A cell wall is a structural layer surrounding some types of cells, just outside the cell membrane. It can be tough, flexible, and sometimes rigid. It provides the cell with both structural support and protection, and also acts as a filtering mechanism

1. Cell Wall
Primary cell wall
Secondary cell wall

2. Introduction
• The cell wall is an outer protective membrane in many cells including
plants, fungi, algae, and bacteria. Animal cells do not have a cell wall.
• The main functions of the cell wall are to provide structure, support,
and protection for the cell.
• The cell wall in plants is composed mainly of cellulose and contains
three layers in many plants. The three layers are the middle lamella,
primary cell wall, and secondary cell wall.
• Bacterial cell walls are composed of peptidoglycan. Gram-positive
bacteria have a thick peptidoglycan layer and gram-negative bacteria
have a thin peptidoglycan layer. The cell wall is the most characteristic
feature of a plant cell

3. • Cell wall composition varies
depending on the organism.
• In plants, the cell wall is
composed mainly of strong
fibers of the carbohydrate
polymer cellulose. Cellulose is
the major component of
cotton fiber and wood, and it
is used in paper production.
• Bacterial cell walls are
composed of a sugar and
amino acid polymer called
peptidoglycan.
• The main components of
fungal cell walls are chitin,
glucans, and proteins.

4. The middle lamella
• The middle lamella is a pectin layer which
functions to cement the two adjoining cells
together of the cell wall.
• This is essential to plants as it gives them
stability, and allows that plants can form
plasmodesmata between cells.
• The middle lamella is the first layer that is
formed, which is deposited at the time of
cytokinesis. The cell plate that is molded
during cell division is developed into lamellum
or the middle lamella.
• This layer is basically made up of calcium and
magnesium pectates.
• It is a common structure between adjacent
cells and therefore, binds them with each
other
• The middle lamella remains unlignified in case
of softer living tissues namely Parenchyma,
collenchyma and arenchyma, but in woody
tissues Sclerenchyma it becomes highly lignified

5. Primary cell wall
• 1. Primary wall is laid inner to middle lamella.
• 2. It is formed in young growing cell
• 3. It is capable of extension.
• 4. The wall grows by intussusception or addition of
materials inside.
• 5. It is single layered.
• 6. Hydration is 60%.
• 7. Cellulose content is comparatively low.
• 8. Cellulose micro fibrils are shorter, wavy and loosely
arranged.
• 9. Protein content is high, up to 5%.
• 10. Hemicellulose content is high, up to 50%.
• 11. Lipid content is 5-10%.
• 12. Additional chemicals like lignin are absent.
• 13. Primary wall is thin (0.1-3 µm).
• 14. Pits are usually absent in a primary wall

6. Secondary cell wall
• 1. Secondary wall is laid inner to primary wall.
• 2. Secondary wall is formed when the cell has stopped
growing.
• 3. Extensibility is usually absent.
• 4. It grows by accretion or deposition of materials on the
existing structure.
• 5. Secondary wall is three or more layered known as S1
(outer), S2 (middle) and S3 (inner)
• 6. Hydration is 30—40%.
• 7. Cellulose content is comparatively high.
• 8. Cellulose micro fibrils are longer, closely arranged, straight
and parallel.
• 9. Protein content is low, 1% or less.
• 10. Hemicellulose content is 25% of the total.
• 11. Lipid is absent or negligible.
• 12. Lignin, suberin, etc. are present.
• 13 .Secondary walls is quite thick (3-19 µm).
• 14. Pits often occur in the secondary wall.