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.
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.
allochthonous -- Refers to something formed elswhere than its present location. Antonym of autochthonous.
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.
ambulacra -- Row of tube feet of an echinoderm.
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.
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.
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.
anticline -- A fold of rock layers that is convex upwards. Antonym of syncline.
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.
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.