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Estrella Mountain - Anatomy terms Category: Education > Body parts Date & country: 25/03/2011, USA Words: 586

cell plate
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.

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

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.

central nervous system (CNS)
The division of the nervous system that includes the brain and spinal cord.

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

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.

channels
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.

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

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

chlamydia
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.

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

chorion
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.

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

cilia
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.

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.

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

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

codon
A sequence of three nucleotides in messenger RNA that codes for a single amino acid.

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

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

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

cohesion
The force that holds molecules of the same substance together.

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

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. PICTURE

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.

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

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

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.

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

consumers
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.

contrast
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.

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.

cortisol
The primary glucocorticoid hormone; released by the adrenal cortex.

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.

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

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

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. PICTURE

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.

cuticle
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.

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

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

cystic fibrosis
An autosomal recessive genetic disorder that causes the production of mucus that clogs the airways of the lungs and the ducts of the pancreas and other secretory glands.

cytokinesis
The division of the cytoplasm during cell division.

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

cytology
The branch of biology dealing with cell structure.

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

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.

dark reactions
The photosynthetic process in which food (sugar) molecules are formed from carbon dioxide from the atmosphere with the use of ATP; can occur in the dark as long as ATP is present.

death rate
The ratio between deaths and individuals in a specified population at a particular time.

deletion
The loss of a chromosome segment without altering the number of chromosomes.

dendrochronology
The process of determining the age of a tree or wood used in structures by counting the number of annual growth rings.

depth diversity gradient
The increase in species richness with increasing water depth until about 2000 meters below the surface, where species richness begins to decline.

dermis
One of the two layers of skin; a connective tissue layer under the epidermis containing elastic and collagen fibers, capillary networks, and nerve endings.

desert biome
Characterized by dry conditions and plants and animals that have adapted to those conditions; found in areas where local or global influences block rainfall.

desmosome
A circular region of membrane cemented to an adjacent membrane by a molecular glue made of polysaccharides; found in tissues that undergo stretching.

deuterostomes
Animals in which the first opening that appears in the embryo becomes the anus while the mouth appears at the other end of the digestive system. Main groups include chordates and echinoderms.

diatomaceous earth
Fossilized deposits of diatoms; used for abrasives, polishes and as a filtering agent.

diencephalon
Part of the forebrain; consists of the thalamus and hypothalamus.

diploid
Cells that contain homologous chromosomes. The number of chromosomes in the cells is the diploid number and is equal to 2n (n is the number of homologous pairs).

discontinuous variation
Occurs when the phenotypes of traits controlled by a single gene can be sorted into two distinct phenotypic classes.

distal tubule
The section of the renal tubule where tubular secretion occurs.

divergent plate boundary
The boundary between two tectonic plates that are moving apart.

diversity
The different types of organisms that occur in a community.

DNA hybridization
The formation of hybrid DNA molecules that contain a strand of DNA from two different species. The number of complementary sequences in common in the two strands is an indication of the degree of relatedness of the species.

DNA ligase
In recombinant DNA technology, an enzyme that seals together two DNA fragments from different sources to form a recombinant DNA molecule.

DNA polymerase
In DNA replication, the enzyme that links the complementary nucleotides together to form the newly synthesized strand.

dominance
The property of one of a pair of alleles that suppresses the expression of the other member of the pair in heterozygotes.

dominance hierarchy
A social structure among a group of animals in which one is dominant and the others have subordinate nonbreeding positions.

dominant
Refers to an allele of a gene that is always expressed in heterozygotes.

duplication
An extra copy of a chromosome segment without altering the number of chromosomes.

eccrine glands
Sweat glands that are linked to the sympathetic nervous system and are widely distributed over the body surface.

ecological niche
The role an organism occupies and the function it performs in an ecosystem; closely associated with feeding.

ecological time
A timescale that focuses on community events that occur on the order of tens to hundreds of years.

ecology
The study of how organisms interact with each other and their physical environment.

ecosystem
The community living in an area and its physical environment.

ecotype
A subdivision of a species; a stage in the formation of a species such that reproductive isolation has occurred.

ectoderm
The outer layer of cells in embryonic development; gives rise to the skin, brain, and nervous system. Also, the outermost tissue layer in

ectotherms
Animals with a variable body temperature that is determined by the environment. Examples: fish, frogs, and reptiles.

effector
In a closed system, the element that initiates an action in response to a signal from a sensor. In human systems, a muscle or gland often serves as an effector.

ejaculatory duct
In males, a short duct that connects the vas deferens from each testis to the urethra.

electron
A subatomic particle with a negative charge. Electrons circle the atom's nucleus in regions of space known as orbitals.

electron acceptor
A molecule that forms part of the electron transport system that transfers electrons ejected by chlorophyll during photosynthesis. Part of the energy carried by the electrons is transferred to ATP, part is transferred to NADPH, and part is lost in the transfer system.

electrostatic attraction
The attraction between atoms of opposite charge that holds the atoms together in ionic bonds.