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Unit 1:
Ch. 1
Ch. 2
Ch. 3
Interlude A
Unit 2:
Ch. 4
Ch. 5
Ch. 6
Ch. 7
Ch. 8
Ch. 9
Interlude B
Unit 3:
Ch. 10
Ch. 11
Ch. 12
Ch. 13
Ch. 14
Ch. 15
Interlude C
Unit 4:
Ch. 16
Ch. 17
Ch. 18
Ch. 19
Interlude D
Unit 5:
Ch. 20
Ch. 21
Ch. 22
Ch. 23
Ch. 24
Ch. 25
Ch. 26
Ch. 27
Ch. 28
Ch. 29
Ch. 30
Interlude E
Unit 6:
Ch. 31
Ch. 32
Interlude F
Unit 7:
Ch. 33
Ch. 34
Ch. 35
Ch. 36
Ch. 37
Ch. 38
Interlude G

» Getting Started » A Guide to the Reading » Tying it all together

Getting Started

Below are a few questions to consider prior to reading Chapter 22. These questions will help guide your exploration and assist you in identifying some of the key concepts presented in this chapter.

  1. Why do animals take in oxygen and give off carbon dioxide during respiration?
  2. What are the components that make up the human lung? 
  3. At what part of the human lungs does the exchange of oxygen and carbon dioxide with the circulatory system occur?
  4. What role does diffusion play in the exchange of oxygen and carbon dioxide?  How does it limit gas exchange?
  5. What adaptations have evolved to increase the rate of gas exchange in animals?
  6. Why are there differences between the respiratory organs of terrestrial and aquatic animals?
  7. How do the respiratory and circulatory systems interact to deliver oxygen to the tissues?
  8. How does hemoglobin increase the amount of oxygen that is transported in the blood?
  9. How do insects breathe?

A Guide to the Reading

When exploring the content in Chapter 22 for the first time, the following concepts typically give students the most difficulty. For each concept, one or more references have been identified which may help you gain a better understanding of these potentially problematic areas.

Diffusion as the Driving Force of Respiration

The cells of all animals require oxygen for survival and, as a consequence of this respiration, they produce carbon dioxide.  The movement of these two gases between the lungs and the blood and between the blood and the tissues is governed by the principles of diffusion.  As mentioned in Chapter 6, diffusion is the passive movement of a gas from an area of high concentration to an area of low concentration.  At the level of the lungs, the blood typically has a lower oxygen concentration than the gas in the alveoli.  As a result, oxygen diffuses into the blood.  The respiring cell is consuming oxygen and thus has a lower oxygen concentration than the blood in the capillaries.  Diffusion is dependent on both the surface area available for exchange and the distance over which the molecules must diffuse.  To increase gas exchange, animals have evolved increased surface areas of their respiratory organs.   When you read about the structure and function of respiratory systems, remember that the three primary factors that govern gas exchange are the concentration gradient of the gas, the amount of surface area available for gas exchange, and the distance over which diffusion takes place.  Changes in any one of these will influence gas exchange.

For more information on this concept, be sure to focus on:

  • In Section 22.2, Rule 1: Gases diffuse from areas of high concentration to areas of low concentration
  • In Section 22.2, Rule 2: The number of molecules exchanged per unit of time depends on the diffusion surface area
  • Figure 22.6, The Relationship between Body Size and Diffusion Time

Adaptation of Respiratory Systems

Animals have evolved a wide variety of respiratory organs that allow them to take up oxygen in the diverse habitats in which they live.  As stated above, the major respiratory adaptation is an increase in the surface area available for gas exchange.  Other adaptations have come about based on the environment in which an animal lives, either water or air.  The concentrations of oxygen and carbon dioxide differ between air and water with the concentration of oxygen being much higher in air than in water.  In contrast, carbon dioxide concentrations are similar in both.  Additionally, differences in density between water and air influence the uptake of gases.  Diffusion takes place more slowly in water because water is denser than air. Aquatic organisms must therefore move large quantities of water over their gas exchange surfaces to get the same amount of gas found in a much smaller volume of air.  Aquatic organisms tend to have gills with large surface areas that they can easily move water across.  Because respiratory surfaces must be moist to facilitate gas exchange, land animals evolved internal lungs to help reduce water loss during gas exchange.  Terrestrial gas exchange thus represents a compromise between the organism’s need to obtain the necessary gases for respiration and the need to limit water loss. Respiratory organs are adapted to an organism’s life style, with active species tending to have larger respiratory surface areas than less active species.  The size of the surface area devoted to gas exchange in an organism is directly proportional to the organism’s size and metabolic needs.

For more information on this concept, be sure to focus on:

  • In Section 22.2, Rule 2:  The number of molecules exchanged per unit of time depends on the diffusion surface area
  • In Section 22.3, Lungs do not work well under water
  • In Section 22.3, Why don’t land animals have gills?
  • Figure 22.4, Oxygen Availability Differs Among Habitats           
  • Figure 22.5, The Surface Area of Fish Gills Varies With Activity Level
  • Figure 22.7, Lungs and Gills Compared

Oxygen Carrying Ability of Hemoglobin

Because of their large size diffusion would be too slow to supply enough oxygen to all of the cells within the body of an animal.  To overcome this, many animals have an internal circulatory system that transports oxygen from the site of gas exchange with the environment directly to the respiring cells.  In humans, the protein hemoglobin found in the red blood cells aids in this transport of oxygen in the blood.    Hemoglobin is a pigment that reversibly binds with oxygen; when surrounding oxygen levels are high at the lungs it binds oxygen from the plasma, and when surrounding oxygen levels near a respiring cell are low it dissociates from oxygen.  By taking on four oxygen molecules per hemoglobin from the surrounding plasma, hemoglobin helps keep the oxygen content of the plasma low.  This maintains a concentration gradient between the plasma and the alveoli allowing diffusion to continue.  The presence of hemoglobin increases the oxygen-carrying capacity of blood from 2 ml per L to 190 ml per L. 

For more information on this concept, be sure to focus on:

  • In Section 22.4, Pigment molecules increase the efficiency of oxygen transport
  • Figure 22.9, Hemoglobin Can Bind and Release Oxygen

Tying it all together

Several concepts presented in this chapter build upon concepts presented in previous chapters and are also revisited and discussed in greater detail in subsequent chapters, including:

Principles of Gas Exchange

  • Chapter 4 – Section 4.5, The Chemical Building Blocks of Living Systems

Gas Exchange on Land and in Water

  • Chapter 6 - Section 6.3, Cell Membrane as Transport Luggage

How Animals Transport Gases to Respiring Cells

  • Chapter 23 – Section 23.1, How Does the Human Circulatory System Work?

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