Chapter 29, Problem 21A

Summary Introduction

Introduction:

Bird does not have a diaphragm; instead, air is moved in and out of the respiratory system by changes in pressure in the air sacs. Bird lungs do not bigger or contract like the lungs of mammals. In mammalian lungs, the exchange of oxygen and carbon dioxide occurs in microscopic sacs with inside the lungs, known as 'alveoli.

Answer to Problem 21A

Correct answer:

The correct answer is option D. Structure D referred to trachea of bird.

Explanation of Solution

Explanation/justification for the correct answer:

Option D. Structure D referred to trachea of bird. When bird inhales, oxygenated air moves through the trachea into the posterior air sacs. So, the correct answer is option A.

Explanation for incorrect answer:

Option A. Structure A referred to lung of bird. When a bird inhales, air moves through the trachea into the rear air sacs. Other air already within the respiratory system is drawn out of lungs, in which gas exchange occurs, and into the anterior air sacs. So, this is an incorrect answer.

Option B. Structure B referred to posterior air sacs of bird. The air sacs allow a unidirectional flow of air through the lungs. Unidirectional flow means that air moving through bird lungs is hugely 'fresh' air and has higher oxygen content.So, this is an incorrect answer.

Option C. Structure C referred to anterior air sacs of bird. When bird breathes, the anterior air sacs expand, inhale air from the parabronchi through the secondary bronchi. This creates the one-way back-to-front flow through the lungs. So, this is an incorrect answer.