The correct option is:
Osmosis is the movement of water across a membrane; diffusion is the movement of molecules from a higher to a lower concentration, with or without the presence of a membrane.
Here's a brief explanation of the concepts:
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Diffusion refers to the movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached. This process can occur with various types of molecules and does not necessarily require a membrane.
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Osmosis is a specific type of diffusion that refers exclusively to the movement of water molecules across a semi-permeable membrane, from an area of lower solute concentration to an area of higher solute concentration.