LS 1 Terms

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LS 1 Terms
2013-06-10 19:21:32

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  1. A mode of natural selection in which no single allele is favored in all populations of a species at all times. Instead, there is a balance among alleles in terms of fitness and frequency.
    balancing selection (26)
  2. A mode of natural selection that favors one extreme phenotype with the result that the average phenotype of a population changes in one direction. Generally reduces overall genetic variation in a population. Compare with disruptive selection and stabilizing selection.
    directional selection (26)
  3. A mode of natural selection that favors extreme phenotypes at both ends of the range of phenotypic variation. Maintains overall genetic variation in a population. Compare with stabilizing selection and directional selection.
    disruptive selection (26)
  4. Also known as environmental selection. A type of natural selection that favors individuals with heritable traits that enhance their ability to survive and reproduce in a certain physical and/or biological environment, excluding their ability to obtain a mate. Compare with sexual selection.
    ecological selection (26)
  5. A change in allele frequencies that often occurs when a new population is established from a small group of individuals (founder event) due to sampling error (i.e., the small group is not a representative sample of the source population).
    founder effect (26)
  6. A pattern of selection in which certain alleles are favored only when they are rare; a form of balancing selection.
    frequency-dependent selection (26)
  7. The movement of alleles between populations; occurs when individuals leave one population, join another, and breed.
    gene flow (26)
  8. All the alleles of all the genes in a certain population.
    gene pool (26)
  9. A reduction in allelic diversity resulting from a sudden reduction in the size of a large population (population bottleneck) due to a random event.
    genetic bottleneck (26)
  10. Any change in allele frequencies due to random events. Causes allele frequencies to drift up and down randomly over time, and eventually can lead to the fixation or loss of alleles.
    genetic drift (26)
  11. A genetic locus that can be identified and traced in populations by laboratory techniques or by a distinctive visible phenotype.
    genetic marker (26)
  12. (1) The number and relative frequency of alleles present in a particular population.
    (2) The proportion of phenotypic variation in a trait that is due to genetic rather than environmental influences in a certain population in a certain environment.
    genetic variation (26)
  13. A principle of population genetics stating that genotype frequencies in a large population do not change from generation to generation in the absence of evolutionary processes (e.g., mutation, gene flow, genetic drift, and selection), and nonrandom mating.
    Hardy–Weinberg principle (26)
  14. A pattern of natural selection that favors heterozygous individuals compared with homozygotes. Tends to maintain genetic variation in a population, thus is a form of balancing selection.
    heterozygote advantage (26)
  15. Mating between closely related individuals. Increases homozygosity of a population and often leads to a decline in the average fitness via selection (inbreeding depression).
    inbreeding (26)
  16. In inbred offspring, fitness declines due to deleterious recessive alleles that are homozygous, thus exposed to selection.
    inbreeding depression (26)
  17. The sexual selection of an individual of one gender for mating by an individual of the other gender (usually by female choice).
    intersexual selection (26)
  18. Competition among members of one gender for an opportunity to mate (usually male–male competition).
    intrasexual selection (26)
  19. Any change in the hereditary material of an organism (DNA in most organisms, RNA in some viruses). The only source of new alleles in populations.
    mutation (26)
  20. Selection that lowers the frequency of or even eliminates deleterious alleles.
    purifying selection (26)
  21. The selection of a nonrepresentative sample from some larger population, due to chance.
    sampling error (26)
  22. Any trait that differs between males and females.
    sexual dimorphism (26)
  23. A type of natural selection that favors individuals with traits that increase their ability to obtain mates. Acts more strongly on males than females. (Compare with ecological selection.)
    sexual selection (26)
  24. A mode of natural selection that favors phenotypes near the middle of the range of phenotypic variation. Reduces overall genetic variation in a population. Compare with disruptive selection and directional selection.
    stabilizing selection (26)
  25. An area that is actively defended by an animal from others of its species and that provides exclusive or semi-exclusive use of its resources by the owner.
    territory (26)
  26. Speciation that occurs when populations of the same species become geographically isolated, often due to dispersal or vicariance. Compare with sympatric speciation.
    allopatric speciation (27)
  27. Condition in which two or more populations live in different geographic areas. Compare with sympatry.
    allopatry (27)
  28. (adjective: allopolyploid) The state of having more than two full sets of chromosomes (polyploidy) due to hybridization between different species. Compare with autopolyploidy.
    allopolyploidy (27)
  29. (adjective: autopolyploid) The state of having more than two full sets of chromosomes (polyploidy) due to a mutation that doubled the chromosome number. All the chromosomes come from the same species. Compare withallopolyploidy.
    autopolyploidy (27)
  30. The study of how species and populations are distributed geographically.
    biogeography (27)
  31. The definition of a species as a population or group of populations that are reproductively isolated from other groups. Members of a species have the potential to interbreed in nature to produce viable, fertile offspring but cannot interbreed successfully with members of other species. Compare with morphospecies and phylogenetic species concepts.
    biological species concept (27)
  32. See monophyletic group.
    clade and lineage (27)
  33. A species that cannot be distinguished from similar species by easily identifiable morphological traits.
    cryptic species (27)
  34. A geographic area where interbreeding occurs between two species, sometimes producing fertile hybrid offspring.
    hybrid zone (27)
  35. The definition of a species as a population or group of populations that have measurably different anatomical features from other groups. Also called morphological species concept. Compare with biological species concept and phylogenetic species concept.
    morphospecies concept (27)
  36. The range of resources that a species can use and the range of conditions that it can tolerate. More broadly, the role that species plays in its ecosystem.
    niche (27)
  37. The definition of a species as the smallest monophyletic group in a phylogenetic tree. Compare with biological species concept and morphospecies concept.
    phylogenetic species concept (27)
  38. A species that has two or more distinct phenotypes in the same interbreeding population at the same time.
    polymorphic species (27)
  39. (adjective: polyploid) The state of having more than two full sets of chromosomes, either from the same species (autopolyploidy) or from different species (allopolyploidy).
    polyploidy (27)
  40. Reproductive isolation resulting from mechanisms that operate after mating of individuals of two different species occurs. The most common mechanisms are the death of hybrid embryos or reduced fitness of hybrids.
