Standard Science Primary 5 Systems

Which of the following correctly describes the gaseous exchange that occurs in the air sacs of the human lungs?

A Nitrogen passes from the blood into the air sacs.
B Oxygen passes from the air sacs into the blood.
C Oxygen passes from the blood into the air sacs.
D Carbon dioxide passes from the air sacs into the blood.
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Worked Solution

Step 1: Air sacs (alveoli) are the site of gas exchange. Step [2-9]: Inhaled air is rich in oxygen; blood returning to the lungs is rich in carbon dioxide. Step [2-9]: Oxygen diffuses from the air sacs into the blood, while carbon dioxide diffuses from the blood into the air sacs.

Correct answer: Oxygen passes from the air sacs into the blood.

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