What is cellulose primarily composed of?

Cellulose is primarily composed of a complex carbohydrate that serves as a crucial structural component of plant cell walls. It is made up of long chains of glucose molecules linked together by β(1→4) glycosidic bonds. This structure provides rigidity and strength to the plant cell walls, allowing plants to maintain their shape and resist external pressures. The ability of cellulose to form strong fibers is essential for the plant's overall integrity and plays a significant role in the process of photosynthesis by supporting the cells that carry out this vital function.

The other choices are not correct because they describe different macromolecules or their functions. Simple sugar molecules are primarily used for immediate energy needs and do not convey the structural properties of cellulose. Proteins, while essential for various cellular functions, are composed of amino acids and do not form the structural component of cell walls in plants. Similarly, lipids are responsible for energy storage and other functions but are not involved in providing the rigidity and structure that cellulose offers to plant cells. Understanding cellulose's role highlights its importance in plant biology and the ecosystem.