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A fungus (/ˈfʌŋɡəs/;
) is a member
of a large group of
eukaryotic organisms that
such as yeasts and molds
(British English: moulds),
as well as the more
These organisms are
classified as a kingdom,
Fungi, which is separate
from plants, animals,
protists and bacteria. One
major difference is that
fungal cells have cell
walls that contain chitin,
unlike the cell walls of
plants and some protists,
which contain cellulose, and unlike the cell walls of bacteria. These and other differences show that the
fungi form a single group of related organisms, named the Eumycota (true fungi or Eumycetes), that share
a common ancestor (is a monophyletic group). This fungal group is distinct from the structurally similar
myxomycetes (slime molds) and oomycetes (water molds). The discipline of biology devoted to the study
of fungi is known as mycology (from the Greek μύκης, mukēs, meaning "fungus"). Mycology has often
been regarded as a branch of botany, even though it is a separate kingdom in biological taxonomy.
Genetic studies have shown that fungi are more closely related to animals than to plants.
Abundant worldwide, most fungi are inconspicuous because of the small size of their structures, and their
cryptic lifestyles in soil, on dead matter, and as symbionts of plants, animals, or other fungi. They may
become noticeable when fruiting, either as mushrooms or molds. Fungi perform an essential role in the
decomposition of organic matter and have fundamental roles in nutrient cycling and exchange. They have
long been used as a direct source of food, such as mushrooms and truffles, as a leavening agent for bread,
and in fermentation of various food products, such as wine, beer, and soy sauce. Since the 1940s, fungi
have been used for the production of antibiotics, and, more recently, various enzymes produced by fungi
are used industrially and in detergents. Fungi are also used as biological pesticides to control weeds, plant
diseases and insect pests. Many species produce bioactive compounds called mycotoxins, such as
alkaloids and polyketides, that are toxic to animals including humans. The fruiting structures of a few
species contain psychotropic compounds and are consumed recreationally or in traditional spiritual
ceremonies. Fungi can break down manufactured materials and buildings, and become significant
pathogens of humans and other animals. Losses of crops due to fungal diseases (e.g. rice blast disease) or
food spoilage can have a large impact on human food supplies and local economies.
The fungus kingdom encompasses an enormous diversity of taxa with varied ecologies, life cycle
strategies, and morphologies ranging from single-celled aquatic chytrids to large mushrooms. However,
little is known of the true biodiversity of Kingdom Fungi, which has been estimated at 1.5 million to 5
million species, with about 5% of these having been formally classified. Ever since the pioneering 18th
and 19th century taxonomical works of Carl Linnaeus, Christian Hendrik Persoon, and Elias Magnus
Fries, fungi have been classified according to their morphology (e.g., characteristics such as spore color
or microscopic features) or physiology. Advances in molecular genetics have opened the way for DNA
analysis to be incorporated into taxonomy, which has sometimes challenged the historical groupings
based on morphology and other traits. Phylogenetic studies published in the last decade have helped
reshape the classification of Kingdom Fungi, which is divided into one subkingdom, seven phyla, and ten
A group of all the fungi present in a particular area or geographic region is known as mycobiota (plural
noun, no singular), e.g. "the mycobiota of Ireland".
Protists /ˈproʊtɨst/ are a
diverse group of
Historically, protists were
treated as a biological
kingdom formally called
the Protista and included
organisms that did not fit
into the other kingdoms.
Molecular information has
been used to redefine this
group in modern
taxonomy as diverse and
often distantly related
phyla. The group of
protists is now considered
to mean diverse phyla that
are not closely related
through evolution and
have different life cycles, trophic levels, modes of locomotion and cellular structures.
relatively simple levels of organization, the protists do not have much in common.
They are unicellular,
or they are multicellular without specialized tissues, and this simple cellular organization distinguishes the
protists from other eukaryotes, such as fungi, animals and plants.
The term protista was first used by Ernst Haeckel in 1866. Protists were traditionally subdivided into
several groups based on similarities to the "higher" kingdoms: the unicellular "animal-like" protozoa, the
"plant-like" protophyta (mostly unicellular algae), and the "fungus-like" slime molds and water molds.
These traditional subdivisions, largely based on superficial commonalities, have been replaced by
classifications based on phylogenetics (evolutionary relatedness among organisms). However, the older
terms are still used as informal names to describe the morphology and ecology of various protists.
Protists live in almost any environment that contains liquid water. Many protists, such as the algae, are
photosynthetic and are vital primary producers in ecosystems, particularly in the ocean as part of the
plankton. Other protists, such as the kinetoplastids and apicomplexans, are responsible for a range of
serious human diseases, such as malaria and sleeping sickness.
Some protists are significant pathogens of both animals and plants; for example there are five species of
the parasitic genus Plasmodium, which cause malaria in humans; and the oomycete Phytophthora
infestans, which causes late blight in potatoes.
A more thorough understanding of protist biology may
allow these diseases to be treated more efficiently.
Recent papers have proposed the use of viruses to treat infections caused by protozoa.
Researchers from the Agricultural Research Service are taking advantage of protists as pathogens in an
effort to control red imported fire ant (Solenopsis invicta) populations in Argentina. With the help of
spore-producing protists such as Kneallhazia solenopsae (this is more widely recognized as belonging to
the fungus kingdom now) the red fire ant populations can be reduced by 53-100%.
also found a way to infect phorid flies with the protist without harming the flies. This is important
because the flies act as a vector to infect the red fire ant population with the pathogenic protist.
