The key difference between cell wall and cell membrane is that the cell wall is a fully permeable cell layer present in bacteria, plants, fungi and algae while the cell membrane is a selectively permeable membrane present in all cell types including the animal cells.
Cell membrane (plasma membrane) and cell wall are the outermost cell layers that separate cell organelles from the external environment. These special layers provide shape to the cells, and also act as a mechanical barrier to protect the internal cell organelles. However, unlike the cell membrane that is present in all types of cells, the cell wall is present only in the cells of plants, fungi and most protists, except animal cells. This article will discuss the difference between cell wall and cell membrane in animal and plant cells in detail.
CONTENTS
1. Overview and Key Difference
2. What is a Cell Wall
3. What is a Cell Membrane
4. Similarities Between Cell Wall and Cell Membrane
5. Side by Side Comparison – Cell Wall vs Cell Membrane in Tabular Form
6. Summary
What is a Cell Wall?
Cell wall is the outermost layer of many cells except in animal cells. Bacteria, plants, fungi and most protists contain a cell wall surrounding the cell membrane of their cells. Structurally, it is a rigid layer that provides a definite shape to the cell. However, the composition of the cell wall differs among the different organisms. Peptidoglycan is the main compound that is present in the bacterial cell wall. In contrast, chitin is the main component present in the fungal cell wall. Plant cell wall contains cellulose as its main compound. Likewise, the main compound that gives a characteristic feature to their cell wall differs between the groups of the organisms and facilitates the easy identification.
Figure 01: Plant Cell Wall
Unlike the cell membrane, cell wall is a fully permeable layer. It does not select the compounds that are going in and out the cell. However, it prevents the cells from bursting. Since the cell wall is the outer most layer present in many cells, it fulfils several functions such as providing structural strength, giving a definite shape to the cell, and protecting the cell against pathogens and mechanical injuries, etc.
What is a Cell Membrane?
Cell membrane or plasma membrane is a selectively permeable layer present in all most all cell types. It encloses the cell and separates its content from the outer environment. Moreover, it is a flexible membrane, which is about 5 to 10 nm thick. Structurally, it is a phospholipid bilayer. Apart from the two leaflets of the phospholipid molecules, two types of protein molecules are also present in the cell membrane. They are integral proteins and peripheral proteins. Among these two types, integral proteins permanently attach with the phospholipid layer while the peripheral proteins temporally attach with the phospholipid layer. Some integral proteins are transmembrane proteins that span across the phospholipid bilayer. The “fluid mosaic model” is the model that nicely describes the above-mentioned structure of cell membrane.
Figure 02: Cell Membrane
All these components of the cell membrane provide several other functions other than the structural support and protection. Especially, transmembrane proteins act as carrier proteins that facilitate the membrane transportation of molecules. They involve active and passive transport, and also they work as channel proteins and receptor proteins. In addition to proteins and phospholipids, there are carbohydrate chains that associate with proteins (glycoproteins) and lipid bilayer (glycolipids) of the cell membrane. Basically, they are important in ‘self’ recognition and tissue recognition of cells. Furthermore, there are some lipid molecules called cholesterol and glycolipids which assist the structure of the cell membrane.
What are the Similarities Between Cell Wall and Cell Membrane?
- Cell wall and cell membrane are parts of the cells.
- They are layers that protect the cell from the external environment.
- Also, they completely surround the cell interior.
- Moreover, both layers allow molecules to pass in and out the cell.
- Both are composed of various compounds
- Besides, they provide structural support to the cell.
- Furthermore, they provide a shape to the cell.
What is the Difference Between Cell Wall and Cell Membrane?
A cell has different parts. Among them, cell wall and cell membrane are two important parts of a cell. However, animal cells lack a cell wall unlike the plant, fungal, algal and bacterial cells. Therefore, cell wall is the outermost layer of the plant, fungal, bacterial and algal cells while the cell membrane is the outermost layer of the animal cells. Hence, this is a difference between cell wall and cell membrane. However, the key difference between cell wall and cell membrane lies with their permeability. The cell wall is completely permeable while the cell membrane is selectively or partially permeable.
Another difference between cell wall and cell membrane is the composition. That is; the cell wall contains cellulose, chitin, peptidoglycan, etc. while the cell membrane contains phospholipids, proteins, carbohydrates, etc.
The following infographic further illustrates the difference between cell wall and cell membrane.
Summary – Cell Wall vs Cell Membrane
Cell wall is a completely permeable barrier that covers the plant, fungal, bacterial and algal cells. In contrast, the cell membrane is a partially and selectively permeable barrier present in all cell types. This is the major difference between cell wall and cell membrane. Furthermore, cell wall is made up of cellulose, chitin, peptidoglycan, etc., while the cell membrane is made up of phospholipids, proteins, carbohydrates and lipids. Both cell wall and cell membrane protect the cell interior from the external environment.
Reference:
1.Lodish, Harvey. “Membrane Proteins.” Molecular Cell Biology. 4th Edition., U.S. National Library of Medicine, 1 Jan. 1970. Available here
2.“Cell Wall.” Wikipedia, Wikimedia Foundation, 14 Oct. 2018. Available here
Image Courtesy:
1.”Plant Cell Wall”By RIT RAJARSHI – Own work, (CC BY-SA 4.0) via Commons Wikimedia
2.”Cell membrane detailed diagram edit2″By LadyofHats Mariana Ruizderivative work, edited by Alokprasad84, (CC BY-SA 3.0) via Commons Wikimedia