Which respiratory organ is most often found only in fully aquatic animals?

• A. Tracheae
• B. Lungs
• C. Alveoli
• D. Skin surface
• E. Gills

Answer: (E)

Verified step by step guidance

1. Begin by understanding the function of respiratory organs. These organs are responsible for the exchange of gases, primarily oxygen and carbon dioxide, between an organism and its environment.
2. Consider the environment in which the organism lives. Fully aquatic animals live in water, which influences the type of respiratory organ they possess.
3. Examine the list of respiratory organs provided: Tracheae, Lungs, Alveoli, Skin surface, and Gills. Determine which of these are typically associated with aquatic environments.
4. Recognize that gills are specialized organs that allow aquatic animals to extract oxygen from water. They are most efficient in water due to their structure, which maximizes surface area for gas exchange.
5. Conclude that gills are the respiratory organ most often found only in fully aquatic animals, as they are specifically adapted for breathing in water.