cell membrane

[ sel-mem-breyn ]
/ ˈsɛl ˈmɛm breɪn /
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noun Biology.
the semipermeable membrane enclosing the cytoplasm of a cell.


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Origin of cell membrane

First recorded in 1865–70
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2022


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.

Why is the cell membrane important?

To understand why the cell membrane is important, you first have to understand what it does. In essence, the cell membrane serves as the glue that holds the components of the cell together and protects it from outside threats. The membrane regulates what comes into the cell. Among other things, it keeps potentially harmful substances out and keeps nutrients in.

The makeup of the cell membrane includes three crucial components: phospholipids, cholesterol, and proteins. The phospholipids attract and repel water. The layer created by these opposing forces is known as the phospholipid bilayer. It’s responsible for creating the spaces within the membrane and making it a good barrier. Proteins help with transporting cell components across the barrier. Cholesterol also helps with this regulation.

Did you know ... ?

The understanding of the cell membrane is based on what’s called the fluid mosaic model. The fluid mosaic model is a way of describing the structure of cell membranes that likens them to a “mosaic” of different components, consisting of a fluid double layer of molecules. The model was developed by cell biologist S. J. Singer and biochemist Garth L. Nicolson in 1972. It has evolved somewhat since then, but it is now the most accepted way to understand the structure and function of the cell membrane.

What are real-life examples of cell membrane?

Along with the nucleus and the cytoplasm, the cell membrane is one of the main components of a cell. It’s familiar to many biology students.



Quiz yourself!

True or False?

The cell membrane blocks anything from entering.

How to use cell membrane in a sentence

British Dictionary definitions for cell membrane

cell 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 cellAlso called: plasmalemma, plasma membrane
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Scientific definitions for cell membrane

cell membrane

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. Also called plasma membrane Compare cell wall. See more at cell.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

Cultural definitions for cell membrane

cell membrane

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.

The New Dictionary of Cultural Literacy, Third Edition Copyright © 2005 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.