Organism
In
biology [Overview of topic] and
ecology [Overview of topic] , an organism is a living complex adaptive system of organs that influence each other in such a way that they function in some way as a stable whole.
An organism is in a non-equilibrium thermodynamic state, maintaining a
homeostatic [Overview of topic] internal
environment [Overview of topic] , and a continuous input of
energy [Overview of topic] is required to maintain this state.
The
origin of life [Overview of topic] and the relationships between its major lineages are controversial. Two main grades may be distinguished, the prokaryotes and
eukaryote [Overview of topic] s.
Encyclopedia
In
biology [Overview of topic] and
ecology [Overview of topic] , an
organism is a living complex adaptive system of organs that influence each other in such a way that they function in some way as a stable whole.
An organism is in a non-equilibrium thermodynamic state, maintaining a
homeostatic [Overview of topic] internal
environment [Overview of topic] , and a continuous input of
energy [Overview of topic] is required to maintain this state.
The
origin of life [Overview of topic] and the relationships between its major lineages are controversial. Two main grades may be distinguished, the prokaryotes and
eukaryote [Overview of topic] s. The prokaryotes are generally considered to represent two separate
domains [Overview of topic] , called the
Bacteria [Overview of topic] and
Archaea [Overview of topic] , which are not closer to one another than to the eukaryotes. The gap between prokaryotes and eukaryotes is widely considered a major missing link in evolutionary history. Two
eukaryotic [Overview of topic]
organelle [Overview of topic] s, namely
mitochondria [Overview of topic] and
chloroplast [Overview of topic] s, are generally considered to be derived from endosymbiotic bacteria.
The phrase
complex organism describes any organism with more than one cell.
Semantics
The word "organism" may broadly be defined as
an assembly of molecules that influence each other in such a way that they function as a more or less stable whole and have properties of life. However, many sources, lexical and scientific, add conditions that are problematic to defining the word.
The
Oxford English Dictionary [Overview of topic] defines an organism as "[an] individual animal, plant, or single-celled life form" This definition problematically excludes non-animal and plant multi-cellular
life form [Overview of topic] s such as some
fungi [Overview of topic] and
protista [Overview of topic] . Less controversially, perhaps, it excludes
virus [Overview of topic] es and theoretically-possible man-made non-organic life forms.
Chambers Online Reference provides a much broader definition: "any living structure, such as a plant, animal, fungus or bacterium, capable of growth and reproduction". The definition emphasises life; it allows for any life form, organic or otherwise, to be considered an organism. This does encompass all cellular life, as well as possible synthetic life. This definition does lack the anything approximating to the word "individual" which would exclude viruses.
The word "organism" usually describes an independent collections of systems , or agro-ecosystems
- As ecosystems of inland waters, such as lentic ecosystems such as lake [Overview of topic] s or pond [Overview of topic] s; or lotic ecosystems such as river [Overview of topic] s
- As oceanic ecosystems.
Another classification can be done by reference to its communities, such as in the case of an human ecosystem.
Spatial relationships and subdivisions of land
Ecosystems are not isolated from each other, but are interrelated. For example,
water [Overview of topic] may circulate between ecosystems by the means of a
river [Overview of topic] or
ocean current [Overview of topic] . Water itself, as a liquid medium, even defines ecosystems. Some species, such as
salmon [Overview of topic] or freshwater
eel [Overview of topic] s move between marine systems and fresh-water systems. These relationships between the ecosystems lead to the concept of a
biome.
A biome is a homogeneous ecological formation that exists over a large region as
tundra [Overview of topic] or
steppe [Overview of topic] s. The
biosphere [Overview of topic] comprises all of the Earth's biomes -- the entirety of places where life is possible -- from the highest mountains to the depths of the oceans.
Biomes correspond rather well to subdivisions distributed along the latitudes, from the
equator [Overview of topic] towards the poles, with differences based on to the physical environment and to the
climate [Overview of topic] . Their variation is generally related to the distribution of species according to their ability to tolerate temperature and/or dryness. For example, one may find
photosynthetic [Overview of topic]
algae [Overview of topic] only in the
photic part of the ocean , while
conifer [Overview of topic] s are mostly found in mountains.
