The primary difference in the cell walls of plant and bacterial cells lies in their composition. Plant cell walls are primarily made of cellulose, a polysaccharide, providing structural integrity and support. In contrast, bacterial cell walls contain peptidoglycan, which offers rigidity and protection. This distinction is important in understanding how different organisms interact with their environments and how certain antibiotics can target bacterial cell walls without affecting plant cells, highlighting the importance of cell wall composition in microbiology.