The document summarizes key information about plant cell walls. It describes the different layers of the plant cell wall (middle lamella, primary wall, secondary wall) and their compositions. The primary wall is thin, elastic and composed of cellulose, hemicellulose and pectin. It allows growing cells to expand. The secondary wall is thicker, rigid and composed mainly of cellulose, hemicellulose, and lignin. It provides strength to non-growing cells. The cell wall protects cells and allows them to withstand water pressure within the cell.

1. Cell Wall
By: Dr. Sunita Sangwan
Assistant professor, Dept of botany,
Govt. college, Bhiwani

2. Introduction
 . Cell wall is protective layer in function and provides mechanical support to the
cell.
 Cell wall determines the shape of the cells and any cell which has lost its cell wall
becomes amorphic or in other words loses definite shape.
 The cell wall was first observed by Robert Hooke in the year 1665 in cork cells of
oak tree.
 Originally it was thought that the cell wall was a non-living secretion of the
protoplasm, but now it is known to be metabolically active and is capable of
growth.
 It can be tough, flexible and rigid which provides cell with both structural support
and protection.

3. Types of cell wall
On the basis of chemical composition of cell wall there are three
types of cell wall:
1) Bacterial Cell Wall : made up of Mucopeptide and Muramic acid.
2) Cell wall of Fungi: made up of Chitin.
3) Plant Cell wall: made up of Cellulose.

4. Plant Cell Wall
The plant cell wall is a remarkable structure. It provides the most
significant difference between plant cells and other eukaryotic cells.
The wall is rigid(up to many micrometers in thickness) and gives
plant cells a very defined shape.
While most cells have a outer membrane , none is comparable in
strength to the plant cell wall. The cell wall is the reason for the
difference between plant and animal cell functions. Because the plant
has evolved this rigid structure.

5. Components Of Plant Cell Wall
The plant cell wall composed of :
1. The Middle Lamella
2. The Primary Cell Wall
3. The Secondary Cell Wall
4. The Tertiary Cell Wall

7. Middle lamella
It is the outer most layer of the cell wall connecting the two
adjoining cells like the cementing layer.
 Chemically it is composed of calcium and magnesium pectates.
It is thin and amorphous layer. It is an isotropic or optically inactive
layer of the cell.
In addition to these substances proteins are also present in the
middle lamellae.
It is the first formed layer of the cell wall during the cell division.
The cell plate formed during the cytokinesis itself develops into the
middle lamellum.

8. Primary wall
It is the layer present just under the inner side of middle lamella.
 It is thin, elastic and extensible in growing cells. Due the elastic
nature of the primary wall, it helps in increasing the cell volume.
 It is anisotropic layer or optically active layer of the cell.
Parenchymatous and meristematic cells possess only primary wall
and no secondary wall

9. Chemical composition of Primary wall
Chemically primary cell wall is composed
of cellulose, hemicellulose and pectin.
A loose network of cellulose microfibrils
embedded in a gel like matrix.
The matrix is mainly composed of water,
hemicellulose, pectin and glycoprotein.
Pectin is the filling material of the
matrix. Hemicellulose binds the
microfibrils with the matrix and the
glycoproteins control the orientation of
the microfibrils.

10. Plasmodesmata
Certain thinner areas present in the primary cell wall are called as
primary pit fields.
 In multicellular plants, cytoplasmic connections pass through these
pit fields from one cell to other. These cytoplasmic bridges found
between two cells are called plasmodesmata.
Plasmodesmata help in intercellular transportation of cellular
material from cell to cell.
Diameter is 40-50 nm.

11. Plasmodesmata
They form a protoplasmic band called Symplast. It consists of a canal, lined by
plasma membrane.
It has a simple or branched tubule known as desmotubule. Desmotubule is an
extension of endoplasmic reticulum.
Plasmodesmata serve as a passage for many substances and they also have a
role in the relay of stimuli.

12. Secondary Cell Wall
 It is extremely rigid and provides
strength.
 It is not found in all cell types.
 It consists of three layers known
as S1(outer),S2(middle) and
S3(inner).
 It is composed of cellulose,
hemicellulose and lignin.

13. Chemical composition of Secondary Wall
Chemically secondary wall is made up of a framework of cellulose microfibrils
and interfibrillar spaces are mostly filled with lignin, suberin, pectin and cutin.
 Secondary walls are hard, tough and inelastic in nature due to the presence of
wall materials like lignin.
It grows in thickness, layer by layer with the deposition of materials over the
existing structures.
The formation of secondary wall is not uniform in all the cells and this result
in differentiation of various types of cells like parenchyma, collenchyma and
tracheids.
 The areas in the secondary wall where wall material is not deposited are
called pits.

