abdomen
The portion of a tetrapod's body between the thorax and pelvic
girdle.The region of an arthropod's body behind the thorax.
It contains the visceral organs.
abducens A nerve.
abduct An action.
abductor A muscle that performs the action.
abioticfactor Nonliving
component in the environment.
abiotic A
non-living (physical or chemical) component of the environment.
Compare biotic.
abomasum Fourth and last chamber of the
stomach of ruminant mammals.
aboral The
part of the body farthest from the mouth.
aboral surface The
surface opposite the mouth (or oral surface) in echinoderms.
abrasion The
mechanical process of gradually breaking down a hard layer, as
in a seed coat.
abscess Dead cells and tissue fluid confined
in a localized area, causing swelling.
abscisic acid A
plant hormone associated with dormancy, abscission of organs,
and water stress.
abscission The
detachment of leaves, flowers, or fruit from a plant, usually
at a mechanically weak location, termed the abscission zone.
absorption spectrum Graph
of absorbance values for different wavelengths of light.
absorption The
process of taking in, as uptake by roots.
absorptive feeding A
means of taking up dissolved foodmaterial through specialized
organs or across the body wall.
absorptive heterotroph Mode
of nutrition in which organisms secrete digestive enzymes into
a substrate and then absorb the products of digestion; nutritional
mode of fungi.
abyssal plains
Flat, sediment-covered areas in the ocean basin usually 3,000
to 5,000 m deep.
abyssal zone The bottom from a depth of approximately 4,000 m (13,000 ft) to 6,000 m (13,100 to 20,000 ft).
abyssopelagic zone
The pelagic environment from a depth of 4,000 m (13,000 ft) to
6,000 m (20,000 ft) .
acanthella Developing
acanthocephalan larva, between an acanthor and a cystacanth, in
which the definitive organ systems are developed.
Acanthocephala The
phylum of aschelminths commonly called the spiny-headed worms.
acanthodians A group of the earliest known true jawed
fishes from Lower Silurian to Lower Permian.
acanthor Acanthocephalan
larva (first larval stage) that hatches from the egg. The larva
has a rostellum with hooks that are used in penetrating the host's
tissues.
accessory buds Those
buds adjacent to a primary bud and usually smaller in size.
accessory fruit Most
or part of the fruit is derived from tissue other than the ovary
of a flower.
accessory pigment One
of several nongreen photosynthetic pigments found in marine plants
that absorbs light energy from the center of the visible light
spectrum and transfers it to the green pigment chlorophyll.
accidental myiasis Presence
within a host of a fly not normally parasitic.Also called pseudomyiasis.
accidental parasite Parasite
found in other than its normal host. Also called an incidental
parasite.
acclimation The
change in tolerance of an animal for a condition in its environment.
acclimatization Gradual physiological adaptation
in response to relatively long-lasting environmental changes.
accommodation The
adjustment of the eye for various distances.
acetabulum True sucker, especially in flukes
and leeches; the socket in the hip bone that receives the thigh
bone.
Acetospora The
protozoan phylum characterized by members having multicellular
spores; all parasitic in invertebrates. Examples: acetosporans
(Paramyxa, Halosporidium).
acetylcholine A
neurotransmitter liberated by certain neurons. It is excitatory
at neuromuscular junctions and inhibitory at other synapses.
achene A
small, dry, one-seeded indehiscent fruit; the pericarp is
easily separated from the seed coat.
acicula Needlelike supporting bristle in parapodia
of some polychaetes.
acid rain The
combination of sulfur dioxide and nitrogen oxides with water in
the atmosphere. This combination produces acidicprecipitation
called acid rain. The burning of fossil fuels is a major contributor
to acid rain.
acid H+(proton)
donor; a substance that associates to release H+ and thus cause
the pH of the solution to be less than 7.0.
acidic Possessing
a relatively large number of hydrogen ions; having a pH less than
7.0.
acinar Cellular arrangement of some glands.
acinus A small lobe of a compound gland or a saclike
cavity at the termination of a passage.
acoelomate Lacking
a body cavity between the gut and the outer body wall musculature,as
in flatworms and proboscis worms.
acontium Threadlike structure bearingnematocysts located on mesentery of sea anemone.
acorn worms (or
enteropneusts)See hemichordates.
acoustic to hear.
acquired immunity Immunity
arising from a specific immune response, stimulated by antigen
in the host's body (active) or in the body of another individual
with the antibodies or lymphocytes transferred to the host (passive).
acquisition Gaining
a response in a learning paradigm.
acridine dyes Organic
pigment molecules that are capable of causing permanent genetic
changes (mutations).
acrocentric Chromosome with centromere near
the end.
acromion A process on the
scapula.
acron Preoral region of an insect.
acrorhagi Nematocyst-armed
defensive structures of anemones.
acrosome The
enzyme-filled cap on the head of a sperm. Used in egg penetration.
actin A
protein in a muscle fiber that, together with myosin, is responsible
for contraction and relaxation.
actinomorphic Regular
or radially symmetric flowers.
actinotroch Larval form found in Phoronida.
action potential The sequence of electrical changes occurring when a nerve cell membrane is exposed to a stimulus that exceeds its threshold.
activational effects Effects
of hormones that act as triggering influences on the expression
of particular behavior patterns, response is rapid, in hours or
days. Contrast with organizational effects.
