Diverse class of cytoskeletal elements that differ in diameter and composition depending upon cell type. Constructed from keratin subunits. More permanent than microfilaments and microtubules. Compose the nuclear lamina, lining the nuclear envelope's interior. Most cells produce coats that are external to the plasma membrane.
Chemical composition varies from cell to cell and species to species.
Basic design includes strong cellulose fibers embedded in a matrix of other polysaccharides and proteins. Functions to protect plant cells, maintain their shape, and prevent excess water uptake. Has membrane-lined channels, plasmodesmata , that connect the cytoplasm of neighboring cells.