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Glossary C

A hormone produced by the thyroid that plays a role in regulating calcium levels.

calcium carbonate

Chemical that also occurs in limestone and marble.

Geologic period that begins the Paleozoic Era 570 million years ago. Marked in its beginning by a proliferation of animals with hard, preservable parts, such as brachiopods, trilobites, and archaeocyathids.

campodactyly

A dominant trait in which a muscle is improperly attached to bones in the little finger, causing the finger to be permanently bent.

Diseases in which abnormal cells divide and grow unchecked. Cancer can spread from its original site to other parts of the body and can also be fatal if not treated adequately.

candidate gene

A gene, located in a chromosome region suspected of being involved in a disease, whose protein product suggests that it could be the disease gene in question.

capillaries

Small, thin-walled blood vessels that allow oxygen to diffuse from the blood into the cells and carbon dioxide to diffuse from the cells into the blood.

capillary bed

A branching network of capillaries supplied by arterioles and drained by venules.

1. Structure produced around certain bacteria; 2. Structure produced by the bryophyte sporophyte that contains spores produced by meiosis.

carbohydrates

Organic molecules composed of carbon, hydrogen, and oxygen that serve as energy sources and structural materials for cells of all organisms.

Any of the various types of cancerous tumors that form in the epithelial tissue, the tissue forming the outer layer of the body surface and lining the digestive tract and other hollow structures. Examples of this kind of cancer include, breast, lung, and prostate cancer.

cardiac cycle

One heartbeat; consists of atrial contraction and relaxation, ventricular contraction and relaxation, and a short pause.

cardiac muscle

The type of muscle that is found in the walls of the heart. Cardiac muscle is striated but branched, unlike the straight-shaped striated skeletal muscle cells.

cardiovascular system

The human circulatory system consisting of the heart and the vessels that transport blood to and from the heart.

carotenoids

Major group of accessory pigments in plants; includes beta carotene.

The bones that make up the wrist joint.

The female reproductive structures of a flower; consisting of the ovary, style, and stigma.

carrageenan

Chemical extracted from red algae that is added to commercial ice creams as an emulsifying agent.

carrying capacity

The maximum population size that can be regularly sustained by an environment; the point where the population size levels off in the logistic growth model.

Casparian strip

In plants, an impermeable waxy layer between the cells of the endodermis that stops water and solutes from entering the xylem, except by passing through the cytoplasm of adjacent cells. 1 2

catabolic reactions

Reactions in cells in which existing chemical bonds are broken and molecules are broken down; generally produce energy, involve oxidation, and lead to a decrease in atomic order.

cDNA library

A collection of DNA sequences generated from mRNA sequences. This type of library contains only protein-coding DNA (genes) and does not include any non-coding DNA.

cell

The basic unit of any living organism. It is a small, watery, compartment filled with chemicals and a complete copy of the organism's genome.

In a neuron, the part that contains the nucleus and most of the cytoplasm and the organelles. 1 2

The sequence of events from one division of a cell to the next; consists of mitosis (or division) and interphase.

In plants, a membrane-bound space produced during cytokinesis by the vesicles of the Golgi apparatus. The cell plate fuses with the plasma membrane, dividing the cell into two compartments.

cell theory

One of the four (or five) unifying concepts in biology. The cell theory states that all living things are composed of at least one cell and that the cell is the fundamental unit of function in all organisms. Corollaries: the chemical composition of all cells is fundamentally alike; all cells arise from preexisting cells through cell division.

Structure produced by some cells outside their cell membrane; variously composed of chitin, peptidoglycan, or cellulose.

cell-mediated immunity

Immune reaction directed against body cells that have been infected by viruses and bacteria; controlled by T cells.

The smallest structural units of living matter capable of functioning independently. 1 2

cellular respiration

The transfer of energy from various molecules to produce ATP; occurs in the mitochondria of eukaryotes, the cytoplasm of prokaryotes. In the process, oxygen is consumed and carbon dioxide is generated.

A polysaccharide that is composed of unbranched chains of glucose; the major structural carbohydrate of plants, insoluble in water, and indigestible in the human intestine. 1 2

Cenozoic Era

The period of geologic time beginning after the end of the Mesozoic Era 65 million years ago and encompassing the present. Commonly referred to as the age of mammals.

central nervous system (CNS)

The division of the nervous system that includes the brain and spinal cord.

