Bacteria live almost everywhere and are microscopic, so they can only be seen with a microscope.  A bacterium is a prokaryote that lacks a nucleus. It typically ranges in size from one to five micrometers.  Prokaryotes are identified by characteristics such as shape, the chemical nature of their cell walls, and the way they move and obtain energy.

Bacteria are classified by their three different shapes.  For example, bacilli are rod-shaped bacteria; cocci are spherical-shaped bacteria; spirilla are spiral or corkscrew-shaped bacteria. Bacteria have a cell membrane that protects the cell wall.  The cell wall, which consists of peptidoglycan, provides them with structural support.   They have cytoplasm, where their DNA is found.  They have ribosomes but no nucleus, mitochondria, or chloroplasts.  Gram staining is a testing method used to determine if the bacteria’s cell wall is composed mainly of peptidoglycan or not.

Some bacteria are propelled by flagella, or whip-like structures, while others glide on the slime they secrete. Some may be carried by air, water, or other modes.  Some bacteria can make their own food either by using the sun or chemicals, while other types of bacteria need to take in food by consuming other organisms or food that organisms make.  Like many other organisms, most bacteria use respiration to break down food for energy.  While some are free-living, others are parasites that live on or in other living things.

In favorable conditions, bacteria can divide rapidly. Since they are prokaryotic, there is no male or female bacterium.  Instead, they reproduce asexually, where a parent produces an identical genetic copy of itself.  Bacteria reproduce by binary fission, which is a process that involves only one parent in which one cell divides to form two identical cells.  However, bacteria can acquire new DNA through the process of conjugation.  Conjugation is when a hollow bridge forms between two bacterial cells that allow genes to move from one cell to another.  When a bacterium is low on food, it can produce highly resistant cells to survive.  An endospore is a spore that is formed when a bacterium produces a thick internal wall that encloses its DNA. It will remain dormant until more favorable growth conditions are present.

Review:

1. How are prokaryotes identified?
2. What is the function of the flagella?
3. What is binary fission?