Intestinal Sugar Absorption Mechanisms

Steps:

• Recall that glucose absorption in the small intestine uses secondary active transport via SGLT1 cotransporter with sodium ions to move against its concentration gradient.
• Note that arabinose, a pentose sugar, lacks a specific active transporter and relies on passive diffusion down its concentration gradient.
• Compare options: Active transport requires energy and specificity; diffusion is passive and non-specific.
• Match: Arabinose fits diffusion, glucose fits active transport, selecting B.

Why B is correct:

• Glucose absorption follows the secondary active transport law, using Na+ electrochemical gradient (via Na+/K+ ATPase) to enable uphill movement, as defined in epithelial transport physiology.

Why the others are wrong:

• A: Arabinose uses diffusion, not active transport, due to no dedicated cotransporter.
• C: Glucose requires active transport, not diffusion, to overcome low luminal concentrations.
• D: Glucose does not use simple diffusion; it needs active uptake for efficient absorption.

Final answer: B