activational effects of hormones
Events that occur in the
behavior of an animal where an external stimulus triggers a hormonally
mediated response by the organism.
active avoidance learning A
form of operant conditioning where the animal has to act in order
to avoid some noxious consequence (e.g., shock).
active continental margin A
continental margin that is colliding with another plate and as
a result is geologically active.Compare passive continental
margin.
active transport A
process that requires an expenditure of ATP energy to move molecules
across a cell membrane; usually moved against the concentration
gradient with the aid of specific transport proteins.
adaptation An anatomical structure, physiological process,
or behavioral trait that evolved by natural selection and improves
an organism's ability to survive and leave descendants.
adaptive behavior Behavior
patterns that make an organism more fit to survive and reproduce
in comparison with other members of the same species.
adaptive radiation Evolutionary
diversification that produces numerous ecologically disparate
lineages from a single ancestral one, especially when this diversification
occurs within a short interval of geological time.
adaptive value Degree
to which a characteristic helps an organism to survive and reproduce
or lends greater fitness in its environment; selective advantage.
adaptive zone A
characteristic reaction and mutual relationship between environment
and organism ("way of life") demonstrated by a group
of evolutionarily related organisms.
addictive drug Substance
that induces an addiction by causing physiological dependence,
psychological dependence, and/or tolerance.
adduct An action.
adductor A muscle that draws a part toward
a median axis, or a muscle that draws the two valves of a mollusc
shell together.
adenine A purine base; component of nucleotides
and nucleic acids. A nitrogen base found in both DNA and RNA.
adenohypophysis An endocrine gland.
adenophorea The
class of nematodes formerly called Aphasmidia. Examples: Trichinella,
Trichuris.
adenosine diphosphate (ADP)
The building block for ATP; by adding a terminal phosphate group
and a large amount of energy, ATP can be formed.
adenosine monophosphate AMP
molecule; created when the terminal phosphate is lost from a molecule
of adenosine diphosphate.
adenosinetriphosphate (ATP)
A complex organic compound composed of the molecule adenosine
and three phosphates, which serves in short-term energy storage
and conversion in all organisms.
adenosine (di-,
tri) phosphate (ADP and ATP). A nucleotide composed of adenine,
ribose sugar, and two (ADP) or three (ATP) phosphate units; ATP
is an energy-rich compound that, with ADP, serves as a phosphate
bond-energy transfer system in cells.
adhesio Interthalamica Part of the brain.
adhesion Attraction
between unlike molecules. The polar nature of water molecules
causes them to adhere to a surface.
adhesion The
attraction of unlike particles; water particles adhere to the
surface of clays.
adhesive disc Suckerlike
circular organ or organelle used for attachment.
adhesive gland Attachment glands in Turbellaria that produce a chemical that attaches part of the turbellarian to a substrate.
adipose Fatty tissue; fatty.
adipose tissue Fat-storing
tissue.
adoptive immunity Immune
state conferred by inoculation of lymphocytes, not antibodies,
from an immune animal rather than by exposure to the antigen itself.
ADP (adenosine diphosphate) A
nucleotide diphosphate that is often phosphorylated to form ATP.
adrenal glands
Paired endocrine glands, located next to the kidneys in the abdomen.
The adrenal cortex produces steroid hormones involved in water
balance, glucose metabolism, and electrolyte balance. The adrenal
medulla produces adrenaline and noradrenaline, which are involved
in glucose metabolism, heart rate, and blood pressure.
adrenaline A hormone produced
by the adrenal, or suprarenal, gland; epinephrine.
Adrenocorticotrophic A hormone secreted by the pituitary.
adsorption The adhesion of molecules to solid
bodies.
adventitious A
structure arising at some location not usually expected, such
as on a stem.
adventitous root A
root produced by a stem or leaf rather than by a root.
aeciospore Binucleate
spore produced in an aecium.
aecium Cup-shaped structure in rust fungi composed of binucleate
hyphae; aeciospores are formed here.
aedeagus Copulatory
organ or penis in insects and acarines.
aerate To
supply with oxygen.
aerial Pertaining
to being in the air, such as a root projecting from an aboveground
stem.
aerobic Having
molecular oxygen present; an oxygen-dependent form of respiration.
aerobic respiration Respiration in the presence of oxygen.
aerobic Oxygen-dependent form of respiration.
aestivation The
condition of dormancy or torpidity during the hot summer months.
afferent Adjective meaning leading or bearing
toward some organ, for example, nerves conducting impulses toward
the brain or blood vessels carrying blood toward an organ; opposed
to efferent.
aflatoxin A
complex of four mycotoxins produced by Aspergillus flavus; often
found in peanut products.
afterbirth The
placental and fetal membranes expelled from the uterus after childbirth.
agar Gelatinous
product extracted from the walls of some red algae; used in growth
media for microorganisms and in tissue culture.
age structure The
proportion of a population that is in preproductive, reproductive,
and postreproductive classes.
agent orange A
herbicide used as a defoliant in the Vietnam War; composed of
2,4-D and 2,4,5-T.
agregate fruit A
fruit derived from a single flower with several separate ovaries;
example: blackberry.
aggregated Describes
the concentration of most parasites of a single species in a minority
of hosts.Also called overdispersed.
aggression Behavior
that appears to be intended to inflict noxious stimulation or
destruction on another organism.
aggressive mimicry A
technique for capturing prey in which the predator uses lures
or other means to misinform the prey.
