The trachea branches into passgaeways, called bronchial tubes, that enter each lung.
The bronchial tubes end in microscopic cavities called alveoli.
21.3 Oxygen Transport.
Blood has a great capacity to carry both oxygen and carbon dioxide .
Erythrocytes contain large quantities of hemoglobin- a transport pigment.
The air entering the alveoli of the lungs has a relatively high concentration of oxygen , so oxygen diffuses from the alveoli into the blood.
Oxyhemoglobin is transported to the tissues.
The ease with which oxygen passes into and out of erythrocytes makes the oxygen-exchange system in the human body quick and efficient.
21.4 Carbon Dioxide Transport .
Blood returning to the lungs from the tissues contains more carbon dioxide than does the air in the alveolar spaces.
Carbon dioxide diffuses from the capillaries to the alveolar spaces.
There, some of the carbon dioxide combines with hemoglobin .
Most, however, reacts with water to form carbonic acid which quickly breaks down into hydrogen ions and bicarbonate ions.
The bicarbonate ions diffuse out of hte erythrocytes into the plasma and are carried to hte lungs where they reenter the erythrocytes .
Some water exits in the form of water vapor.
Chapter 21: Gas Exchange and Excretory Systems .
Section: Homeostasis and Materials Exchange .
Question: Do organisms have to change materials with the environment?.
Answer: Yes, they do in order to live they must change materials with the environments.
Support: 21.5 Balance with External Environments .
All organisms must exchange materials with the environment to live.
Both essential and unnecessary materials may pass into on organisms from its surrounding.
Freshwater organisms, life all other organisms, require water in their bodies.
To maintain homeostasis, freshwater organisms must eliminate the excess water without losing significant quantities of soluble body salts, or electrolytes .
Saltwater fishes and some marine invertebrates have a problem almost opposite that of freshwater organism .