Green plants have very different cellular structures than other organisms. In addition to containing chlorophyll, the substance in green plants that results in the conversion of light to usable sugars via photosynthesis, green plant cells contain two distinct cell walls.
Cell Wall Structure
The cell walls in green plants have two layers: the primary layer and the secondary layer. Each layer serves a different function. (In contrast, most animal cells only have a single-layer membrane, rather than a cell wall.) This dual-layer construction allows for more structural stiffness in green plant cells than in comparable single-walled cells. Primary cell walls are responsible for stiffness and shape, while secondary walls give the cell its strength.
The primary cell wall provides protection for growing green plants. The primary wall is responsible for creating the cell's shape and protecting the cell against disease and liquid loss. The primary wall of the cell is isolated from other cellular structures and is composed of minerals, polysaccharides and structural proteins that give the primary wall a rigidity that, when combined with the primary walls of other cells, give green plants their structure.
Secondary cell walls are actually thicker than the primary and contain most of the carbohydrates stores in the cells of green plants. The secondary wall is responsible for giving green plant cells their rigid strength. Dead secondary plant cell walls are a major component in wood. Although both primary and secondary plant walls contain cellulose, secondary walls contain proportionally more.