General

Cell wall


Definition:

The cell wall is an extracellular organelle that ensures stability and protection against external influences in plants, fungi and bacteria. Depending on the form of life, the main component of the cell wall varies considerably. In plants, the majority of cell walls are made of cellulose, mushrooms of chitin and bacteria of murein. All of these organic compounds are called polysaccharides (polyhydric sugars) and consist essentially of carbohydrates, which ultimately give the cell its stability.
Only the organisms mentioned above have cell walls. Humans and animals have no cell wall. Your cells are surrounded by a cell membrane, which usually consists of a lipid bilayer and is permeable only to certain substances (SemipermeabilitŠ´t).

Structure of the cell wall

This picture shows some E. coli bacteria. The cell wall is not entirely on the outside but is enveloped by the so-called glycocalyx, a mucous capsule. Only under the Glykokalyx is the actual cell wall.

The internal structure of the cell wall comprises several layers that are firmly connected to each other but interrupted by intermediary filaments. In the microscopic "cross section" through a cell wall, the middle lamella, the primary wall and the secondary wall emerge. All these media are closed outward through the tertiary wall.
In the further investigation of the fine construction of the cell walls, it is shown that a so-called middle lamella is interposed between the primary and the secondary wall. This has extremely small pores or Plasmodesmen (only in plant cells!), Which support a certain water permeability. The plasmodesms are also used to connect between similar cells in a cell network. This condition is important so that the cells can exchange water and nutrients with each other.

Function of the cell wall

The cell wall has several indispensable functions for the cell: it protects the protoplasm from destruction and stabilizes the cell shape.
By finishing with a slightly stretchable membrane, it is also possible to react to the expansion of the cell body if too much water is absorbed. Otherwise it could happen that the cell wall ruptures and the organelles are flushed out. That would be synonymous with cell death.
The cell is also able to perform a metabolism-regulating task via the cell wall. The cell walls are semi-permeable and thus contribute to the control of osmotic pressure. By maintaining and building up the wall pressure, cell walls also keep the cells from dehydration to some degree.
The formation of the secondary cell wall is stopped only when the cell has stopped growing. The microfibrils are then parallel to each other and there is an increasing storage of stabilizing lignins (only in plant cells!).