Aim for FiveBiology

Analyze a model or visual representation

Glucose absorption by intestinal cells

  • Unit 2
  • 4 points
  • About 10 minutes

You can use a calculator on this question, just like on exam day.

A short question built around a model or diagram of a biological process. You describe what the model shows, explain how its parts relate, add to or use the model, and connect it to a bigger biological idea. On the exam: Question 5 of 6 in Section II; about 10 minutes suggested.

The question and its sources

Cells lining the small intestine absorb glucose from digested food. Figure 1 is a model of one of these cells.

Figure 1 (described)

The model shows one intestinal cell. Its top surface (apical membrane) faces the inside of the intestine (the lumen), and its bottom surface (basolateral membrane) faces the blood. The apical membrane is folded into many fingerlike projections called microvilli.

In the apical membrane, protein SGLT moves 2 Na⁺ and 1 glucose molecule together from the lumen into the cell. In the basolateral membrane, the Na⁺/K⁺ pump uses ATP to move 3 Na⁺ out of the cell into the blood and 2 K⁺ into the cell. Also in the basolateral membrane is protein GLUT2, a carrier protein that lets glucose cross the membrane without ATP.

Concentrations labeled in the model: Na⁺ is 140 mM in the lumen, 12 mM in the cytosol and 145 mM in the blood. Glucose is 5 mM in the lumen, 20 mM in the cytosol and 5 mM in the blood.

Source: Simplified model; concentrations are hypothetical

Suggested time: 10 minutes

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Part (a)

1 point

Based on Figure 1, describe the type of transport carried out by the Na⁺/K⁺ pump.

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Part (b)

1 point

Based on Figure 1, explain how the Na⁺/K⁺ pump makes it possible for SGLT to move glucose into the cell against glucose's concentration gradient.

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Part (c)

1 point

On Figure 1, an arrow would be drawn through GLUT2 to show the net movement of glucose. Using the model, state the direction of this arrow and identify the type of transport it represents.

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Part (d)

1 point

Explain how the microvilli on the apical membrane relate to the rate at which an intestinal cell can absorb glucose.

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