What are bacteria?
A: Bacteria are ubiquitous, mostly free-living organisms often consisting of
one biological cell.
Typically a few micrometers in length, bacteria were
among the first life forms to do what?
A: To appear on Earth, and are present in most of its habitats.
Bacteria inhabit soil, water, acidic hot springs,
radioactive waste, and the deep biosphere of what?
A: Earth's crust.
Bacteria are vital in many stages of the nutrient cycle
by doing what?
A: Recycling nutrients such as the fixation of nitrogen from the atmosphere.
The nutrient cycle includes the decomposition of dead
bodies; bacteria are responsible for what?
A: The putrefaction stage in this process.
In the biological communities surrounding hydrothermal
vents and cold seeps, extremophile bacteria provide the nutrients needed to
sustain life by doing what?
A: By converting dissolved compounds, such as hydrogen sulphide and methane,
to energy.
Bacteria also live in symbiotic and parasitic
relationships with what?
A: Plants and animals.
Most bacteria have not been characterized and there are
many species that cannot be grown where?
A: In the laboratory.
The study of bacteria is known as what?
A: Bacteriology, a branch of microbiology.
Humans and most other animals carry how many bacteria?
A: Millions.
Most bacteria on humans are where?
A: In the gut, and there are many on the
skin.
Most of the bacteria in and on the body are harmless or
rendered so by the protective effects of what?
A: The immune system, though many are beneficial, particularly the ones in
the gut.
However, several species of bacteria are pathogenic and
cause what?
A: Infectious diseases, including cholera, syphilis, anthrax, leprosy,
tuberculosis, tetanus and bubonic plague.
What are the most common fatal bacterial diseases?
A: Respiratory infections.
What are used to treat bacterial infections and are
also used in farming?
A: Antibiotics, making antibiotic resistance a growing problem.
Once regarded as plants constituting the class
Schizomycetes ("fission fungi"), bacteria are now classified as what?
A: Prokaryotes.
Unlike cells of animals and other eukaryotes, bacterial
cells do not contain what?
A: A nucleus and rarely harbor membrane-bound organelles.
Although the term bacteria traditionally included all
prokaryotes, the scientific classification changed after the discovery in
the 1990s that prokaryotes consist of what?
A: Two very different groups of organisms that evolved from an ancient
common ancestor.
These evolutionary domains are called what?
A: Bacteria and Archaea.
The ancestors of bacteria were unicellular
microorganisms that were the first forms of life to appear on Earth, about
how long ago?
A: 4 billion years ago.
For about 3 billion years, most organisms were
microscopic, and bacteria and archaea were the what?
A: The dominant forms of life.
The most recent common ancestor of bacteria and archaea
was probably a what?
A: A hyperthermophile that lived about 2.5 billion–3.2 billion years ago.
Bacteria were also involved in the second great
evolutionary divergence, that of what?
A: Archaea and eukaryotes.
Bacteria are ubiquitous, living in every possible
habitat on the planet including soil, underwater, deep in Earth's crust and
even such extreme environments as what?
A: Acidic hot springs and radioactive waste.
There is approximately 2×1030 bacteria on Earth,
forming a biomass that is only exceeded by what?
A: Plants.
Most do not cause diseases, are beneficial to their
environments, and are essential for what?
A: Life.
The soil is a rich source of bacteria, and a few grams
contain how many of them?
A: Around a thousand million of them.
They are all essential to soil ecology by doing what?
A: By breaking down toxic waste and recycling nutrients.
They are even found in the atmosphere and one cubic
meter of air holds how many?
A: Around one hundred million bacterial cells.
The oceans and seas harbor around 3 x 1026 bacteria
which provide up to 50% of what?
A: The oxygen humans breathe.
How many bacterial species have been fully studied?
A: Around 2%.
Among the smallest bacteria are members of the genus
Mycoplasma, which measure only 0.3 micrometers, as small as what?
A: The largest viruses.