Life Science Dictionary C


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 Plant: A plant that prefaces the Calvin cycle with reactions that incorporate CO2 into a four-carbon compound, the end product of which supplies CO2 for the Calvin cycle.
Cadherins: An important class of cell-to-cell adhesion molecules.
Calcitonin: A hormone secreted by the thyroid gland that lowers blood calcium levels by promoting calcium deposition in bone and calcium excretion from the kidneys.
Calllus: A mass of dividing, undifferentiated cells at the cut end of a shoot.
Calorie (cal): The amount of heat energy required to raise the temperature of 1g of water by 1C°. Calorie (with a capital C) is used to indicate the energy content of food, is a kilocalorie.
Calvin cycle: The second of two major stages in photosynthesis, following the light reaction. It involves atmospheric CO2 fixation and reduction of the fixed carbon into carbohydrate.
Calyptra: A protective cap of gametophyte tissue that wholly or partially covers an immature capsule in may mosses.
CAM plant: A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions. Carbon dioxide entering open stomata during the night is converted into organic acids, which releases CO2 for the Calvin cycle during the day when stomata is closed.
Cambrian explosion: A burst of evolutionary origins when most of the major body plans of animals appeared in a relatively short time in geological history; recorded in the fossil record 542-525 million years ago.
Camouflage: concealment by some means that alters or obscure the appearance.
Canalization: The buffering of development such that the same form is produced despite genetic and environmental perturbations.
Candidate gene: A gene that is thought to influence the trait of interest, usually because major mutations at the gene affect the trait.
Canonical code: The genetic code that is used almost universally.
Canopy: The upper most layer of vegetation in a terrestrial biome.
Capillary: A microscopic blood vessel that penetrates tissues and consist of a single layer of endothelial cells that allow exchange between the blood and interstitial fluid.
Capillary bed: A network of capillaries that infiltrate every organ and tissue in the body.
Capsid: A protein casing that makes up the outside of a virus particle.
Capsule: (1) A sticky layer that surrounds that cell wall of some prokaryotic, protecting the cell surface and sometimes helping to glue the cell to surfaces. (2)  the sporangium of a bryophyte (moss, liverwort, or hornwort).
Carbohydrate: A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides).
Carbon fixation: The incorporation of carbon from CO2 into an organic compound by an autotrophic organism (plant, another photosynthetic organism, or  a chemoautotroph organism).
Carbonyl group: A functional group present in aldehydes and ketones and consisting of a carbon atom double bonded to an oxygen atom.
Carboxyl group: A functional group present in organic acids and consisting of a single carbon atom double bonded to an oxygen and also bonded to a hydroxyl group.
Cardiac cycle: The alternating contraction and relaxation of the heart.
Cardiac muscle: 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 disease: Diseases of the heart and blood vessels.
Cardiovascular system: A close circulatory system with a heart and branching network of arteries, capillaries, and veins. The system is characteristic of vertebrates.
Carnivore: An animal that eats other animals such as a hawk, spiders, sharks.
Carotenoid: An accessory pigment, either yellow or orange, in the chloroplasts or plants. By absorbing wavelengths of light that chlorophyll cannot, carotenoids broaden the spectrum of colors that can drive photosynthesis.
Carpel: The ovule-producing reproductive organ of a flower, consisting of stigma, style, and ovary.
Carrier: In genetics, an individual who is heterozygous for a given genetic locus, with one normal allele and one potentially harmful recessive allele.
Carrying capacity: The maximum population size that can be supported by the available resources.
Cartilage: A type of flexible connective tissue with an abundance of collagenous fibers embedded in chondroitin sulphate.
Casparian strip: A water-impermeable ring of wax in the endodermal cells of plants that bocks the passive flow of water and solutes into the stele by the way of cell walls.
Case-controlled study:  A form of association study in which “case” individuals with, for example, a disease are compared with “control” individuals without it.
Catabolic pathway: A metabolic pathway that releases energy by breaking down complex molecules to simpler compounds.
Catalysis: The facilitation of a chemical reaction by a molecule that is not itself altered by the reaction.
Catalyst: A chemical agent that changes the rate of a reaction without being consumed by the reaction.
Catastrophism: The hypothesis of George Cuvier that each boundary between strata corresponds in time to a catastrophe, such as flood or drought, that had destroyed many of the species living there at that time.
