Robert Hooke first observed cells under a microscope in tree bark. Plant cell walls have three layers: the secondary cell wall, middle lamella, and primary cell wall. The cell wall provides structure, protects the cell, prevents over-expansion from water, and allows for the passage of small molecules through plasmodesmata, which connect adjacent cells and allow for communication. Cell walls vary between organisms, with plant cell walls containing cellulose, hemicellulose, pectin, and lignin, while bacterial cell walls contain peptidoglycan and fungal cell walls contain chitin.

1. CELL WALL
Dr. Sarita Nanda
Associate Professor
Daulat Ram College

2. CELL WALL

4. HISTORY OF CELL
 Robert Hooke was the first scientist to observe the
cell under the microscope.
 He observed it in the bark of a tree.

5. COMPOSITION OF OUTER LAYER OF PLANT
CELL
 Secondary cell wall- it is like primary cell wall but
is more rich in lignin.
 Middle lamella-it is rich in pectin and enzymes
 Primary cell wall-it is rich in cellulose,
hemicellulose, pectin

6. FUNCTION OF CELL WALLS
 To prevent over expansion of cell by water.
 The cell wall is seen in plants , bacteria and fungi
 The substance in cell wall differs from one species
to another
 They provide rigidity and strength
 They prevent toxic substances to enter in.
 A structure that protects and supports the cell.
 It gives shape to the cell.

7. PLASMADESMATA
 The cell walls are connected by plasmadesmata –
channels through the walls.
 They are connections between two adjacent cells.
 This allows cytoplasm of one cell to have
connection with the other cells.
 It is like the gap junctions of animal cells
 They allow cell to act in synctium as molecules and
ions can pass through it.
 The passage of these molecules is regulated.
 They have continued endoplasmic reticulum
between the cell which forms desmotubules.

8.  The primary cell wall is semipermeable and permits
passage of small molecules of 30-60kDa
 Water and CO2 can easily pass through it
 pH is an important determinant for the passage of
the molecules.
 The cell wall is a flexible structure and is not rigid
structure.
 The plant cell walls must have sufficient tensile
strength to withstand the turgor pressure.

9. PLASMADESMATA

10. PLASMADESMATA

11. COMPOSITION
The composition of the cell wall varies from one plant
to another. It essentially contains the following
components
 Hemicellulose- 20-35% xylan
 Cellulose
 Pectin
 Liginin

12. DIFFERENT KINDS OF CELL WALLS
 Plant- made of cellulose
 Bacterial – made of peptidoglycan
 Fungi- made of chitin
 Yeast-

13. CELL WALL STRUCTURE

15. CELL WALL OF FUNGI

16. BACTERIA

17. CELL WALL OF BACTERIA

18. GRAM POSITIVE AND GRAM NEGATIVE

19. DIFFERENCE BETWEEN GRAM POSITIVE AND
GRAM NEGATIVE BACTERIA

20. CELLULOSE AND PECTIN