What cell structure is responsible for processes like diffusion and osmosis?

The cell membrane is the correct answer because it plays a crucial role in regulating the movement of substances into and out of the cell, a process that includes both diffusion and osmosis. The cell membrane is semi-permeable, meaning it allows certain molecules to pass while blocking others. This selective permeability is essential for maintaining the cell's internal environment and is fundamental to processes like diffusion, where particles move from an area of higher concentration to an area of lower concentration, and osmosis, which specifically refers to the movement of water across the cell membrane.

The cell wall, present in plants and some microorganisms, primarily provides structural support and protection rather than directly regulating the movement of substances. Cytoplasm is the fluid within the cell that holds organelles but does not serve the function of selectively allowing substances to move into or out of the cell. The nucleus contains genetic material and is involved in cell regulation and reproduction, but it does not influence the processes of diffusion and osmosis directly. Therefore, the cell membrane is uniquely suited to facilitating these critical processes.