Catecholamine: Any class of compounds including the hormone epinephrine and norepinephrine, that are synthesized from the amino acid tyrosine.
Cation: An ion with a positive charge, produced by the loss of one or more electrons.
Cation exchange: A process in which positive charged minerals are made available to a plant when hydrogen ions in the soil displace mineral ions from the clay particles.
CD4: A surface protein, present in most helper T cells, that binds to class II MHC molecules on antigen presenting cells, enhancing the interaction between T cells and the antigen-presenting cell.
CD8: A surface protein present in most cytotoxic cells, that binds to class I MHC molecules in target cells, enhancing the interaction between the T cell and the target cell.
cDNA: Complementary DNA
cDNA library: A limited gene library using cDNA. The library includes only the genes that were transcribed in the cells examined.
Cecum: A blind outpocket of a hollow organ such as an intestine.
Cell: Life’s fundamental unit of structure and function.
Cell adhesion molecules (CAMs): Glycoproteins that contribute to cell migration and stable tissue structure.
Cell body: The part of a neuron that houses the nucleus and other organelles.
Cell cycle: An ordered sequence of events in the life of a eukaryotic cell, from its origin in the division of a parent cell until its own division into two; it is composed of M, G1, S, and G2 phases.
Cell cycle control system: A cyclically operating set of molecules in the cell that triggers and coordinates key events in the cell cycle.
Cell 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.
Cell division: The reproduction of cells.
Cell fractionation: The disruption of a cell and separation of its organelles by centrifugation.
Cell lineage: The ancestry of a cell.
Cell-mediated immune response: The branch of acquired immunity that involves the activation of cytotoxic T cells, which defend against infected cells, cancer cells, and transplanted cells.
Cell plate: A double membrane across the midline of a dividing plant cell between which the new cell wall forms during cytokinesis.
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.
Cellular slime mold:  A type of protist that has unicellular amoeboid cells and aggregate reproductive bodies in its life cycle.
Cellulose: A structural polysaccharide of cell walls, consisting of glucose monomers joined by β-1,4-glycosidic linkages.
Cell wall: A protective layer external to the plasma membrane in plant cells, prokaryotes, fungi, and some protists.
Celcius 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.
CentiMorgan (cM): A distance on the genetic map that corresponds to a 1% recombination rate.
Central canal: The narrow cavity in the center of the spinal cord that is continuous with fluid-filled ventricles of the brain.
Central dogma: Information can pass from nuclei acid to protein but not in the opposite direction.
Central nervous system (CNS): In vertebrate animals, the brain and spinal cord.
Central vacuole: A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development.
Centriole: 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 involved in cell division.
Centromere: The region of chromosome that attaches to the spindle at mitosis and meiosis.
Centrosome: Material present in the cytoplasm of all eukaryotic cells, important during cell division; the microtubule organizing center. Centrosomes consist of a pair of centrioles surrounded by pericentriolar material; which nucleates spindle microtubules.
Cephalization: An evolutionary trend toward the concentration of sensory equipment on the anterior end of the body.
Cephalodia: Pockets of cyanobacteria in lichens.
Cerebellum: Part of the vertebrate hindbrain located dorsally, functions in unconscious coordination of movement and balance.
Cerebral cortex: The surface of the cerebrum, the largest and more complex part of the mammalian brain, containing motor and sensory nerve cell bodies of the cerebrum.
Cerebral hemisphere: The right or left side of the vertebrate brain.
Cerebrospinal fluid: Blood-derived fluid that surrounds, protects against infection, nourish, and cushions the brain and spinal cord.
Cerebrum: The dorsal portion of the vertebrate forebrain, composed of right and left hemispheres. The integrating center for memory, learning, emotions and other highly complex functions of the central nervous system.
Cervix: The neck of the uterus, which opens into the vagina.
Chaetonagth: Any worm of the phylum Chaetognatha, commonly called an arrowworm. This is a transparent marine worm with horizontal lateral and caudal fins and a row of movable curved spines at each side of the mouth.
Chaparral: A scrubland biome of dense, spiny evergreen shrubs found at midlatitudes along coasts where cold ocean currents circulate offshore; characterized by mild, rainy and long, hot, dry summers.
Chaperone: A protein that assist other proteins in achieving a properly folded state.
Character: An observable heritable feature.
Character displacement: The tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species.
Character state reconstruction:  A method used to infer ancestral and derived character states and traits.