Agnatha A
superclass of vertebrates whose members lack jaws and paired appendages
and possess a cartilaginous skeleton and a persistent notochord.
Lampreys and hagfishes.
Agonist The "prime mover" or muscle
of reference.
agonistic behavior A
suite of behavior patterns used during conflict with a conspecific,
usually indicating whether an individual is going to submit to
the other animal or fight if the other does not submit.
agricultural infrastructure The
complexities of processing, storing, packaging, and transporting
farm products.
ahermatypic coral A
coral that does not build reefs.
air sacs Lateral
branches of the nasal passages of smaller toothed whales; sources
of echolocation sounds.
airfoil A
surface, such as a wing, that provides lift by using currents
of air it moves through.
ala Term often applied to winglike structure on plants or
animals: the lateral winglike expansions of the branchiuran carapace
to form respiratory alae, cuticular winglike expansions of nematodes,
and others.
Alare Usually a bone process shaped like a wing.
alate Winged.
albedo A
description of a surface's reflective properties.
albumin Any of a large class of simple proteins
that are important constituents of vertebrate blood plasma and
tissue fluids and also present in milk, whites of eggs, and other
animal substances.
alcoholic fermentation A
form of anaerobic respiration in which sugar is degraded to alcohol
and CO2
and energy is released.
aleurone layer A
group of cells rich in protein granules and located as the outer
layer of the endosperm of many grain seeds.
aleurone Protein-rich,
outermost layer of endosperm in a cereal grain.
alga A photosynthetic protist containing plastids. Any of several
groups of autotrophs that lack the structural features (true leaves,
roots, and stems) of the higher plants.
algal bloom A
proliferation of algae due to a nutrient-rich medium, usually
resulting in a green scum on the water surface.
algal grazer An
animal that consumes either large algae or thin algal films.
algal ridge A
ridge of coralline algae that is found on the outer edge of some
coral reefs.
algal turf A
dense growth of often filamentous algae.
algin A
polysaccharide derived from brown algae and used for many industrial
processes.
alginic acid Gelatinous
material extracted from the wall of certain brown algae; used
in a variety of commercial and industrial products.
alien species (exotic
species)A species introduced by humans.
alimentary Having to do with nutrition or nourishment.
alisphenoid A bone. (Note: Latin and Greek
roots are sometimes combined in the same term.)
alkaline Denoting
substances that release hydroxyl (OH_) ions into solution; see
basic.
alkaloid A
group of nitrogen-containing compounds having diverse structures;
many alkaloids have medicinal, hallucinogenic, or toxic properties.
all-or-none law The
phenomenon in which a muscle fiber contracts completely when it
is exposed to a stimulus of threshold strength. Also, the principle
that states a neuron will "fire" at full power or not
at all.
allantois One of the extraembryonic membranes
of the amniotes that functions in respiration and excretion in
birds and reptiles and plays an important role in the development
of the placenta in most mammals.
allee effect The
unfavorable consequences of undercrowding, as when populations
fail to breed when numbers are below some critical density.
allele Alternative forms of genes coding for
the same trait; situated at the same locus in homologous chromosomes.
allelopathy The
release of chemicals by certain plants that inhibit the growth
of competing plants.
allergens Substances
that activate the immune system and cause an allergic response;
may not be directly antigenic themselves but may make other materials
antigenic.
allograft A piece of tissue or an organ transferred
from one individual to another individual of the same species,
not identical twins; homograft.
allometry Relative growth of a part in
relation to the whole organism.
allopatric speciation The
formation of new species by a process involving geographic barriers.
allopatric In separate and mutually
exclusive geographical regions.
allopatry Populations
or species with nonoverlapping geographic distributions. Contrast
with sympatry.
alpha-helix Literally the first spiral
arrangement of the genetic DNA molecule; regular coiled arrangement
of polypeptide chain in proteins; secondary structure of proteins.
alpine The
high, treeless biogeographic zone of mountains that consists of
slopes above the timberline.
alternate arrangement One
leaf borne per node.
alternate host The
alternate plant required to complete the life cycle of some microorganisms.
For example, for Puccinia graminis tritice, wheat is the primary
host and Berberis vulgaris is the alternate host.
alternate Leaf
arrangement in which there is only one leaf.
alternation of generations A
reproductive cycle in which a sexual stage alternates with an
asexual one, as in the case of a gametophyte alternating with
a sporophyte.
altricial An animal that is helpless
at hatching or birth.
altricial young Young
that are born or hatched in a relatively immature or helpless
condition. Compare with precocial.
altruism The
principle or practice of unselfish concern for, or devotion to,
the welfare of others.
altruistic preservation A
philosophy of preserving nature for its own sake.
alula A
group of feathers on the wing of a bird that is supported by the
bones of the medial digit. The alula reduces turbulent airflow
over the upper surface of the wing.
amebocyte Cell in metazoan invertebrate,
often functioning in defense against invading particles.
ameboid Ameba-like in putting forth
pseudopodia.
ameboma Granuloma
containing active trophozoites, occasionally resulting from a
chronic amebic ulcer; rare except in Central and South America.
amebula Daughter
cell resulting from mitosis and cytokinesis of an encysted ameba.
