C
(1) (immunol.) complement.
(2) (mol. biol.) Cytosine (or the corresponding nucleoside or
nucleotide) in a nucleic acid.
(3)Cysteine (see amino acids).
c
See C value.
C (immunol.)
complement.
1-C compounds
See C1 compounds.
C forms
See azospirillum.
C loop
See bacteriophage p1.
c-onc
See oncogene.
C period
See Helmstetter–Cooper Model.
C-reactive protein (CRP)
An acute-phase protein, increased amounts of which circulate in the body
e.g. during inflammatory processes. CRP is precipitated by so-called C-reactive
substances which occur in various microorganisms – e.g. Streptococcus
pneumoniae (the basis of the C-reactive protein diagnostic test) and Aspergillus
fumigatus. Changes in CRP titre may
help to distinguish between bacterial and viral infections: a rise in the serum
level of CRP is more likely to reflect a bacterial infection because viral
infections usually do not produce such a change.
C-reactive substance
See c-reactive protein. (cf. c substances.)
C region (of Ig)
See Immunoglobulins.
C ring
See flagellum (a).
c strand
(C strand) Complementary strand, e.g., the strand complementary to the
genomic (viral, v) strand in the RF of an ssDNA virus.
C3 pathway
See Calvin cycle.
C3 plant
A plant
that uses the Calvin cycle for the initial steps that incorporate CO2 into
organic material, forming a three-carbon compound as the first stable
intermediate.
C4 pathway
The set
of reactions by which some plants initially fix carbon in the four-carbon
compound oxaloacetic acid; the carbon dioxide is later released in the interior
of the leaf and enters the Calvin cycle.
C4 plant
A plant
that prefaces the Calvin cycle with reactions that incorporate CO2 into
four-carbon compounds, the end-product of which supplies CO2 for
the Calvin cycle.
calcitonin
(kal-sih-toh-nin)
A mammalian thyroid hormone that lowers blood calcium levels.
A mammalian thyroid hormone that lowers blood calcium levels.
callus
[L. callos, hard
skin]
In plants, undifferentiated tissue; a term used in tissue culture, grafting, and wound healing.
In plants, undifferentiated tissue; a term used in tissue culture, grafting, and wound healing.
calmodulin
(kal-mod-yoo-lin)
An intracellular protein to which calcium binds in its function as a second messenger in hormone action.
An intracellular protein to which calcium binds in its function as a second messenger in hormone action.
calorie
(cal)
[L. calor, heat]
The amount of heat energy required to raise the temperature of 1 g of water 1°C; the amount of heat energy that 1 g of water releases when it cools by 1°C. The Calorie (with a capital C), usually used to indicate the energy content of food, is a kilocalorie.
The amount of heat energy required to raise the temperature of 1 g of water 1°C; the amount of heat energy that 1 g of water releases when it cools by 1°C. The Calorie (with a capital C), usually used to indicate the energy content of food, is a kilocalorie.
Calvin
cycle
The
second of two major stages in photosynthesis (following the light reactions),
involving atmospheric CO2 fixation and reduction of the fixed
carbon into carbohydrate.
calyx
[Gk. kalyx, a
husk, cup]
Collectively, the sepals of a flower.
Collectively, the sepals of a flower.
CAM
photosynthesis
See Crassulacean acid metabolism.
CAM plant
A plant
that uses crassulacean acid metabolism, an adaptation for photosynthesis in
arid conditions, first discovered in the family Crassulaceae. Carbon dioxide
entering open stomata during the night is converted into organic acids, which
release CO2 for the Calvin cycle during the day, when stomata
are closed.
Cambrian
explosion
A burst
of evolutionary origins when most of the major body plans of animals appeared
in a relatively brief time in geological history; recorded in the fossil record
about 545 to 525 million years ago.
capillary
(kap-ill-air-ee)
[L. capillaris, relating to hair]
A microscopic blood vessel that penetrates the tissues and consists of a single layer of endothelial cells that allows exchange between the blood and interstitial fluid.
A microscopic blood vessel that penetrates the tissues and consists of a single layer of endothelial cells that allows exchange between the blood and interstitial fluid.
capillary
action
The
movement of water or any liquid along a surface; results from the combined
effect of cohesion and adhesion.
capsid
The
protein shell that encloses the viral genome; rod-shaped, polyhedral, or more
completely shaped.
capsule
(kap-sul)
[L. capsula, a little chest]
(1) A slimy layer around the cells of certain bacteria. (2) The sporangium of a bryophyte.
(1) A slimy layer around the cells of certain bacteria. (2) The sporangium of a bryophyte.
carbohydrate
[L. carbo, charcoal
+ hydro, water]
A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides).