    postzygotic isolation (27)
  41. Reproductive isolation resulting from any one of several mechanisms that prevent individuals of two different species from mating.
    prezygotic isolation (27)
  42. In evolutionary biology, the natural selection for traits that prevent interbreeding between recently diverged species.
    reinforcement (27)
  43. Closely related species that occupy adjacent branches in a phylogenetic tree.
    sister species (27)
  44. An evolutionarily independent population or group of populations. Generally distinct from other species in appearance, behavior, habitat, ecology, genetic characteristics, and so on.
    species (27)
  45. A population that has distinctive traits and some genetic differences relative to other populations of the same species but that is not distinct enough to be classified as a separate species.
    subspecies (27)
  46. The divergence of populations living within the same geographic area into different species as the result of their genetic (not physical) isolation. Compare with allopatric speciation.
    sympatric speciation (27)
  47. Condition in which two or more populations live in the same geographic area, or close enough to permit interbreeding. Compare with allopatry.
    sympatry (27)
  48. A shared, derived trait found in two or more taxa that is present in their most recent common ancestor but is missing in more distant ancestors. Useful for inferring evolutionary relationships.
    synapomorphy (27)
  49. The physical splitting of a population into smaller, isolated populations by a geographic barrier.
    vicariance (27)
  50. A trait found in the ancestors of a particular group.
    ancestral trait (28)
  51. The average rate of low-level extinction that has occurred continuously throughout much of evolutionary history. Compare with mass extinction.
    background extinction (28)
  52. (1) A part of a phylogenetic tree that represents populations through time.
    (2) Any extension of a plant's shoot system.
    branch (28)
  53. A type of fossil, formed when the decay of a body part leaves a void that is then filled with minerals that later harden.
    cast (28)
  54. The most recent interval of geologic time, beginning 65.5 million years ago, during which mammals became the dominant vertebrates and angiosperms became the dominant plants.
    Cenozoic era (28)
  55. Any genetic, morphological, physiological, or behavioral characteristic of an organism to be studied.
    character (28)
  56. A method for constructing a phylogenetic tree that is based on identifying the unique traits (shared, derived characters, called synapomorphies) of each monophyletic group.
    cladistic approach (28)
  57. The independent evolution of similar traits in distantly related organisms due to adaptation to similar environments and a similar way of life.
    convergent evolution (28)
  58. A trait that is clearly homologous with a trait found in an ancestor of a particular group, but that has a new form.
    derived trait (28)
  59. All the animal species characteristic of a particular region, period, or environment.
    fauna (28)
  60. Any physical trace of an organism that existed in the past. Includes tracks, burrows, fossilized bones, casts, and so on.
    fossil (28)
  61. (adjective: homoplastic) Similarity among organisms of different species due to reasons other than common ancestry, such as convergent evolution. Features that exhibit such similarity (e.g., the wings of birds and bats) are said to be homoplastic, or convergent. Compare with homology.
    homoplasy (28)
  62. The hypothesis that a collision between the Earth and an asteroid caused the mass extinction at the K–P boundary, 65 million years ago.
    impact hypothesis (28)
  63. The extinction of a large number of diverse evolutionary groups during a relatively short period of geologic time (about 1 million years). May occur due to sudden and extraordinary environmental changes. Compare with background extinction.
    mass extinction (28)
  64. The interval of geologic time, from 251 million to 65.5 million years ago, during which gymnosperms were the dominant plants and dinosaurs the dominant vertebrates. Ended with extinction of the dinosaurs (except birds).
    Mesozoic era (28)
  65. An evolutionary unit that includes an ancestral population and all of its descendants but no others. Also called a clade or lineage. Compare with paraphyletic group and polyphyletic group.
    monophyletic group (28)
  66. (1) In animals, any small thickening (e.g., a lymph node).
    (2) In plants, the part of a stem where leaves or leaf buds are attached.
    (3) In a phylogenetic tree, the point where two branches diverge, representing the point in time when an ancestral group split into two or more descendant groups. Also called fork.
    node (28)
  67. A taxon that is closely related to a particular monophyletic group but is not part of it.
    outgroup (28)
  68. Scientists who study the fossil record and the history of life.
    paleontologists (28)
  69. The interval of geologic time, from 542 million to 251 million years ago, during which fungi, land plants, and animals first appeared and diversified. Began with the Cambrian explosion and ended with the extinction of many invertebrates and vertebrates at the end of the Permian period.
    Paleozoic era (28)
  70. A group that includes an ancestral population and some but not all of its descendants. Compare with monophyletic group.
    paraphyletic group (28)
  71. The interval between the formation of the Earth, about 4.6 billion years ago, and the appearance of most animal groups about 542 million years ago. Unicellular organisms were dominant for most of this era, and oxygen was virtually absent for the first 2 billion years.
    Precambrian (28)
  72. The second most abundant class of transposable elements in human genomes; can create copies of itself and insert them elsewhere in the genome. Compare with LINEs.
    SINEs (short interspersed nuclear elements) (28)
  73. The end of a branch on a phylogenetic tree. Represents a specific species or larger taxon that has not (yet) produced descendants—either a group living today or a group that ended in extinction. Also called terminal node.
    tip (28)
  74. Any substance, such as penicillin, that can kill or inhibit the growth of bacteria.
    antibiotic (29)
  75. One of the three taxonomic domains of life, consisting of unicellular prokaryotes distinguished by cell walls made of certain polysaccharides not found in bacterial or eukaryotic cell walls, plasma membranes composed of unique isoprene-containing phospholipids, and ribosomes and RNA polymerase similar to those of eukaryotes. Compare with Bacteria and Eukarya.
    Archaea (29)
  76. One of the three taxonomic domains of life, consisting of unicellular prokaryotes distinguished by cell walls composed largely of peptidoglycan, plasma membranes similar to those of eukaryotic cells, and ribosomes and RNA polymerase that differ from those in archaeans or eukaryotes. Compare with Archaea and Eukarya.