ametabolous metamorphosis Development
in which the number of molts is variable; immature stages resemble
adults, and molting continues into adulthood.
amictic Pertaining to female
rotifers, which produce only diploid eggs that cannot be fertilized,
or to the eggs produced by such females. Compare with mictic.
amino acid An
organic molecule including one or more amino (_NH2)
and acid (_COOH) groups; one of the 20 nitrogen-containing
molecules that make up proteins.
amino group (_NH2)
A chemical part of a molecule that imparts basic properties to
an amino acid.
amitosis A form of cell division in which mitotic
nuclear changes do not occur; cleavage without separation of daughter
chromosomes.
ammonotelic excretion Having
ammonia as the chief excretory product of nitrogen metabolism;
occurs in freshwater fishes.
amniocentesis Procedure
for withdrawing a sample of fluid around the developing embryo
for examination of chromosomes in the embryonic cells and other
tests.
amnion One
of the extraembryonic membranes of the embryos of reptiles, birds,
and mammals. The amnion encloses the embryo in a fluid-filled
sac.
amniote lineage The
evolutionary lineage of vertebrates leading to modern reptiles,
birds, and mammals.
amniote
Having an amnion; as a noun, an animal that develops an amnion
in embryonic life, that is, reptiles, birds, and mammals.
amniotic egg The
egg of reptiles, birds, and mammals. It possesses a series of
extraembryonic membranes that help prevent desiccation, store
wastes, and promote gas exchange. These adaptations allowed vertebrates
to invade terrestrial habitats.
amoeboid movement A
form of movement similar to that found in amoebae. Fluid endoplasm
(plasmasol) flows forward inside the cell and changes state to
viscous ectoplasm (plasmagel) on reaching the tip of a pseudopodium.
At the opposite end of the cell, ectoplasm is converted into endoplasm.
amphibia The
class of vertebrates whose members are characterized by skin with
mucoid secretions, which serves as a respiratory organ. Developmental
stages are aquatic and are usually followed by metamorphosis to
an amphibious adult. Frogs, toads, and salamanders.
amphiblastula Free-swimming
larval stage of certain marine sponges; blastula-like but
with only the cells of the animal pole flagellated; those of the
vegetal pole unflagellated.
amphid One
of a pair of chemosensory organs found on the anterior end of
certain nematodes.
amphipathic Adjective
to describe a molecule with one part soluble in water (polar)
and another part insoluble in water (nonpolar).
amphipods A
group of small, laterally compressed crustaceans that includes
beach hoppers and others.
amphistome Fluke
with the ventral sucker located at the posterior end.
amplexus The
positioning of a male amphibian dorsal to female amphibian, his
forelimbs around her waist. During amplexus, the male releases
sperm as the female releases eggs.
amplitude The
maximum absolute value of a periodically varying quantity, as
the peak in activity in a circadian or circannual cycle.
ampulla of Lorenzini
One of several sensory structures
in the head of sharks that detect weak electric fields.
ampulla Membranous vesicle; dilation at one end of each semicircular
canal containing sensory epithelium; muscular vesicle above tube
foot in water-vascular system of echinoderms.
ampullary organ A
receptor that can detect electrical currents. These electroreceptors
are found in most fishes, some amphibians, and the platypus.
amygdaloid A part of the brain.
amylase An enzyme that
breaks down starch into smaller units.
amylopectin Component
of starch consisting of highly branched chains of repeating glucose
units; insoluble in water.
amyloplast Starch-storing
plastid.
amylose Component
of starch consisting of unbranched chains of repeating glucose
units; soluble in water.
anabolic Chemical
reactions that synthesize and require energy.
anabolism Any
constructive metabolic process by which organisms convert substances
into other components of the organism's chemical architecture.
System of biosynthetic reactions in a cell by which large molecules
are made from smaller ones.
anadromous Refers to fishes that migrate up streams
from the sea to spawn.
anaerobic The
phase of cellular respiration that occurs in the absence of oxygen;
lacking oxygen.
anaerobic bacteria Bacteria
that do not need oxygen.
anaerobic respiration The
incomplete intracellular breakdown of sugar or other organic compounds
in the absence of oxygen that releases some energy and produces
organic acids and/or alcohol.
anaerobic Not dependent on oxygen for
respiration.
anal fin Each
of the last pair of ventral fins of fishes.
analgesic Pain-relieving
remedy.
analogous Structures
that have similar functions in two organisms but have not evolved
from a common ancestral form.
analogy Similarity of function but not of origin.
anamnestic response Immune
response to a challenge or secondary antigen inoculation, marked
by more rapid and stronger manifestation of the immune reaction
(specifically, antibody titer) than after the primary immunizing
dose.
anamorphic The
asexual or imperfect stage in a fungus life cycle.
anaphase The
stage in mitosis and meiosis, following metaphase, in which the
centromeres divide and the chromatids, lined up on the mitotic
spindle, begin to move apart toward the poles of the spindle to
form the daughter chromosomes.
anaphylaxis A systemic (whole body) immediate
hypersensitivity reaction.
anapolysis Detachment
of a senile proglottid after it has shed its eggs.
anapsid Amniotes in which the skull lacks
temporal openings, with turtles the only living representatives.
anastomose Coming together; usually of blood
vessels.
anastomosis A union of two or more blood vessels,
fibers, or other structures to form a branching network.
anatomy The
study of the structure of an organism and its parts.
anautogeny In some Diptera the necessity of a blood meal before eggs can develop within the female.
