Organism

An organism is any complete, individual living thing. As a living thing, an organism necessarily has certain attributes or displays certain characteristics that make it different from a nonliving thing. The things that organisms must do to maintain life are called life processes.

Although both living and nonliving things are made up of many of the same types of atoms (the building blocks of an element that come together to form a molecule), there are drastic differences between the two in terms of how energy is used and how materials are organized. A bacterium living in a cow's gut is an organism, as is a worm or a tree—but a rock or a fire is not. Despite how dissimilar organisms can often appear, they exhibit certain features that are common to all. Knowing these life characteristics allows us to determine whether something is alive (and therefore is an organism) or not.

METABOLIC ACTIVITY

All organisms share the characteristics of taking in materials and releasing waste. Plants take in carbon dioxide and water and use sunlight to make food. Animals eat plants or other animals to take in nutrients or food. Plants give off oxygen and animals give off carbon dioxide and other waste materials. After taking in materials, all organisms show some form of metabolic activity. This means that organisms are able to break down materials and release the energy these materials contain. They can store this energy or use it to fuel their life processes. An organism can also build more of itself and grow or increase its size. It can repair itself and grow new and larger cells.

Organisms pass through their own life cycles. These cycles include a series of changes called development. All organisms also use part of their energy to produce more of their own kind. Reproduction is another characteristic of life. Every organism is itself the product of reproduction. This means that every organism is the offspring of one or more parent organisms. An individual organism can also be terminated or its life processes stopped permanently. If this happens because of an outside cause, then something has killed the organism. Whether or not it is killed, every organism still goes out of existence because of death. Death is therefore a characteristic of life.

INTERNAL ORGANIZATION AND HOMEOSTASIS

There are other characteristics of life important to organisms. All organisms show a capacity for internal organization. They are not a random jumble of cells, but are instead very organized internally and externally. Each organism has its own individual form of organization, so that a worm has a characteristic pattern that is quite different from a shrub. Another characteristic of organisms is their reactions, or responses to changes in their environment or surroundings. Animals often respond by movement, but nonmoving plants respond as well. A typical example of a plant responding to its environment is a potato plant forming an overwintering tuber (an underground bulb) as the days get shorter, or an onion plant forming bulbs during the long, hot days of summer. Organisms also react to their environment by making internal adjustments called homeostasis. Through homeostasis, organisms adjust their internal environment so that they maintain balanced or stable conditions. Organisms instinctively work at keeping things in control and constant. In terms of their behavior, all organisms have some degree of adaptive potential, which means that they can adjust to environmental changes over both the short term and the long term. This long-term adjustment occurs through the process of evolution (the changes an organism goes through over generations). A final characteristic of organisms is that their cells all contain deoxyribonucleic acid (DNA), which carries the genetic information specific to each organism. This DNA is carried in almost every cell within an organism and contains the instructions for reproducing traits that are to be inherited, or passed on, from parent to offspring.

An organism displays all of these traits or life processes. A nonliving thing may show some. For example, a fire can move, consume or take in materials, and give off a gas, or an automobile engine takes in materials and gives off a waste product. However, no nonliving thing can show all of them as an organisms does.

BASIC NEEDS

Organisms also have certain basic needs that must be met if they are to continue to live. Given the great variety of living things, those essential needs can be generalized by the following four requirements: energy, water, appropriate gases, and proper temperature. Organisms also share one common trait that is perhaps the most basic. All organisms are made up of one or more cells. Therefore, each organism shares the cell as the basic unit of life. Thus, a single-celled algae is as much an organism as a human being made up of trillion of cells.

[See alsoHomeostasis; Metabolism ]

Organism

An organism is any individual living entity. Organisms range in size and complexity from microorganisms to multicellular plants and animals. Modern biologists classify Earth's organisms into five kingdoms on the basis of common patterns of the design of life, that is, in their cellular and sub-cellular organization, metabolism , reproduction, and behavior . Listed in order of their earliest appearance in the fossil record of life, these kingdoms are:

