D

dead space The pharynx, the trachea, and the upper third of the lungs, which contain air not used in gas exchange. 742

deciduous tree dah-SID-u-us TREE Tree that sheds leaves at the end of a growing season. 546

decomposers dee-kom-POZ-erz Organisms that consume feces and dead organisms. 8, 862, 873

degenerate codons de-JEN-er-at KO-donz Different codons that specify the same amino acid. 344

dehydration synthesis de-hi-DRA-shun SYN-theh-sis Formation of a covalent bond between two molecules by loss of water. 43

deletion A chromosome missing genetic material. 301

dendrite DEN-drite Thin neuron branches that receive messages. 596, 611

denitrifying bacteria de-ni-tri-fy-ing bak-TEAR-e-a Bacteria that convert nitrites and nitrates to nitrogen gas. 865.

dense connective tissue Connective tissue that has dense collagen tracts. 594

density-dependent factor Event that kills when populations are large. 843

density-independent factor Event that kills irrespective of population size. 842

deoxyhemoglobin de-OX-ee-HEEM-o-GLO-bin Hemoglobin that is deep red after releasing its oxygen to tissues. 715

deoxyribonucleic acid de-OX-ee-RI-bo-nu-KLAY-ic AS-id (DNA) A double-stranded nucleic acid composed of nucleotides containing a phosphate group, a nitrogenous base (A, T, G, or C), and deoxyribose. 5, 51

deoxyribose de-OX-ee-RI-bose A five-carbon sugar that is part of DNA. 311

deposit feeder Animal that eats soil and strains out nutrients. 521

dermal tissue DER-mal TISH-ew Tissue that covers a plant. 534

dermis DER-miss In humans, the middle skin layer. 599

descending limb de-sen-ding LIM The proximal portion of the loop of the nephron, which descends into the kidney's medulla. 783

determinate cleavage de-TER-min-et CLEEV-edge An early embryo in which cell fate is determined. 514

deuteromycete doo-ter-o-mi-SEET Fungus that lacks a distinctive sexual phase. 478

deuterostome DOO-ter-o-stome One of two coelomate lineages, characterized by radial cleavage, an anus, and indeterminate cleavage. 512

developmental pathway Series of events that forms a particular anatomical structure. 211

diaphragm A broad sheet of muscle that separates the thoracic cavity from the abdominal cavity. 742

diastole di-ASS-tole-ee Relaxation of the heart. 720

diatom DIE-a-tom An alga with distinctive silica walls. 467

dicot DI-kot A plant that has two seed leaves. 541

differentiate diff-er-en-shee-ate Specialize. 211

diffusion de-FUZE-jhun Movement of a substance from a region where it is highly concentrated to an area where it is less concentrated without energy input. 88

dihybrid cross DI-HI-brid KROS Mating between individuals heterozygous for two particular genes. 269

dilution effect di-LEW-shun e-fekt A behavior that decreases the chance of an event occurring. 822

dimorphic di-MOR-fik A fungus with unicellular and multicellular phases to the life cycle. 477

dinoflagellate di-no-FLADJ-el-et An alga with characteristics of two flagella. 466

diploblastic dip-lo-BLAS-tik An animal whose adult tissues arise from two germ layers in the embryo. 509

diploid cell DIP-loid SEL A cell with two copies of each chromosome. Also known as 2n. 192

direct development Animals that hatch from eggs or are born resembling adults of the species. 512

directional selection Changes in the prevalence of a characteristic that reflects differential survival of individuals better adapted to a particular environment. 410

disaccharide di-SAK-eh-ride A sugar that consists of two bonded monosaccharides. 43

disruptive selection A population in which two extreme expressions of a trait are equally adaptive. 411

distal convoluted tubule DIS-tel kon-vo-lu-tid TU-bule The region of the kidney distal to the loop of the nephron and proximal to a collecting duct. 783

disulfide bond di-SUL-fide bond Attraction between two sulfur atoms within a protein molecule. 49

dizygotic twins di-zi-GOT-ik TWINZ Fraternal twins. 279

DNA polymerase DNA po-LIM-er-ase An enzyme that inserts new bases and corrects mismatched base pairs in DNA replication. 317

domain A taxonomic designation that supercedes kingdom. 12, 430

dominance hierarchy dom-eh-nance HI-er-ar-kee A social ranking of members of a group of the same sex, which distributes resources with minimal aggression. 828

dominant An allele that masks the expression of another allele. 265

dormancy DOR-man-see A state of lowered metabolism that enables a plant to survive harsh climatic conditions. 587

dorsal DOOR-sal The back side. 512

double-blind An experimental protocol where neither participants nor researchers know which subjects received a placebo and which received the treatment being evaluated. 25

duodenum do-o-DEE-num The first section of the small intestine. 761

duplication A repeated portion of DNA in a chromosome. 301

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