A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides).
carbon
cycle
Worldwide
circulation and reutilization of carbon atoms, chiefly due to metabolic
processes of living organisms. Inorganic carbon, in the form of carbon dioxide,
is incorporated into organic compounds by photosynthetic organisms; when the
organic compounds are broken down in respiration, carbon dioxide is released.
Large quantities of carbon are "stored" in the seas and the
atmosphere, as well as in fossil fuel deposits.
carbon
fixation
The
incorporation of carbon from CO2 into an organic compound by an
autotrophic organism (a plant, another photosynthetic organism, or a
chemoautotrophic bacterium).
carbonyl
group
(kar-buh-nil)
A functional group present in aldehydes and ketones, consisting of a carbon atom double-bonded to an oxygen atom.
A functional group present in aldehydes and ketones, consisting of a carbon atom double-bonded to an oxygen atom.
carboxyl
group
(kar-box-ul)
A functional group present in organic acids, consisting of a single carbon atom double-bonded to an oxygen atom and also bonded to a hydroxyl group.
A functional group present in organic acids, consisting of a single carbon atom double-bonded to an oxygen atom and also bonded to a hydroxyl group.
carcinogen
(kar-sin-oh-jen)
A chemical agent that causes cancer.
A chemical agent that causes cancer.
cardiac
muscle
(kar-dee-ak)
A type of muscle that forms the contractile wall of the heart; its cells are joined by intercalated discs that relay each heartbeat.
A type of muscle that forms the contractile wall of the heart; its cells are joined by intercalated discs that relay each heartbeat.
cardiac
output
The
volume of blood pumped per minute by the left ventricle of the heart.
cardiovascular
system
[Gk. kardio, heart
+ L. vasculum, a small vessel]
A closed circulatory system with a heart and branching network of arteries, capilleries, and veins.
A closed circulatory system with a heart and branching network of arteries, capilleries, and veins.
carnivore
[L. caro,
carnis, flesh + voro, to devour]
An animal, such as a shark, hawk, or spider, that eats other animals.
An animal, such as a shark, hawk, or spider, that eats other animals.
carotenoids
(keh-rot-en-oydz)
[L. carota, carrot]
Accessory pigments, yellow and orange, in the chloroplasts of plants; by absorbing wavelengths of light that chlorophyll cannot, they broaden the spectrum of colors that can drive photosynthesis.
Accessory pigments, yellow and orange, in the chloroplasts of plants; by absorbing wavelengths of light that chlorophyll cannot, they broaden the spectrum of colors that can drive photosynthesis.
carpel
(kar-pel)
[Gk. karpos, fruit]
The female reproductive organ of a flower, consisting of the stigma, style, and ovary.
The female reproductive organ of a flower, consisting of the stigma, style, and ovary.
carrying
capacity
The
maximum population size that can be supported by the available resources,
symbolized as K.
cartilage
(kar-til-ij)
[L. cartilago, gristle]
A type of flexible connective tissue with an abundance of collagenous fibers embedded in chondrin.
A type of flexible connective tissue with an abundance of collagenous fibers embedded in chondrin.
Casparian
strip
(kas-par-ee-un)
(after Robert Caspary, German botanist)
A water-impermeable ring of wax around endodermal cells in plants that blocks the passive flow of water and solutes into the stele by way of cell walls.
A water-impermeable ring of wax around endodermal cells in plants that blocks the passive flow of water and solutes into the stele by way of cell walls.
catabolic
pathway
(kat-uh-bol-ik)
A metabolic pathway that releases energy by breaking down complex molecules into simpler compounds.
A metabolic pathway that releases energy by breaking down complex molecules into simpler compounds.
catabolism
[Gk. katabole, throwing
down]
Within a cell or organism, the sum of all chemical reactions in which large molecules are broken down into smaller parts.
Within a cell or organism, the sum of all chemical reactions in which large molecules are broken down into smaller parts.
catabolite
activator protein (CAP)
(ka-tab-ul-lite)
In E. coli, a helper protein that stimulates gene expression by binding within the promoter region of an operon and enhancing the promoter's ability to associate with RNA polymerase.
In E. coli, a helper protein that stimulates gene expression by binding within the promoter region of an operon and enhancing the promoter's ability to associate with RNA polymerase.
catalyst
[Gk. katalysis, dissolution]
A substance that lowers the activation energy of a chemical reaction by forming a temporary association with the reacting molecules; as a result, the rate of the reaction is accelerated. Enzymes are catalysts.
A substance that lowers the activation energy of a chemical reaction by forming a temporary association with the reacting molecules; as a result, the rate of the reaction is accelerated. Enzymes are catalysts.
category
[Gk. kategoria, category]
In a hierarchical classification system, the level at which a particular group is ranked.
In a hierarchical classification system, the level at which a particular group is ranked.
cation
(kat-eye-on)
An ion with a positive charge, produced by the loss of one or more electrons.
