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HarperCollins Dictionary of Biology
By W. G. Hale
HarperCollins Publishers, Inc.Copyright ©2006 W. G. Hale
All right reserved.
A abbrev. 1 ABSORBANCE.
2 the nitrogenous base ADENINE in NUCLEIC ACIDS.
Å abbrev. ANGSTROM.
a- prefix denoting not, without, away.
Ab abbrev. ANTIBODY.
ab- prefix denoting from, out of, away, apart.
A-band the dark band of the muscle sarcomere which corresponds to the thick myosin filaments. See MUSCLE CONTRACTION.
abaxial (of a leaf surface) facing away from the stem of the plant.
abdomen that part of the body of vertebrates containing the viscera (i.e. the kidneys, liver, stomach and intestines). In mammals it is separated from the thorax, which contains the heart and lungs, by the diaphragm. In arthropods it is that part of the body directly behind the thorax; in many other invertebrates the abdomen is divided into segments that have a superficial similarity.
abducens nerve the cranial nerve of vertebrates that supplies the external rectus muscle of the eye (see EYE MUSCLE); it is mainly MOTOR in function.
abductor or levator any muscle that moves a limb away from the body. An example of an abductor is the abductor pollicis, which moves the thumboutward. Compare ADDUCTOR.
abiogenesis see SPONTANEOUS GENERATION.
abiotic factor any contribution to the ENVIRONMENT or ecosystem that is of a nonliving nature, e.g. climate; pH.
ablactation the ending of milk production in female mammals; the process of WEANING
ablation the removal or destruction of any part of an organism.
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