Cell Wall

The plant cell wall is a remarkable structure. It provides the most significant difference between plant cells and other eukaryotic cells. The cell wall is rigid (up to many micrometers in thickness) and gives plant cells a very defined shape. While most cells have a outer membrane, none is comparable in strength to the plant cell wall. The cell wall is the reason for the difference between plant and animal cell functions. Because the plant has evolved this rigid structure, they have lost the opportunity to develop nervous systems, immune systems, and most importantly, mobility.
The cell wall is composed of cellulose fiber, polysaccharides, and proteins. In new cells the cell wall is thin and not very rigid. This allows the young cell to grow. This first cell wall of these growing cells is called the primary cell wall. When the cell is fully grown, it may retain its primary wall, sometimes thickening it, or it may deposit new layers of a different material, called the secondary cell wall.
On the whole, each cell's cell wall interacts with its neighbors to form a tightly bound plant structure. Despite the rigidity of the cell wall, chemical signals and cellular excretions are allowed to pass between cells.

The Extracellular Matrix
The extracellular matrix (ECM) is a complex structural entity surrounding and supporting cells that are found within mammalian tissues. The ECM is often referred to as the connective tissue. The ECM is composed of 3 major classes of biomolecules:
1. Structural proteins: collagen and elastin.
2. Specialized proteins: e.g. fibrillin, fibronectin, and laminin.
3. Proteoglycans: these are composed of a protein core to which is attached long chains of repeating disaccharide units termed of glycosaminoglycans (GAGs) forming extremely complex high molecular weight components of the ECM.