An ion with a positive charge, produced by the loss of one or more electrons.
cation
exchange
A process
in which positively charged minerals are made available to a plant when
hydrogen ions in the soil displace mineral ions from the clay particles.
cell
[L. cella, a
chamber]
A basic unit of living matter separated from its environment by a plasma membrane; the fundamental structural unit of life.
A basic unit of living matter separated from its environment by a plasma membrane; the fundamental structural unit of life.
cell
center
A region
in the cytoplasm near the nucleus from which microtubules originate and
radiate.
cell
cycle
An
ordered sequence of events in the life of a dividing eukaryotic cell, composed
of the M, G1, S, and G2 phases.
cell-cycle
control system
A
cyclically operating set of proteins that triggers and coordinates events in
the eukaryotic cell cycle.
cell
fractionation
The
disruption of a cell and separation of its organelles by centrifugation.
cell-mediated
immunity
The type
of immunity that functions in defense against fungi, protists, bacteria, and
viruses inside host cells and against tissue transplants, with highly
specialized cells that circulate in the blood and lymphoid tissue.
cell
membrane
The outer
membrane of the cell; the plasma membrane.
cell
plate
A double
membrane across the midline of a dividing plant cell, between which the new
cell wall forms during cytokinesis.
cell
theory
All
living things are composed of cells; cells arise only from other cells. No
exception has been found to these two principles since they were first proposed
well over a century ago.
cell wall
A
protective layer external to the plasma membrane in plant cells, bacteria,
fungi, and some protists. In the case of plant cells, the wall is formed of
cellulose fibers embedded in a polysaccharide-protein matrix. The primary cell
wall is thin and flexible, whereas the secondary cell wall is stronger and more
rigid, and is the primary constituent of wood.
cellular
differentiation
The
structural and functional divergence of cells as they become specialized during
a multicellular organism's development; dependent on the control of gene
expression.
cellular
respiration
The most
prevalent and efficient catabolic pathway for the production of ATP, in which
oxygen is consumed as a reactant along with the organic fuel.
cellulose
(sell-yoo-lose)
[L. cellula, a little cell]
A structural polysaccharide of cell walls, consisting of glucose monomers joined by (1-4) glycosidic linkages.
A structural polysaccharide of cell walls, consisting of glucose monomers joined by (1-4) glycosidic linkages.
Celsius
scale
A
temperature scale (°C) equal to 5/9 (°F – 32) that measures the freezing point
of water at 0°C and the boiling point of water at 100°C.
central
nervous system (CNS)
In
vertebrate animals, the brain and spinal cord.
centriole
(sen-tree-ole)
[Gk. kentron, center]
A structure in an animal cell, composed of cylinders of microtubule triplets arranged in a 9 + 0 pattern. An animal cell usually has a pair of centrioles, which are involved in cell division.
A structure in an animal cell, composed of cylinders of microtubule triplets arranged in a 9 + 0 pattern. An animal cell usually has a pair of centrioles, which are involved in cell division.
centromere
(sen-tro-mere)
[Gk. kentron, center + meros, a part]
The centralized region joining two sister chromatids.
The centralized region joining two sister chromatids.
centrosome
Material
present in the cytoplasm of all eukaryotic cells and important during cell
division; also called microtubule-organizing center.
cephalochordate
A
chordate without a backbone, represented by lancelets, tiny marine animals.
cerebellum
(seh-reh-bell-um)
[L. dim. of cerebrum, brain]
Part of the vertebrate hindbrain (rhombencephalon) located dorsally; functions in unconscious coordination of movement and balance.
Part of the vertebrate hindbrain (rhombencephalon) located dorsally; functions in unconscious coordination of movement and balance.
cerebral
cortex
(seh-ree-brul)
[L. cerebrum, brain]
The surface of the cerebrum; the largest and most complex part of the mammalian brain, containing sensory and motor nerve cell bodies of the cerebrum; the part of the vertebrate brain most changed through evolution.
The surface of the cerebrum; the largest and most complex part of the mammalian brain, containing sensory and motor nerve cell bodies of the cerebrum; the part of the vertebrate brain most changed through evolution.
cerebrum
(seh-ree-brum)
[L. brain]
The dorsal portion, composed of right and left hemispheres, of the vertebrate forebrain; the integrating center for memory, learning, emotions, and other highly complex functions of the central nervous system.
The dorsal portion, composed of right and left hemispheres, of the vertebrate forebrain; the integrating center for memory, learning, emotions, and other highly complex functions of the central nervous system.
chaparral
(shap-uh-ral)
A scrubland biome of dense, spiny evergreen shrubs found at midlatitudes along coasts where cold ocean currents circulate offshore; characterized by mild, rainy winters and long, hot, dry summers.