    Bacteria (29)
  77. A complex community of bacteria enmeshed in a polysaccharide-rich, extracellular matrix that allows them to attach to a surface.
    biofilm (29)
  78. An organism (bacteria or archaea) that produces ATP by oxidizing inorganic molecules with high potential energy such as ammonia (NH3) or methane (CH4). Also called lithotroph. Compare with chemoorganotroph.
    chemolithotroph (29)
  79. An organism that produces ATP by oxidizing organic molecules with high potential energy such as sugars. Also called organotroph. Compare with chemolithotroph.
    chemoorganotroph (29)
  80. A lineage of photosynthetic bacteria formerly known as blue-green algae. Likely the first life-forms to carry out oxygenic photosynthesis.
    cyanobacteria (29)
  81. A technique for identifying and studying microorganisms that cannot be grown in culture. Involves detecting and amplifying copies of certain specific genes in the microorganisms' DNA, sequencing these genes, and then comparing the sequences with the known sequences from other organisms.
    direct sequencing (29)
  82. An organism that lives in a symbiotic relationship inside the body of its host.
    endosymbiont (29)
  83. A method of detecting and obtaining cells with specific characteristics by placing a sample, containing many types of cells, under a specific set of conditions (e.g., temperature, salt concentration, available nutrients) and isolating those cells that grow rapidly in response.
    enrichment culture (29)
  84. A bacterium or archaean that thrives in an "extreme" environment (e.g., high-salt, high-temperature, low-temperature, or low-pressure).
    extremophile (29)
  85. A structure formed in some prokaryotes, fungi, and protists for spore dispersal; usually consists of a base, a stalk, and a mass of spores at the top.
    fruiting body (29)
  86. The theory that infectious diseases are caused by bacteria, viruses, and other microorganisms.
    germ theory of disease (29)
  87. A dye that distinguishes the two general types of cell walls found in bacteria. Used to routinely classify bacteria as Gram-negative or Gram-positive.
    Gram stain (29)
  88. Describing bacteria that look pink when treated with a Gram stain. These bacteria have a cell wall composed of a thin layer of peptidoglycan and an outer phospholipid layer. Compare with Gram-positive.
    Gram-negative (29)
  89. Describing bacteria that look purple when treated with a Gram stain. These bacteria have cell walls composed of a thick layer of peptidoglycan and no outer phospholipid later. Compare with Gram-negative.
    Gram-positive (29)
  90. Any organism that cannot synthesize reduced organic compounds from inorganic sources and that must obtain them from other organisms. Some bacteria, some archaea, and virtually all fungi and animals are heterotrophs. Also called consumer. Compare with autotroph.
    heterotroph (29)
  91. Four criteria used to determine whether a suspected infectious agent causes a particular disease.
    Koch's postulates (29)
  92. Four criteria used to determine whether a suspected infectious agent causes a particular disease.
    Koch's postulates (29)
  93. The inventory of all the genes in a community or ecosystem by sequencing, analyzing, and comparing the genomes of the component organisms. Sequencing of all or most of the genes present in an environment directly (also called environmental sequencing).
    metagenomics (29)
  94. A prokaryote that produces methane (CH4) as a by-product of cellular respiration.
    methanogen (29)
  95. An organism (bacteria or archaea) that uses methane (CH4) as its primary electron donor and source of carbon.
    methanotroph (29)
  96. Any microscopic organism, including bacteria, archaea, and various tiny eukaryotes.
    microbe (29)
  97. The field of study concerned with microscopic organisms.
    microbiology (29)
  98. (plural: mycelia) A mass of underground filaments (hyphae) that form the body of a fungus. Also found in some protists and bacteria.
    mycelium (29)
  99. The movement of nitrogen among terrestrial ecosystems, the oceans, and the atmosphere.
    nitrogen cycle, global (29)
  100. The incorporation of atmospheric nitrogen (N2) into ammonia (NH3), which can be used to make many organic compounds. Occurs in only a few lineages of bacteria and archaea.
    nitrogen fixation (29)
  101. (adjective: pathogenic) Any entity capable of causing disease, such as a microbe, virus, or prion.
    pathogen (29)
  102. The complex biological process that converts the energy of light into chemical energy stored in glucose and other organic molecules. Occurs in most plants, algae, and some bacteria.
    photosynthesis (29)
  103. An organism (most plants, algae, and some bacteria) that produces ATP through photosynthesis.
    phototroph (29)
  104. A bacterium or archaean that thrives in very hot environments.
    thermophile (29)
  105. A poison produced by a living organism, such as a plant, animal, or microorganism.
    toxin (29)
  106. A life cycle involving alternation of a multicellular haploid stage (gametophyte) with a multicellular diploid stage (sporophyte). Occurs in most plants and some protists.
    alternation of generations (30)
  107. See cell crawling.
    amoeboid motion (30)
  108. The emission of light by a living organism via an enzyme-catalyzed reaction.
    bioluminescence (30)
  109. The worldwide movement of carbon among terrestrial ecosystems, the oceans, and the atmosphere.
    carbon cycle, global (30)
  110. See detrivore.
    decomposer (30)
  111. A layer of dead organic matter that accumulates at ground level or on seafloors and lake bottoms.
    detritus (30)
  112. An association between organisms of two different species in which one lives inside the cell or cells of the other.
    endosymbiosis (30)
  113. One of the three taxonomic domains of life, consisting of unicellular organisms (most protists, yeasts) and multicellular organisms (fungi, plants, animals) distinguished by a membrane-bound cell nucleus, numerous organelles, and an extensive cytoskeleton. Compare with Archaea and Bacteria.
