The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a semipermeable biological membrane that separates and protects the interior of a cell from the outside environment (the extracellular space).[1][2] The cell membrane is a lipid bilayer, usually consisting of phospholipids and glycolipids; eukaryotes and some archaea typically have sterols (such as cholesterol in animals) interspersed between them as well, maintaining appropriate membrane fluidity at various temperatures. The membrane also contains membrane proteins, including integral proteins that span the membrane and serve as transporters, and peripheral proteins that attach to the surface of the cell membrane, acting as enzymes to facilitate interaction with the cell's environment.[3] Glycolipids embedded in the outer lipid layer serve a similar purpose.🧫 1. What is the Cell Wall?
The cell wall is the rigid outer covering found in plant cells, fungi, and some protists, but absent in animal cells.
🔍 Composition in Plants:
Cellulose (primary component)
Hemicellulose
Pectin
Lignin (in secondary walls)
🧱 Structure:
Middle lamella – pectin-rich, binds adjacent cells
Primary wall – flexible, first formed
Secondary wall – thick, strong, deposited later
🧪 Functions:
Provides mechanical support
Maintains cell shape
Prevents osmotic bursting
Allows free water movement via plasmodesmata
🧠 Mnemonic:
“Cellulose Builds Cell Walls”
🔬 2. Cell Membrane (Plasma Membrane)
The cell membrane is a semi-permeable phospholipid bilayer present in all cells, including plant and animal cells.
🔍 Composition:
Phospholipids – bilayer base
Proteins – integral and peripheral
Carbohydrates – glycoproteins & glycolipids
Cholesterol – in animal membranes (adds fluidity)
🧱 Structure – Fluid Mosaic Model
Proposed by Singer and Nicolson (1972):
➡ Lipid bilayer = fluid
➡ Proteins = mosaic pattern
🧪 Functions:
Selective permeability
Transport of molecules
Cell signaling
Endocytosis and exocytosis
🧠 Mnemonic:
“FLUID MOSAIC = Flexible Lipid + Proteins Floating”
🔁 Cell Wall vs. Cell Membrane
Feature Cell Wall Cell Membrane
Found in Plants, fungi, bacteria All cells
Composition Cellulose (plants) Lipids + proteins
Thickness Thick (rigid) Thin (flexible)
Permeability Fully permeable Selectively permeable
Function Support, shape Transport, protection
🎯 NEET Booster Points
✅ Cell wall = non-living, formed outside plasma membrane
✅ Middle lamella = calcium & magnesium pectates
✅ Plasma membrane = living, controls movement
✅ Plasmodesmata = cell-to-cell cytoplasmic connection