A scrubland biome of dense, spiny evergreen shrubs found at midlatitudes along coasts where cold ocean currents circulate offshore; characterized by mild, rainy winters and long, hot, dry summers.
character
displacement
A
phenomenon in which species that live together in the same environment tend to
diverge in those characteristics that overlap; exemplified by Darwin's finches.
chemical
bond
An
attraction between two atoms resulting from a sharing of outer-shell elctrons
or the presence of opposite charges on the atoms; the bonded atoms gain
complete outer electron shells.
chemical
equilibrium
In a
reversible chemical reaction, the point at which the rate of the forward
reaction equals the rate of the reverse reaction.
chemical
reaction
A process
leading to chemical changes in matter; involves the making and/or breaking of
chemical bonds.
chemiosmosis
(kee-mee-os-moh-sis)
The production of ATP using the energy of hydrogen-ion gradients across membranes to phosphorylate ADP; powers most ATP synthesis in cells.
The production of ATP using the energy of hydrogen-ion gradients across membranes to phosphorylate ADP; powers most ATP synthesis in cells.
chemiosmotic
coupling
The
mechanism by which ADP is phosphorylated to ATP in mitochondria and
chloroplasts. The energy released as electrons pass down an electron transport
chain is used to establish a proton gradient across an inner membrane of the
organelle; when protons subsequently flow down this electrochemical gradient,
the potential energy released is captured in the terminal phosphate bonds of
ATP.
chemoautotroph
(kee-moh-aw-toh-trohf)
An organism that needs only carbon dioxide as a carbon source but that obtains energy by oxidizing inorganic substances.
An organism that needs only carbon dioxide as a carbon source but that obtains energy by oxidizing inorganic substances.
chemoheterotroph
(kee-moh-het-er-oh-trohf)
An organism that must consume organic molecules for both energy and carbon.
An organism that must consume organic molecules for both energy and carbon.
chemoreceptor
A
receptor that transmits information about the total solute concentration in a
solution or about individual kinds of molecules.
chemosynthetic
Applied
to autotrophic bacteria that use the energy released by specific inorganic
reactions to power their life processes, including the synthesis of organic
molecules.
chiasma pl. chiasmata
(ky-as-muh)
The X-shaped, microscopically visible region representing homologous chromatids that have exchanged genetic material through crossing over during meiosis.
The X-shaped, microscopically visible region representing homologous chromatids that have exchanged genetic material through crossing over during meiosis.
chitin
(ky-tin)
[Gk. chiton, a tunic, undergarment]
A structural polysaccharide of an amino sugar found in many fungi and in the exoskeletons of all arthropods.
A structural polysaccharide of an amino sugar found in many fungi and in the exoskeletons of all arthropods.
chlorophyll
[Gk. chloros, green
+ phyllon, leaf]
A green pigment located within the chloroplasts of plants; chlorophyll a can participate directly in the light reactions, which convert solar energy to chemical energy.
A green pigment located within the chloroplasts of plants; chlorophyll a can participate directly in the light reactions, which convert solar energy to chemical energy.
chloroplast
(klor-oh-plast)
[Gk. chloros, green + plastos, formed]
An organelle found only in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.
An organelle found only in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.
cholesterol
(kol-ess-teh-rol)
A steroid that forms an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other biologically important steroids.
A steroid that forms an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other biologically important steroids.
Chondrichthyes
The
vertebrate class of cartilaginous fishes, represented by sharks and their
relatives.
chondrin
A
protein-carbohydrate complex secreted by chondrocytes; chondrin and collagen
fibers form cartilage.
chordate
(kor-date)
A member of a diverse phylum of animals that possess a notochord; a dorsal, hollow nerve cord; pharyngeal gill slits; and a postanal tail as embryos.
A member of a diverse phylum of animals that possess a notochord; a dorsal, hollow nerve cord; pharyngeal gill slits; and a postanal tail as embryos.
chorion
(core-ee-on)
[Gk. skin, leather]
The outermost of four extraembryonic membranes; contributes to the formation of the mammalian placenta.
The outermost of four extraembryonic membranes; contributes to the formation of the mammalian placenta.
chorionic
villus sampling (CVS)
(kor-ee-on-ik vill-us)
A technique for diagnosing genetic and congenital defects while the fetus is in the uterus. A small sample of the fetal portion of the placenta is removed and analyzed.
A technique for diagnosing genetic and congenital defects while the fetus is in the uterus. A small sample of the fetal portion of the placenta is removed and analyzed.
chromatid
(crow-ma-tid)
[Gk. chroma, color]
Either of the two strands of a replicated chromosome, which are joined at the centromere.
Either of the two strands of a replicated chromosome, which are joined at the centromere.
chromatin
(kro-muh-tin)
[Gk. chroma, color]
The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope.
