Question

What transport mechanism allows water to cross the apical surface of an absorptive cell in the mucosa of the GI tract?

Facilitated diffusion

Osmosis

Primary active transport

Secondary active transport

Simple diffusion

Answer 1

Option b-Osmosis.

Movement of Water across the apical surface of an absorptive cell in the mucosa of the GI tract is by Osmosis.

[Osmosis-movement of Solvent(Water)from its higher concentration to its lower concentration through a Semipermiable Membrane]

Since Electrolytes like Na+ & K+ are absorbed by other methods like active transport.[For Example SGLT Cotransporter that transport Na+ along With Glucose across Apical Surface of Absorptive cells in the Mucosa].

This makes Concentration of Water more in the Chyme,Less in the Absorptive cells[Absorptive cells is more concentrated due to the presence of ions Like Na+]

So water Absorption occur by the concentration gradient of the water ,That is From chyme to Absorptive cells.

Simple diffusion:Refers to Movement of solutes without the Help of any transmembrane proteins.The movement of Solvent(Water)across semipermiable membrane is called Osmosis.

Primary active transport:Active tranport Involving energy expenditure in the Form of ATP(Na+K+ATPase)

Secondary active transport:Active transport with Energy Expenditure in forms Otherthan ATP(Eg:SGLT cotransport)