Anconeus elbow.
androecium A collective term referring to the
stamens within a flower.
androgen
Any substance
that contributes to masculinization, such as the hormone testosterone.
androgenic gland
Gland
located near the vas deferens in many Crustacea. Its secretions
are responsible for development of male secondary sexual characteristics.
androsterone An
animal hormone not synthesized by plants.
anecdysis Ecdysis
in which successive molts are separated by quite long intermolt
phases; referred to as terminal anecdysis when maximal size is
reached and no more ecdyses occur.
anemia Low
levels of hemoglobin due to iron deficiency or lack of red blood
cells.
aneuploidy Loss
or gain of a chromosome, cells of the organism have one fewer
than normal chromosome number, or one extra chromosome, for example,
trisomy 21 (Down syndrome).
angiosperm The
group of plants characterized by having flowers as their sexual
reproductive structures.
angiotensin Blood protein formed
from the interaction of renin and a liver protein, causing increased
blood pressure and stimulating release of aldosterone and ADH.
Angstrom A unit of one ten-millionth
of a millimeter (one ten-thousandth of a micrometer); it
is represented by the symbol Å.
Angularis sharply bent.
anhydrase An enzyme involved
in the removal of water from a compound. Carbonic anhydrase promotes
the conversion of carbonic acid into water and carbon dioxide.
animal behavior Activities
animals perform during their lifetime.
animal pole The
region of a fertilized egg where meiosis is completed. It contains
less yolk and is more metabolically active than the opposite vegetal
pole.
animalia The
kingdom of organisms whose members are multicellular, eukaryotic,
and heterotrophic. The animals.
animals Members
of the kingdom Animalia, which consists of heterotrophic, eukaryotic,
and multicellular organisms.
anisogametes
Outwardly
dissimilar male and female gametes. Anisogamy is the condition
of having dissimilar male and female gametes.
anisogamy The
condition in which the female gamete (ovum) is larger than the
male gamete (sperm).
anlage Rudimentary form; primordium.
annelida The
phylum of triploblastic, coelomate animals whose members are metameric
(segmented) and wormlike. Annelids have a complete digestive tract
and a ventral nerve cord.
annelids See
segmented worms.
annual ring Ring
of xylem in woody stem composed of springwood and summerwood that
corresponds in temperate regions to a chronological year.
annual A
plant that lives for a single growing season.
annulation External
division of a worm-shaped body into a series of conspicuous
rings.
annuli
Rings on the body of a parasite; not necessarily indicative of
internal segmentation.
annulus Any ringlike structure, such as superficial rings on leeches.
annulus In fern sporangia, a row of cells with both thin
and thickened cell walls which facilitate the opening of the sporangia
and the release of spores because of the unequal expansion and
tension produced as they are moistened and dried.
anoxic Lacking
oxygen.
antagonism The
condition of being an opposing principle, force, or factor, as
when two hormones have opposite effects on target tissues.
antagonist The muscle or muscles opposing the
agonist.
ante before [a prefix].
antebrachium anti = against; brachium = the arm.
antenna A sensory appendage on the head of arthropods, or
the second pair of the two such pairs of structures in crustaceans.
antennae (second
antennae of crustaceans) Second pair of appendages in Crustacea,
with bases usually immediately posterior to antennules; primarily
sensory but sometimes adapted for other functions; derived from
appendages on primitive third preoral somite; no homologous appendage
in insects.
antennal gland The
excretory organ in some crustaceans (crayfish). Called antennal
glands because of their location near the base of each second
antenna and their green color; also called green glands.
antennules (first
antennae) Anteriormost pair of appendages of Crustacea; primarily
sensory but often adapted for additional or other functions in
particular species; derived from appendages on primitive second
preoral somite; homologous to antennae of insects.
anterior station Development
of a protozoan in the middle or anterior intestinal portions of
its insect host, such as the section Salivaria of Trypanosomatidae.
anterior The head end of an organism, or
(as an adjective) toward that end.
anther The
male reproductive organ enclosing and containing the pollen grains.
antheridiophore in some liverworts, a stalk
that bears antheridia embedded on an elevated and expanded tip.
antheridium The multicellular male sex structure of plants other than seed plants.
anthocyanins A
group of water-soluble red to blue flavonoid pigments found
in certain plants; especially important pigmentation in flower
petals.
anthozoa The
class of cnidarians whose members are solitary or colonial polyps.
Medusae absent; gametes originate in the gastrodermis; mesenteries
divide the gastrovascular cavity. Sea anemones and corals.
anthozoans (class
Anthozoa)Cnidarians whose life cycle consists of a complex polyp
and no medusa.
anthracosaurs A group of Paleozoic
labyrinthodont amphibians.
anthropocentric The
belief that humans hold a special place in nature; being centered
primarily on humans and human affairs.
anthropomorphism The
attribution of human characteristics to nonhuman beings and objects.
antibiosis The
inhibition of growth of a microorganism by a substance produced
by another microorganism.
antibiotic Substance
that inhibits the growth of microorganisms, antibodiesProteins
(immunoglobulins) in cell surfaces and dissolved in blood, capable
of combining with the antigens that stimulated their production.
antibody
Immunoglobulin protein, produced by B cells (or plasma cells derived
from B cells), that binds with a specific antigen.
