Cell Wall and Cell Membrane – Definition, Diagram, Difference and Important Questions

Cell Wall and Cell Membrane: In this article you will get detail explanation about Cell Wall and Cell Membrane, diagrams of Cell Wall and Cell Membrane, difference between Cell Wall and Cell Membrane.

GENIUS 2023

A cell is the structural and functional working unit of life and also been described as building blocks and fundamental unit of an organism.  The term cell was coined by an English scientist Robert Hooke in the year 1665. The shape and size of the cells vary according to their functions and compositions. There are different types of cells and can be differentiated based on the presence and absence of few cell organelles.

Cell Wall and Cell Membrane

What is a Cell Wall?

The cell wall is a rigid, outermost, structural layer found in bacterial, archeal, fungal and plant cells. Structural support and the protection is provided by the cell wall. It also acts as a pressure vessel which prevents the over-expansion of the cell. Structure and composition varies between species.

Cell Wall Structure

Functions of Cell Wall

  • Cell wall gives rigidity and the strength to the cell.
  • It also protects the cell against mechanical stress.
  • Cell wall can bend with a considerable tensile strength.
  • Secondary cell wall components such as lignin and cellulose give rigidity to plants.
  • Hydraulic turgor pressure gives rise to rigidity in the cell.
  • Cell wall permits a definite shape to the cell.
  • Secondary cell wall is also waterproof.
  • On the other hand, cell wall is a completely permeable structure. But, it prevents the entry of large molecules into the cell like toxins.
  • In most plants, primary cell wall is completely permeable to small molecules.
  • Cell wall creates a stable osmotic environment since it prevents the osmotic lysis and helps to retain water.

What is a Cell Membrane?

The cell membrane is a biological membrane which separates the cell interior from the outside environment. Cell membrane is also called the plasma membrane and cytoplasmic membrane. It is selectively-permeable to substances like ions and organic molecules. Cell membrane maintains a constant environment inside the protoplasm by controlling the passage of substances in and out of the cell. It also protects the cell from its surroundings.

Cell Membrane

Function of Cell Membrane

  • Cell membrane physically separates the cytoplasm from its extracellular environment.
  • It also anchors the cytoskeleton, providing the shape of the cell.
  • On the other hand, cell membrane is attached to the other cells in the tissue, providing the mechanical support to the cell.
  • Cell membrane is selectively permeable, regulating a constant internal environment for the functioning of the cell.
  • The movement across the cell membrane can occur either in passive or active diffusion.
  • Four transport mechanisms can be identified in the cell membrane.
  • Small molecules like carbon dioxide, oxygen and ions move across the membrane by passive osmosis and diffusion.
  • Nutrients like sugar, amino acids and metabolites move across passively, through transmembrane protein channels.
  • Aquaporins are a kind of protein channels which transport water by facilitated diffusion.
  • Absorption of molecules into the cell by engulfing them is referred to as the endocytosis.
  • Solid particles are engulfed by phagocytosis and small molecules and ions are engulfed by pinocytosis.
  • Some undigested residues are removed from the cell by invagination and formation of a vesicle. This process is referred to as the exocytosis.

Difference between Cell Wall and Cell Membrane

CELL WALL CELL MEMBRANE
Present only in plants and in some fungi, bacteria, algae. Present in all types of cells, in humans, animals, plants, bacteria, etc.
It is the outermost part of the plant cell It is the outermost covering the animal cells
It is made up of pectin, chitin, lignin, glycoproteins, glycolipids, sugar, and cellulose. It is a lipid bilayer. And is composed of lipoproteins and carbohydrates.
The cell wall is 0.1 μm to several μm in thickness The cell membrane is 7.5–10 nm in thickness
It is the thick and rigid structure with a fixed shape. It is a thin and delicate structure. It is flexible to change the shape as needed.
It protects the cell from the external environment. It protects and maintains the internal environment of the cell.
The cell wall is metabolically inactive The cell membrane is metabolically active.
The cell wall grows in thickness over time. Further, it occupies the whole cell in the plant as the cell ages and dies. It is of the same thickness for the lifetime of the organism.
The cell wall is fully permeable to smaller molecules with the size of 30-60 kDa. The membrane is selectively permeable and controls the movement of the substance into and outside the cell.
Functions include protection from the external environment. Functions include permeability, signal reception, motility conduction, cell division, sexual reproduction, etc.


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By Team Learning Mantras