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Cell Wall - What's it for?
While cell membranes might be around every cell, cell walls made of cellulose
are only found around plant cells. Cell walls are made of specialized sugars
called cellulose. Cellulose provides a protected framework for a plant cell to
survive. It's like taking a water balloon and putting it in a cardboard box. The
balloon is protected from the outside world. Cellulose is called a structural
carbohydrate (complex sugar) because it is used in protection and support.
Cell walls also help a plant keep its shape. While they do protect the cells, cell
walls and cellulose also allow plants to grow to great heights. While you have a
skeleton to hold you up, a 100-foot tall redwood tree does not. It uses the strong
cell walls to maintain its shape. For smaller plants, cell walls are slightly elastic.
Wind can push them over and then they bounce back. Big redwoods need
strength in high winds and sway very little (except at the top).
Another Hole in the Wall
A cell wall is not a fortress around the delicate plant cell. There are small holes in
the wall that let nutrients, waste, and ions pass through. Those holes are called
plasmodesmata. These holes have a problem: water can also be lost. But even
when the plant cell loses water, the basic shape is maintained by the cell walls.
So if a plant is drooping because it needs water, it can recover when water is
added. It will look just the same as when it started.
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More Than Walls in Plants
You may hear about cell walls in other areas of biology. Bacteria also have a
structure called a cell wall. Fungi and some protozoa also have cell walls. They
are not the same. Only plant cell walls are made out of cellulose. The other walls
might be made from proteins or a substance called chitin. They all serve the
same purpose of protecting and maintaining structure, but they are very different
molecules.