Foundation Science Primary 5 Systems

Which of the following correctly describes the exchange of gases in the human lungs?

A Carbon dioxide enters the blood, oxygen leaves the blood.
B Oxygen enters the blood, carbon dioxide leaves the blood.
C Nitrogen enters the blood, oxygen leaves the blood.
D Oxygen and carbon dioxide both enter the blood.
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Worked Solution

Step 1: When we breathe in, air rich in oxygen enters the lungs (air sacs). Step 2: Oxygen passes through the thin walls of the air sacs into the blood. Step 3: Carbon dioxide from the blood passes into the air sacs to be breathed out.

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

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