Plant cell wall
With prokaryotes and the three plant-like kingdoms of eukaryotes, we see a well-defined structural layer called the cell wall outside the cell membrane. The cell wall provides extra structural stability and protection from intrusion It can be flexible or rigid, as needed by the particular species.
Plant cell walls can be between 0.1 and several micrometers thick and composed of up to three (3) layers: primary wall, secondary wall, and middle lamella. The primary wall is generally thin and flexible and is composed entirely of cellulose and hemicellulose, both of which are special types of a structural sugar called polysaccharides. Once the cell is fully grown, in many plant cell types, a thick layer called the secondary wall forms inside the primary wall (or as part of the cell wall that is adjacent to the cell membrane). In some cells, the secondary walls even contain lignin – a structural, naturally-occurring polymer – and this lignin adds rigidity to the wall and makes it waterproof by driving water out of the spaces within the cell wall. The middle lamella is the outermost layer of the plant cell wall, made up of mostly pectin, another polysaccharides. The middle lamella both offers the plant cell wall further protection and stability and provides an interface by which similar plant cells can collaborate. As plantae is one of the most evolved and advanced kingdom, a key feature of its cellular structure is its cells’ ability to work with each other, to act together, forming living tissues, which in turn collaborate to form living organs, which are essential to the livelihood of the plant.
Plant cell walls also contain structural proteins. Certain species have specialized cells that give the plant cell wall additional rigidity and/or protection. Suberin is a waxy substance that acts as a waterproofing agent in the cork cells of the bark of some trees. The secondary walls in grasses often contain silicon dioxide. This also adds to the strength of the cell walls. Plant cell walls contain numerous enzymes that help in the maintenance of the cell wall, another highly advanced function. In some species, the cell wall can also be used as storage of carbohydrates that can be used by the plant at a later time.
Plant cells include an extra rigid layer outside the cell membrane called the cell wall. Cell walls envelop the cell membrane and add an extra layer of stability, with ranging elasticity depending upon the species its type of cell wall. The cell wall is at least two layers: the primary wall and the middle lamella. Many plants also have thick secondary walls that form as part of their primary walls once the plant is fully grown, adding greater stability to the plant. Plant cell walls also play host to structural proteins, waterproofing substances, maintenance enzymes, and food storage.