Which exterior structure is a slimy capsule of polysaccharides?

• A. Rigid cell wall
• B. Outer membrane
• C. Slimy capsule of polysaccharides
• D. Pili or flagella

Answer: (C)

A capsule is a slimy, gelatinous coating that sits outside the cell wall, and it is mainly made of polysaccharides. This exterior layer forms a protective, sticky shell around the bacterium, helping it adhere to surfaces and form biofilms, while also aiding in evading the host immune system by masking surface features. It’s distinct from the rigid cell wall, which provides structural support and is not slimy, and from the outer membrane found in some bacteria, which is a lipid-protein barrier rather than a polysaccharide capsule. Pili or flagella are protein filaments used for attachment or movement, not capsules made of polysaccharides. So the description of a slimy capsule of polysaccharides refers to the capsule itself.