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Cell wall structure and functions

The document discusses the structure and functions of plant cell walls. It describes how plant cell walls are composed of multiple layers including the primary cell wall, secondary cell wall, and middle lamella. The primary cell wall lies inside the middle lamella and is composed of cellulose microfibrils interwoven into a network. The secondary cell wall is deposited inside the primary cell wall in cells that have stopped growing. It provides strength and is composed of parallel cellulose microfibrils arranged in successive layers. The cell wall provides rigidity and shape to plant cells and protects the protoplasm.

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PLANT CELL WALL STRUCTURE AND FUNCTIONS DR. DILIP V. HANDE ASSOCIATE PROFESSOR, DEPT OF BOTANY SHRI SHIVAJI SCIENCE COLLEGE, AMRAVATI MS.
CELL WALL – STRUCTURE AND FUNCTION .
CELL WALL  The cell wall is perforated at one or more places through which the cytoplasm of a cell is connected with that of adjacent cells.  These cytoplasmic bridges interconnecting any two adjacent cells are termed as pldsmodesmata.  These are of great physiological importance because they allow flow of cytoplasmic materials from one cell to the other.  Between the walls of any two adjacent cells intercellular substance is deposited in the
CELL WALL  In plants the middle lamella is formed of calcium pectate.  The intercellular matrix cements the cells together cell wall to cell wall or pellicle to pellicle.  The middle lamella and outer cell wall or pellicles are emphasized as non-living because of the fact that they do not play important role in the life of cell.
CELL WALL  The cell wall or pellicle can be removed from a number of plant and animal cells by microsurgery and other techniques.  In plants the cell wall can be differentiated into primary, secondary and sometimes tertiary layers.  The secondary layer is deposited on the inner face of the primary membrane and the tertiary layer below the secondary one.
CELL WALL  Electron microscopy has revealed that the primary cell wall is composed of sub- microscopic strands of cellulose.  which in turn can be split into even finer threads by means of ultrasonic irradiations.  These microfibrils of the primary wall layer are interwoven to form a very dense network.
CELL WALL  The microfibrils of cellulose in the secondary cell wall tend to lie in parallel fashion forming successive lamellae instead of forming a network.  In the successive layers of secondary wall the orientation of the parallel microfibrils is changed.
CELL WALL  At certain places the microfibrils of secondary wall materials are not deposited, resulting thereby depressions or perforations.  Such characteristic perforations in the secondary "walls are known as pits.  There are micro capillary spaces between the microfibrils of cellulose in the secondary wall.
CELL WALL  In these microcapillary spaces lignin, cutin, suberine, hemicelluloses, minerals and some other wall materials are deposited.  which make the secondary wall tensile and sometime impermeable to water and gases .
CELL WALL  In general, the structure and the chemical constitution of cell walls will vary according to the physiology of plant tissue in which they are found.  The cell wall provides rigidity and support to the cells.  It also protects the protoplasm from mechanical injury and maintains the characteristic shape of cell.
STRUCTURE:  In plant cell wall is present outside the plasma membrane of every cell.  It is made up of dead matter secreted by the protoplasm.  Its structure and thickness varies in different tissue of the plants.  It is relatively thin in parenchymatous tissue and is probably thickest in xylem vessels.
STRUCTURE:  In plant cell wall is present outside the plasma membrane of every cell.  It is made up of dead matter secreted by the protoplasm.  Its structure and thickness varies in different tissue of the plants.  It is relatively thin in parenchymatous tissue and is probably thickest in xylem vessels.
ULTRASTRUCTURE C E L L W A L L
STRUCTURE  The plant cell wall is differentiated into following layers:  Middle lamella  It is the intracellular matrix between adjacent cells and holds the cells of the tissue together.  It is always found between the primary cell wall of neibouring cells.  It is composed of pectates of calcium and magnesium along with protein component.  It can be dissolved by strong acids.
ULTRASTRUCTURE  Primary cell wall  It is the true cell wall which develops in the still growing cells and lies on the inner side of the middle lamella.  It is formed of pectates, cellulose, hemicelluloses and some polysaccharides.
SECONDARY CELL WALL-  It is found in the mature or non-growing cells.  It is laid down on the inner side of the primary wall and develops only in those cells which have ceased to grow.  It is thick and rigid and provides great tensile strength to the cell.  It is composed of three successive layers of cellulose microfibrils in gelatinous matrix, formed of hemicelluloses and other polysaccharides.  In addition, it may be deposited with inorganic salts, tannins, waxes, calcium salts, silica, lignin, suberin and cutin etc.
ULTRASTRUCTURE  When cell wall after maceration, is studied under the electron microscope, it reveals two main parts- the matrix and fibril.  The matrix-  It is the ground substance in which fibrils are embedded. It is amorphous and is deposited with pectin, lignin or hemicelluloses.
ULTRASTRUCTURE  The fibrils-  The fibrils are composed of cellulose. The cellulose molecules are polymer of disaccharide cellobiose having approx. 3000 glucose unit which are arranged in linear order.  The cellulose molecules of the primary wall are arranged along the longitudinal axis of the cells in definitely organized longitudinal bundles.  These bundles are known as macrofibrils.
ULTRASTRUCTURE  The microfibrils are about 100-150A in diameter and about 1µ long.  These are thread like structures called microfibrills.  Each microfibrills is composed of 20 micelles.  Micelles are composed of about 100 individual cellulose chains.
FUNCTIONS  The function of the plant cell wall: 1. Maintains cell shape. 2. Prevents the rupture of the cell when excess water enters the cell by osmosis. 3. Filters out large molecules but allows smaller proteins and nutrients to enter. 4. The plant cell wall is mostly made up of cellulose, a linear polymer made up of several hundred to ten thousand D-glucose molecules chemically joined together. 5. As there is hydrogen bonding in between in the glucose molecules in different strands, this makes the whole cell wall rigid and inflexible.
FUNCTIONS  6. Thus when excess water enters the cell by osmosis, the cell expands and presses on the cell wall. Since the cell wall is inflexible, it exerts a force back on the cell.  7. Allows plant cell to stay in hypotonic solution (animal cells go through hemolysis because they lack a cell wall) 8. Function as building material for plants
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