A specialized region on each chromatid to which kinetochores and sister chromatids attach.

cephalization

The concentration of sensory tissues in the anterior part of the body (head).

That part of the brain concerned with fine motor coordination and body movement, posture, and balance; is part of the hindbrain and is attached to the rear portion of the brain stem.

cerebral cortex

The outer layer of gray matter in the cerebrum; consists mainly of neuronal cell bodies and dendrites in humans; associated with higher functions, including language and abstract thought.

The part of the forebrain that includes the cerebral cortex; the largest part of the human brain.

The lower neck of the uterus that opens into the vagina.

Transport proteins that act as gates to control the movement of sodium and potassium ions across the plasma membrane of a nerve cell.

chemical equilibrium

The condition when the forward and reverse reaction rates are equal and the concentrations of the products remain constant.

chemiosmosis

The process by which ATP is produced in the inner membrane of a mitochondrion. The electron transport system transfers protons from the inner compartment to the outer; as the protons flow back to the inner compartment, the energy of their movement is used to add phosphate to ADP, forming ATP. 1 2

chemotrophs

Organisms (usually bacteria) that derive energy from inorganic reactions; also known as chemosynthetic.

The site where the exchange of chromosome segments between homologous chromosomes takes place (crossing-over) (pl.: chiasmata).

A polysaccharide contained in fungi; also forms part of the hard outer covering of insects.

A sexually transmitted disease caused by a parasitic bacterium that lives inside cells of the reproductive tract.

chlorofluorocarbons (CFCs)

Chemical substances used in refrigerators, air conditioners, and solvents that drift to the upper stratosphere and dissociate. Chlorine released by CFCs reacts with ozone, eroding the ozone layer.

chlorophyll

The pigment in green plants that absorbs solar energy.

chlorophyll a

The green photosynthetic pigment common to all photosynthetic organisms.

chlorophyll b

An accessory chlorophyll found in green algae and plants.

chlorophyll c

An accessory chlorophyll found in some protistans.

chloroplasts

Disk-like organelles with a double membrane found in eukaryotic plant cells; contain thylakoids and are the site of photosynthesis. ATP is generated during photosynthesis by chemiosmosis.

cholecystokinin

A hormone secreted in the duodenum that causes the gallbladder to release bile and the pancreas to secrete lipase.

The two-layered structure formed from the trophoblast after implantation; secretes human chorionic gonadotropin.

chorionic villi sampling (CVS)

A method of prenatal testing in which fetal cells from the fetal side of the placenta (chorionic villi) are extracted and analyzed for chromosomal and biochemical defects.

Generally refers to a strand of a replicated chromosome; consists of DNA and protein.

A complex of DNA and protein in eukaryotic cells that is dispersed throughout the nucleus during interphase and condensed into chromosomes during meiosis and mitosis.

One of the threadlike "packages" of genes and other DNA in the nucleus of a cell. Different kinds of organisms have different numbers of chromosomes. Humans have 23 pairs of chromosomes, 46 in all: 44 autosomes and two sex chromosomes. Each parent contributes one chromosome to each pair, so children get half of their chromosomes from their mothers and half from their fathers.

chromosome theory of inheritance

Holds that chromosomes are the cellular components that physically contain genes; proposed in 1903 by Walter Sutton and Theodore Boveri.

chromosomes

Structures in the nucleus of a eukaryotic cell that consist of DNA molecules that contain the genes.

Chrysophytes

Protistan division that is referred to as the golden brown algae; includes the diatoms. 1 2

Hair-like organelles extending from the membrane of many eukaryotic cells; often function in locomotion (sing.: cilium).

circadian rhythms

Biorhythms that occur on a daily cycle.

circulatory system

One of eleven major body organ systems in animals; transports oxygen, carbon dioxide, nutrients, and waste products between cells and the respiratory system and carries chemical signals from the endocrine system; consists of the blood, heart, and blood vessels.

circulatory system, closed

A system that uses a continuous series of vessels of different sizes to deliver blood to body cells and return it to the heart; found in echinoderms and vertebrates.

circulatory system, open

A system in which the circulating fluid is not enclosed in vessels at all times; found in insects, crayfish, some mollusks, and other invertebrates.