The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope.
Chromista
In some
classification systems, a kingdom consisting of brown algae, golden algae, and
diatoms.
chromosome
[Gk. chroma, color
+ soma, body]
A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins. See chromatin.
A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins. See chromatin.
chromosome
map
A diagram
of the linear order of the genes on a chromosome.
chytrid
Fungus
with flagellated stage; possible evolutionary link between fungi and protists.
cilium pl. cilia
(silly-um)
[L. eyelash]
A short cellular appendage specialized for locomotion, formed from a core of nine outer doublet microtubules and two inner single microtubules ensheathed in an extension of plasma membrane.
A short cellular appendage specialized for locomotion, formed from a core of nine outer doublet microtubules and two inner single microtubules ensheathed in an extension of plasma membrane.
circadian
rhythms
[L. circa, about
+ dies, day]
A physiological cycle of about 24 hours, present in all eukaryotic organisms, that persists even in the absence of external cues.
A physiological cycle of about 24 hours, present in all eukaryotic organisms, that persists even in the absence of external cues.
cladistics
(kluh-dis-tiks)
A taxonomic approach that classifies organisms according to the order in time at which branches arise along a phylogenetic tree, without considering the degree of morphological divergence.
A taxonomic approach that classifies organisms according to the order in time at which branches arise along a phylogenetic tree, without considering the degree of morphological divergence.
cladogenesis
(klay-doh-gen-eh-sis)
[Gk. clados, branch + genesis, origin]
A pattern of evolutionary change that produces biological diversity by budding one or more new species from a parent species that continues to exist; also called branching evolution.
A pattern of evolutionary change that produces biological diversity by budding one or more new species from a parent species that continues to exist; also called branching evolution.
cladogram
A
dichotomous phylogenetic tree that branches repeatedly, suggesting a
classification of organisms based on the time sequence in which evolutionary
branches arise.
class
A
taxonomic grouping of related, similar orders; category above order and below
phylum.
classical
conditioning
A type of
associative learning; the association of a normally irrelevant stimulus with a
fixed behavioral response.
cleavage
The
process of cytokinesis in animal cells,
characterized by pinching of the plasma membrane; specifically, the succession
of rapid cell divisions without growth during early embryonic development that
converts the zygote into a ball of cells.
cleavage
furrow
The first
sign of cleavage in an animal cell; a shallow groove in the cell surface near
the old metaphase plate.
cline
[Gk. klinein, to
lean]
Variation in features of individuals in a population that parallels a gradient in the environment.
Variation in features of individuals in a population that parallels a gradient in the environment.
cloaca
(kloh-ay-kuh)
A common opening for the digestive, urinary, and reproductive tracts in all vertebrates except most mammals.
A common opening for the digestive, urinary, and reproductive tracts in all vertebrates except most mammals.
clonal
selection
(kloh-nul)
The mechanism that determines specificity and accounts for antigen memory in the immune system; occurs because an antigen introduced into the body selectively activates only a tiny fraction of inactive lymphocytes, which proliferate to form a clone of effector cells specific for the stimulating antigen.
The mechanism that determines specificity and accounts for antigen memory in the immune system; occurs because an antigen introduced into the body selectively activates only a tiny fraction of inactive lymphocytes, which proliferate to form a clone of effector cells specific for the stimulating antigen.
clone
[Gk. klon, twig]
(1) A lineage of genetically identical individuals or cells. (2) In popular usage, a single individual organism that is genetically identical to another individual. (3) As a verb, to make one or more genetic replicas of an individual or cell. Also, see gene cloning.
(1) A lineage of genetically identical individuals or cells. (2) In popular usage, a single individual organism that is genetically identical to another individual. (3) As a verb, to make one or more genetic replicas of an individual or cell. Also, see gene cloning.
cloning
vector
An agent
used to transfer DNA in genetic engineering, such as a plasmid that moves
recombinant DNA from a test tube back into a cell, or a virus that transfers
recombinant DNA by infection.
closed
circulatory system
A type of
internal transport in which blood is confined to vessels.
cnidocyte
(ni-do-site)
[Gk. knide, nettle + kytos, vessel]
A stinging cell containing a nematocyst; characteristic of cnidarians.
A stinging cell containing a nematocyst; characteristic of cnidarians.
cochlea
(koh-klee-uh)
[Gk. kochlias, snail]
The complex, coiled organ of hearing that contains the organ of Corti.
The complex, coiled organ of hearing that contains the organ of Corti.
codominance
A
phenotypic situation in which both alleles are expressed in the heterozygote.
codon
(koh-on)
A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.
A three-nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code.
coelom
(see-lome)
[Gk. koilos, a hollow]
A body cavity completely lined with mesoderm.