    Eukarya (30)
  114. In organisms undergoing alternation of generations, the multicellular haploid form that arises from a single haploid spore and produces gametes. Compare with sporophyte.
    gametophyte (30)
  115. (plural: hyphae) One of the long, branching strands of a fungal mycelium (the mesh-like body of a fungus). Also found in some protists.
    hypha (30)
  116. A human disease caused by five species of the protist Plasmodium and passed to humans by mosquitoes.
    malaria (30)
  117. The state of being composed of many cells that adhere to each other and do not all express the same genes, with the result that some cells have specialized functions.
    multicellularity (30)
  118. Uptake by a cell of small particles or cells by invagination and pinching off of the plasma membrane to form small, membrane-bound vesicles; one type of endocytosis.
    phagocytosis (30)
  119. Drifting organisms (animals, plants, archaea, or bacteria) in aquatic environments.
    plankton (30)
  120. The monophyletic group that includes red, green, and glaucophyte algae, and land plants.
    Plantae (30)
  121. Any organism that creates its own food by photosynthesis or from reduced inorganic compounds and that is a food source for other species in its ecosystem. Also called autotroph.
    primary producer (30)
  122. Any eukaryote that is not a green plant, animal, or fungus. Protists are a diverse paraphyletic group. Most are unicellular, but some are multicellular or form aggregations called colonies.
    protist (30)
  123. (plural: pseudopodia) A temporary bulge-like extension of certain protist cells used in cell crawling and ingestion of food.
    pseudopodium (30)
  124. Permanently attached to a substrate; not capable of moving to another location.
    sessile (30)
  125. A hard, protective outer structure.
    shell (30)
  126. In organisms undergoing alternation of generations, the multicellular diploid form that arises from two fused gametes and produces haploid spores. Compare with gametophyte.
    sporophyte (30)
  127. (adjective: symbiotic) Any close and prolonged physical relationship between individuals of two different species. See commensalism, mutualism, and parasitism.
    symbiosis (30)
  128. A flowering vascular plant that produces seeds within mature ovaries (fruits). The angiosperms form a single lineage. Compare with gymnosperm.
    angiosperm (31)
  129. Referring to a plant whose life cycle normally lasts only one growing season—less than one year. Compare with perennial.
    annual (31)
  130. (plural: antheridia) The sperm- producing structure in most land plants except angiosperms.
    antheridium (31)
  131. (plural: archegonia) The egg-producing structure in most land plants except angiosperms.
    archegonium (31)
  132. Describing a plant that sheds leaves or other structures at regular intervals (e.g., each autumn).
    deciduous (31)
  133. Any flowering plant (angiosperm) that has two cotyledons (embryonic leaves) upon germination. The dicots do not form a monophyletic group. Also called dicotyledonous plant. Compare with eudicot and monocot.
    dicot (31)
  134. All the organisms that live in a geographic area, together with the nonliving (abiotic) components that affect or exchange materials with the organisms; a community and its physical environment.
    ecosystem (31)
  135. An increasingly popular name for the lineage called land plants; reflects their retention of a fertilized egg.
    Embryophyta (31)
  136. A plant that nourishes its embryos inside its own body. All land plants are embryophytes.
    embryophyte (31)
  137. A triploid (3n) tissue in the seed of a flowering plant (angiosperm) that serves as food for the plant embryo. Functionally analogous to the yolk in some animal eggs.
    endosperm (31)
  138. (adjective: epiphytic) A nonparasitic plant that grows on the trunks or branches of other plants and is not rooted in soil.
    epiphyte (31)
  139. A member of a monophyletic group (lineage) of angiosperms that includes complex flowering plants and trees (e.g., roses, daisies, maples). All eudicots have two cotyledons, but not all dicots are members of this lineage. Compare with dicot and monocot.
    eudicot (31)
  140. In angiosperms, the part of a plant that contains reproductive structures. Typically includes a calyx, a corolla, and one or more stamens and/or carpels. See perfect and imperfect flower.
    flower (31)
  141. The large leaves of ferns.
    fronds (31)
  142. In flowering plants (angiosperms), a mature, ripened plant ovary (or group of ovaries), along with the seeds it contains and any adjacent fused parts; often functions in seed dispersal. See aggregate, multiple, and simple fruit.
    fruit (31)
  143. (plural: gametangia) (1) The gamete-forming structure found in all land plants except angiosperms. Contains a sperm-producing antheridium and an egg-producing archegonium.
    (2) The gamete-forming structure of some chytrid fungi.
    gametangium (31)
  144. (plural: gemmae) A small reproductive structure that is produced asexually in some plants during the gametophyte phase and can grow into a mature gametophyte; most common in non-vascular plants, particularly liverworts and club mosses, and in ferns
    gemma (31)
  145. A paraphyletic group of photosynthetic organisms that contain chloroplasts similar to those in green plants. Often classified as protists, green algae are the closest living relatives of land plants and form a monophyletic group with them.
    green algae (31)
  146. A vascular plant that makes seeds but does not produce flowers. The gymnosperms include five lineages of green plants (cycads, ginkgoes, conifers, redwoods, and gnetophytes). Compare with angiosperm.
    gymnosperm (31)
  147. (adjective: heterosporous) In seed plants, the production of two distinct types of spores: microspores, which become the male gametophyte, and megaspores, which become the female gametophyte. Compare with homospory.
    heterospory (31)
  148. (adjective: homosporous) In seedless vascular plants, the production of just one type of spore. Compare with heterospory.
    homospory (31)
  149. A substance, found in the secondary cell walls of some plants, that is exceptionally stiff and strong; a complex polymer built from six-carbon rings. Most abundant in woody plant parts.
    lignin (31)
  150. (plural: megasporangia) In heterosporous species of plants, a spore-producing structure that produces megaspores, which go on to develop into female gametophytes.
    megasporangium (31)
  151. In seed plants, a haploid (n) spore that is produced in a megasporangium by meiosis of a diploid (2n) megasporocyte; develops into a female gametophyte. Compare with microspore.
    megaspore (31)
  152. (plural: microsporangia) In heterosporous species of plants, a spore-producing structure that produces microspores, which go on to develop into male gametophytes.
    microsporangium (31)
  153. In seed plants, a haploid (n) spore that is produced in a microsporangium by meiosis of a diploid (2n) microsporocyte; develops into a male gametophyte. Compare with megaspore.
    microspore (31)
  154. Any flowering plant (angiosperm) that has a single cotyledon (embryonic leaf) upon germination. Monocots form a monophyletic group. Also called a monocotyledonous plant. Compare with dicot.
    monocot (31)
  155. The sugary fluid produced by flowers to attract and reward pollinating animals.
    nectar (31)
  156. A paraphyletic group of land plants that lack vascular tissue and reproduce using spores. The non-vascular plants include three lineages of green plants (liverworts, mosses, and hornworts). These lineages are sometimes called bryophytes.