Checkpoint: A critical control point in the cell cycle where stop and go-ahead signals can regulate the signal.
Chelicera: One of a pair of claw-like feeding appendages characteristic of cheliceriforms.
Cheliceriforms: An arthropod that has chelicerae and a body divided into a cephalothorax and an abdomen. Extant cheliceriforms include sea spiders, horseshoe crabs, scorpions, ticks, and spiders.
Chemical bond: An attraction between two atom, resulting from sharing outer shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells.
Chemical energy: Energy stored in the chemical bond of molecules, a form of potential energy.
Chemical equilibrium: In a reversible chemical reaction, the points at which the rate of the forward reaction is equal to the rate of the reverse reaction.
Chemical evolution: Chemical reactions that could have generated complex compounds from simple ones prior to the origin of life.
Chemical reaction: A process leading to chemical changes in matter, involves the making and/or breaking of chemical bonds.
Chemiosmosis: An energy coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work such as the synthesis of ATP.
Chemoautotroph:  An organism that needs only carbon dioxide as a carbon source but that obtain energy by oxidizing  inorganic substances.
Chemoheterotroph: An organism that must obtain both energy and carbon by consuming organic molecules.
Chemokine: Proteins secreted by many cell types near a site of injury or infection, that help direct migration of white blood cells to an injury site and induces other changes central to inflammation.
Chemoreceptor: A receptor that transmit information about the total soluble concentration in a solution or about individual kinds of molecules.
Chemostat: A device that allows populations of microorganisms to be maintained in a steady state by controlling the rate of nutrient supply.
Chemotaxis: Taxis toward or away from the source of a specific chemical.
Chemotropism: tropism to or from a specific chemical.
Chert: Very fine-grained silica (SiO2) that forms layers or nodules in sequences of sedimentary rocks.
Chiasma: The cross-like structure formed by crossing over during meiosis.
Chimera: An organism with a mixture of genetically different cells.
Chitin: (Greek: chiton, coat of mail/garment) A structural component of the fungal cell wall, a polymer of N-acetylglucosamine.
Chlamydospore: (Greek: chlamys, cloak) Thick walled, usually asexual, resting spore.
Chlorophyll: A green pigment located within the chloroplasts of plants. Chlorophyll a can participate directly in the light reactions which convert solar energy into chemical energy.
Chlorophyll a: A type of blue-green photosynthetic pigment that participates directly in the light reactions.
Chlorophyll b: A type of yellow-green accessory photosynthetic pigment that transfers energy to Chlorophyll a.
Chlorophyte: Member of a phylum of eukaryotes that are all single-celled green algae and closely related to plants.
Chloroplast: A photosynthetic organelle found in many plants, algae, and other microbial eukaryotes that is evolutionary derived from cyanobacteria.
Choanocyte: A flagellated feeding cell found in sponges, also called a collar cell because it has a collar-like ring that traps food particles around the base of its flagellum.
Choanoflagellate: Member of a phylum of eukaryotes including single-celled flagellated species. This is a sister phylum to animals.
Cholesterol: A steroid that form an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other important  steroids.
Chondrichthyan: Member of the class Chondrichthyes, vertebrates with skeletons made mostly of cartilage, such as sharks and rays.
Chondrocyte: Cartilage cell that secretes collagen and chondroitin sulphate.
Chordate: Member of a major phylum (Chordata) within the deuterostomes, which includes the vertebrates and closely allied invertebrates such as tunicates and amphioxus. All chordates contain a solid rod, called the notochord, along the length of the body during embryogenesis and a dorsal nerve cord and pharyngeal pouches.
Chorion: The outer most of four extraembryonic membranes, contributes to the formation of the mammalian placenta.
Choroid: A thin, pigmented inner layer of the vertebrate eye.
Chromatid: One of the two copies of a chromosome after it has been replicated.
Chromatin: A compact structure of DNA and protein found in eukaryotic nuclei.
Chromatin conformation capture (3C): A method that measures the frequency with which two DNA fragments interact within the 3D nuclear space.
Chromosome: A threadlike gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins.
Chylomicron: One of the small intracellular globules composed of fats that are mixed with cholesterol and coated with special proteins.
Chytrid: Member of the fungal phylum Chytridiomycota, mostly aquatic fungi with flagellated zoospores that probably represent the most primitive fungal lineage.
Ciliary body: A portion of the vertebrate eye associated with the lens. It produces the clear, watery aqueous humor that fills the anterior cavity of the eye.
