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Glucose and galactose enter intestinal cells by co-transport with sodium. How does fructose enter?
ABy active transport using ATP
BBy co-transport with sodium too
CBy endocytosis at the membrane
DBy facilitated diffusion alone
Answer & Solution
Correct answer: D. By facilitated diffusion alone
1. All carbohydrates are absorbed as monosaccharides, at a rate of about 120 grams per hour.
2. Glucose and galactose share common protein carriers and move by co-transport with sodium ions.
3. Fructose does not use that sodium-linked route.
4. It is absorbed and transported by facilitated diffusion alone, using a carrier but no energy input.
5. That is why the option naming co-transport with sodium is the trap set by the stem itself.
6. Active transport and endocytosis both consume ATP, which facilitated diffusion does not.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 23 "The Digestive System", section 23.7 Chemical Digestion and Absorption: A Closer Look_
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