Taxonomic subcategories of phyla.

The collar bone.

cleavage furrow

A constriction of the cell membrane at the equator of the cell that marks the beginning of cytokinesis in animal cells. The cell divides as the furrow deepens.

climax community

The stage in community succession where the community has become relatively stable through successful adjustment to its environment.

A short shaft with a sensitive tip located where the labia minora meet; consists of erectile tissue and is important in female sexual arousal.

An exact copy of a DNA segment; produced by recombinant DNA technology.

The process of making copies of a specific piece of DNA, usually a gene. When geneticists speak of cloning, they do not mean the process of making genetically identical copies of an entire organism.

closed community

A community in which populations have similar range boundaries and density peaks; forms a discrete unit with sharp boundaries.

codominance

A type of inheritance in which heterozygotes fully express both alleles.

Three bases in a DNA or RNA sequence which specify a single amino acid.

In animals, a body cavity between the body wall and the digestive system that forms during preadult development.

Animals that have a coelom or body cavity lined with mesoderm.

Chemicals required by a number of enzymes for proper functioning; also known as enzyme cofactors.

The force that holds molecules of the same substance together.

cohesion-adhesion theory

Describes the properties of water that help move it through a plant. Cohesion is the ability of water molecules to stick together (held by hydrogen bonds), forming a column of water extending from the roots to the leaves; adhesion is the ability of water molecules to stick to the cellulose in plant cell walls, counteracting the force of gravity and helping to lift the column of water. 1 2 3

collenchyma

One of the three major cell types in plants; are elongated and have thicker walls than parenchyma cells and are usually arranged in strands; provide support and are generally in a region that is growing. 1 2

1. Level of organization intermediate between unicellular and multicellular - organisms are composed of multiple cells but fail to exhibit specialization of those cells. Examples: Volvox, a colonial alga. Click HERE to view a series of images of Volvox. 2. Term applied to organisms that occur in a fixed location, with one generation growing atop previous generations, as in coral reefs.

commensalism

A symbiotic relationship in which one species benefits and the other is not affected.

All species or populations living in the same area.

community age

One of the factors that helps cause the latitudinal diversity gradient. Tropical communities have had more time to evolve because they have been less disrupted by advancing ice sheets and other relatively recent climatic changes.

community simplification

The reduction of overall species diversity in a community; generally caused by human activity.

community succession

The sequential replacement of species in a community by immigration of new species and by local extinction of old ones.

compact bone

The outer dense layer that forms the shaft of the long bones; made up of concentric layers of mineral deposits surrounding a central opening.

companion cells

Specialized cells in the phloem that load sugars into the sieve elements and help maintain a functional plasma membrane in the sieve elements. 1 2

competition

One of the biological interactions that can limit population growth; occurs when two species vie with each other for the same resource.

competitive exclusion

Competition between species that is so intense that one species completely eliminates the second species from the area.

competitive release

Occurs when one of two competing species is removed from an area, thereby releasing the remaining species from one of the factors that limited its population size.

complement system

A chemical defense system that kills microorganisms directly, supplements the inflammatory response, and works with, or complements, the immune system.

complementary nucleotides

The bonding preferences of nucleotides, Adenine with Thymine, and Cytosine with Guanine. Also referred to as complementary base pairing.

complete dominance

The type of inheritance in which both heterozygotes and dominant homozygotes have the same phenotype.

A substance formed by two or more elements combined in a fixed ratio.

compound leaf

A leaf in which the blade forms small leaflets. Compound leaves that have several small leaflets originating from a central axis are termed pinnately compound; example: rose. Compound leaves that have their leaflets originating from a common point are termed palmately compound; example: palm.

conditioned response

The response to a stimulus that occurs when an animal has learned to associate the stimulus with a certain positive or negative effect.

Light receptors in primates' eyes that operate in bright light; provide color vision and visual acuity.

Any trait or condition that exists from birth.

Group of gymnosperms that reproduce by cones and have needle-like leaves (in general); includes the pines.

The higher levels in a food pyramid; consist of primary consumers, which feed on the producers, and secondary consumers, which feed on the primary consumers.

