Question

Transport of glucose into epithelial cells lining your small intestine is dependent on a pre-existing electrochemical gradient of sodium (Na⁺) ions across the apical plasma membrane. If that gradient is eliminated, glucose transport stops. This is one example of ____________________.

		passive transport
		secondary active transport (coupled transport)
		primary active transport
		an aquaporin

Answer 1

Ans.

Secondary active transport (coupled transport)

Concentration of Na+ outside of the cell is almost 145 mM, and inside of the cell is 12 mM.

While concentration of glucose outside of the is almost 3 mM and inside the cell is almost 3000mM.

In this transport glucose and Na+ are co-transported by a specific transporter known as SGLT 1 (Sodium dependent glucose transporter)

This tranaporter, transport Na+ along the concentration gradient 145 -----> 12 mM.

While glucose against the concentration gradient 3 -------> 3000 mM.

In which two Na+ are transported along the concentration from outside to inside. And energy released in this transport used in the transfer of glucose from the outside to inside (against the concentration gradient)

Hence this transport is couples transport because without Na+ SGLT will not be able to transport glucose from outside to inside.

Secondary active transport is a energy driven process but the energy is used from the difference in concentration gradient of ions (here Na+), not from ATP.