A body cavity completely lined with mesoderm.
coelomate
(see-loh-mate)
An animal whose body cavity is completely lined by mesoderm, the layers of which connect dorsally and ventrally to form mesenteries.
An animal whose body cavity is completely lined by mesoderm, the layers of which connect dorsally and ventrally to form mesenteries.
coenocytic
(sen-oh-sit-ik)
Referring to a multinucleated condition resulting from the repeated division of nuclei without cytoplasmic division.
Referring to a multinucleated condition resulting from the repeated division of nuclei without cytoplasmic division.
coenzyme
[L. co, together
+ Gk. en, in + zyme, leaven]
An organic molecule serving as a cofactor. Most vitamins function as coenzymes in important metabolic reactions.
An organic molecule serving as a cofactor. Most vitamins function as coenzymes in important metabolic reactions.
coevolution
[L. co, together
+ e-, out + volvere, to roll]
The mutual influence on the evolution of two different species interacting with each other and reciprocally influencing each other's adaptations.
The mutual influence on the evolution of two different species interacting with each other and reciprocally influencing each other's adaptations.
cofactor
Any
nonprotein molecule or ion that is required for the proper functioning of an
enzyme. Cofactors can be permanently bound to the active site or may bind
loosely with the substrate during catalysis.
cohesion
[L. cohaerere, to
stick together]
The binding together of like molecules, often by hydrogen bonds.
The binding together of like molecules, often by hydrogen bonds.
cohesion
species concept
The idea
that specific evolutionary adaptations and discrete complexes of genes define
species.
cohesion-tension
theory
A theory
accounting for the upward movement of water in plants. According to this
theory, transpiration of a water molecule results in a negative (below 1
atmosphere) pressure in the leaf cells, inducing the entrance from the vascular
tissue of another water molecule, which, because of the cohesive property of
water, pulls with it a chain of water molecules extending up from the cells of
the root tip.
cold
aclimation response
The
process by which plants increase their tolerance to freezing by exposure to
low, nonfreezing temperatures.
coleoptile
(coal-ee-op-tile)
[Gk. koleon, sheath + ptilon, feather]
The sheath enclosing the apical meristem and leaf primordia of a germinating monocot.
The sheath enclosing the apical meristem and leaf primordia of a germinating monocot.
collagen
[Gk. kolla, glue]
A glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom.
A glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom.
collecting
duct
The
location in the kidney where filtrate from renal tubules is collected; the
filtrate is now called urine.
collenchyma
cell
(koal-en-keh-muh)
[Gk. kolla, glue]
A flexible plant cell type that occurs in strands or cylinders that support young parts of the plant without restraining growth.
A flexible plant cell type that occurs in strands or cylinders that support young parts of the plant without restraining growth.
colony
A group
of organisms of the same species living together in close association.
commensalism
(kuh-men-sul-iz-um)
[L. com, together + mensa, table]
A symbiotic relationship in which the symbiont benefits but the host is neither helped nor harmed. See Symbiosis.
A symbiotic relationship in which the symbiont benefits but the host is neither helped nor harmed. See Symbiosis.
community
All the
organisms that inhabit a particular area; an assemblage of populations of
different species living close enough together for potential interaction.
companion
cell
A type of
plant cell that is connected to a sieve-tube member by many plasmodesmata and
whose nucleus and ribosomes may serve one or more adjacent sieve-tube members.
competition
Interaction
between members of the same population or of two or more populations using the
same resource, often present in limited supply.
competitive
exclusion principle
The
concept that when the populations of two species compete for the same limited
resources, one population will use the resources more efficiently and have a
reproductive advantage that will eventually lead to the elimination of the
other population.
competitive
inhibitor
A
substance that reduces the activity of an enzyme by entering the active site in
place of the substrate whose structure it mimics.
complement
fixation
An immune
response in which antigen-antibody complexes activate complement proteins.
complement
system
A group
of at least 20 blood proteins that cooperate with other defense mechanisms; may
amplify the inflammatory response, enhance phagocytosis, or directly lyse
pathogens; activated by the onset of the immune response or by surface antigens
on microorganisms or other foreign cells.
complementary
DNA (cDNA)
A DNA
molecule made in vitro using mRNA as a template and the enzyme reverse
transcriptase. A cDNA molecule therefore corresponds to a gene, but lacks the
introns present in the DNA of the genome.
complete
digestive tract
A
digestive tube that runs between a mouth and an anus; also called alimentary
canal. An incomplete digestive tract has only one opening.
complete
flower
A flower
that has sepals, petals, stamens, and carpels.
compound
[L. componere, to
put together]
A chemical combination, in a fixed ratio, of two or more elements.
