Up to this point, we have looked at how the cytoskeleton maintains the shape of cells. We have also seen how the stable association of animal cells with one another and with the extracellular matrix is made possible by cell junctions, and that these junctions are reinforced by the cytoskeleton. As important as the cytoskeleton and cell junctions are to the structure of cells and tissues, it is the extracellular matrix that provides the molecular framework that ultimately determines the structural architecture of plants and animals.

The extracellular matrix is an insoluble meshwork composed of proteins and polysaccharides. Its components are synthesized, secreted, and modified by many different cell types. There are many different forms of extracellular matrix, which differ in the amount, type, and organization of the proteins and polysaccharides that make them up. In both plants and animals, the extracellular matrix not only contributes structural support but also provides informational cues that determine the activity of the cells that are in contact with it.

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