Bacteria are microscopic, single-celled organisms that exist in virtually every environment on Earth, from deep-sea vents to the human digestive tract. They are , meaning they lack a nucleus and membrane-bound organelles. While often associated with disease, the vast majority of bacteria are either harmless or essential to life. 1. Structure and Classification

Bacteria reproduce asexually through , a process where a single cell duplicates its DNA and splits into two identical daughter cells. Under optimal conditions, some species can double their population every 20 minutes. They can also exchange DNA through conjugation , which allows for the rapid spread of traits like antibiotic resistance. 3. Ecological and Industrial Importance

They break down organic matter, recycling carbon and nutrients back into the ecosystem.

Scientists use a Gram stain to classify them. Gram-positive bacteria have a thick peptidoglycan layer that retains purple dye, while Gram-negative bacteria have a thinner layer and an outer membrane, appearing pink.

Bacteria play a critical role in maintaining the planet's balance:

Common forms include cocci (spherical), bacilli (rod-shaped), and spirilla (spiral).