1.6. Cell Wall

The cell wall is a salient characteristic of plant cells. Prokaryotes, algae, and fungi also have walls around their cells, though these walls have a different chemical composition than those of plants. Animal cells do not have external walls (except marine tunicates), and instead build up extensive cytoskeletons within them to maintain structure. The main scaffolding units of the cell wall are polymers called cellulose. At a chemical level, cellulose consists of many sugar units linked together by chemical bonds like a chain - many chains wind together with one another to form cellulose microfibrils in the same way that many strings intertwine together to form rope. Microfibrils are 10 nanometers in diameter, stronger than an equivalently sized strand of steel, and are woven together around the cell.

The primary role of the cell wall is structural support, both for single cells as well as entire plants, forming an exoskeleton of sorts. The giant redwood trees in California that reach heights in excess of 300 feet are supported almost entirely by the strong cell walls of their trunks. The rigid structure of the wall provides a framework for the entire cell, determining its overall shape and restricting its ability to expand. The protoplast, and especially the vacuole, is full of water and exerts a positive outward pressure against the cell wall.  Without the outward turgor pressure and inward counteracting force exerted by the rigid cell wall, the plant would wilt. 

Humans use the walls of plant cells in unnoticeably countless ways in our day to day lives. Cell walls are raw materials for numerous manmade products such as clothing, wood for burning or construction, and paper for books. Herbivorous cattle use their gut bacteria to digest cell walls for nutrients, making them an indirect source of food for us humans. And most of the dietary fiber that we consume comes from the cell walls as well. It is well nigh impossible for us to comprehend a day without using something that makes use of plant cell walls.