[Campbell Biology P.959] How is most water reabsorbed in the small intestine, according to t... | Practice Question

How is most water reabsorbed in the small intestine, according to the provided text?

  • A: By active transport of water molecules directly.
  • B: Through osmosis, following the active pumping of sodium and other ions out of the lumen.
  • C: By simple diffusion down its concentration gradient without ion involvement.
  • D: Through facilitated diffusion involving specific aquaporin channels.

Explanation

The text explicitly states: 'There is no mechanism for active transport of water. Instead, water is reabsorbed by osmosis when sodium and other ions are pumped out of the lumen of the small intestine.' This clearly indicates that water reabsorption is an osmotic process driven by the active transport of ions.