Plants are unique amongst the eukaryotes, organisms whose cells have membrane-enclosed nuclei and organelles because they can manufacture their food. Chlorophyll, which gives plants their green color, enables them to use sunlight to convert water and carbon dioxide into sugars and carbohydrates; chemicals the cell uses for fuel. Like the fungi, another kingdom of eukaryotes, plant cells have retained the protective cell wall structure of their prokaryotic ancestors. The basic plant cell has the basic construction of a typical eukaryote cell but does not have centrioles, lysosomes, cilia, or flagella as does the animal cell. Plant cells do have specialized structures: a rigid cell wall, central vacuole, plasmodesmata, and chloroplasts.
             One of the most important distinguishing features of plant cells is the presence of a cell wall, a which serves a variety of functions. The cell wall protects the cellular contents, gives rigidity to the plant structure, provides a porous medium for the circulation and distribution of water, minerals, and other small nutrient molecules. It contains specialized molecules that regulate growth and protect the plant from disease. A structure of great tensile strength, the cell wall is formed from fibrils of cellulose molecules, embedded in a water-saturated matrix of polysaccharides and structural glycoproteins. Many plant cells have both a primary cell wall, while the cell is growing, and a secondary cell wall, which is produced inside the primary wall after the cell has stopped growing. Conduits called plasmodesmata penetrate both the primary and secondary cell walls, providing pathways for transporting cytoplasmic molecules from one cell to another. The primary chemical component of cell walls is cellulose, which is made up of several thousand glucose molecules linked end to end. Other chemicals that make up cell walls are lignins, which add rigidity, and waxes, such as cutin and suberin, which reduc...