Cell membrane

A cell membrane is a thin, living covering around a cell that acts like a “gatekeeper,” controlling what enters and leaves the cell.

• Boundary and protection: It forms the cell’s outer boundary in animal cells and helps keep the inside of the cell separate from the outside environment.
• Selectively permeable (smart filter): It is not an open sieve. It allows useful materials like water, oxygen, and dissolved food to enter, and lets wastes like carbon dioxide move out.
• Helps cells stay organised: By separating one cell from another, it helps each cell maintain its own internal conditions so life processes can happen properly.
• Made of a flexible layer: The membrane is mainly made of fats (lipids) and proteins. This makes it thin and flexible rather than hard.
• Easy analogy: Think of it like the security gate of a school—students and teachers are allowed in, strangers are stopped, and exits are controlled too.

In plant cells, a strong cell wall lies outside the cell membrane, but the cell membrane is still present and still does the “in-and-out control” job.