    non-vascular plants (31)
  157. Semi-decayed organic matter that accumulates in moist, low-oxygen environments such as Sphagnum (moss) bogs.
    peat (31)
  158. Describing a plant whose life cycle normally lasts for more than one year. Compare with annual.
    perennial (31)
  159. In seed plants, a male gametophyte enclosed within a protective coat of sporopollenin.
    pollen grain (31)
  160. Suites of flower characters that are associated with certain types of pollinators and that have evolved through natural selection imposed by the interaction between flowers and pollinators.
    pollination syndrome (31)
  161. In land plants, an opening in the epithelium that allows gas exchange. See also stoma.
    pore (31)
  162. The hairlike structure that anchors a non-vascular plant to the substrate.
    rhizoid (31)
  163. A modified stem that runs horizontally underground and produces new plants at the nodes (a form of asexual reproduction). Compare with stolon.
    rhizome (31)
  164. The thickened inner layer of a plant cell wall formed by certain cells as they mature and have stopped growing; in water-conducting cells, contains lignin. Provides support or protection.
    secondary cell wall (31)
  165. In ferns, a cluster of spore-producing structures (sporangia) usually found on the underside of fronds.
    sori (31)
  166. (plural: sporangia) A spore-producing structure found in seed plants, some protists, and some fungi (e.g., chytrids).
    sporangium (31)
  167. A watertight material that encases spores and pollen of modern land plants.
    sporopollenin (31)
  168. (plural: stomata) Generally, a pore or opening. In plants, a microscopic pore, surrounded by specialized cells that open the pore, on the surface of a leaf or stem through which gas exchange occurs. See also guard cells.
    stoma (31)
  169. In vascular plants, a long, thin, water- conducting cell that has pits where its lignin- containing secondary cell wall is absent, allowing water movement between adjacent cells. Compare with vessel element.
    tracheid (31)
  170. In plants, tissue that transports water, nutrients, and sugars. Made up of the complex tissues xylem and phloem, each of which contains several cell types. Also called vascular tissue system.
    vascular tissue (31)
  171. In vascular plants, a short, wide, water-conducting cell that has gaps through both the primary and secondary cell walls, allowing unimpeded passage of water between adjacent cells. Compare with tracheid.
    vessel element (31)
  172. Xylem resulting from secondary growth; forms strong supporting material. Also called secondary xylem.
    wood (31)
  173. Fungi from the Glomeromycota lineage whose hyphae enter the root cells of their host plants. Also called endomycorrhizal fungi.
    arbuscular mycorrhizal fungi (AMF) (32)
  174. (plural: asci) Specialized spore-producing cell found at the ends of hyphae in "sac fungi" (Ascomycota).
    ascus (32)
  175. (plural: basidia) Specialized spore- producing cell at the ends of hyphae in club fungi, members of the Basidiomycota.
    basidium (32)
  176. Containing many nuclei and a continuous cytoplasm through a filamentous body, without the body being divided into distinct cells. Some fungi are coenocytic.
    coenocytic (32)
  177. (adjective: commensal) A symbiotic relationship in which one organism (the commensal) benefits and the other (the host) is not harmed. Compare withmutualism and parasitism.
    commensalism (32)
  178. Describing a cell or fungal mycelium having two haploid nuclei that are genetically distinct.
    dikaryotic (32)
  179. Fungi whose hyphae form a dense network that covers their host plant's roots but do not enter the root cells.
    ectomycorrhizal fungi (EMF) (32)
  180. See arbuscular mycorrhizal fungi (AMF).
    endomycorrhizal fungi (32)
  181. adjective: endophytic) A fungus that lives inside the aboveground parts of a plant in a symbiotic relationship. Compare with epiphyte.
    endophyte (32)
  182. Digestion that takes place outside of an organism, as occurs in many fungi that make and secrete digestive enzymes.
    extracellular digestion (32)
  183. A lineage of eukaryotes that typically have a filamentous body (mycelium) and obtain nutrients by absorption.
    fungi (32)
  184. Any substance that can kill fungi or slow their growth.
    fungicide (32)
  185. A glycoprotein that is abundant in the hyphae of arbuscular mycorrhizal fungi; when hyphae decay, it is an important component of soil.
    glomalin (32)
  186. Describing a cell or fungal mycelium containing two or more haploid nuclei that are genetically distinct.
    heterokaryotic (32)
  187. Fusion of two haploid nuclei to form a diploid nucleus. Occurs in many fungi, and in animals and plants during fertilization of gametes.
    karyogamy (32)
  188. A symbiotic association of a fungus, often in the Ascomycota lineage, and a photosynthetic alga or cyanobacterium.
    lichen (32)
  189. Organism that is a participant and partner in a mutualistic relationship. See mutualism.
    mutualist (32)
  190. (plural: mycorrhizae) A mutualistic association between certain fungi and the roots of most vascular plants, sometimes visible as nodules or nets in or around plant roots.
    mycorrhiza (32)
  191. (adjective: parasitic) A symbiotic relationship between two organisms that is beneficial to one organism (the parasite) but detrimental to the other (the host). Compare with commensalism and mutualism.
    parasitism (32)
  192. Fusion of the cytoplasm of two individuals. Occurs in many fungi.
    plasmogamy (32)
  193. A node in a phylogenetic tree that depicts an ancestral branch dividing into three or more descendant branches; usually indicates that insufficient data were available to resolve which taxa are more closely related.
    polytomy (32)
  194. An organism that feeds primarily on dead plant material.
    saprophyte (32)
  195. (plural: septa) Any wall-like structure. In fungi, septa divide the filaments (hyphae) of mycelia into cell-like compartments.
    septum (32)
  196. Any fungus growing as a single-celled form. Also, a specific lineage of Ascomycota.
    yeast (32)
  197. (plural: zygosporangia) The distinctive spore-producing structure in fungi that are members of the Zygomycota.
    zygosporangium (32)
  198. A bilaterian animal that lacks an internal body cavity (coelom). Compare withcoelomate and pseudocoelomate.
    acoelomate (33)
  199. A sexually mature individual.
    adult (33)
  200. A member of a major lineage of eukaryotes (Animalia) whose members typically have a complex, large, multicellular body; eat other organisms; and are mobile.
