What are the plant cell walls made from ?

Plant cell walls are made from cellulose, the woody stuff in trees. So when you saw down a tree, you are sawing down cellulose and lignin. If you look down a microscope, what you see is brick-shaped cells. The outermost part of each cell is the cell wall, and inside that is the cell membrane. Sometimes the outside can be lignified, which makes the cell stiff so plants can stand up straight. It's also how you make paper. All the cellulose and woody bits from the plant cell wall are the fibres you see in paper.