What are the differences between cell wall and cell membrane?

The cell wall and cell membrane are distinct structures with different compositions, locations, and functions. The cell membrane (plasma membrane) is a thin, flexible lipid bilayer composed primarily of phospholipids, proteins, and cholesterol, present in all cells—both plant and animal. It serves as the selective barrier controlling what enters and exits the cell. In contrast, the cell wall is a rigid outer layer made of cellulose in plants, chitin in fungi, and peptidoglycan in bacteria, found only in plant cells, fungi, and prokaryotes, positioned outside the cell membrane.

Functionally, the cell membrane is selectively permeable and actively regulates molecular transport through diffusion, osmosis, and active transport mechanisms, playing crucial roles in cell signaling and recognition. The cell wall, however, provides mechanical strength, structural support, and protection against mechanical stress and pathogen invasion. While the cell membrane is living and metabolically active, the cell wall is non-living once formed. The cell wall prevents the plant cell from bursting when placed in hypotonic solutions by providing counter-pressure (turgor pressure), whereas animal cells, lacking this wall, rely entirely on the fragile membrane and are more vulnerable to osmotic lysis. This fundamental difference explains why plant cells maintain definite shapes while animal cells are generally more flexible and variable in form.