Q.In small intestine active absorption occurs in case of:

Amino acids, sodium ions and glucose are each absorbed across the intestinal mucosa by active transport, which requires ATP and often works via coupled (symport) mechanisms.

Absorption in the small intestine occurs by several mechanisms — passive diffusion, facilitated diffusion, and active transport. For the substances listed:

• Na+ ions are actively pumped out of the intestinal epithelial cells into blood by the Na+/K+-ATPase pump on the basal membrane, and are also taken up at the apical membrane via active/co-transport mechanisms, creating the gradient that drives absorption of other nutrients. …

The large intestine lacks villi (villi are a small-intestine feature for nutrient absorption); it does, however, absorb water from the undigested residue — so (A) is false but (R) is true, option (d).

Villi are finger-like projections of the mucosa that dramatically increase surface area for nutrient absorption, and they are a defining structural feature of the SMALL intestine (along with microvilli on each epithelial cell). The large intestine's mucosa is comparatively smooth, without villi, because its main jobs are different from the small intestine's:

• Assertion (A), "Large intestine also shows the presence of villi like small intestine," is FALSE — the large intestine does not possess villi. …