antibody titer Measure
of the amount of antibody present, usually given in units per
milliliter of serum.
anticoagulant
Substance that prevents blood clotting.
anticodon A
sequence of three bases on transfer RNA that pairs with codons
of messenger RNA to position amino acids during protein synthesis.
anticodon loop The
portion of a tRNA molecule responsible for the anticodon triplet,
which pairs with the codon of mRNA.
antigen A
foreign (nonself) substance (such as a protein, nucleoprotein,
polysaccharide, and some glycolipids) to which lymphocytes respond;
also known as an immunogen because it induces the immune response.
antigen challenge Dose
or inoculation with an antigen given to an animal some time after
primary immunization with that antigen has been achieved.
antigenic determinant Area
on an antigen molecule that binds with antibody or specific receptor
sites on the sensitized lymphocyte; it "determines"
the specificity of the antibody or lymphocyte. See epitope.
antiparallel Refers
to opposing strands of DNA that are oriented in opposite directions.
antipodal One
of several cells (usually three) of the embryo sac (female gametophyte)
of angiosperms. They are located opposite the egg and synergids.
antipodal cell The
three haploid cells at the end of the embryo sac away from the
micropyle.
antrum antrum = a cave.
aorta
aorta = great artery. Large artery carrying blood away from
the heart
aorta aperture An opening; the opening into
the first whorl of a gastropod shell.
apex Highest or uppermost point; the lower pointed end of
the heart. The tip of a structure; a leaf apex, for example, is
the tip of the leaf.
aphotic zone The
portion of the ocean where the absence of sunlight prohibits plant
growth.
apical complex Dense
ring and conelike structure, along with associated microtubules,
micronemes, and rhoptries, at the anterior end of an apicomplexan
sporozoite. (apical = at the apex.)A certain combination of
organelles found in the protozoan phylum Apicomplexa.
apical dominance The
phenomenon leading to controlled growth of lateral shoots; growth
occurs primarily at the top of the plant.
apical meristem A group of cells at the tip
of the stem and root that give rise by cell division to the primary
tissues and are ultimately responsible for the structural organization
of the entire primary plant body.
apical organ Organ
of unknown function at the apex of a cestode's scolex.
apical Pertaining to the tip or apex.
apicomplexa
The protozoan phylum characterized by members having an apical
complex used for penetrating host cells; cilia and flagella lacking,
except in certain reproductive stages. Examples include the gregarines
(Monocystis), coccidians (Eimeria, Isospora, Sarcocystis, Toxoplasma),
Pneumocystis, and Plasmodium.
aplacophora The
class of molluscs whose members lack a shell, mantle, and foot.
Wormlike, burrowing animals with head poorly developed. Some authors
divide this group into two classes: Caudofoveata and Solengasters.
apneustic breathing Breathing
pattern exhibited by marine mammals in which several rapid breaths
alternate with a prolonged cessation of breathing.
apocrine Applies to a type of mammalian
sweat gland that produces a viscous secretion by breaking off
a part of the cytoplasm of secreting cells.
apodeme Spinelike
inward projection of the cuticle in arthropods on which a muscle
inserts; a ridgelike projection is an apophysis.
apodous larva Larva
with no legs and with reduced head; usual in Hymenoptera, Diptera,
some Coleoptera; requires maternal care or deposition in or on
food source.
apolysis Disintegration
or detachment of a gravid tapeworm segment; also, the detachment
of the hypodermis from the old procuticle in arthropods before
molting.
apomorphic
Adjective that refers to the form of characters, in particular
characters whose form differs from that of the same character
in an outgroup.
aponeurosis Dense connective
tissue forming a broad tendon.
apoplast Pathway
of water entering a root that flows along intercellular spaces
and cell walls.
apoplastic Pertaining to the movement of water in the free space of tissue; free space includes cell walls and intercellular spaces.
apoptosis Genetically
determined cell death, "programmed" cell death.
apopyle In sponges, opening of the radial
canal into the spongocoel.
aposematic coloration Sharply
contrasting colors of an animal that warn other animals of unpleasant
or dangerous effects.
appendicular skeleton The
bones of the upper and lower extremities; includes the shoulder
and pelvic girdles.
appendicular Pertaining to appendages; pertaining
to vermiform appendix.
appendicularians See
larvaceans.
appendix Refers
to the appendix vermiformis of the colon.
appetitive behavior The
flexible introductory phase of a behavior sequence during which
the organism is searching to obtain something to meet a need,
as in seeking food, a mate, stimulation of a specific type, etc.
