Correct Option: D. Water across a semi-permeable membrane from solution of low concentration to high concentration Detailed Explanation: Definition of Osmosis: Osmosis is a specific type of passive transport that refers to the movement of water molecules through a semi-permeable membrane. This process occurs in response to differences in solute concentration on either side of the membrane. Why Option D is Correct: - Water Movement: Osmosis specifically involves the movement of water, not just any molecules. In this case, water moves from a region where there is a lower concentration of solute (more water) to a region where there is a higher concentration of solute (less water). - Semi-Permeable Membrane: The term "semi-permeable membrane" is crucial because it allows only certain molecules (like water) to pass through while blocking others (like solutes). This selective permeability is what drives the osmotic process. - Concentration Gradient: The movement of water continues until equilibrium is reached, meaning the concentration of solute is equal on both sides of the membrane. This movement is driven by the concentration gradient of solutes, not water. Why the Other Options are Incorrect: Option A: Molecules from solution of higher concentration to low concentration - Incorrect Focus: This option does not specify that it is water that is moving. It suggests a general movement of molecules, which could apply to any type of molecule, not just water. - Direction of Movement: It incorrectly states that molecules move from high concentration to low concentration, which is not the case in osmosis. In osmosis, water moves from low solute concentration to high solute concentration. Option B: Molecules from solution of low concentration to high concentration - Incorrect Focus: Similar to Option A, this option does not specify that it is water. It also misrepresents the process of osmosis. - Direction of Movement: While it correctly states that movement occurs from low to high concentration, it fails to mention that this is specifically about solute concentration, not the movement of molecules in general. Option C: Water from solution of high concentration to low concentration - Incorrect Direction: This option incorrectly states the direction of water movement. In osmosis, water moves from low solute concentration (high water concentration) to high solute concentration (low water concentration), not the other way around. - Misleading Terminology: The term "high concentration" here is misleading because it does not clarify whether it refers to solute or solvent concentration. Summary of Key Points:

• Osmosis is the movement of water through a semi-permeable membrane.
• Water moves from areas of low solute concentration to areas of high solute concentration.
• The process continues until equilibrium is reached, balancing solute concentrations on both sides of the membrane.
• Understanding the role of the semi-permeable membrane is crucial in defining osmosis.

Revision Summary:

• Osmosis is the movement of water across a semi-permeable membrane.
• Water moves from low solute concentration to high solute concentration.
• The process is driven by the concentration gradient of solutes.
• It is essential to differentiate between the movement of water and other molecules in biological processes.