    animal (33)
  201. Living at the bottom of an aquatic environment.
    benthic (33)
  202. An animal body pattern in which one plane of symmetry divides the body into a left side and a right side. Typically, the body is long and narrow, with a distinct head end and tail end. Compare with radial symmetry.
    bilateral symmetry (33)
  203. A member of a major lineage of animals (Bilateria) that are bilaterally symmetrical at some point in their life cycle, have three embryonic germ layers, and have a coelom. All protostomes and deuterostomes are bilaterians.
    bilaterian (33)
  204. The basic architecture of an animal's body, including the number and arrangement of limbs, body segments, and major tissue layers.
    body plan (33)
  205. A large mass of neurons, located in the head region of an animal, that is involved in information processing; may also be called the cerebral ganglion.
    brain (33)
  206. The rapid diversification of animal body types and lineages that occured between the species present in the Doushantuo faunas (around 570 mya), Ediacaran faunas (565–542 mya), and the Early Cambrian faunas (525–515 mya).
    Cambrian explosion (33)
  207. (adjective: carnivorous) An animal whose diet consists predominantly of meat, or other animals. Most members of the mammalian taxon Carnivora are carnivores. Some plants are carnivorous, trapping and killing small animals and then absorbing nutrients from the prey's body. Compare with herbivore and omnivore.
    carnivore (33)
  208. Large numbers of neurons aggregated into clusters called ganglia in bilaterian animals. In vertebrates, the central nervous system consists of the brain and spinal cord. Compare with nerve net and peripheral nervous system (PNS).
    central nervous system (CNS) (33)
  209. The formation in animals of a distinct anterior region (the head) where sense organs and a mouth are clustered.
    cephalization (33)
  210. A specialized, flagellated feeding cell found in choanoflagellates (protists that are the closest living relatives of animals) and sponges (the most ancient animal phylum).
    choanocyte (33)
  211. A specialized stinging cell found in cnidarians (e.g., jellyfish, corals, and anemones) and used in capturing prey.
    cnidocyte (33)
  212. An internal, usually fluid-filled body cavity that is completely or partially lined with mesoderm.
    coelom (33)
  213. An animal that has a true coelom, completely lined with mesoderm. Compare withacoelomate and pseudocoelomate.
    coelomate (33)
  214. An assemblage of individuals. May refer to an assemblage of semi-independent cells or to a breeding population of multicellular organisms.
    colony (33)
  215. An animal that eats its way through a food-containing substrate.
    deposit feeder (33)
  216. An organism whose diet consists mainly of dead organic matter (detritus). Various bacteria, fungi, protists, and animals are detritivores. Also called decomposer.
    detritivore (33)
  217. A major lineage of bilaterian animals that share a pattern of embryological development, including formation of the anus earlier than the mouth, and formation of the coelom by pinching off of layers of mesoderm from the gut. Includes echinoderms and chordates. Compare with protostomes.
    deuterostomes (33)
  218. (adjective: diploblastic) An animal whose body develops from two basic embryonic cell layers or tissues—ectoderm and endoderm. Compare with triploblast.
    diploblast (33)
  219. A major lineage of protostomes (Ecdysozoa) that grow by shedding their external skeletons (molting) and expanding their bodies. Includes arthropods, nematodes, and other groups. Compare with lophotrochozoans.
    ecdysozoans (33)
  220. The outermost of the three basic cell layers (germ layers) in most animal embryos; gives rise to the outer covering and nervous system. Compare with endoderm and mesoderm.
    ectoderm (33)
  221. A parasite that lives on the outer surface of the host's body.
    ectoparasite (33)
  222. The innermost of the three basic cell layers (germ layers) in most animal embryos; gives rise to the digestive tract and organs that connect to it (liver, lungs, etc.). Compare with ectoderm and mesoderm.
    endoderm (33)
  223. A parasite that lives inside the host's body.
    endoparasite (33)
  224. (plural: epithelia) An animal tissue consisting of sheetlike layers of tightly packed cells that line an organ, a gland, a duct, or a body surface. Also called epithelial tissue.
    epithelium (33)
  225. See suspension feeder.
    filter feeder (33)
  226. (plural: ganglia) A mass of neurons in a centralized nervous system.
    ganglion (33)
  227. In animals, one of the three basic types of tissue formed during gastrulation; gives rise to all other tissues. See endoderm, mesoderm, and ectoderm.
    germ layer (33)
  228. (adjective: herbivorous) An animal that eats primarily plants and rarely or never eats meat. Compare with carnivore and omnivore.
    herbivore (33)
  229. A system of body support involving a body wall in tension surrounding a fluid or soft tissue under compression.
    hydrostatic skeleton (33)
  230. A paraphyletic group composed of animals without a backbone; includes about 95 percent of all animal species. Compare with vertebrates.
    invertebrates (33)
  231. An individual that has adult-like morphology but is not sexually mature.
    juvenile (33)
  232. (plural: larvae) An immature stage of an animal species in which the immature and adult stages have different body forms.
    larva (33)
  233. A major lineage of protostomes (Lophotrochozoa) that grow by extending the size of their skeletons rather than by molting. Many phyla have a specialized feeding structure (lophophore) and/or ciliated larvae (trochophore). Includes rotifers, flatworms, segmented worms, and mollusks. Compare with ecdysozoans.
    lophotrochozoans (33)
  234. An animal that ingests chunks of food.
    mass feeder (33)
  235. (plural: medusae) The free-floating stage in the life cycle of some cnidarians (e.g., jellyfish). Compare with polyp.
    medusa (33)
  236. The middle of the three basic cell layers (germ layers) in most animal embryos; gives rise to muscles, bones, blood, and some internal organs (kidney, spleen, etc.). Compare with ectoderm and endoderm.
    mesoderm (33)
  237. A gelatinous material, containing scattered ectodermal cells, that is located between the ectoderm and endoderm of cnidarians (e.g., jellyfish, corals, and anemones).
    mesoglea (33)
  238. A nervous system in which neurons are diffuse instead of being clustered into large ganglia or tracts; found in cnidarians and ctenophores.