Though this is a simplification of more complicated scheme,
latitude [Overview of topic] and altitude approximate a good representation of the distribution of
biodiversity [Overview of topic] within the biosphere. Very generally, the richness of biodiversity is decreasing most rapidly near the
equator [Overview of topic] and less rapidly as one approaches the poles.
The biosphere may also be divided into
ecozone [Overview of topic] , which are very well defined today and primarily follow the continental borders. The ecozones are themselves divided into ecoregions, though there is not agreement on their limits.
Ecosystem productivity
In an ecosystem, the connections between species are generally related to
food [Overview of topic] and their role in the
food chain [Overview of topic] . There are three categories of organisms:
- Producers -- usually plants which are capable of photosynthesis [Overview of topic] but could be other organisms such as bacteria around ocean vents that are capable of chemosynthesis.
- Consumers -- animals, which can be primary consumers , or secondary or tertiary consumers .
- Decomposers -- bacteria [Overview of topic] , mushrooms [Overview of topic] which degrade organic matter of all categories, and restore minerals to the environment.
These relations form sequences, in which each individual consumes the preceding one and is consumed by the one following, in what are called
food chain [Overview of topic] s or food network. In a food network, there will be fewer organisms at each level as one follows the links of the network up the chain.
These concepts lead to the idea of
biomass [Overview of topic] , of
primary productivity [Overview of topic] and of secondary productivity .
These two last ideas are key, since they make it possible to evaluate the load capacity -- the number of organisms which can be supported by a given ecosystem. In any food network, the energy contained in the level of the producers is not completely transferred to the consumers. And the higher one goes up the chain, the more energy and resources is lost and consumed. Thus, from an energy-and environmental-point of view, it is more efficient for humans to be primary consumers than as secondary consumers and still more so than as a tertiary consumer . An ecosystem is unstable when the load capacity is overrun and is especially unstable when a population doesn't have an ecological niche and overconsumers.
The productivity of ecosystems is sometimes estimated by comparing three types of land-based ecosystems and the total of aquatic ecosystems:
- The forests contain dense biomasses and are very productive. The total production of the world's forests corresponds to half of the primary production.
- Savannas, meadows, and marshes contain less dense biomasses, but are productive. These ecosystems represent the major part of what humans depend on for food.
- Extreme ecosystems in the areas with more extreme climates -- deserts and semi-deserts, tundra, alpine meadows, and steppes -- have very sparse biomasses and low productivity
- Finally, the marine and fresh water ecosystems contain very sparse biomasses .
Humanity's actions over the last few centuries have seriously reduced the amount of the Earth covered by forests , and have increased agro-ecosystems . In recent decades, an increase in the areas occupied by extreme ecosystems has occurred .
References
External links
- Citat: "...It means that some of the lowliest creatures in the plant and animal kingdoms, such as slime and amoeba, may not be as primitive as once thought...."
- download Publication quality photos
- Hesiocaeca methanicola In 1997, Charles Fisher, professor of biology at Penn State, discovered this remarkable creature living on mounds of methane ice under half a mile of ocean on the floor of the Gulf of Mexico.
- Citat: "...Bacillus simplex and Staphylococcus pasteuri...Engyodontium album...The strains cultured by Dr Wainwright seemed to be resistant to the effects of UV - one quality required for survival in space...."
- Citat: "..."It appears that this organelle has been conserved in evolution from prokaryotes to eukaryotes, since it is present in both,"..."
- Citat: "...Number of kingdoms has not been resolved...Bacteria present a problem with their diversity...Protista [Overview of topic] present a problem with their diversity...",
- . Species 2000 has the objective of enumerating all known species of plants, animals, fungi and microbes on Earth as the baseline dataset for studies of global biodiversity. It will also provide a simple access point enabling users to link from here to other data systems for all groups of organisms, using direct species-links.
- .
