The cell wall is a structure that is present in plant cells which surrounds the cell membrane. This is a special characteristic feature which helps distinguish plant cells from animal cells. The cell wall is one of the plant cell parts which is different, in that, it is composed of polysaccharides which are complex carbohydrates built from monosaccharides. In simple words, there is cellulose, hemicellulose, pectic polysaccharides, lignin, protein, certain lipids and water. The cell wall is formed during cell division itself, when the cell plate is formed between daughter cell nuclei. After its initial formation, there is thickening of the cell wall, which causes the lumen of the cell to shrink, as it occurs at the expense of the lumen. The reason why we need to know in detail about the cell wall structure is because the cell wall function and structure are complementary in nature. Given below is each function of cell wall explained in detail.
Cell Wall Functions
Determining Cell Shape
The shape of the plant cell is primarily determined by the cell wall. The cell wall can be compared to the skeleton of the human body, thus, it is the main supporting structure of the cell and is the skeleton of the cell. Due to this cell wall function, the rate and direction of growth of the cell is also monitored.
One of the important cell wall functions is providing strength to the cell. Although the cell wall is rigid in nature, it is also flexible to a certain extent. This is so because the cellulose fibrils are deposited in alternating layers. However, in plants, there is a secondary cell wall which is thicker in nature as it has an additional layer of cellulose, which is the main structure that provides rigidity to the cell. This is one of the important cell wall functions because the contents of the cell are floating in the plasma within the cell membrane, which does not provide any kind of strength to the cell.
Controlling Turgor Pressure
An important function of cell wall is to maintain turgor pressure. Turgor pressure or turgidity is defined as the pressure applied by the cell constituents on the cell wall. It is determined by the amount of water present in the one of the plant cell organelles, the vacuoles, which directly corresponds to the osmotic pressure. This force that is exerted gives the plant rigidity and helps to keep it erect. However, there needs to be a balance between the pressure exerted on the cell wall and the rigidity of the cell wall, as excess pressure can cause bursting of the cell while less pressure can make the cell flaccid.
Passage of Substances
One of the important cell wall functions is related to its semi-permeable nature. This feature of the cell wall is what allows exchange of substances, like passage of small molecules and small proteins in and out of the cell. Other important substances, like water and carbon dioxide, are also distributed throughout each plant cell with the help of cell wall to cell wall contact. Thus, one of the cell wall functions is maintenance of homeostasis in the cell.
The cell wall is the first line of defense for the cell during an attack from pathogens and microorganisms. Its property of being rigid prevents pathogens and other harmful foreign bodies from entering. It also offers protection against mechanical stress to the cell.
The cell wall is an important reserve of carbohydrates, which can in dire situations, be used by the cell for other metabolic purposes. It also said that the cell wall contains oligosaccharins which act as hormones for the cell, as they stimulate the synthesis of ethylene, chitinase and other such enzymes in the cell.
Thus, these were the various cell wall functions seen in plant cells. Often underestimated, the cell wall is a special feature of the plant cell which serves a variety of purposes. Thus, it is imperative to understand cell wall functions to truly appreciate the importance of this external complex structure.