Cell wall | structure composition and Functions

Cell wall | structure composition and Functions
A cell wall is an outer layer surrounding certain cells that is outside of the cell membrane. All cells have cell membranes, but generally only plants, fungi, algae, most bacteria, and archaea have cells with cell walls. The cell wall provides strength and structural support to the cell, and can control to some extent what types and concentrations of molecules enter and leave the cell. The materials that make up the cell wall differ depending on the type of organism. The cell wall has evolved many different times among different groups of organisms.
The cell wall has a few different functions. It is flexible, but provides strength to the cell, which helps protect the cell against physical damage. It also gives the cell its shape and allows the organism to maintain a certain shape overall. The cell wall can also provide protection from pathogens such as bacteria that are trying to invade the cell. The structure of the cell wall allows many small molecules to pass through it, but not larger molecules that could harm the cell.
The main component of the plant cell wall is cellulose, a carbohydrate that forms long fibers and gives the cell wall its rigidity. Cellulose fibers group together to form bundles called microfibrils. Other important carbohydrates include hemicellulose, pectin, and liginin.

1. Cell wall structure composition and Functions ( plant cell wall)

2. CELL WALL

3. THE OBJECTIVE ARE: DEFINATION OF CELL WALL LAYERS OF CELL WALL FORMATION OF CELL WALL STRUCTURE OF CELL WALL THICKENING OF CELL WALL COMPOSITION OF CELL WALL FORMATION OF INTERCELLULAR SPACES

4. DEFINATION OF CELL WALL: THE OUTERMOST LAYER OF CELL IN PLANT,BACTERIA FUNGI AND MANY ALGAE THAT GIVE SHAPE TO THE CELL AND PROTECTS IT FROM INFECTION.IN PLANT THE CELL IS MADE UP OF MOSTLY CELLULOSE DETERMINS TISSUE TEXTURE AND OFTEN IS CRUCIAL TO CELL FUNCTION.COMPARE CELL MEMBRANE REFRENCE.

5. LAYERS OF CELL WALL: There are four layers of cell wall: Middle lamella P rimary wall Secondary wall Tertiary wall

6. LAYERS OF CELL WALL: Middle lamella: It is the cement that holds the individual cells together and it is found between the primary cell walls of neighboring cells. I t is an amorphous substance and isotropic. Primary wall: It is the first wall that develops in the new cell by protoplasm.The wall is formed cellouse.It is the wall that develops in growing cells.It is thin and elastic. Secondary wall: It is formed on the inner surface of the primary wall.It begins to develop in cells or parts of them which have ceased to grow.Generally,three layers of secondary wall can be observed,the outer layer,the central layer and the inner layer.

7. FORMATION OF CELL WALL: During cell division,at telophase,new cell wall formation takes place .The phragmoplast,a fibrous structure formed by macrotubules,appears during mitosis between the two daughter nuclei and within the cell plate which divides the parent cell in two.

8. STRUCTURE OF CELL WALL: PRIMARY STRUCTURE: Cell wall has complex structure and can be divided into different layers: PRIMARY WALL MIDDLE LAMELLA SECONDARY WALL

9. ULTRA-STRUCTURE OF CELL WALL: Structurally the cell wall is considered to be a fine interwoven network of cellulose strands varying complexity and size. The compound microscope show that the cell wall is composed of large fibrils. The electron microscope reveals that the fundamental units of the micellar system is chain like cellulose molecules of diffrent lengths formed of about (3000-6000 glucose molecules linked together) Approximately 100 cellulose chains aggregate to from an elementary fibril or micelle.

10. THICKENING OF CELL WALL: The secondary thickening due to lignification is uniform all around the cell but in tracheids and vessels the thickening due to localized to specific areas.The secondary thickenings of lignin may form various patterns. These are: ANNULAR SPIRAL SCALARIFORM RETICULATE PITTED

11. THICKENING OF CELL WALL: ANNULAR: (ring-like);Ring of lignin are deposited one above the other in the interior of the original cell wall. SPIRAL: (helices-like);Thickening of lignin are deposited in the form of spiral bands. SCALARIFORM: (ladder-type);Lignin is deposited in the form of the steps of a ladder along the inner side of the cell wall. RETICULATE: The lignin thickening is deposited in irregular manner and a network is formed. PITTED: The entire inner surface of the cell wall is tkickened,leaving small unthickenend areas called pits.

