Which of the following is an example of secondary active transport?

Which of the following is an example of secondary active transport?

• A. The favorable movement of one solute down its concentration gradient is coupled with the unfavorable movement of a second solute up its concentration gradient
• B. The Na+/K+ pump
• C. The glucose uniporter
• D. The Na+/glucose symporter

Answer: (D)

Secondary active transport involves the movement of one substance against its concentration gradient, powered by the movement of another substance down its concentration gradient. The Na+/glucose symporter is a prime example of this process. It utilizes the sodium gradient created by the Na+/K+ pump, which transports sodium out of the cell while bringing glucose into the cell. In this case, sodium moves into the cell down its concentration gradient, providing the energy necessary to transport glucose against its gradient. This mechanism is crucial for nutrient absorption, particularly in the intestines and kidneys. The specific coupling of the sodium ion's concentration gradient with the transportation of glucose highlights the defining feature of secondary active transport: reliance on the energy stored in the gradients of other substances rather than direct ATP usage. In contrast, the other options represent different transport mechanisms. The Na+/K+ pump is a classic example of primary active transport, as it directly utilizes ATP to move ions against their gradients. The glucose uniporter facilitates passive transport, moving glucose down its gradient without any coupling to ion gradients. Thus, the Na+/glucose symporter stands out as a clear demonstration of secondary active transport.

Secondary active transport involves the movement of one substance against its concentration gradient, powered by the movement of another substance down its concentration gradient. The Na+/glucose symporter is a prime example of this process. It utilizes the sodium gradient created by the Na+/K+ pump, which transports sodium out of the cell while bringing glucose into the cell. In this case, sodium moves into the cell down its concentration gradient, providing the energy necessary to transport glucose against its gradient.

This mechanism is crucial for nutrient absorption, particularly in the intestines and kidneys. The specific coupling of the sodium ion's concentration gradient with the transportation of glucose highlights the defining feature of secondary active transport: reliance on the energy stored in the gradients of other substances rather than direct ATP usage.

In contrast, the other options represent different transport mechanisms. The Na+/K+ pump is a classic example of primary active transport, as it directly utilizes ATP to move ions against their gradients. The glucose uniporter facilitates passive transport, moving glucose down its gradient without any coupling to ion gradients. Thus, the Na+/glucose symporter stands out as a clear demonstration of secondary active transport.