Ciliate: Member of a phylum of eukaryotes including single-celled species. They belong to the kingdom of the Alveolata. Most are coated on the outside with cilia, which are used for movement and cellular functions.
Cilium: (plural cilia): 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 the plasma membrane.
Circadian rhythm: A physiological  cycle of about 24 hours that is present in all eukaryotic organisms and that persist even in the absence of external cues.
Circannual: pertaining to a biological activity or cycle that recurs yearly.
cis: Arrangement of two noncarbon atoms each bound to one of the carbons in a carbon-carbon double bond, where the two noncarbon atoms are in the same side relative to the double bond.
Cis-regulation: Refers to the regulation of when and where a gene is transcribed by DNA sequences that lie to either side (5′ or 3′) of the gene or within the introns of the gene.
Cis-regulatory elements: Non-coding DNA sequences that regulate the transcription of nearby genes.
Citric acid cycle: A chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules to carbon dioxide, occurs within the mitochondrion.
Clade: A group of species or genes that include all descendants of an ancestral species or gene.
Cladistics: A method of classification that is based on the order of branching in a phylogenetic tree rather than on phenotypic similarity.
Cladogram: A phylogenetic tree in which the only information given is about the relationships among taxa (i.e. the length of the branches is not meaningful).
Class: In classification, the taxonomic category above order.
Class I MHC molecules: A collection of cell surface proteins found on nearly all nucleated cells.
Class II MHC molecules: A collection of cell surface proteins restricted to a few specialized cell types called antigen-presenting cells (dendritic cells, macrophages, and B cells).
Classical conditioning: A type of associative learning; the association of a normally irrelevant stimulus with a fixed behavioral response.
Classical view: The view that genetic variation is mostly due to deleterious mutations. This contrast with the balance view that most variation is maintained by balancing selection.
Cleavage:  (1) The process of cytokinesis in animal cells, characterized by pinching of the plasma membrane. (2) 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.
Climate: The prevailing weather conditions at a locality.
Climograph: A plot of the temperature and precipitation in a particular region.
Cline: a boundary defining a region of similar conditions. In biology, these are often seen as “range maps” for a particular species.
Cloaca: A common opening for the digestive, urinary, and reproductive tracts found in many nonmammalian vertebrates but in few mammals.
Clonal selection:  During acquired immune response, it is process by which an antigen selectively  binds to and activates only those lymphocytes bearing receptors specific for that antigen. The selected lymphocytes proliferates and differentiated into  a clone of effector cells and a clone of memory cells specific for the stimulating antigen.
Clonal interference: In an asexual population, different clone, each favored by selection, compete with each other so that only one can succeed.
Clone: A set of genetically identical individuals. In genetic engineering, a line of microbes that carry a particular sequence from another species.
Cloning: Using a somatic cell from a multicellular organism to make one or more genetically identical individuals.
Cloning vector: An agent used to transfer DNA in genetic engineering. For example, a plasmid that moves recombinant DNA from a test tube back into a cell, or a virus that transfer recombinant DNA by infection.
Closed circulatory system: A circulatory system in which blood is confined to vessels and is kept separated from the interstitial fluid.
Cnidocyte: A specialized cell for which the phylum Cnidaria is named, contains a capsule containing a fine coiled threat, which when discharged functions in defense and prey capture.
Cnidarian: Member of a major phylum (Cnidaria) that include corals, sea anemones, hydra, and jelly fish. The group is characterized by the presence of stinging cells called nematocysts.
Coalescence: The merging of two genetic lineages into a single common ancestor.
Coalescence time: The time back when two genes share a common ancestor.
Coancestry: A measure of relatedness of two individuals. it is the chance that two randomly chosen genes, one from each individual, are identical by descent.
Cochlea:  The complex, coiled organ of hearing that contains the organ of Corti.
Codominance: The situation in which the phenotypes of both alleles are exhibited in the heterozygote.
Codon: Three bases that code for a single amino acid.
Codon usage: The frequency with which each of the alternative codons that code for an amino acid is used.
Codon usage bias: A bias toward use one of the several alternative codons that code for the same amino acid.
Coefficient of relatedness: The probability that a particular gene present in one individual will also be inherited from a common parent or ancestor in a second individual.
Coelom: A body cavity completely lined with mesoderm.