A chemical combination, in a fixed ratio, of two or more elements.
compound
eye
A type of
multifaceted eye in insects and crustaceans consisting of up to several
thousand light-detecting, focusing ommatidia; especially good at detecting
movement.
concentration
gradient
A regular
increase of decrease in the intensity or density of a chemical substance. Cells
often maintain concentration gradients of H+ ions across their
membranes. When a gradient exists, the ions or other chemical substances
involved tend to move from where they are more concentrated to where they are
less concentrated.
condensation
See Dehydration synthesis.
condensation
reaction
A
reaction in which two molecules become covalently bonded to each other through
the loss of a small molecule, usually water; also called dehydration reaction.
cone cell
(1) In
plants, the reproductive structure of a conifer. (2) In vertebrates, a type of
photoreceptor cell in the retina, concerned with the perception of color and
with the most acute discrimination of detail.
conidium pl. conidia
A naked,
asexual spore produced at the ends of hyphae in ascomycetes.
conifer
A gymnosperm whose reproductive
structure is the cone. Conifers include pines, firs, redwoods, and other large
trees.
conjugation
(kon-joo-gay-shun)
[L. conjugatio, a joining, connection]
In bacteria, the transfer of DNA between two cells that are temporarily joined.
In bacteria, the transfer of DNA between two cells that are temporarily joined.
connective
tissues
Animal
tissue that functions mainly to bind and support other tissues, having a sparse
population of cells scattered through an extracellular matrix.
conservation
biology
A
goal-oriented science that seeks to counter the biodiversity crisis, the
current rapid decrease in Earth's variety of life.
consumer,
in ecological systems
A
heterotroph that derives its energy from living or freshly killed organisms or
parts thereof. Primary consumers are herbivores; higher-level consumers are
carnivores.
continental
drift
The
gradual movement of the Earth's continents that has occurred over hundreds of
millions of years.
continuous
variation
A
gradation of small differences in a particular trait, such as height, within a
population; occurs in traits that are controlled by a number of genes.
contraception
The
prevention of pregnancy.
convection
The mass
movement of warmed air or liquid to or from the surface of a body or object.
convergent
evolution
[L. convergere, to
turn together; evolutio, to unfold]
The independent development of similarity between species as a result of their having similar ecological roles and selection pressures.
The independent development of similarity between species as a result of their having similar ecological roles and selection pressures.
cooperativity
(koh-op-ur-uh-tiv-eh-tee)
An interaction of the constituent subunits of a protein causing a conformational change in one subunit to be transmitted to all the others.
An interaction of the constituent subunits of a protein causing a conformational change in one subunit to be transmitted to all the others.
cork
[L. cortex, bark]
A secondary tissue that is a major constituent of bark in woody and some herbaceous plants; made up of flattened cells, dead at maturity; restricts gas and water exchange and protects the vascular tissues from injury.
A secondary tissue that is a major constituent of bark in woody and some herbaceous plants; made up of flattened cells, dead at maturity; restricts gas and water exchange and protects the vascular tissues from injury.
cork
cambium
[L. cortex, bark
+ cambium, exchange]
A cylinder of meristematic tissue in plants that produces cork cells to replace the epidermis during secondary growth.
A cylinder of meristematic tissue in plants that produces cork cells to replace the epidermis during secondary growth.
corolla
(ko-role-a)
[L. dim. of corona, wreath, crown]
Petals, collectively; usually the conspicuously colored flower parts.
Petals, collectively; usually the conspicuously colored flower parts.
corpus
callosum
[L.
callous body]
In the vertebrate brain, a tightly packed mass of myelinated nerve fibers connecting the two cerebral hemispheres.
In the vertebrate brain, a tightly packed mass of myelinated nerve fibers connecting the two cerebral hemispheres.
corpus
lutuem
[L.
yellowish body]
A secreting tissue in the ovary that forms from the collapsed follicle after ovulation and produces progesterone.
A secreting tissue in the ovary that forms from the collapsed follicle after ovulation and produces progesterone.
cortex
[L. bark]
(1) The outer, as opposed to the inner, part of an organ, as in the adrenal gland. (2) In a stem or root, the primary tissue bounded externally by the epidermis and internally by the central cylinder of vascular tissue.
(1) The outer, as opposed to the inner, part of an organ, as in the adrenal gland. (2) In a stem or root, the primary tissue bounded externally by the epidermis and internally by the central cylinder of vascular tissue.
cortisol
A steroid
hormone, produced by the adrenal cortex, that promotes the formation of glucose
from protein and fat; also suppresses the inflammatory and immune responses.
cotransport
The
coupling of the "downhill" diffusion of one substance to the
"uphill" transport of another against its own concentration gradient.
cotyledon
(kot-eh-lee-don)
[Gk. kotyledon, a cup-shaped hollow]
The one (monocot) or two (dicot) seed leaves of an angiosperm embryo.
