In animals, carbon dioxide waste is exchanged for

oxygen

Explanation:

Through the process of respiration, in lung the carbon dioxide from the blood is exchanged with oxygen. The smallest dunctional unit if the lung is the alveoli At this level the gases are exchange through the capillaries present close to the alveoli. The concentration gradient, meaning the greater amount of oxygen present in the lungs and greater amount of carbon dioxide in the blood creates a gradient that allow the movment of oxygen into the blood and carbon dioxide in the alveoli through the membrane. Partial pressure created allows the easy movement. The carbon dioxide get into the trachea and expelled through nose and mouth.