See consummatory behavior.
applied animal behavior A
subdiscipline concerned with all aspects of the behavioral biology
of pets, domestic animals, animals in zoos and circuses, and animals
in aquaria.
applied research Research
conducted to address a specific problem for the purpose of application
for productivity or commercial gain.
aquaculture The
farming of marine and freshwater organisms. Also see mariculture.
aquifer Underground
water reservoir.
aquifers Porous,
water-bearing layers of sand, gravel, and rock below the
earth's surface; reservoirs for groundwater.
arachnida The
class of chelicerate arthropods whose members are mostly terrestrial,
possess book lungs, or tracheae, and usually have four pairs of
walking legs as adults. Spiders, scorpions, ticks, mites, and
harvestmen.
arachnoid The weblike middle covering (meninge) of the central nervous system.
arachnoid Part of the membranes covering
the brain.
arbor arbor = a tree.
arboreal Living in trees.
archaea (archebacteria)
Early prokaryotes, differing from bacteria
in having unusual types of metabolism, membrane lipids, and amino
acid and DNA and RNA base sequences. Inhabit extreme environments.
archaeocytes Ameboid cells of
varied function in sponges.
archegonium Female gametangium in which the female gamete or
egg is produced and housed.
archenteron The main cavity of an embryo
in the gastrula stage; it is lined with endoderm and represents
the future digestive cavity.
archinephric archi = beginning, original; nephros = kidney.
archinephros
Ancestral vertebrate
kidney, existing today only in the embryo of hagfishes.
archosaur Advanced diapsid vertebrates,
a group that includes the living crocodiles and the extinct pterosaurs
and dinosaurs.
arcuate arcus = an arch, bow.
areolar A small area, such as spaces between fibers
of connective tissue.
areolus A
unit of diatom frustules.
arginine phosphate Phosphate
storage compound (phosphagen) found in many invertebrates and
used to regenerate stores of ATP.
aril Thick,
fleshy seed covering around some seeds.
arista Flagellumlike appendage on the antenna of a fly of the suborder Brachycera and some members of the Nematocera.
Aristotle's lantern The
set of jaws and associated muscles used by sea urchins to bite
off food.
arithmetic growth A
pattern of growth that increases at a constant amount per unit
time, such as 1, 2, 3, 4 or 1, 3, 5, 7.
arrhenotoky
Parthenogenetic production of males. See haplodiploidy.
arrhythmic activity Activity
that does not exhibit any clear cyclical pattern.
arrow worms (chaetognaths;
phylum Chaetognatha)Planktonic invertebrates characterized by
a streamlined, transparent body.
arteriole (A small artery that delivers
blood to capillaries.
artery A blood vessel that carries blood away from
the heart and toward a peripheral cavity.
artesian well The
result of a pressurized aquifer intersecting the surface or being
penetrated by a pipe or conduit, from which water gushes without
being pumped; also called a spring.
arthroidial arthrodia = gliding. A type of joint.
arthropoda The
phylum of animals whose members possess metamerism with tagmatization,
a jointed exoskeleton, and a ventral nervous system. Insects,
crustaceans, spiders, and related animals.
arthropodization Evolutionary
development of the combination of characteristics associated with
the Arthropoda, including a firm cuticular exoskeleton containing
chitin.
arthropods (phylum
Arthropoda)Invertebrates that have jointed appendages and a
chitinous, segmented exoskeleton.
articular
articularis = a joint.
articulate
articulatus = jointed.
Articulation
A joint or union of two
bones.
artificial selection Selective
breeding as practiced by humans on domesticated plants and animals.
artificially acquired active immunity
The type of immunity that
results from immunizing an animal with a vaccine.
artificially acquired passive immunity
The type of immunity that
results from introducing antibodies that have been produced either
in another animal or by specific in vitro methods into an animal.
artiodactyl One of an order of mammals with
two or four digits on each foot.
arytenoid
Cartilages in the larynx.
ascaridine Protein
of unknown function in the sperm of Ascaris.
ascaroside Glycoside
found in Ascaris, made of the sugar ascarylose and a series of
secondary monol and diol alcohols.
aschelminth Any
animal in the phyla Gastrotricha, Rotifera, Kinorhyncha, Nematoda,
Nematomorpha, Acanthocephala, Loricitera, Priapulida, or Entoprocta.
Aschoff's Rule Pertaining
to circadian rhythms, the rule stating that when nocturnal animals
are held in constant darkness, their free-running period
becomes slightly shorter each day and when a diurnal animal is
held in constant darkness, the free-running period becomes
slightly longer.
ascidiacea A
class of urochordates whose members are sessile as adults, and
solitary or colonial.
ascites Edema,
or accumulation of tissue fluid, in the mesenteries and abdominal
cavity.
ascocarp The
dense, compact mass of hyphae constituting the fruiting body of
the Ascomycetes.
ascogonium A female reproductive structure in some ascomycetes.
Ascomycetes A group of fungi whose spores are borne in an ascus
or bag.
ascon The
simplest of the three sponge body forms. Asconoid sponges are
vaselike, with choanocytes directly lining the spongocoel.
asconoid Simplest form of sponges, with canals leading
directly from the outside to the interior.
ascospore Sexual
spore of an ascomycete fungus that is produced by meiosis, followed
by mitosis.
ascus Saclike
reproductive structure of ascomycetes in which meiosis, followed
by mitosis, produces eight haploid cells called ascospores.
asexual Lacking
sexual reproduction; vegetative reproduction.
asexual (vegetative) reproduction
The type of reproduction
that takes place without the formation of gametes. Compare sexual
reproduction.
aspartate Four-carbon
amino acid found with malate to be the first products of the C4.
aspect ratio Index
of propulsive efficiency obtained by dividing the square of a
fish's fin height by the fin area.
asphyxiants Chemicals
that exclude oxygen or actively interfere with oxygen uptake and
distribution; includes inert chemicals, such as nitrogen gas or
halothane, that can displace oxygen and fill enclosed spaces.
assimilation Absorption and building
up of digested nutriments into complex organic protoplasmic materials.