Coelomate: Animal that possesses a true coelom (fluid-filled body cavity lined by tissue completely derived from mesoderm).
Coevolution: The joint evolution of two species, with each responding to selection imposed by the other.
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.
Cognition: The ability of an animal nervous system to perceive, store, process, and use information obtained by its sensory receptors.
Cognitive ethology: The scientific study of cognition; the study of the connection between data processing by nervous systems and animal behavior.
Cognitive map: A representation within the nervous system of spatial relations between objects in an animal environment.
Cohesion: The binding together of like molecules, often by hydrogen bonds.
Cohort: A group of individuals of the same age, from birth until all are dead.

Coiled coils: A left-handed superhelical array formed by winding two or more α-helices around each other
Coleoptile: The covering of the young shoot of the embryo of a grass seed.
Coleorhiza: The covering of the young root of the embryo of a grass seed.
Collagen: 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.
Collagenous fiber: A tough fiber of the extracellular matrix. Collagenous fibers are made of collagen, are nonelastic, and do not tear easily when pulled lengthwise.
Collecting duct: The location in the kidney where filtrate from renal  tubules is collected, the filtrate is now called urine.
Collenchyma cell: A flexible plant cell type that occurs in strands or cylinders that support young parts of the plant without restraining growth.
Colloid: A mixture made up of a liquid and particles that (because of their large size) remain suspended in that liquid.
Colon: large intestine.
Colony: (1) An assemblage of hyphae that often develops from a single source and grows in a coordinated way. Synonymous with mycelium. (2) A collection of autonomously replicating cells of the same species.
Columnar: The column shape of a type of epithelial cell.
Commensalism: A symbiotic relationship in which one organism benefits but the other is neither helped nor harmed.
Communication: Animal behavior involving transmission of, reception of,  and response to signals.
Community: All the organisms that inhabit a particular area; an assemblage of populations of different species living close enough together for potential interaction.
Community ecology: The study of how interactions between species affect community structure and organization.
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.
Compartmentalization:  Subdivision of molecules, cells, or genetic functions into discrete temporal or spatial units.
Competence: The uptake of DNA directly from the environment.
Competitive exclusion: Species that use exactly the same resources cannot coexist in stable equilibrium.
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 system: A group of about 30 blood proteins that may amplify the inflammatory response, enhance phagocytosis, or direct lyse pathogens. The complement system is activated in a cascade initiated by surface antigens on microorganisms or by antigen-antibody complexes.
Complementary DNA (cDNA): DNA that is complementary to RNA. By producing cDNA using reverse transcriptase from mRNA, actively expressed genes can be identified.
Complementation test: A test for determining whether two mutations are in the same gene (they do not complement) or different genes (they complement).
Complete dominance: A situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.
Complete flower: A flower that has all four floral organs: sepals, petals, stamens, and carpels.
Complete metamorphosis: The transformation of a larva into an adult that looks very different, and often functions very differently in its environment, than the larva.
Compound: A substance consisting of two or more elements in a fixed ratio.
Compound eye: A type of multifaceted eye in insects and crustaceans consisting of up to several thousand light-detecting, focusing ommatidia; specially good at detecting movement.
Concentration gradient: An increase or decrease in the density of a chemical substance in an area. Cells often maintain concentration gradients of ions across their membranes.
Concerted evolution: The evolution of repeated sequences which tend to remain homogenous because of processes such unequal crossover and gene conversion.
Conception: The fertilization of the egg by a sperm cell in humans.
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.
Condont: Ancient lineage of jawless vertebrates that arose during the Cambrian period.
Conduction: The direct transfer of thermal motion (heat) between molecules of objects in direct contact with each other.
Cone cell: One of two types of photoreceptors in the vertebrate eye; detects color during the day.
Confidence interval: The range of parameter values that do not deviate significantly from a null hypothesis.
Conformer: A characterization of an animal in regard to environmental variables. A conformer allows some conditions within its body to vary with certain external changes.
Conidiophore: A hypha that gives rise to conidia.
Conidium (-a):  An asexual spore produced on the surface of a mycelium, not within the sporangium.
Conifer: A member of the largest gymnosperm phylum. Most  conifers are cone-bearing trees, such as pines and firs.
Coniferous forest: A terrestrial biome characterized by long, cold winters and dominated by cone-bearing trees.
