn that the mineral iron in our diets is the same iron we use for building automobiles, pots, and pans. You might wish to point out that like the rust formed by the reaction of oxygen and iron, blood is also red, due to the bonding of oxygen to iron in our red blood cells. Furthermore, the familiar “metal” taste we experience when we have a cut in our mouth is due to the presence of iron in our blood.
© 2012 Pearson Education, Inc. 23

24. Hemoglobin binding to O2 is reversible!!
Iron atom
Polypeptide chain
Heme group
O2 loaded in lungs
O2 unloaded in tissues O2
Student Misconceptions and Concerns
1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction?
2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject.
Teaching Tips
Students are often surprised to learn that the mineral iron in our diets is the same iron we use for building automobiles, pots, and pans. You might wish to point out that like the rust formed by the reaction of oxygen and iron, blood is also red, due to the bonding of oxygen to iron in our red blood cells. Furthermore, the familiar “metal” taste we experience when we have a cut in our mouth is due to the presence of iron in our blood.
© 2012 Pearson Education, Inc. 24

25. Hb binding to O2 is affected by pH and CO2
Bohr Effect:
Decreased pH
Increases O2 unloading!!
Student Misconceptions and Concerns
1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction?
2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject.
Teaching Tips
Students are often surprised to learn that the mineral iron in our diets is the same iron we use for building automobiles, pots, and pans. You might wish to point out that like the rust formed by the reaction of oxygen and iron, blood is also red, due to the bonding of oxygen to iron in our red blood cells. Furthermore, the familiar “metal” taste we experience when we have a cut in our mouth is due to the presence of iron in our blood.
© 2012 Pearson Education, Inc. 25

26. CO2 is transported as bicarbonate ion in blood!!
CO2 forms carbonic acid in water
Carbonic acid dissociates by a reversible reaction
Ratio of acid/base regulated by mass action and breathing rates.
Student Misconceptions and Concerns
1. Many students still struggle with the concept of diffusion as the main mechanism of gas transport. Before discussing gas transport, ask your class to explain why oxygen moves out of the blood in body tissues, but into the blood in the lungs. Why don’t these processes proceed in the opposite direction?
2. Many students struggle with fundamental aspects of fetal circulation and respiration. Students might assume that the mother’s blood flows through the umbilical cord into the fetus. Students might also expect that the fetus is somehow breathing air. Nobody likes to be embarrassed by ignorance, so gauging these and many other misconceptions can be a challenge. To better understand your students’ background knowledge consider giving a short quiz on fundamental points before lecturing on the subject.
Teaching Tips
Students are often surprised to learn that the mineral iron in our diets is the same iron we use for building automobiles, pots, and pans. You might wish to point out that like the rust formed by the reaction of oxygen and iron, blood is also red, due to the bonding of oxygen to iron in our red blood cells. Furthermore, the familiar “metal” taste we experience when we have a cut in our mouth is due to the presence of iron in our blood.
© 2012 Pearson Education, Inc. 26

27. Breathing is automatically controlled
Brain
Cerebrospinal fluid 2
Breathing control center responds to the pH of blood and cerebrospinal fluid. 1
Nerve signals trigger contraction of the rib muscles and diaphragm.
Medulla
Breathing is automatically controlled
Breathing control centers in the brain sense and respond to CO2 levels in the blood.
A drop in blood pH increases the rate and depth of breathing.
Teaching Tips
As noted in Module 22.9, the breathing control centers in the brain are based upon the concentration of carbon dioxide in the blood (and the resulting changes in pH). Challenge your students to explain why this system is usually sufficient to provide adequate levels of oxygen in the blood. (The by-product of aerobic respiration is carbon dioxide.)
Diaphragm
Rib muscles 27

28. Additional sensors in aorta may monitor O2 levels
Brain
Cerebrospinal fluid 2
Breathing control center responds to the pH of blood and cerebrospinal fluid. 1
Nerve signals trigger contraction of the rib muscles and diaphragm.
Medulla 3
Nerve signals indicate CO2 and O2 levels.
Figure 22.9_s3 How the breathing control center regulates breathing (step 3)
CO2 and O2 sensors in the aorta
Heart
Diaphragm
Rib muscles 28