The correct answer is B. Diffusion.

Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration, following the concentration gradient, until equilibrium is reached.

Explanation of Other Options:
- A. Transpiration: The loss of water vapor from plant leaves through stomata.
- C. Translocation: The movement of nutrients (e.g., sugars) through the phloem in plants.
- D. Osmosis: The movement of water molecules through a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration.
- E. Plasmolysis: The process where a plant cell loses water, causing the cell membrane to shrink away from the cell wall due to water loss in a hypertonic solution.

Thus, Diffusion is the correct choice because it describes the movement of molecules from high to low concentration without needing a membrane.