What are Bacteria? Give a short note on different sizes of bacteria.

Bacteria are microscopic, single celled prokaryotic organisms without nucleus and other cell organelles.
Although majority of bacterial species exist as single celled forms, some appear to be filaments of loosely joined cells.

• The size varies from less than 1 to 10 μm in length and 0.2 to 1 μm micrometer in width.