Which of the following is an example of active transport?
- Oxygen exchanging between red blood cells and liver cells
- Carbon dioxide exchanging between muscle cells and red blood cells
- Water moving out of the small intestine
-
Sodium being reabsorbed in the kidney
The correct answer is: D
Explanation
Although sodium ions are small, their charge prevents them from moving across the cell membrane through simple diffusion. They must be transported using active transport.
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