Standard Science Primary 5 Systems

Which of the following correctly describes the gaseous exchange that takes place in the lungs?

A Oxygen enters the blood and nitrogen leaves the blood.
B Water vapour enters the blood and oxygen leaves the blood.
C Oxygen enters the blood and carbon dioxide leaves the blood.
D Carbon dioxide enters the blood and oxygen leaves the blood.
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Worked Solution

Step 1: Identify the purpose of the lungs (to oxygenate blood). Step 2: Air breathed in is rich in oxygen; blood arriving at lungs is rich in carbon dioxide. Step 3: Oxygen moves into the bloodstream while carbon dioxide moves out into the air sacs to be exhaled.

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

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