UCMP Glossary: A

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abdomen -- Region of the body furthest from the mouth. In insects, the third body region behind the head and thorax.

absorption -- The taking in of water and dissolved minerals and nutrients across cell membranes. Contrast with ingestion.

abyssal plain -- The ocean floor offshore from the continental margin, usually very flat with a slight slope.

accrete -- v. To add terranes (small land masses or pieces of crust) to another, usually larger, land mass.

adaptation -- Change in a organism resulting from natural selection; a structure which is the result of such selection.

adult -- The mature stage of an organism, usually recognized by the organism's attaining the ability to reproduce.

adventitious roots -- A root that grows from somewhere other than the primary root, for example, roots that arise from stems or leaves.

aerobic -- Pertaining to the presence of free oxygen. Aerobic organisms require oxygen for their life processes.

alginate -- component of the cell walls of many rhodophytes and kelps. Alginates have an affinity for water, and so help to slow dessication when the algae are exposed to the air; they are commercially important in the production of paper, toothpaste, beer, and frozen foods.

alkaline -- Term pertaining to a highly basic, as opposed to acidic, subtance. For example, hydroxide or carbonate of sodium or potassium.

allochthonous -- Refers to something formed elswhere than its present location. Antonym of autochthonous.

alluvial fan -- n. A fan-shaped deposit of sand, mud, etc. formed by a stream where its velocity has slowed, such as at the mouth of a ravine or at the foot of a mountain.

alluvium -- n. a deposit of sand, mud, etc., formed by flowing water; alluvial - adj.

alternation of generations -- Life cycle in which haploid and diploid generations alternate with each other.

altricial -- adj. Refers to animals with young that are unable to move on their own after hatching or birth, and require extensive parental care. Songbirds, dogs, and humans are examples of species with altricial young.

amber -- Fossilization where the organism is entrapped in resin and preserved whole.

ambulacra -- Row of tube feet of an echinoderm.

amino acid -- unit molecule from which proteins are constructed by polymerization.

ammonite -- n. One of a group of extinct, shelled, marine cephalopods related to squids; cephalopods are within the larger group Mollusca, which includes clams and snails. Ammonite shells were generally coiled, though some non-coiled forms did exist. The group went extinct 65 million years ago at the end of the Cretaceous Period.

amniotic egg -- n. An egg that can be laid on land due to the presence of a fluid-filled amniotic sac (amnion) that cushions and protects the developing embryo. amniote - n. Any of a group of land-dwelling vertebrates that have an amnion during embryonic development, including reptiles, birds, and mammals. Most extant mammals give live birth, the egg being retained inside the body during gestation.

amoeboid -- Having no definite shape to the cell, able to change shape.

amphiesma -- The outer covering of a dinoflagellate, consisting of several membrane layers.

anaerobic -- Pertaining to the absence of free oxygen. Anaerobic organisms do not require oxygen for their life processes, in fact oxygen is toxic to many of them. Most anaerobic organisms are bacteria or archaeans.

anagensis -- Evolutionary change along an unbranching lineage; change without speciation.

anapsid -- n. A vertebrate distinguished by a skull with no openings in the side behind the eyes, e.g. turtles.

ancestor -- Any organism, population, or species from which some other organism, population, or species is descended by reproduction.

andesite -- Igneous volcanic rock, less mafic than basalt, but more mafic than dacite; rough volcanic equivalent of diorite.

anemophily -- Seed plants which are pollinated by wind are said to be anemophilous.

angiosperm -- n. A group of plants that produce seeds enclosed within an ovary, which may mature into a fruit; flowering plants.

anther -- The pollen producing tip of a stamen; part of a flower. More info?

antheridium -- The organ on a gametophyte plant which produces the sperm cells.

anthophyte -- A flowering plant, or any of its closest relatives, such as the Bennettitales, Gnetales, or Pentoxylales.

anticline -- A fold of rock layers that is convex upwards. Antonym of syncline.

anus -- End of the digestive tract, or gut, through which waste products of digestion are excreted, as distinct from the mouth.

aperture -- Small opening, for example the opening in the test of a foram.

apical meristem -- Group of cells at the growing tip of a branch or root. It divides cells to create new tissues.

archegonium -- The organ on a gametophyte plant which produces the egg cell, and nurtures the young sporophyte.

archipelago -- n. A group of islands; an expanse of water with scattered islands.

asexual reproduction -- A type of reproduction involving only one parent that usually produces genetically identical offspring. Asexual reproduction occurs without meiosis or syngamy, and may happen though budding, by the division of a single cell, or the breakup of an entire organism into two or more parts.

asphalt -- A dark bituminous substance found in natural beds. Residue from petroleum distillation.

ATP -- "adenosine triphosphate". A relatively stable, high energy molecule used to fuel chemical reactions within cells.

autochthonous -- Refers to something formed in its present location. Antonym of allochthonous.

autotroph -- Any organism that is able to manufacture its own food. Most plants are autotrophs, as are many protists and bacteria. Contrast with consumer. Autotrophs may be photoautotrophic, using light energy to manufacture food, or chemoautotrophic, using chemical energy.

Avalonia -- n. A separate plate in the Early Paleozoic consisting of much of Northern Europe, Newfoundland, Nova Scotia, and some coastal parts of New England.

axil -- The angle formed between a leaf stalk and the stem to which it is attached. In flowering plants, buds develop in the axils of leaves.