Question

Which of the following occur without coupling transport of the solute to the movement of a second solute?

(a) import of glucose into gut epithelial cells
(b) export of Ca₂₊ from the cytosol
(c) export of H+ from animal cells for pH regulation
(d) the export of Na+ from cells to maintain resting membrane potential

Answer 1

The process that occurs without coupled transport is the export of Ca₂⁺ from the cytosol, as it involves an ATP-powered pump that works independently of the movement of any other solute.

Step-by-step explanation:

The question asks which of the following processes occur without coupling transport of the solute to the movement of a second solute. To address this, let's first define coupled transport. It involves the movement of one substance alongside another, such as via symport (same direction) or antiport (opposite direction) mechanisms.

Now, we'll consider each option provided in the student's question:

• (a) Import of glucose into gut epithelial cells: This is an example of secondary active transport, which is dependent on the electrochemical gradient of sodium ions established by the Na+/K+ ATPase. Glucose is imported along with Na+ ions via a symport mechanism. Thus, this process involves coupled transport.
• (b) Export of Ca₂⁺ from the cytosol: This process typically occurs via an ATP-powered pump, which works independently of the movement of another solute. Therefore, it does not involve coupled transport.
• (c) Export of H+ from animal cells for pH regulation: This can be both an active transport process, using proton pumps, and a coupled transport process, as in the antiport with other ions. Therefore, not all H+ exports are uncoupled from another solute's movement.
• (d) The export of Na+ from cells to maintain resting membrane potential: The Na+/K+ ATPase pump is responsible for maintaining the resting membrane potential by moving Na+ out of the cell against its gradient, using ATP, and not directly coupled to the transport of any other solute in this specific action. However, the maintenance of the gradient does facilitate other coupled transport processes.

Considering the given options, the process that occurs without coupled transport is the export of Ca₂⁺ from the cytosol (b), as it is an active transport process powered directly by ATP rather than being linked with another solute's movement.