Which of the following processes best describes the movement of water across a selectively permeable membrane from areas of lower solute concentration to areas of higher solute concentration?
Diffusion
Active transport
Osmosis
Facilitated diffusion
Correct Answer:C
Explanation
The correct option is C. Osmosis.
Detailed Explanation:
Understanding Osmosis:
Osmosis is the process specifically defined as the movement of water molecules across a selectively permeable membrane. This movement occurs from an area of lower solute concentration (where there are fewer solute particles) to an area of higher solute concentration (where there are more solute particles). The goal of osmosis is to equalize solute concentrations on both sides of the membrane.
Selectively Permeable Membrane:
A selectively permeable membrane allows certain molecules (like water) to pass through while restricting others (like solutes). This property is crucial for maintaining cellular homeostasis, as it regulates the internal environment of cells.
Mechanism of Osmosis:
Water moves through specialized channels called aquaporins or directly through the lipid bilayer of the membrane. The movement is driven by the concentration gradient of solutes, not by the water itself. Water will continue to move until equilibrium is reached, meaning the concentration of solutes is equal on both sides of the membrane.
Why Other Options Are Incorrect:
A. Diffusion:
Diffusion refers to the movement of solute particles from an area of higher concentration to an area of lower concentration. While it is a passive process like osmosis, it does not specifically involve water movement and is not limited to selectively permeable membranes.
B. Active Transport:
Active transport is the movement of molecules against their concentration gradient (from lower to higher concentration) and requires energy (usually in the form of ATP). This process is not applicable to the movement of water, which occurs passively in osmosis.
D. Facilitated Diffusion:
Facilitated diffusion is a type of passive transport that involves the movement of molecules across a membrane via specific transport proteins. While it does not require energy, it is primarily concerned with solutes, not water. Therefore, it does not describe the movement of water across a membrane.
Summary of Key Points:
Osmosis is the movement of water from areas of lower solute concentration to areas of higher solute concentration across a selectively permeable membrane.
It is a passive process that does not require energy and aims to achieve equilibrium in solute concentrations.
Diffusion and facilitated diffusion involve solute movement, while active transport requires energy to move substances against their concentration gradient.
Revision Summary:
Osmosis is the specific term for water movement across a membrane.
It occurs from low to high solute concentration.
It is a passive process, unlike active transport.
Understanding the differences between osmosis, diffusion, and facilitated diffusion is crucial for grasping cellular processes.