Protozoa are a diverse group of unicellular eukaryotic organisms,
many of which are motile. Originally, protozoa had been defined as
unicellular protists with animal-like behavior, e.g., movement.
Protozoa were regarded as the partner group of protists to protophyta,
which have plant-like behaviour, e.g. photosynthesis.
Algae (/ˈældʒiː/ or /ˈælɡiː/; singular alga /ˈælɡə/, Latin for
"seaweed") are a very large and diverse group of simple, typically
autotrophic organisms, ranging from unicellular to multicellular forms,
such as the giant kelp (large brown alga), that may grow up to
50 meters in length. Most are photosynthetic and "simple" because
they lack many of the distinct cell organelles and cell types found in
land plants. The largest and most complex marine forms are called
Though the prokaryotic cyanobacteria are informally referred to as
blue-green algae, this usage is incorrect
since they are regarded as bacteria.
The term algae is now
restricted to eukaryotic organisms.
All true algae therefore have a nucleus enclosed within a membrane
and plastids bound in one or more membranes.
Algae constitute a polyphyletic group
since they do
not include a common ancestor, and although their plastids seem to have a single origin, from
they were acquired in different ways. Green algae are examples of algae that have
primary chloroplasts derived from endosymbiotic cyanobacteria. Diatoms are examples of algae with
secondary chloroplasts derived from an endosymbiotic red alga.
Slime mold or slime mould is a broad term describing some organisms
that use spores to reproduce. Slime molds were formerly classified as
fungi but are no longer considered part of this kingdom.
Their common name refers to part of some of these organisms' life
cycles where they can appear as gelatinous "slime". This is mostly seen
with the myxomycetes, which are the only macroscopic slime molds.
Found in a wide variety of colors, more than 900 species of slime mold
occur all over the world and feed on microorganisms that live in any
type of dead plant material. They contribute to the decomposition of dead vegetation, and feed on
bacteria, yeasts, and fungi. For this reason, these organisms are usually found in soil, lawns, and on the
forest floor, commonly on deciduous logs. However, in tropical areas they are also common on
inflorescences, fruits and in aerial situations (e.g., in the canopy of trees). In urban areas, they are found
on mulch or even in the leaf mold in gutters, and also grow in air conditioners, especially when the drain
is blocked. One of the most commonly encountered slime molds is the yellow Physarum polycephalum,
found both in nature in forests in temperate zones, as well as in classrooms and laboratories.
Most slime molds are smaller than a few centimeters, but some species may reach sizes of up to several
square meters and masses of up to 30 grams.
Bacteria ( i
constitute a large domain
or kingdom of prokaryotic
Typically a few
micrometres in length,
bacteria have a wide
range of shapes, ranging
from spheres to rods and
spirals. Bacteria were
among the first life forms
to appear on Earth, and
are present in most
habitats on the planet.
Bacteria inhabit soil,
water, acidic hot springs,
the deep portions of
Earth's crust. Bacteria also live in plants, animals (see symbiosis), and have flourished in manned space
There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of
fresh water. There are approximately 5×1030
bacteria on Earth,
forming a biomass that exceeds that of
all plants and animals.
Bacteria are vital in recycling nutrients, with many steps in nutrient cycles
depending on these organisms, such as the fixation of nitrogen from the atmosphere and putrefaction. In
the biological communities surrounding hydrothermal vents and cold seeps, bacteria provide the nutrients
needed to sustain life by converting dissolved compounds such as hydrogen sulphide and methane to
energy. On 17 March 2013, researchers reported data that suggested bacterial life forms thrive in the
Mariana Trench, the deepest spot on the Earth.
Other researchers reported related studies that
microbes thrive inside rocks up to 1900 feet below the sea floor under 8500 feet of ocean off the coast of
the northwestern United States.
According to one of the researchers,"You can find microbes
everywhere — they're extremely adaptable to conditions, and survive wherever they are."
Most bacteria have not been characterised, and only about half of the phyla of bacteria have species that
can be grown in the laboratory.
The study of bacteria is known as bacteriology, a branch of
There are approximately ten times as many bacterial cells in the human flora as there are human cells in
the body, with large numbers of bacteria on the skin and as gut flora.
The vast majority of the bacteria
in the body are rendered harmless by the protective effects of the immune system, and some are
beneficial. However, several species of bacteria are pathogenic and cause infectious diseases, including
cholera, syphilis, anthrax, leprosy, and bubonic plague. The most common fatal bacterial diseases are
respiratory infections, with tuberculosis alone killing about 2 million people a year, mostly in sub-
In developed countries, antibiotics are used to treat bacterial infections and also in
farming, so antibiotic resistance is becoming common. In industry, bacteria are important in sewage
treatment and the breakdown of oil spills, the production of cheese and yogurt through fermentation, the
recovery of gold, palladium, copper and other metals in the mining sector,
as well as in biotechnology,
and the manufacture of antibiotics and other chemicals.
Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes.
Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and rarely harbour
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 two very
different groups of organisms that evolved from an ancient common ancestor. These evolutionary
domains are called Bacteria and Archaea.