Conjugation: In prokaryotes, the direct transfer of DNA between two cells that are temporarily joined by a pilus. The transfer through a pilus of DNA from one bacterium or archaeon to another. In Ciliates, a sexual process in which two cells exchange haploid micronuclei.
Conjunctiva: A mucous membrane that helps keep the eye moist, lines the inner surface of the eyelid and covers the front of the eyeball, except the cornea.
Connective tissue: Animal tissue that functions mainly to bind and support other tissues, having a sparse population of cells scattered through an extracellular matrix.
Conodont: An early, soft-body vertebrate with prominent eyes and dental elements.
Conservative DNA transposon: A DNA-based transposable element that moves itself to a new place in the genome but does not leave a copy in the original location.
Conservation Biology: The integral study of ecology, evolutionary biology, physiology, molecular biology, genetics, and behavioral biology in an effort to sustain biological diversity at all levels.
Consolidate: To unite, solidify, to make something concrete.
Constitutive: Refers to a gene that is always expressed.
Contingency loci: Loci made up of satellite repeats (e.g. ATATAT) in which, when the number of repeats changes, the phenotype of the cells changes drastically. These are common is some bacterial pathogens.
Contraception: The prevention of pregnancy.
Contractile vacuole: A membranous sac that helps move excess water out of certain cells.
Control element: A segment of non-coding DNA that helps regulate transcription of a gene by binding proteins called transcription factors.
Controlled experiment: An experiment in which an experimental group is compared to a control group that varies only in the factor being tested.
Convection: The mass movement of warmed air or liquid to or from the surface of a body or object.
Convergent evolution: The process by which features with no common ancestral become similar as a result of selection.
Convergent extension: A mechanism of cell crawling in which the cells of a tissue layer rearrange themselves in such a way that the sheet of cells becomes narrower while it becomes longer.
Cooperativity: An interaction of the constituent subunits of a protein whereby a conformational change in one subunit is transmitted to all the others.
Copecod: Any of a group of small crustaceans that are important members of marine and freshwater plankton communities.
Coprohilous: Dung inhabiting
Copy number variation (CNV): variation in the number of copies of nucleotide sequence between individuals.
CpG: a cytosine adjacent to a guanine residue in the DNA sequence. The main site of DNA methylation in animal genomes.
Coral reef: A warm-water tropical ecosystem dominated by the hard skeletal structures secreted primarily by the resident cnidarians.
Corepressor: A small molecule that cooperates with a repressor protein to switch an operon off.
Cork cambium: A cylinder of meristematic tissue in woody plants that replaces the epidermis with thicker, tougher cork cells.
Cornea: The transparent frontal portion of the sclera, which admits light into the vertebrate eye.
Corpus callosum: The thick band of nerve fibers that connects the right and left cerebral hemispheres in placental mammals, enabling  the hemispheres to process information together.
Corpus luteum: A secreting tissue in the ovary that forms from the collapsed follicle after ovulation and produces progesterone.
Correlate: two things are related so that one directly implies or correspond to the other. Statistical relationship that quantifies the degree to which two variables are associated.
Corroborate: to support with evidence or authority. To confirm.
Cortex: Ground tissue that is between the vascular tissue and dermal tissue in a root or dicot stem.
Cortical granules: Vesicles located just under the plasma of an egg cell That undergo  exocytosis during the cortical reaction.
Cortical nephrons: Nephrons located almost entirely in the renal cortex. These nephrons have a reduce loop of Henle.
Cortical reaction: Exocytosis of enzymes from cortical granules in the egg cytoplasm during fertilization.
Corticosteroid: Any steroid hormone produced and secreted by the adrenal cortex.
Cosexual: Producing both male and female gametes. It is equivalent to hermaphrodite.
Cost of genome dilution: The disadvantage to a female who reproduces sexually, and therefore devote resources to propagate her mate’s genes.
Cotransport: The coupling of the ‘downhill’ diffusion of one substance to the ‘uphill’ transport of another against its own concentration gradient.
Cotyledon: A seed leaf of an angiosperm embryo. Some species have one cotyledon, other two.
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.
Countercurrent heat exchanger: An arrangement of blood vessels that helps trap heat in the body core and important in reducing heat loss in many endotherms.
Countercurrent multiplier system:  A countercurrent system in which energy is expended in active transport to facilitate exchange of material and create concentration gradients.
Covalent bond: A type of strong chemical bond in which two atoms share one or more pairs of valence electrons.
