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Plant cell walls. Coloured transmission electron micrograph (TEM) of cell walls in wood of the Canadian yew (Taxus canadensis). The outermost layer of a cell wall, the middle lamella (red), is shared between adjacent cells. Inside this is the primary cell wall (pale green) of cellulose fibrils in a matrix of pectin. Woody plant tissues also have a secondary cell wall (orange) of cellulose and lignin. Inside the secondary cell wall and next to the cell contents (black) is the plasma membrane. Cell walls provide plants with structure and support as they grow, and regulate the movement of substances between cells. Magnification: x63,000 when printed 10cm ewide.
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