The cell wal is a very important feature in plant cells. It determines the mechanical strength of the cell, ascts as an exoskeletion controlling shape and allowing high turgot pressure to develop, and acts as a barrier by limiting the size of molecules that can reach the plasma membrane. Additionally, the cell wall can expand and change shape, whic controls the overrall shape of the cell. Plant cells walls are the most abundant source of organic carbon in nature.
There are two cell walls in plants. The primary cell wall is forme by growing cells and is relatively unspecialized. It is the outermost cell wall layer. The primary cell wall includes the Zone of Cell Elongation and the Zone of Cell Division.
The secondary cell wall is formed after cell growh has stopped and id highly specialized - both in structure and composition. This is determined by how the cell has differentiated. This is the next inner cell wall layer. This includes the Zone of Cell Differentiation and the mature cells layer. Plant cells also have a plasma membrane, on the inside of the secondary cell wall.
It is very important for cells to keep ions, sugars, and metabolite levels controlled in their cells. The plasma membrane plays an important role in this. It is permeable to water, oxygen, and carbon dioxied, but other compounds need to actively transported into the cells via protein channels. H+ is an exmple of an ion that needs to be actively transported across the membrane. A difference in H+ concentrations inside and outside the cell causes a pH gradient across the membrane. Proton gradients and electrical gradients are be harnessed to actively transport other molecules.
Osmosis can help to change the size of the cell because the plasma membrane is permeable to water, but not solutes or ions dissolved in the water. This means that if there is a high concentration of ios inside the cell, osmosis will drive the water inside of the cell as well, to balance out the high amount of solutes. Thus, the cell will swell, as there will be a lot of water entering it. This movement of water causes turgor pressure.
This turgor pressure happens due to the cell wall in plant cells. When the cell swells with water inside of the plasma membrane, the plasma membrane will eventually reach a point where it is fully stretched out and is pressed up against the secondary cell wall in the plants. The cell wall will push back against the cell, and won't allow more water to enter the cell. The plasma membrane and the cell wall pushing against each other causes a pressure called turgor pressure inside the cell.
Water can enter the cell through simple diffusion, or it could enter the cell through aquaporins- portein channels that are selective for water specifically. If there is high turgor pressure in the cell, enzymes in the cell wall will work to loosen the cell wall sugars so that the cell wall itself is loosened, and thus the cell wall expands. There will be less pressure with an expanded cell wall because the plasma membrane will no longer be pressing up right against it. This will then allow for more water to enter the cell, as the turgor pressure has been reduceed due to the expanded cell wall. Thus, an uptake of water will cause plant cells to grow, due to turgor pressure.