The one (monocot) or two (dicot) seed leaves of an angiosperm embryo.
countercurrent
exchange
The
opposite flow of adjacent fluids that maximizes transfer rates; for example,
blood in the gills flows in the opposite direction in which water passes over
the gills, maximizing oxygen uptake and carbon dioxide loss.
coupled
reactions
In cells,
the linking of endergonic (energy-requiring) reactions to exergonic
(energy-releasing) reactions that provide enough energy to drive the endergonic
reactions forward.
covalent
bond
(koh-vay-lent)
[L. con, together + valere, to be strong]
A chemical bond formed as a result of the sharing of one or more pairs of electrons.
A chemical bond formed as a result of the sharing of one or more pairs of electrons.
Crassulacean
acid metabolism
A process
by which some species of plants in hot, dry climates take in carbon dioxide
during the night, fixing it in organic acids; the carbon dioxide is released
during the day and used immediately in the Calvin cycle.
crista pl. cristae
(kris-tuh)
An infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzyme catalyzing the synthesis of ATP.
An infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzyme catalyzing the synthesis of ATP.
cross-fertilization
Fusion of
gametes formed by different individuals; as opposed to self-fertilization.
crossing
over
The
reciprocal exchange of genetic material between nonsister chromatids during
synapsis of meiosis I.
cryptic
coloration
(krip-tik)
A type of camouflage that makes potential prey difficult to spot against its background.
A type of camouflage that makes potential prey difficult to spot against its background.
cuticle
(kyoo-teh-kul)
[L. cuticula, dim. of cutis, the skin]
(1) A waxy covering on the surface of stems and leaves that acts as an adaptation to prevent desiccation in terrestrial plants. (2) The exoskeleton of an arthropod, consisting of layers of protein and chitin that are variously modified for different functions.
(1) A waxy covering on the surface of stems and leaves that acts as an adaptation to prevent desiccation in terrestrial plants. (2) The exoskeleton of an arthropod, consisting of layers of protein and chitin that are variously modified for different functions.
cyanobacteria
(sy-an-oh-bak-teer-ee-uh)
Photosynthetic, oxygen-producing bacteria (formerly know as blue-green algae).
Photosynthetic, oxygen-producing bacteria (formerly know as blue-green algae).
cyclic
AMP
Cyclic
adenosine monophosphate, a ring-shaped molecule made from ATP that is a common
intracellular signaling molecule (second messenger) in eukaryotic cells, for
example, in vertebrate endocrine cells. It is also a regulator of some
bacterial operons.
cyclic
electron flow
A route
of electron flow during the light reactions of photosynthesis that involves
only photosystem I and produces ATP but not NADPH or oxygen.
cyclin
(sy-klin)
A regulatory protein whose concentration fluctuates cyclically.
A regulatory protein whose concentration fluctuates cyclically.
cyclin-dependent
kinase (Cdk)
A protein
kinase that is active only when attached to a particular cyclin.
cytochrome
(sy-toh-krome)
[Gk. kytos, vessel + chroma, color]
An iron-containing protein, a component of electron transport chains in mitochondria and chloroplasts.
An iron-containing protein, a component of electron transport chains in mitochondria and chloroplasts.
cytokines
In the
vertebrate immune system, protein factors secreted by macrophages and helper T
cells as regulators of neighboring cells.
cytokinesis
(sy-toh-kin-ee-sis)
[Gk. kytos, vessel + kinesis, motion]
The division of the cytoplasm to form two separate daughter cells immediately after mitosis.
The division of the cytoplasm to form two separate daughter cells immediately after mitosis.
cytokinin
(sy-toh-ky-nins)
[Gk. kytos, vessel + kinesis, motion]
A class of related plant hormones that retard aging and act in concert with auxins to stimulate cell division, influence the pathway of differentiation, and control apical dominance.
A class of related plant hormones that retard aging and act in concert with auxins to stimulate cell division, influence the pathway of differentiation, and control apical dominance.
cytoplasm
(sy-toh-plaz-um)
[Gk. kytos, vessel + plasma, anything molded]
The entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane.
The entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane.
cytoplasmic
determinants
In animal
development, substances deposited by the mother in the eggs she produces that
regulate the expression of genes affecting the early development of the embryo.
cytoplasmic
streaming
A
circular flow of cytoplasm, involving myosin and actin filaments, that speeds
the distribution of materials within cells.
cytoskeleton
(sy-toh-skel-eh-ton)
A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions.
A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions.
cytosol
(sy-toh-sol)
The semifluid portion of the cytoplasm.
The semifluid portion of the cytoplasm.
cytotoxic
T cell (TC)
A type of
lymphocyte that kills infected cells and cancer cells.
Tags:
C-reactive protein
calcitonin
calmodulin
CAM photosynthesis
catabolite activator protein
chromosome
clonal selection