Final answer:
Bacteria are microscopic, single-celled organisms with diverse shapes like spheres, rods, and spirals. They lack nuclei and membrane-bound organelles.
Step-by-step explanation:
The characteristics that describe bacteria are:
They are microscopic: Bacteria are so small that they can only be seen with a microscope.They are single-celled: Each bacterium is made up of a single cell.They have shapes that include spheres, rods, and spirals: Bacteria can be classified by their shape, including cocci (spheres), bacilli (rods), and spirilli (spirals).They do not have nuclei and membrane-bound organelles: Bacteria have a nucleoid, which is a circular DNA, and lack membrane-bound organelles like eukaryotic cells.