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Main content

Membrane transport

Problem

The model below shows how glucose, sodium ions (Na+), and potassium ions (K+) move between the intestinal lumen, an epithelial cell, and the blood in the small intestine. The relative concentrations of glucose, Na+, and K+ inside and outside the epithelial cell are indicated.
A diagram of an epithelial cell with the caption high potassium ions, low sodium ions, and high glucose. On the bottom of the cell is the label blood with the caption low potassium ions, high sodium ions and low glucose. On the top of the cell is the label intestinal tubule lumen with the caption high sodium ions, medium glucose. Between the epithelial cell and the intestinal lumen there is a blue circle with 2 arrows pointing from the intestinal lumen into the epithelial cell. One arrow is labeled sodium and the other arrow is labeled glucose. Between the epithelial cell and the blood there are 2 circles. The first circle is red and has 2 arrows. One arrow is pointing from the epithelial cell towards the blood and is labeled sodium ions. The other arrow is pointing from the blood towards the epithelial cell and is labeled potassium ions. The second circle is blue and has an arrow pointing from the epithelial cell towards the blood and is labeled glucose ions.
Based on the model, which of the following movements does not require an input of energy?
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