Question

In intestinal epithelial cells, a transport protein moves the bulky, polar glucose molecules through the membrane into the cytoplasm, while simultaneously transporting Na+ through the membrane into the cell down its electrochemical gradient. Which example correctly describes this cotransport of glucose and sodium?

a primary active transport by an antiporter
b. secondary active transport by a symporter
c. primary active transport by a symporter
d. secondary active transport by an antiporter

Answer 1

b. secondary active transport by a symporter

Step-by-step explanation:

Glucose is a monosaccharide, one of the digestion products of carbohydrates. Glucose is a polar molecule and can not diffuse through the hydrophobic core of the cell membrane of absorptive cells of the small intestine.

A symporter transports one glucose and two sodium ions from the cavity of the small intestine into the absorptive cells of the villi. Since both Na+ and glucose are transported in the same direction, it is a symport. Here, the energy of the ionic concentration gradient of Na+ serves as a source of energy for glucose transport, the process of glucose transport is secondary active transport.