Kingdom Monera comprises prokaryotic organisms, primarily bacteria. These single-celled organisms lack a true nucleus and membrane-bound organelles. Bacteria exhibit diverse shapes, including cocci (spherical), bacilli (rod-shaped), and spirilla (spiral). They reproduce mainly through binary fission and are classified based on morphology and Gram staining. While some bacteria are pathogenic, others play crucial roles in decomposition, nitrogen fixation, and biotechnology. Understanding bacteria is essential for fields such as medicine, agriculture, and environmental science.