14. Pits and their types
Pits are the areas on the cell wall where secondary wall is not deposited.
The pits of adjacent cells are opposite to each other.
Each pit consists of a pit chamber and a pit membrane. The pit membrane
consists of middle lamella and primary wall. Pit membrane has many minute
pores and thus it is permeable.
The Pits help in the translocation of substances between two adjacent cells.
Generally pits develop in pairs. In other words, when a pit is present on the
secondary wall of one cell, a similar or dissimilar pit will be present on the
opposite side of the adjacent cell. Such type of pits form morphological and
functional units called pit pairs.
Pits are of two types namely: simple pits and bordered pits.

15. Simple pits
In simple pits, usually the pit cavities are uniformly wide on all sides. The
pit cavity is not enclosed by secondary cell wall.

16. Bordered pits
 In bordered pit, the secondary wall bends like an arch over the pit,
this gives a border like appearance and hence the name. The portion
of the middle lamellum crossing the pits become thickened and is
known as torus.

17. Tertiary Cell Wall
Tertiary cell wall is deposited in few cells.
 It is considered to be dry residue of protoplast . Besides cellulose
and hemi-cellulose, xylan is also present.

18. Composition Of Cell Wall
The cell wall is mainly composed of carbohydrate materials. The
major components of cell wall are
cellulose,
pectins,
hemicelluloses,
proteins and
 phenolics.

19. Cellulose
It provides shape and strength to the cell wall.
It composes 20-30 % of the dry weight of primary wall and accounts
40-90% of the dry weight of secondary wall.

20. Pectins
They are group of polysaccharides, which are rich in galacturonic
acid, rhamnose, arabinose and galactose.
Pectins are present in high concentration in the middle lamella
where they presumably serve the function of cementing adjacent cells
together.

21. Hemicelluloses
These are matrix polysaccharides built up of a variety of different
sugars. They differ in different species and in different cell types.
Xylan: It typically makes up roughly 5% of primary cell wall and
20% of secondary cell wall in dicots. This hemi cellulosic
polysaccharide is linked with xylose and arabinose.

22. Proteins
Different varieties of protein are present in the cell wall, most of
which are linked with carbohydrate forming glycoprotein.
The cell wall glycoprotein extensin contains an unusual amino acid
hydroxyproline (about 40%), which is generally absent from the
protoplast.
 Extensins are present in the primary cell walls of dicots making up
one to ten percent of the wall.

23. Primary Cell Wall vs Secondary Cell Wall
1. It is formed in the growing cells
2. It lies on the inside of the middle
lamella
3. It is present in all the plant cells
4. Primary cell wall is elastic and
flexible in nature
5. It consists of single layer of all
material
6. Chemically it is composed of
Cellulose 5%, Hemicellulose 50%,
Proteins 5%, Lipids 5-10%
1. It is formed in the mature non-
growing cells
2. It lies on the inside of the primary
cell wall
3. It is present only in certain types of
plant cells
4. Secondary cell wall is rigid and non-
flexible in nature
5. It is formed of three or more layers
6. Chemically it is composed of,
Cellulose 50-94%, Hemicellulose
25%, Proteins in very small
amounts, No lipids
Primary cell wall Secondary cell wall

24. Primary Cell Wall vs Secondary Cell Wall
7. It is about 1-3µ in thickness
8. Cellulose microfibrils are very
loosely arranged
9. Pits are formed in primary cell wall
10. No additional material like lignin
or suberin is found
11. Primary cell wall grows in
thickness by the process of
intussusception
7. It is about 5-10µ in thickness
8. Cellulose microfibrils ae compactly
arranged
9. Pits are formed in secondary cell
wall
10. Additional material like lignin and
suberin is often found
impregnated
11. Secondary cell wall increases in
thickness by apposition
Primary cell wall Secondary cell wall

25. Functions Of Cell Wall
1. Cell wall provides tensile strength and plasticity which are important
for keeping cells from rupturing by turgor pressure.
2. Thick cell walls give definite shape and mechanical support to the cell.
3. Cutinization in the cell wall protects the cell from water loss.
4. It protects the internal protoplasm against injury
5. Physiological and biochemical activities in the cell wall promote cell-
to-cell communication

26. Functions Of Cell Wall
6. Cell wall also helps in growth and development.
7. It prevents the bursting of plant cells due to endosmosis.
8. The walls of xylem vessels, tracheids and sieve tubes are
specialized for long distance transport.
9. In many cases, the cell wall takes part in offense and defense
against insects and pathogens.