Understanding Water Movement Across Selectively Permeable Membranes

The question asks about the net movement of water from a dilute solution to a concentrated solution through a selectively permeable membrane. This specific type of movement is a fundamental concept in biology and chemistry.

Defining Key Terms

Let's look at the options provided to understand the differences between them:

• Diffusion: This is the general movement of particles (like molecules, atoms, ions) from an area of higher concentration to an area of lower concentration. This movement doesn't necessarily involve a membrane, or if it does, the membrane is usually permeable to the moving substance. Diffusion can happen in gases, liquids, and even solids.
• Dispersion: This term generally means the spreading out of something over a wide area. While related to movement, it doesn't specifically describe the movement of water across a membrane based on concentration gradients.
• Osmosis: This is a special type of diffusion involving the movement of a solvent (usually water in biological systems) across a selectively permeable membrane. The movement is from a region of higher solvent concentration (which corresponds to a dilute solute concentration) to a region of lower solvent concentration (which corresponds to a concentrated solute concentration). This movement continues until equilibrium is reached or until pressure opposes the movement.
• Absorption: This refers to the process where one substance is taken up by another, such as a liquid being soaked up by a solid or liquid. While cells absorb water, the term absorption itself doesn't specifically define the mechanism of water movement across a selectively permeable membrane driven by concentration differences.

Analyzing the Specific Process Described

The question specifies three key elements:

1. Net movement of water.
2. From a dilute solution (meaning higher water concentration).
3. To a concentrated solution (meaning lower water concentration).
4. Through a selectively permeable membrane (a membrane that allows some substances, like water, to pass through but restricts others, like many solutes).

Comparing these points with the definitions above, the process perfectly matches the definition of Osmosis. Water moves from where it is more concentrated (the dilute solution) to where it is less concentrated (the concentrated solution) across a membrane that is selective for water.

Based on this comparison and the definitions, the net movement of water from a dilute to a concentrated solution through a selectively permeable membrane is precisely what Osmosis describes.

Conclusion on Net Water Movement

The process specifically involving the net movement of water across a selectively permeable membrane driven by differences in water concentration (from dilute to concentrated solute solution) is known as Osmosis.

Revision Table: Key Transport Processes

Additional Information on Osmosis and Water Potential

Osmosis is a passive transport process, meaning it doesn't require cellular energy (ATP) to occur. The movement of water is driven by a difference in water potential between the two solutions separated by the membrane.

Water potential ($\Psi_w$) is a measure of the potential energy of water per unit volume relative to pure water in reference conditions. It is influenced by solute potential ($\Psi_s$, also called osmotic potential) and pressure potential ($\Psi_p$). The formula is:

$$ \Psi_w = \Psi_s + \Psi_p $$

• Pure water has the highest water potential (usually taken as 0 under standard conditions).
• Adding solutes lowers the water potential (makes $\Psi_s$ more negative). A dilute solution has a higher water potential than a concentrated solution.
• Water moves from an area of higher water potential to an area of lower water potential. This is consistent with water moving from a dilute solution (higher $\Psi_w$) to a concentrated solution (lower $\Psi_w$).

Understanding water potential helps explain the direction of Osmosis more precisely.