The cellulose wall forms at the plasma membrane of the parent cell, explains Scitable. Cellulose biosynthesis occurs during the growth cycle of plant cells. A growing cell wall contains cellulose microfibrils that are made from protein chains.
When a plant cell reproduces, it forms a new structure called a cell plate, notes the American Society of Plant Biologists. A substance called callose is deposited and synthesized in the cell plate, causing it to expand until it reaches the "zone of attachment" on the mother cell wall. After it's attached, it goes through a maturating process during which the callose is replaced by cellulose and pectin. Cellulose biosynthesis occurs at the plasma membrane, and pectin biosynthesis happens within structures called the Golgi.
Plant cell walls are the primary source of cellulose, the most abundant and useful biopolymer on the Earth, says Scitable. Plant cells are encased in a complex wall that constitutes the raw material used to manufacture textiles, paper, lumber, films, thickeners and other products. The cell wall serves to strengthen the plant body and also has key roles in growth, cell differentiation, intercellular communication, water movement and defense. Without cell walls, plants would look like more like slime molds than trees and bushes.