12. CHEMICAL COMPOSITION OF CELL WALL: The cell wall is composed of the following chemical compounds: CELLULOSE HEMICELLULOSES PECTIC SUBSTANCES LIGNIN CUTIN,SUBERIN,WAXES GUMS AND MUCILAGES

13. COMPOSITION OF CELL WALL: CELLULOSE: It is a carbohydrate and is the most common compound present in the cell walls.It is a hydrophilic,crystalline,compound polysaccharide.The molecules of the cellulose are chain-like and are formed by glucose residues held together by oxygen.

14. COMPOSITION OF CELL WALL: HEMICELLULOSES: It is a group of polysaccharides with different solubilities,such as xylans,mannans,glucans,etc. PECTIC SUBSTANCES: The are closely related to the hemicellulose.They found in three forms,protopectin,pectin and pectic acid and are polymers compound of uronic acid.The pectin compound are amorphous and hydrophilic.They form middle lamella. LIGNIN: It is a polymer of high carbon content,distinct from carbohydrates.The lignin of conifers and dicot from one another. CUTIN,SUBERIN,WAXES: These are fatty substance.Cutin and suberin are closely related,polymerized compound consisting of fatty acids.suberin occurs in association with cellulose in cork cells of periderm. GUMS AND MUCILAGE : These are related to pectin substances and swell up in water.Gums appear in plant due to break-down of walland cell components.

15. FORMATION OF INTERCELLULAR SPACES: The intercellular spaces are formed by two methods: 1.The cell wall is sparated from each other along areas of their contact.The mechanism is thought to involve spilting of the middle lamella.Such intercellular spaces are called Schizogenous intercellular spaces. 2.Sometimes the intercellular space is formed by the dissolution of entire cell.Such intercellular spaces are formed as Lysigenous intercellular spaces. FOR EXAMPLE: Large air spaces are present in aquatic plant and in some monocot roots,and secretory cavities found in citrus.

16. PLASMODESMATA: Cytoplasmic strand-like structures exending from protoplasts into cell wall and interconnecting the living protoplasts of the plant body are called Plasmodesmata.These are found in red algae,mosses,gymnosperms and angiosperms . PITS: Secondary walls are commonly characterized by presence of depressions or cavities called pits .such depressions are also present on the primary walls and these differ from the pits present in the –secondary walls in structure and development these depressions are known as primary pit-fields the primary wall is thin and continuous across the primary pit-field area .while in pits ,the secondary wall is not deposited in the pit region.

17. TYPES OF PITS: The pits are of two types: 1.Simple pits 2.Bordered pits 3.Simple pit-pair 4.Bordered pit-pair 5.Half bordered pit-pair 6.Blind pit 7.Unilateral compound pit 8.Torus

18. TYPES OF PITS: SIMPLE PITS: The secondary walls are deposited in such a way that it does not overarching the pit cavity.Such pits are termed as simple pits. BORDERED PITS: The secondary walls develops over the pit cavity to form an overarching hood with a harrow pore in the centre. SIMPLE PIT-PAIR: If the two pit-pairs are simple,they are knows as simple pit-pairs. BORDERED PIT-PAIRS: If the two pit-pairs are bordered,they are called bordered pit-pairs. HALF BORERDED PIT-PAIRS: If one of the pits is simple and other is bordered,it is knows as half bordered pit-pairs.

19. TYPES OF PITS: BLIND PITS: If the pit is without its opposite partner it an intercellular space is present,it called blind pit. UNILATERAL COMPOUND PIT: Sometime,two or more pits are found opposite one large pit,such an arrangement is called unilateral pitting. TORUS: In some plants,pit membrane of a bordered pit-pair is thickened in the centre in the form of a disc.This thickening is called torus.

20. REFRANCE: Hammad.M.Dr,cell wall:Def,Layers,Structure,Composition etc.Associate Professor of Botany.BOTANY (New edition):PP(172 to 181)