Final answer:
The main component of plant cell walls is cellulose, a strong polysaccharide consisting of glucose units, complemented by hemicellulose and pectin, with some plants also having lignin in their secondary cell walls.
Step-by-step explanation:
The main component of plant cell walls is cellulose, a polysaccharide composed of long, straight chains of glucose units. Cellulose provides plant cell walls with their characteristic strength and rigidity, accounting for over thirty percent of plant matter, making it the most abundant organic compound on Earth. In addition to cellulose, plant cell walls also contain hemicellulose polymers and are embedded in pectin polymers. Some plant cells develop an inner secondary cell wall that includes cellulose and lignin, a complex phenolic polymer that adds further rigidity and support, allowing plants to grow tall and resist the compressive forces of gravity.
Microtubules guide the formation of the plant cell wall, where enzymes lay down cellulose to form the primary cell wall. Secondary cell walls containing lignin are deposited after cell growth has ceased, leading to the strength and woody texture in some plant tissues. This complex three-dimensional structure of cellulose, hemicellulose, and lignin makes the cell wall rigid, offering protection and structural support, and giving shape to plant cells. This fibrous matrix is also a significant dietary component known as fiber due to its cellulose content, providing a crunchy texture to vegetables like celery.