aster
The star-shaped structure seen in a cell during the prophase
of mitosis; composed of a system of microtubules arranged in astral
rays around the centrosome; may emanate from a centrosome or from
a pole of a mitotic spindle.
asteroidea The
class of echinoderms whose members have rays that are not sharply
set off from the central disk; ambulacral grooves with tube feet;
and suction disks on tube feet. Sea stars.
asthma A
distressing disease characterized by shortness of breath, wheezing,
and bronchial muscle spasms.
asymmetry Without
a balanced arrangement of similar parts on either side of a point
or axis.
asynchronous flight See
indirect flight.
atherosclerosis
Disease characterized by fatty plaques forming in the inner lining
of arteries.
athlete's foot A
disease caused by imperfect fungi that flourish under warm, wet
conditions. Usually dissappears if the feet are kept dry.
atmosphere A
unit of pressure equal to 14.7 lbs/in.2 and equivalent to the
pressure created by a 10 m column of water.
atmospheric deposition Sedimentation
of solids, liquids, or gaseous materials from the air. Snow, rain,
and dust are the most familiar examples, but acids, metals, and
toxic organic chemicals also can be transported by winds and deposited
far from the source of origin.
atmospheric pressure Ambient
pressure created near the earth's surface by large air cells that
circulate around the globe.
atoke
Anterior, nonreproductive
part of a marine polychaete, as distinct from the posterior, reproductive
part (epitoke) during the breeding season.
atoll A ring-shaped chain of coral reefs from which a
few low islands project above the sea surface.
atom The
basic unit of matter; the smallest complete unit of the elements,
consisting of protons, neutrons, and electrons.
atomic mass A
mass unit determined by arbitrarily assigning the carbon-12
isotope a mass of 12 atomic mass units.
atomic nucleus Most
of the mass of an atom; composed of protons and neutrons.
atomic number Number
of protons in the atomic nucleus; there is a characteristic number
for each type of element.
atomic weight The
weight of an atom determined by adding the number of protons and
neutrons (the mass of electrons is usually considered to be negligible).
atomic weight unit The
mass of one proton or neutron.
ATP (adenosine triphosphate) A
molecule that stores energy and releases it to power chemical
reactions in organisms.
ATP synthase A
membrane-bound enzyme in mitochondria and chloroplasts that
phosphorylates ADP to form ATP using energy from the passage of
protons through the enzyme.
Atria Chambers of the heart.
atrium One of the chambers of the heart; also, the
tympanic cavity of the ear; also, the large cavity containing
the pharynx in tunicates and cephalochordates.
auricle The portion of the external ear not
connected within the head. Also used to designate an atrium of
a heart. In the class Turbellaria, the sensory lobes that project
from the side of the head.
auricularia A type of larva found in Holothuroidea.
autogamy Condition in which the gametic
nuclei produced by meiosis fuse within the same organism that
produced them to restore the diploid number.
autoimmunity Immune
response to ones' own proteins or other antigens.
autoinfection Reinfection
by a parasite juvenile without its leaving the host.
autosome Any chromosome that is not a sex chromosome.
autotomy
The self amputation of an appendage. For example, the casting
off of a section of a lizard's tail caught in the grasp of a predator.
The autotomized appendage is usually regenerated.
autotroph An organism that makes its organic
nutrients from inorganic raw materials by using an external energy
source, such as light energy.
autotrophic Having
the ability to synthesize food from inorganic compounds.
autotrophic nutrition Nutrition characterized
by the ability to use simple inorganic substances for the synthesis
of more complex organic compounds, as in green plants and some
bacteria.
auxin A
hormone that causes the bending response in Avena coleoptiles.
auxospore The
resistant stage of diatoms that restores the maximum size characteristic
to the species.
Aves
A class of vertebrates whose members are characterized by scales
modified into feathers for flight, endothermy, and amniotic eggs.
The birds.
avicularium Modified
zooid that is attached to the surface of the major zooid in Ectoprocta
and resembles a bird's beak.
awn A
slender bristle.
axial cells Central
cells of a dicyemid mesozoan.
axial skeleton Portion
of the skeleton that supports and protects the organs of the head,
neck, and trunk.
axial Relating to the axis, or stem; on or along the axis.
axil The upper angle between a stem
Axilla axillae = armpit; beneath the axis.
axillary bud A
bud, consisting of an apical meristem and leaf primordia, situated
in the leaf axil.
Axis The second cervical vertebra; any axial
part.
axocoel The most anterior of three coelomic
spaces that appear during larval echinoderm development.
axolotl
Larval
stage of any of several species of the genus Ambystoma (such as
Ambystoma tigrinum) exhibiting neotenic reproduction.
axon A fiber that conducts a nerve impulse away from a neuron cell body.
axon Elongate extension of a neuron that conducts impulses away
from the cell body and toward the synaptic terminals.
axoneme The
axial thread of the chromosome in which is located the axial combination
of genes. The central core of a cilium or flagellum, consisting
of a central pair of filaments surrounded by nine other pairs;
also called axial filament.
axopodium Fine,
needlelike pseudopodium that contains a central bundle of microtubules.
Also called axopod. Found in certain sarcodine protozoa.
axostyle Tubelike
organelle in some flagellate protozoa, extending from the area
of the kinetosomes to the posterior end, where it often protrudes.
Azygous A blood vessel.