Covirus: One of a pair of viruses that have complementary functions and that must coinfect a cell for successful viral transmission.
Cranial nerve: A nerve that leaves the brain and innervates an organ of the head or upper body.
Craniate: A chordate with a head.
Crassulacean acid metabolism (CAM): A type of metabolism in which carbon dioxide is take in at night and incorporated into a variety of organic acids.
CRISPR: (clustered regularly interspaced short palindromic repeats) a technology that allows precise editing of DNA in the genome.
Cristae: Infolded internal membranes, such as that seen in mitochondria and plastids.
Critical load: The amount of added nutrients, usually nitrogen and phosphorus, that can be absorbed by plants without damaging ecosystem integrity.
Critical concentration: The protein concentration above which proteins self-aggregate into a biomolecular condensate.
Crop rotation: The alternation of planting a nonlegume one year and a legume next year to restore concentration of fixed nitrogen in the soil.
Crossover: A recombination event between nonsister chromatids during prophase I of meiosis.
Cross-pollination: In angiosperms, the transfer of pollen from the anther of a flower on one plant to the stigma of a flower in another plant of the same species.
Crown group: That part of a clade of living and fossil organisms that includes the last common ancestor of all the living forms and all its descendants.
Crustacean:  A member of a subphylum of arthropods that include lobsters, crayfish, crabs. shrimps, and barnacles.
Cryogenian: Geological period from 720 to635 Million years ago.
Crypsis: Fitted for concealing, serving to camouflage.
Cryptic coloration: Camouflage, making potential prey difficult to spot against its background.
Ctenophore: Member of a major animal phylum of solitary gelatinous marina animals commonly called comb jellies or sea gooseberries (phylum Ctenophora).
Cuboidal: The cubic shape of a type of epithelial cell.
Cultural evolution: Change in culture (i.e. information passed on by learning rather that by biological inheritance).
Culture: The ideas, customs, skills, rituals, and similar activities of a people or group that are pass along to succeeding generations.
Culturing: The growth of a particular microorganism in the laboratory in isolation from other organisms.
Cuticle: (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 modify for different functions. (3) A tough coat that covers the body of a nematode.
Cyanobacteria: One of the major phyla of bacteria. Most species are photosynthetic, and chloroplasts are derived from this group.
Cyclic AMP: Cyclic Adenosine monophosphate, a ring shaped molecule made from ATP That is a common intracellular signaling molecule (second messenger) in eukaryotic 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 that produces ATP but not NADH or oxygen.
Cyclin: A regulatory protein whose concentration fluctuates cyclically.
Cyclin-dependent kinase (Cdk): A protein kinase that is active only when attached to a particular cyclin.
Cyst: A spherical cell, derived from the swimming spores of zoosporic fungi by cell wall formation (encystment).
Cystic fibrosis: A human genetic disorder caused by a recessive allele for a chloride channel protein; characterized by excessive secretion of mucus and consequently vulnerability to infections.
Cytochrome: An iron containing protein, a component of electron transfer chains in mitochondria and chloroplasts.
Cytogenetic map: Chart of a chromosome that locates genes with respect to chromosomal features.
Cytokine: Any of a group of proteins secreted by a number of cell types, including macrophages, helper T cells, that regulate the function of lymphocytes and other cells of the immune system,
Cytokinesis: The division of the cytoplasm to form two separated daughter cells immediately after mitosis.
Cytokinins: A class of related plant hormones that retard aging and act in concert with auxin to stimulate cell division, influence the pathway to differentiation, and control apical dominance.
Cytology: Study of cells.
Cytoplasm: The entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane.
Cytoplasmic determinants:  The maternal substances in the egg that influence the course of early development by regulating the expression of genes that affect the developmental fate of cells.
Cytoplasmic male sterility: Loss of male function due to a cytoplasmic inherited factor in flowering plants.
Cytoplasmic streaming:  A circular flow of cytoplasm, involving actin filaments and myosin, that speeds the distribution of materials within the cell.
Cytoskeleton: The system of protein filaments; microtubules, microfilaments, and intermediate filaments in the cytoplasm of eukaryotic cells that gives the cell its shape, directs transport of molecules within a cell, organizes the cytoplasm, and builds the spindle needed to segregate genetic material.
Cytosol: The semifluid portion of the cytoplasm
Cytotoxic T cell: A type of lymphocyte that when activated, kills infected cells, cancer cells, and transplanted cells.