Abjad D
JEJAK
MAHASISWA
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Dibuat
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dalton
(DAWL-ton) The atomic mass unit; a measure of mass for atoms and subatomic particles.
Darwinian fitness
A measure of the relative contribution of an individual to the gene pool of the next generation.
day-neutral plant
A plant whose flowering is not affected by photoperiod.
decomposers
Saprotrophic fungi and bacteria that absorb nutrients from nonliving organic material such as corpses, fallen plant material, and the wastes of living organisms, and convert them into inorganic forms.
deletion
(1) A deficiency in a chromosome resulting from the loss of a fragment through breakage. (2) A mutational loss of a nucleotide from a gene.
demography
The study of statistics relating to births and deaths in populations.
denaturation
For proteins, a process in which a protein unravels and loses its native conformation, thereby becoming biologically inactive. For DNA, the separation of the two strands of the double helix. Denaturation occurs under extreme conditions of pH, salt concentration, and temperature.
dendrite
(DEN-dryt) One of usually numerous, short, highly branched processes of a neuron that conveys nerve impulses toward the cell body.
density
The number of individuals per unit area or volume.
density-dependent factor
Any factor influencing population regulation that has a greater impact as population density increases.
density-dependent inhibition
The phenomenon observed in normal animal cells that causes them to stop dividing when they come into contact with one another.
density-independent factor
Any factor influencing population regulation that acts to reduce population by the same percentage, regardless of size.
deoxyribonucleic acid
(DNA) (DEE-oks-ee-ry-boh-noo-KLAY-ik) A double-stranded, helical nucleic acid molecule capable of replicating and determining the inherited structure of a cell's proteins.
deoxyribose
The sugar component of DNA, having one less hydroxyl group than ribose, the sugar component of RNA.
depolarization
An electrical state in an excitable cell whereby the inside of the cell is made less negative relative to the outside than at the resting membrane potential. A neuron membrane is depolarized if a stimulus decreases its voltage from the resting potential of -70 mV in the direction of zero voltage.
deposit-feeder
A heterotroph, such as an earthworm, that eats its way through detritus, salvaging bits and pieces of decaying organic matter.
dermal tissue system
The protective covering of plants; generally a single layer of tightly packed epidermal cells covering young plant organs formed by primary growth.
desmosome
(DEZ-muh-some) A type of intercellular junction in animal cells that functions as an anchor.
determinate cleavage
A type of embryonic development in protostomes that rigidly casts the developmental fate of each embryonic cell very early.
determinate growth
A type of growth characteristic of animals, in which the organism stops growing after it reaches a certain size.
determination
The progressive restriction of developmental potential, causing the possible fate of each cell to become more limited as the embryo develops.
detritus
(deh-TRY-tis) Dead organic matter.
deuterostomes
(DOO-ter-oh-stomes) One of two distinct evolutionary lines of coelomates, consisting of the echinoderms and chordates and characterized by radial, indeterminate cleavage, enterocoelous formation of the coelom, and development of the anus from the blastopore.
diaphragm
A sheet of muscle that forms the bottom wall of the thoracic cavity in mammals; active in ventilating the lungs.
diastole
(dy-ASS-toh-lee) The stage of the heart cycle in which the heart muscle is relaxed, allowing the chambers to fill with blood.
dicot
(DY-kot) A subdivision of flowering plants whose members possess two embryonic seed leaves, or cotyledons.
differentiation
See cellular differentiation.
diffusion
The spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area.
digestion
The process of breaking down food into molecules small enough for the body to absorb.
dihybrid cross
(DY-HY-brid) A breeding experiment in which parental varieties differing in two traits are mated.
dikaryon
(dy-KAH-ree-on) A mycelium of certain septate fungi that possesses two separate haploid nuclei per cell.
dioecious
(dy-EE-shus) Referring to a plant species that has staminate and carpellate flowers on separate plants.
diploid cell
(DIP-loyd) A cell containing two sets of chromosomes (2n), one set inherited from each parent.
directional selection
Natural selection that favors individuals on one end of the phenotypic range.
disaccharide
(dy-SAK-ur-ide) A double sugar, consisting of two monosaccharides joined by dehydration synthesis.
dispersion
The distribution of individuals within geographical population boundaries.
diversifying selection
Natural selection that favors extreme over intermediate phenotypes.
DNA ligase
(LY-gaze) A linking enzyme essential for DNA replication; catalyzes the covalent bonding of the 3' end of a new DNA fragment to the 5' end of a growing chain.
DNA methylation
The addition of methyl groups (-CH3) to bases of DNA after DNA synthesis; may serve as a long-term control of gene expression.
DNA polymerase
An enzyme that catalyzes the elongation of new DNA at a replication fork by the addition of nucleotides to the existing chain.
DNA probe
A chemically synthesized, radioactively labeled segment of nucleic acid used to find a gene of interest by hydrogen-bonding to a complementary sequence.
domain
A taxonomic category above the kingdom level; the three domains are Archaea, Bacteria, and Eukarya.
dominance hierarchy
A linear "pecking order" of animals, where position dictates characteristic social behaviors.
dominant allele
In a heterozygote, the allele that is fully expressed in the phenotype.
double circulation
A circulation scheme with separate pulmonary and systemic circuits, which ensures vigorous blood flow to all organs.
double fertilization
A mechanism of fertilization in angiosperms, in which two sperm cells unite with two cells in the embryo sac to form the zygote and endosperm.
double helix
The form of native DNA, referring to its two adjacent polynucleotide strands wound into a spiral shape.
Down syndrome
A human genetic disease resulting from having an extra chromosome 21, characterized by mental retardation and heart and respiratory defects.
duodenum
(doo-oh-DEE-num) The first section of the small intestine, where acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and gland cells of the intestinal wall.
duplication
An aberration in chromosome structure resulting from an error in meiosis or mutagens; duplication of a portion of a chromosome resulting from fusion with a fragment from a homologous chromosome.
dynein
(DY-nin) A large contractile protein forming the sidearms of microtubule doublets in cilia and flagella.
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