    nerve net (33)
  239. (adjective: omnivorous) An animal whose diet regularly includes both meat and plants. Compare with carnivore and herbivore.
    omnivore (33)
  240. In animals, producing eggs that are laid outside the body where they develop and hatch. Compare with ovoviviparous and viviparous.
    oviparous (33)
  241. In animals, producing eggs that are retained inside the body until they are ready to hatch. Compare with oviparous and viviparous.
    ovoviviparous (33)
  242. An organism that lives on a host species (ectoparasite) or in a host species (endoparasite) and that damages its host.
    parasite (33)
  243. The immotile (sessile) stage in the life cycle of some cnidarians (e.g., jellyfish). Compare with medusa.
    polyp (33)
  244. Any organism that kills other organisms for food.
    predator (33)
  245. A major lineage of animals that share a pattern of embryological development, including formation of the mouth earlier than the anus, and formation of the coelom by splitting of a block of mesoderm. Includes arthropods, mollusks, and annelids. Compare with deuterostomes.
    protostomes (33)
  246. An animal that has a coelom that is only partially lined with mesoderm. Compare with acoelomate and coelomate.
    pseudocoelomate (33)
  247. An animal body pattern that has at least two planes of symmetry. Typically, the body is in the form of a cylinder or disk, and the body parts radiate from a central hub. Compare with bilateral symmetry.
    radial symmetry (33)
  248. Division of the body or a part of it into a series of similar structures; exemplified by the body segments of insects and worms and by the somites of vertebrates.
    segmentation (33)
  249. Stiff spike of silica or calcium carbonate that provides structural support in the body of many sponges.
    spicule (33)
  250. (adjective: triploblastic) An animal whose body develops from three basic embryonic cell layers or tissues: ectoderm, mesoderm, and endoderm. Compare with diploblast.
    triploblast (33)
  251. One of the three major chordate lineages (Vertebrata), comprising animals with a dorsal column of cartilaginous or bony structures (vertebrae) and a skull enclosing the brain. Includes fishes, amphibians, mammals, and reptiles (including birds). Compare with cephalochordates and urochordates.
    vertebrates (33)
  252. Producing live young (instead of eggs) that develop within the body of the mother before birth. Compare with oviparous and ovoviviparous.
    viviparous (33)
  253. A region of the body; in insects, one of the three prominent body regions called tagmata.
    abdomen (34)
  254. Members of the phylum Annelida (segmented worms). Distinguished by a segmented body and a coelom that functions as a hydrostatic skeleton. Annelids belong to the lophotrochozoan branch of the protostomes.
    annelids (34)
  255. (plural: antennae) A long appendage of the head that is used to touch or smell.
    antenna (34)
  256. Members of the phylum Arthropoda. Distinguished by a segmented body; a hard, jointed exoskeleton; paired, jointed appendages; and an extensive body cavity called a hemocoel. Arthropods belong to the ecdysozoan branch of the protostomes.
    arthropods (34)
  257. A structure that exerts biting forces and is associated with the mouth; found in birds, cephalopods, and some insects.
    beak (34)
  258. A lineage of mollusks that have shells made of two parts, or valves, such as clams and mussels.
    bivalves (34)
  259. In crustaceans, a large platelike section of the exoskeleton that covers and protects the cephalothorax (e.g., a crab's "shell").
    carapace (34)
  260. A lineage of mollusks including the squid, octopuses, and nautiluses. Distinguished by large brains, excellent vision, tentacles, and a reduced or absent shell.
    cephalopods (34)
  261. (singular: chaeta) Bristle-like extensions found in some annelids.
    chaetae (34)
  262. A pair of clawlike appendages found around the mouth of certain arthropods called chelicerates (spiders, mites, and allies).
    chelicerae (34)
  263. A lineage of marine mollusks that have a protective shell formed of eight calcium carbonate plates.
    chitons (34)
  264. See holometabolous metamorphosis.
    complete metamorphosis (34)
  265. An eye formed of many independent light-sensing columns (ommatidia); occurs in arthropods. Compare with simple eye.
    compound eye (34)
  266. The cluster of cilia at the anterior end of a rotifer; in many species it facilitates suspension feeding.
    corona (34)
  267. A lineage of arthropods that includes shrimp, lobster, and crabs. Many have a carapace (a platelike portion of the exoskeleton covering the cephalothorax) and mandibles for biting or chewing.
    crustaceans (34)
  268. A protective coating secreted by the outermost layer of cells of an animal or a plant; often functioning to reduce evaporative water loss.
    cuticle (34)
  269. The host species in which a parasite reproduces sexually. Compare with intermediate host.
    definitive host (34)
  270. A hard covering secreted on the outside of the body, used for body support, protection, and muscle attachment. Prominent in arthropods. Compare with endoskeleton.
    exoskeleton (34)
  271. Members of the phylum Platyhelminthes. Distinguished by a broad, flat, unsegmented body that lacks a coelom. Flatworms belong to the lophotrochozoan branch of the protostomes.
    flatworms (34)
  272. One of the three main parts of the mollusk body; a muscular appendage, used for movements such as crawling and/or burrowing into sediment.
    foot (34)
  273. A lineage of mollusks distinguished by a large, muscular foot and a unique feeding structure, the radula. Include slugs and snails.
    gastropods (34)
  274. Any organ in aquatic animals that exchanges gases and other dissolved substances between the blood and the surrounding water. Typically, a filamentous outgrowth of a body surface.
    gill (34)
  275. A type of metamorphosis in which the animal increases in size from one stage to the next, but does not dramatically change its body form. Also called incomplete metamorphosis.
    hemimetabolous metamorphosis (34)
  276. A body cavity, present in arthropods and some mollusks, containing a pool of circulatory fluid (hemolymph) bathing the internal organs. Unlike a coelom, a hemocoel is not lined in mesoderm.
    hemocoel (34)
  277. A type of metamorphosis in which the animal completely changes its form; includes a distinct larval stage. Also called complete metamorphosis.
    holometabolous metamorphosis (34)
  278. See hemimetabolous metamorphosis.
    incomplete metamorphosis (34)
  279. A terrestrial lineage of arthropods distinguished by three tagmata (head, thorax, abdomen), a single pair of antennae, and unbranched appendages.
