cell membrane

American  

[sel mem-breyn] / ˈsɛl ˈmɛm breɪn /

noun

Biology.

1. the semipermeable membrane enclosing the cytoplasm of a cell.

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cell membrane British  

noun

1. Also called: plasmalemma.   plasma membrane.  a very thin membrane, composed of lipids and protein, that surrounds the cytoplasm of a cell and controls the passage of substances into and out of the cell

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cell membrane Scientific  

1. The thin membrane that forms the outer surface of the protoplasm of a cell and regulates the passage of materials in and out of the cell. It is made up of proteins and lipids and often contains molecular receptors. The membranes of organelles within the cell are made of the same basic material as the cell membrane. In plant cells, the cell membrane is surrounded by a rigid cell wall.

2. Also called plasma membrane

3. Compare cell wall See more at cell

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cell membrane Cultural  

1. The structure separating an animal cell from its environment or a plant cell from its cell wall. The cell membrane is a complex system that allows nutrients to enter the cell and waste products to leave, usually through osmosis.

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Usage

What is a cell membrane? The cell membrane is the thin layer that encloses a cell’s cytoplasm, which is the substance between the membrane and the nucleus. It allows beneficial things to pass through while blocking harmful ones. The cell is the basic structural unit of all living organisms. It is a microscopic structure consisting of a nucleus surrounded by the cytoplasm and enclosed by a membrane—the cell membrane. In general, a membrane is a thin barrier or covering. The membrane consists of a double layer made up of lipid molecules and large protein molecules. Lipids and proteins are the basic building blocks of living cells. They move fluidly in the cell membrane and function like a system of gates, giving the membrane its ability to allow molecules to pass through. For this reason, the membrane is described as semipermeable (meaning it is capable of allowing things to pass through it). Plants cells also have a rigid outer wall in addition to a cell membrane. The cell membrane is also called the plasma membrane or the plasmalemma.

Etymology

Origin of cell membrane

First recorded in 1865–70

Compare meaning

How does cell-membrane compare to similar and commonly confused words? Explore the most common comparisons:

• plasma membrane vs. cell membrane
• cell wall vs. cell membrane

Example Sentences

Ras inhibitors block a small protein that sits inside the cell membrane and acts as an on/off switch, setting off a signaling cascade that can make a cell grow or divide.

From Barron's • Apr. 28, 2026

At the center of the idea is the cell membrane, the thin, flexible layer that surrounds every living cell and controls what enters and leaves it.

From Science Daily • Dec. 16, 2025

"With its fin immersed into the cell membrane, it rides along the inner surface and swiftly detoxifies lipid peroxides as it goes."

From Science Daily • Dec. 9, 2025

Finally, the potassium-to-sodium ratio reflects the natural function of cell membrane pumps, which concentrate potassium inside cells while transporting sodium out.

From Salon • Dec. 30, 2024

The epithelial cell membrane allows the water of the blood with certain salts in solution to pass, but rejects the albumen.

From A Practical Physiology by Blaisdell, Albert F.