Which of the following statements about passive transport is correct?
a. Passive transport permits the solute to move in either direction, but the net movement of the population of solute molecules occurs down the concentration gradient of the molecule.
b. Passive transport operates independently of diffusion.
c. In passive transport, solute movement stops when the solute concentration is the same on both sides of the membrane.
The Correct Answer and Explanation is :
The correct statement is: a. Passive transport permits the solute to move in either direction, but the net movement of the population of solute molecules occurs down the concentration gradient of the molecule.
Explanation:
Passive transport is a process by which substances move across a biological membrane without the need for energy input from the cell. This movement occurs due to differences in concentration on either side of the membrane, a process known as diffusion.
- Directionality of Movement: Passive transport allows molecules to move in either direction across the membrane. However, the net movement of molecules is from an area of high concentration to low concentration, following their concentration gradient. This principle is captured in statement a. Individual molecules may move in both directions, but the overall (net) flow will be in the direction that reduces the concentration gradient.
- Relationship with Diffusion: Passive transport operates because of diffusion, not independently of it. Diffusion is the movement of molecules from an area of higher concentration to lower concentration due to random motion. Therefore, statement b is incorrect, as diffusion is a key mechanism of passive transport.
- Equilibrium: In passive transport, molecules continue to move across the membrane even when equilibrium is reached. Equilibrium means that the concentration of the solute is the same on both sides of the membrane, but molecules continue to move back and forth with no net movement. Therefore, statement c is incorrect. Solute movement doesn’t stop at equilibrium, but the rates of movement in both directions become equal.
Thus, the correct choice is a, which aligns with the fundamental concepts of passive transport, diffusion, and concentration gradients.