Answer:
A capsule surrounds the outside of the cell. Since the chemicals in many capsules are similar to those normally found in the body, they may prevent bacteria from being recognized or devoured by defensive cells of the host.
For example, the capsules of Streptococcus pneumoniae enable these prokaryotes to avoid destruction by defensive cells in the respiratory tract and cause pneumonia....uncapsuled strains of these same bacterial species do NOT cause disease b/c the body's defensive cells destroy them.