Question

Glucose is absorbed across the intestinal epithelium into the blood (at the basolateral membrane) by which mechanism?

• A. Secondary active transport
• B. Facilitated diffusion
• C. Simple diffusion
• D. Primary active transport

Hint:

Apical entry is SGLT1 cotransport, but exit into blood via GLUT2 is carrier-mediated and passive.

Answer 1

The Correct Option is B

Step 1: Glucose handling by the enterocyte involves two membranes. At the apical (luminal) membrane glucose enters with sodium via the SGLT1 cotransporter, which is secondary active transport powered by the sodium gradient.
Step 2: At the basolateral membrane glucose then exits the cell into the interstitium and blood through the GLUT2 carrier. This step is carrier-mediated and runs down the glucose concentration gradient without using ATP - that is facilitated diffusion.
Step 3: Facilitated diffusion is defined as the movement of a large, water-soluble molecule across the membrane by a carrier protein, down its gradient; glucose and amino acids are typically transported by this method at the exit step. So option (b) is the intended answer.
Step 4: Simple diffusion (c) cannot move polar glucose through the lipid bilayer; primary active transport (d) directly hydrolyzes ATP (like the Na-K pump) and is not used for glucose carriage; secondary active transport (a) describes the apical SGLT1 entry, not the absorptive exit being asked about.