A chromosome map showing the locations of those regions of a chromosome where contiguous DNA segments overlap. Contig maps are important because they provide the ability to study a complete, and often large segment of the genome by examining a series of overlapping clones which then provide an unbroken succession of information about that region.

continuous variation

Occurs when the phenotypes of traits controlled by a single gene cannot be sorted into two distinct phenotypic classes, but rather fall into a series of overlapping classes.

In relation to microscopes, the ability to distinguish different densities of structures.

convergent evolution

The development of similar structures in distantly related organisms as a result of adapting to similar environments and/or strategies of life. Example: wings of birds and insects, the body shape of dolphins, sharks, and the extinct marine reptiles known as ichthyosaurs.

convergent plate boundary

The boundary between two plates that are moving toward one another.

Fossilized feces.

cork

The outer layer of the bark in woody plants; composed of dead cells.

cork cambium

A layer of lateral meristematic tissue between the cork and the phloem in the bark of woody plants.

coronary arteries

Arteries that supply the heart's muscle fibers with nutrients and oxygen.

corpus callosum

Tightly bundled nerve fibers that connect the right and left hemispheres of the cerebrum.

corpus luteum

A structure formed from the ovulated follicle in the ovary; secretes progesterone and estrogen.

1) The outer part of an organ, e.g., the adrenal cortex, which produces several steroid hormones; 2) in plants, the region of the stem or root between the epidermis and the vascular bundle(s).

The primary glucocorticoid hormone; released by the adrenal cortex.

A leaf-like structure that is present in the seeds of flowering plants; appears during seed germination and sometimes is referred to as a seed leaf.

countercurrent flow

An arrangement by which fish obtain oxygen from the water that flows through their gills. Water flows across the respiratory surface of the gill in one direction while blood flows in the other direction through the blood vessels on the other side of the surface.

courtship behavior

Behavioral sequences that precede mating.

covalent bond

A chemical bond created by the sharing of electrons between atoms.

The braincase; composed of several bones fitted together at immovable joints.

Structures formed by the folding of the inner membrane of a mitochondrion (sing.: crista).

crossing-over

During the first meiotic prophase, the process in which part of a chromatid is physically exchanged with another chromatid to form chromosomes with new allele combinations.

crossopterygians

A type of lobe-finned fish with lungs that were ancestral to amphibians.

crustaceans

A large taxonomic class of arthropods that includes lobsters, shrimps, and crabs.

A film composed of wax and cutin that occurs on the external surface of plant stems and leaves and helps to prevent water loss.

cyanobacteria

Blue-green bacteria; unicellular or filamentous chains of cells that carry out photosynthesis.

Group of gymnosperm seed plants that have large fern-like leaves and reproduce by cones but not flowers.

A recurring sequence of events; e. g., the secretion of certain hormones at regular intervals.

A protein found in the dividing cells of many organisms that acts as a control during cell division.

cystic fibrosis

A hereditary disease whose symptoms usually appear shortly after birth. They include faulty digestion, breathing difficulties and respiratory infections due to mucus accumulation, and excessive loss of salt in sweat. In the past, cystic fibrosis was almost always fatal in childhood, but treatment is now so improved that patients commonly live to their 20s and beyond.

cytogenetic map

The visual appearance of a chromosome when stained and examined under a microscope. Particularly important are visually distinct regions, called light and dark bands, which give each of the chromosomes a unique appearance. This feature allows a person's chromosomes to be studied in a clinical test known as a karyotype, which allows scientists to look for chromosomal alterations.

cytokinesis

The division of the cytoplasm during cell division.

A group of hormones that promote cell division and inhibit aging of green tissues in plants.

The branch of biology dealing with cell structure.

The viscous semiliquid inside the plasma membrane of a cell; contains various macromolecules and organelles in solution and suspension.

One of the pyrimidine nitrogenous bases occurring in both DNA and RNA.

cytoskeleton

A three-dimensional network of microtubules and filaments that provides internal support for the cells, anchors internal cell structures, and functions in cell movement and division.

cytoxic T cells

T cells that destroy body cells infected by viruses or bacteria; also attack bacteria, fungi, parasites, and cancer cells and will kill cells of transplanted organs if they are recognized as foreign; also known as killer T cells.

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