Life and the Biosphere

Living matter and, as such, matter that shows certain attributes that include responsiveness, growth, metabolism, energy transformation, and reproduction. Although a noun, as with other defined entities,...

• abiogenesis

  the idea that life arose from nonlife more than 3.5 billion years ago on Earth. Abiogenesis proposes that the first life-forms generated were very simple and through a gradual process became increasingly complex. Biogenesis, in which life is derived...

• acclimatization

  any of the numerous gradual, long-term responses of an organism to changes in its environment. Such responses are more or less habitual and reversible should environmental conditions revert to an earlier state. The numerous sudden changes that evoke...

• Acetabularia

  genus of one-celled, umbrella-like green algae found in subtropical seas, called the “mermaid’s wine glass.” At the top of the tall, slender stalk, 0.5 to 10 cm (0.2 to 3.9 inches) long, is a ring of branches that may be separate or fused to form a cap....

• acquired character

  in biology, modification in structure or function acquired by an organism during its life, caused by environmental factors. With respect to higher organisms, there is no evidence that such changes are transmissible genetically—the view associated with...

• Acrasieae

  class name for cellular slime molds (division Myxomycophyta). The class contains a single order, Acrasiales, and about a dozen species. The vegetative phase of these slime molds consists of amoeba-like cells (myxamoebas) that group together ultimately...

• Adanson, Michel

  French botanist who devised a natural system of classification and nomenclature of plants, based on all their physical characteristics, with an emphasis on families. In 1749 Adanson left for Senegal to spend four years as an employee with the Compagnie...

• adaptation

  in biology, process by which an animal or plant species becomes fitted to its environment; it is the result of natural selection ’s acting upon heritable variation. Even the simpler organisms must be adapted in a great variety of ways: in their structure,...

• adaptive radiation

  evolution of an animal or plant group into a wide variety of types adapted to specialized modes of life. Adaptive radiations are best exemplified in closely related groups that have evolved in a relatively short time. A striking example is the radiation,...

• adenovirus

  any virus belonging to the family Adenoviridae. This group of viruses was discovered in the 1950s and includes 6 genera and 47 species (formerly referred to as serotypes) that cause sore throat and fever in humans, hepatitis in dogs, and several diseases...

• adipose cell

  connective-tissue cell specialized to synthesize and contain large globules of fat. There are two types of adipose cells: white adipose cells contain large fat droplets, only a small amount of cytoplasm, and flattened, noncentrally located nuclei; and...

• advertising coloration

  in animals, the use of biological coloration to make an organism unique and highly visible as compared with the background, thereby providing easily perceived information as to its location, identity, and movement. Such advertisement may serve the function...

• aggressive mimicry

  a form of similarity in which a predator or parasite gains an advantage by its resemblance to a third party. This model may be the prey (or host) species itself, or it may be a species that the prey does not regard as threatening. An example in which...

• aging

  progressive physiological changes in an organism that lead to senescence, or a decline of biological functions and of the organism’s ability to adapt to metabolic stress. Aging takes place in a cell, an organ, or the total organism with the passage of...

• agriculture

  the active production of useful plants or animals in ecosystems that have been created by people. Agriculture has often been conceptualized narrowly, in terms of specific combinations of activities and organisms—wet-rice production in Asia, wheat farming...

• air pollution

  release into the atmosphere of various gases, finely divided solids, or finely dispersed liquid aerosols at rates that exceed the natural capacity of the environment to dissipate and dilute or absorb them. These substances may reach concentrations in...

• Akeley, Carl E.

  American naturalist and explorer who developed the taxidermic method for mounting museum displays to show animals in their natural surroundings. His method of applying skin on a finely molded replica of the body of the animal gave results of unprecedented...

• Alexander, Samuel

  philosopher who developed a metaphysics of emergent evolution involving time, space, matter, mind, and deity. After studying in Melbourne, Alexander went to Balliol College, Oxford, in 1877 on a scholarship. In 1887 he received the Green Prize for “Moral...

• algae

  members of a group of predominantly aquatic photosynthetic organisms of the kingdom Protista. They range in size from the tiny flagellate Micromonas that is 1 micrometre (0.00004 inch) in diameter to giant kelps that reach 60 metres (200 feet) in length....

• alien

  hypothetical intelligent extraterrestrial being. See extraterrestrial intelligence. See also extraterrestrial life; unidentified flying object.

• Allee, Warder Clyde

  zoologist and ecologist noted for his research on social behaviour, aggregations, and distribution of animals in both aquatic and terrestrial environments. Allee became interested in the problems and patterns of the distribution of marine animals during...