The CELL WALL is a very complex structure. This structure was first discovered some time in the seventeenth-century, by a scientist named Robert Hooke. Hooke cut a thin slice of cork and examined it carefuly through a primitive microscope. Unfortunately, these cork cells were long dead, and the only remaining structure were the cell walls. The main reason for the cell walls being the only organelle left is that it is made up of cellulose. Cellulose is a very strong structure that allows for structural support. This is ideal for the cell wall, which function is to prevent water loss from inside the cell, and to provide structural strength to resist dehydration. Later, through more modern methods of researching the cell, scientists found that cell walls are actually composed of three layers, the Primary cell wall, the Secondary cell wall, and the Middle lamella. These three layers give an added support and protection to the plant cell, even long after it has died.
The cell wall is a non-living structure ranging anywhere from 0.1 to several mm thick. 50% of the cell wall consists of long-chain polymers of a-cellulose. The cellulose are arranged as microfibrils which provide the sructural reinforcement for the cell wall. There is also 5% of an acid known as pectin (mucopolysaccharide), 25% is composed of hemicellulose (which comes from sugars other than glucose), and is also 20% protein. Together, these materials form a matrix, which constrains the cells flexibility. As was stated in the introduction the cell wall is composed of three different layers: Primary cell wall, Middle Lamella, and the Secondary cell wall. The cell wall is made from vessicals of carbohydrates that are made in the golgi appparatus then transported to the cell wall, thus forming its structure.
The primary cell wall is the first section of the wall to be laid down by the plant cell. This primary cell wall is also able to expand as the cell grows in size. This primary cell wall may be impregnated with additional materials (cutin and suberin). These materials form a waxy cuticle, this cuticle is impermiable many types of invading particles.
Some plant cells add a secondary cell wall. The secondary cell wall is found between the cell membrane and the primary cell wall. Some plants have no need for the secondary cell wall. The secondary cell wall is often deposited in several laminated layers, this allows the secondary cell wall to have a strong and durable matrix that gives the plant cell support and protection. However, it is for this reason that some plants lack the need for a secondary cell wall. Such is the case of grasses and other flexible plants. Instead of the cell walls having three layers it only contains two, the primary cell wall and the middle lamella. Wood or other non-flexible plants would be an example of the types of plants that would need a secondary cell wall in the cell.
The primary cell walls of neighboring cells are not in direct contact with other cells. They are are seporated by a layer called the Middle Lamella, a layer of a jellylike polysaccharide called pectin. The middle lamella sticks the cells together, and acts like a bonding agent or glue. This is so that plant cells can stay more closley together.
The three basic function of the cell wall are to protect the plant cell from outside particles, invading or otherwise, with it's cuticle, maintain its shape, and prevent exessive uptake of water, which could lead to the bursting of the cell and the death of the plant or part of the plant affected. What the cell walls do for the plants in generalis that it specializes in holding the plant up, against the force of gravity. The main reason for this support is resist dehydration. The cell wall also plays an important function in the splitting of a plant cell to form two new cells. This forming of two new cells is known as Miosis. The cell wall of a plant takes its part in the last phase of miosis. The cell wall forms a cleff in the center edges of the cell, this cleff is called cleveage. This cleff then continues all the way down the cell until two new plant cells are formed.
The cell wall its self is located just outside the plasma membrane of a plant cell. However, the individual layers of the plant cell are found thusly: The Secondary cell wall is nearest the plasma membrane, as to give the cell more support. Then the Primary cell wall which is located on the outside of the secondary cell wall. Finaly, when there are two or more cells in close proximity with eachother there is a layer known as the Middle Lamella that bonds these many primary cell walls together.
Despite the firmness of the plant cell, the cells are not functionaly isolated. The cell wall has depressions in them known as pores. These pores seemed to be closed by thin membranes, but are in fact open. Across these pores extend strands of cytoplasm called plasmodesmata. These follicles of cytoplasm allow the content of one cell to enter or exit into another cell. This is because the follicles connect to different cells around them.
Robert Hooke was the first man to actually see the cells of a plant. Skilled in the ways of microscopy he used an early microsopy to examine a cork. To his surprise he saw tiny box-like structures, the cell walls. Hooke believed that this was what the cork was composed of. Unfortunately for Hooke he was a little to late at looking at the cork cells. This is because t