1. Monera or prokaryotic microorganisms, which do not have their genetic material organized within a bounded organelle called a nucleus, along with other distinctive characteristics. Earth's simplest organisms occur in this group, in particular viruses, which consist of little more than a proteinaceous shell containing nucleic acids. Viruses are incapable of reproduction without parasitizing the metabolism of an unrelated host cell . Other major groups of monerans are blue-green bacteria and true bacteria.
2. Protista are a diverse group of microorganisms, containing the simplest of the eukaryotic organisms, which have an organized nucleus, one or more flagellae, and generally contain mitochondria and plastids. The most representative group is the protozoans, but some flagellated fungi and algae are placed within this group.
3. Fungi are a diverse group of non-flagellated, unicellular or multicellular organisms, ranging in complexity from single-celled yeasts, through multicellular but microscopic fungi growing as a thread-like mycelium, to relatively complex fungi that develop large mushrooms as their reproductive structures.
4. Plantae, or green plants, utilize solar radiation trapped by chlorophyll or other pigments to fix simple mineral nutrients into energy-rich biochemicals in a metabolic process called photosynthesis . Organisms in this diverse group range from unicellular algae, through multicellular but non-vascular algae, liverworts, and mosses, to vascular plants such as ferns , conifers, and flowering plants.
5. Animalia, or multicellular animals, are heterotrophic organisms that are capable of movement, often in response to sensory stimuli, and with other distinctive characteristics. Animals range in size and complexity from small sponges and arthropods to large vertebrates weighing tons.

All of Earth's organisms are related to varying degrees, sharing certain commonalities of physiology and other functions. Moreover, it is clear that some of Earth's distinctive organisms have a relatively ancient lineage that extends far back into the geological past, while other organisms are enormously more complex in biological organization than others. However, the modern, evolutionary interpretation of life suggests that none of Earth's organisms are "higher" or more "primitive" than any others, and that none have greater intrinsic value. Evolution has not occurred as a progression of types of organisms that represents a logical, directed succession from simple organisms (such as viruses and bacteria) to much more complex organisms (such as birds and mammals ). Earth's diversity of living organisms utilizes body and metabolic plans of varying complexity, but all species represent successful adaptations to the planet's habitable environments.

See also Animal; Plant; Protozoa; Virus.

Bill Freedman

Organism

An organism is any individual living entity. Organisms range in size and complexity from microorganisms to multicellular plants and animals. Earth’s organisms are organized into three domains based on their cellular and sub-cellular organization, metabolism, reproduction, and behavior. The bacteria are unicellular organisms that do not have their genetic material organized within a bounded organelle called a nucleus, along with other distinctive characteristics. The archaea, also unicellular organisms with unbounded nuclei, generally are those that are found in more extreme environments. Several fundamental cellular characteristics separate the bacteria from the archaea, in particular the systems for DNA replication and transcription and the structure of RNA transcriptase. Organisms that do have DNA that is found in nuclei are members of the eukarya. Organisms that belong to the domain Eukarya are classified into four kingdoms: Protista, Fungi Plantae, and Animalia.

Protista are a diverse group of microorganisms, containing the simplest of the eukaryotic organisms, which have an organized nucleus, one or more flagellae, and generally contain mitochondria and plastids. The most representative group is the protozoans, but some flagellated fungi and algae are placed within this group.

Fungi are a diverse group of non-flagellated, unicellular or multicellular organisms, ranging in complexity from single-celled yeasts, through multicellular but microscopic fungi growing as a thread-like mycelium, to relatively complex fungi that develop large mushrooms as their reproductive structures.

Plantae, or green plants, utilize solar radiation trapped by chlorophyll or other pigments to fix simple mineral nutrients into energy-rich biochemicals in a metabolic process called photosynthesis. Organisms in this diverse group range from unicellular algae, through multicellular but non-vascular algae, liverworts, and mosses, to vascular plants such as ferns, conifers, and flowering plants.

Animalia, or multicellular animals, are heterotrophic organisms that are capable of movement, often in response to sensory stimuli, and with other distinctive characteristics. Animals range in size and complexity from small sponges and arthropods to large vertebrates weighing tons.

Viruses are generally not considered organisms because of their inability to independently reproduce. However, the discovery of the mimiviruses, which are as large as some bacteria, in 2006, has opened discussion as to whether some viruses should be considered organisms.

See also Animal; Plant; Protozoa; Virus.

Bill Freedman

or·gan·ism / ˈôrgəˌnizəm/ • n. an individual animal, plant, or single-celled life form. ∎  the material structure of such an individual: the heart's contribution to the maintenance of the human organism. ∎  a whole with interdependent parts, likened to a living being: the upper strata of the American social organism.DERIVATIVES: or·gan·is·mal / ˌôrgəˈnizməl/ adj.or·gan·is·mic / ˌôrgəˈnizmik/ adj.

organism (or-găn-izm) n. any living thing, which may consist of a single cell (see microorganism) or a group of differentiated but interdependent cells.