Bacteria are minute, microscopic and unicellular organisms. They are of primitive type and are present everywhere. They were the first living organism and we come in contact with them in everyday life. We are familiar with that species of bacteria which cause infection. Other species of bacteria are quite unexplored. Scientists have shown a lot of interest in their life style and evolution. They belong to prokaryotes which are also known as Monera. Bacteria do not have a nucleus. It also lacks cell bound organelles like mitochondria, endoplasmic reticulum etc. They have single strand of DNA. The branch of biology which deals with the study of bacteria is known as bacteriology.
Bacteria have different forms and shape. It can be spiral, rod or curved shape. They have flagella for locomotion. Bacteria are protected by hard shell which protects them from outside forces. They may be free living or in combination with other organism. Sometimes they are dependent on host for their living and food and act as pathogenic type which causes cholera and tuberculosis. While some of them support host for break down in their food and provide shelter. Bacteria divide rapidly and their growth is of exponential type. They reproduce by budding and fission. Some of them also exchange genetic information.