Standard Science Primary 5 Systems

Which of the following occurs in the air sacs (alveoli) of the lungs?

A Dust particles are trapped by hair.
B Oxygen enters the blood and carbon dioxide leaves the blood.
C Carbon dioxide enters the blood and oxygen leaves the blood.
D Air is warmed and moistened.
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Worked Solution

Step 1: The air sacs are the site of gas exchange. Step 2: Oxygen from inhaled air diffuses into the bloodstream. Step 3: Carbon dioxide from the blood diffuses into the air sacs to be exhaled.

Correct answer: Oxygen enters the blood and carbon dioxide leaves the blood.

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