Cell wall
Japanese: 細胞壁
A rigid structure outside the cell membrane. Bacteria use peptidoglycan and fungi use chitin and glucan as main components, maintaining cell shape and protecting against environmental stress.
The cell wall is an armor-like structure outside the cell membrane of microorganisms. It protects cells from osmotic pressure changes and physical stress, and maintains their shape.
Bacterial cell walls are made of peptidoglycan, a polymer. Differences in peptidoglycan thickness determine Gram staining results. Penicillin is an antibiotic that kills bacteria by inhibiting peptidoglycan synthesis.
Fungal (mold and yeast) cell walls are composed of chitin and beta-glucan, completely different in composition from bacteria. This is precisely why penicillin does not work against fungi.
Differences in cell walls carry broad implications—from microbial classification to antimicrobial drug design to food processing methods. Knowing the wall is a foundation for knowing the microorganism.