Summary
The thin, selectively permeable phospholipid boundary that separates the inside of a cell from its surroundings.
In depth
The plasma membrane is a phospholipid bilayer about 7 to 10 nm thick studded with proteins and cholesterol. It acts as a selective gate: small nonpolar molecules (O2, CO2) pass freely, while ions and large polar molecules need protein channels or carriers.
Its functions include transport, signal reception, cell recognition through glycoproteins, anchoring to the cytoskeleton and matrix, and enzymatic activity. Membrane proteins can be integral (spanning the bilayer) or peripheral (attached to one surface).
About half the mass of a typical membrane is protein, and the proteins do most of its work: channels, pumps, receptors, enzymes, anchors and recognition tags. Cholesterol in animal membranes acts as a fluidity buffer, stiffening the bilayer when warm and preventing it from packing tightly when cold.
Membrane potential is maintained by selective permeability and pumps: the inside of most animal cells sits near minus 70 millivolts relative to the outside. This stored electrical energy powers nutrient uptake and nerve signalling.
Frequently asked questions
What is Plasma Membrane?
The thin, selectively permeable phospholipid boundary that separates the inside of a cell from its surroundings.
Which area of biology covers Plasma Membrane, and how advanced is it?
Plasma Membrane is one of the 52 topics in Cell Biology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Fluid Mosaic Model, Eukaryotic Cell, Cytoplasm.
Why does Plasma Membrane matter?
The membrane maintains concentration gradients, such as high K+ inside and high Na+ outside, that power nerve impulses and nutrient uptake.
Can you give an example of Plasma Membrane?
Cystic fibrosis results from a faulty chloride channel (CFTR) in the plasma membrane of epithelial cells, which thickens mucus in the lungs.
What should I learn before Plasma Membrane?
Plasma Membrane is a Beginner topic, so no earlier topic is required. Other Beginner topics in Cell Biology that pair well with it include Cell Theory, Prokaryotic Cell, Eukaryotic Cell.
What topics are related to Plasma Membrane?
The closest topics to Plasma Membrane are Fluid Mosaic Model, Eukaryotic Cell, Cytoplasm, Facilitated Diffusion. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Plasma Membrane?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Plasma Membrane. To practise the whole of Cell Biology, use the Cell Biology quiz.
How is Plasma Membrane different from Fluid Mosaic Model?
Plasma Membrane: The thin, selectively permeable phospholipid boundary that separates the inside of a cell from its surroundings. Fluid Mosaic Model: Describes the membrane as a flexible fluid bilayer in which proteins float and move laterally like a mosaic. Read both side by side and note what each one explains.
How should I study Plasma Membrane step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Fluid Mosaic Model and explain the difference aloud. Finally, take the Cell Biology quiz and come back to this page for any question you miss.