Prokaryotes and Their Classification

Prokaryotic cells lack a true nucleus and membrane-bound organelles.
Prokaryotes significantly outweigh eukaryotes in biomass by at least 10 times.
Until recently, all prokaryotes were classified under a single kingdom called Monera.
Biologists now recognize significant differences between prokaryotic groups, leading to classification into separate domains.

Archaea appear similar to eubacteria microscopically.
Archaea are small, lack a nucleus, and have cell walls.
Chemically, archaea differ significantly from eubacteria.
Archaea lack peptidoglycans (a type of chemical found in eubacteria cell walls).
They use different types of membrane lipids compared to eubacteria.
The DNA sequences of their key genes are more similar to eukaryotes than to eubacteria.
Archaea dwell in extreme environments such as swamps, salt lakes, and hot springs.
The term "archaea" translates to "ancient" or "archaic", suggesting they inhabit environments similar to ancient Earth.
Genetic analysis of Archaea reveals at least three distinct groups: methanogens, halophiles, and thermoacidophiles.

Methanogens: These archaea generate energy by converting hydrogen gas and carbon dioxide into methane gas. They thrive in anaerobic environments like deep water, mud, and sewage, as well as cow and termite digestive tracts. A cow can emit 200-400 liters of methane per day.
Halophiles: These "salt-loving" archaea thrive in environments with extremely high salt concentrations like the Great Salt Lake and the Dead Sea.
Thermoacidophiles: These archaea are tolerant of exceptionally high temperatures (over 110°C) and highly acidic environments (pH less than 2). They are often found near hydrothermal vents (like "black smokers") emitting hot, acidic water in Yellowstone National Park. These vents support large worm, clam, and crab communities, with thermoacidophilic archaea being a food source.

Eubacteria are also called "true bacteria."
They come in a vast array of forms and inhabit almost every environment on Earth.
Eubacteria cell walls contain a polysaccharide called peptidoglycan.
Some are harmful and cause diseases, but most are benign or helpful.
Eubacteria are successful due to rapid cell division (doubling in 20 minutes) and diverse metabolisms.
They populate environments uninhabitable by other organisms.

Bacteria are significantly larger than viruses.
Prokaryotes are identified by shape, cell wall materials, movement, and energy sources. Common shapes are cocci (spherical), bacilli (rod-shaped), and spirilla (spiral or curved).

Bacteria are vital to the environment.
Bacteria are essential decomposers, helping recycle essential elements when organisms die.
They facilitate the return of essential elements like carbon and nitrogen back into the environment.
They are used in food production (yogurt, cheese).
Some bacteria help clean up oil spills.

Vaccines can prevent many bacterial diseases.
Vaccines work by introducing a weakened or dead pathogen into the body to stimulate the immune system to develop disease resistance.
This resistance, known as immunity, allows for a rapid response against any future exposures to the infectious pathogen.
Antibiotics are compounds that kill bacteria.
Unlike bacteria, antibiotics do not affect viruses.

Bacteria exhibit rapid growth rates under favorable conditions, doubling their numbers in as little as 20 minutes.
However, factors limit growth, including resource depletion, waste buildup, competition, and predation.
The primary mode of asexual reproduction is binary fission, which involves one cell splitting into two identical cells.

Under unfavorable conditions, many bacteria convert to a dormant form called endospores.
Endospores can resist extreme conditions for extended periods (months to years).
Endospores are revived when favorable growth conditions return.