    insects (34)
  280. The host species in which a parasite reproduces asexually. Compare with definitive host.
    intermediate host (34)
  281. A specialized feeding structure found in some lophotrochozoans and used in suspension (filter) feeding.
    lophophore (34)
  282. Any mouthpart used in chewing. In vertebrates, the lower jaw. In insects, crustaceans, and myriapods, the first pair of mouthparts.
    mandibles (34)
  283. One of the three main parts of the mollusk body; the thick outer tissue that protects the visceral mass and may secrete a calcium carbonate shell.
    mantle (34)
  284. A method of body growth, used by ecdysozoans, that involves the shedding of an external protective cuticle or skeleton, expansion of the soft body, and growth of a new external layer.
    molting (34)
  285. A lineage of arthropods with long segmented trunks, each segment bearing one or two pairs of legs. Includes millipedes and centipedes.
    myriapods (34)
  286. A distinct planktonic larval stage seen in many crustaceans.
    nauplius (34)
  287. See roundworms.
    nematodes (34)
  288. (singular: parapodium) Appendages found in some annelids from which bristle-like structures (chaetae) extend.
    parapodia (34)
  289. Development of offspring from unfertilized eggs; a type of asexual reproduction.
    parthenogenesis (34)
  290. A tubular, often extensible feeding appendage with which food can be obtained.
    proboscis (34)
  291. (plural: pupae) A metamorphosing insect that is enclosed in a protective case.
    pupa (34)
  292. A rasping feeding appendage in mollusks such as gastropods (snails, slugs).
    radula (34)
  293. Member of the phylum Rotifera. Distinguished by a cluster of cilia, called a corona, used in suspension feeding in marine and freshwater environments. Rotifers belong to the lophotrochozoan branch of the protostomes.
    rotifer (34)
  294. Members of the phylum Nematoda. Distinguished by an unsegmented body with a pseudocoelom and no appendages. Roundworms belong to the ecdysozoan branch of the protostomes. Also called nematodes.
    roundworms (34)
  295. An eye with only one light-collecting apparatus (e.g., one lens), as in vertebrates and cephalopods. Compare with compound eye.
    simple eye (34)
  296. A tubelike appendage of many mollusks, often used for feeding or propulsion.
    siphon (34)
  297. (singular: tagma) Prominent body regions in arthropods, such as the head, thorax, and abdomen in insects.
    tagmata (34)
  298. A long, thin, muscular appendage typically used for feeling and feeding. Occurs in different forms in diverse animals such as cephalopod mollusks and sea anemones.
    tentacle (34)
  299. A region of the body; in insects, one of the three prominent body regions, along with the head and abdomen, called tagmata.
    thorax (34)
  300. A larva with a ring of cilia around its middle that is found in some lophotrochozoans.
    trochophore (34)
  301. A distinctive type of larva, found in mollusks.
    veliger (34)
  302. One of the three main parts of the mollusk body; contains most of the internal organs and external gill.
    visceral mass (34)
  303. An animal with a long, thin, tubelike body lacking limbs.
    worm (34)
  304. A solution of water and protein (particularly albumins), found in amniotic eggs, that nourishes the growing embryo. Also called egg white.
    albumen (35)
  305. A major lineage of vertebrates (Amniota) that reproduce with amniotic eggs. Includes all reptiles (including birds) and mammals—all tetrapods except amphibians.
    amniotes (35)
  306. An egg that has a watertight shell or case enclosing a membrane-bound water supply (the amnion), food supply (yolk sac), and waste sac (allantois).
    amniotic egg (35)
  307. A lineage of vertebrates, many of which breathe through their skin and feed on land but lay their eggs in water. Represent the earliest tetrapods; include frogs, salamanders, and caecilians.
    amphibians (35)
  308. Having a life cycle in which adults live in the ocean (or large lakes) but migrate up freshwater streams to breed and lay eggs.
    anadromous (35)
  309. One of the two major lineages of primates, including apes, humans, and all monkeys. Compare with prosimians.
    anthropoids (35)
  310. Walking primarily on two legs; characteristic of hominins.
    bipedal (35)
  311. A type of vertebrate connective tissue consisting of living cells and blood vessels within a hard extracellular matrix composed of calcium phosphate (CaPO4) and small amounts of calcium carbonate (CaCO3) and protein fibers.
    bone (35)
  312. See cranium.
    braincase (35)
  313. One of the three major chordate lineages (Cephalochordata), comprising small, mobile organisms that live in marine sands and suspension feed; also calledlancelets or amphioxus. Compare with urochordates and vertebrates.
    cephalochordates (35)
  314. A bony, cartilaginous, or fibrous case that encloses and protects the brain of vertebrates. Forms part of the skull. Also called braincase.
    cranium (35)
  315. A prehistoric European population of modern humans (Homo sapiens) known from fossils, paintings, sculptures, and other artifacts.
    Cro-Magnon (35)
  316. See nerve chord.
    dorsal hollow nerve chord (35)
  317. A major lineage of deuterostomes (Echinodermata) distinguished by adult bodies with five-sided radial symmetry, a water vascular system, and tube feet. Includes sea urchins, sand dollars, and sea stars.
    echinoderms (35)
  318. Bony and/or cartilaginous structures within the body that provide support. Examples are the spicules of sponges, the plates in echinoderms, and the bony skeleton of vertebrates. Compare with exoskeleton.
    endoskeleton (35)
  319. An animal whose primary source of body heat is internally generated. Compare with ectotherm.
    endotherm (35)
  320. A lineage of mammals (Eutheria) whose young develop in the uterus and are not housed in an abdominal pouch. Also called placental mammals.
    eutherians (35)
  321. One of the three main regions of the vertebrate brain; includes the cerebrum, thalamus, and hypothalamus. Compare with hindbrain and midbrain.
    forebrain (35)
  322. In aquatic vertebrates, a curved region of tissue between the gills. Gills are suspended from the gill arches.
    gill arch (35)
  323. Animals with jaws. Most vertebrates are gnathostomes.
    gnathostomes (35)
  324. In taxonomy, a group of species that share some, but not all, of the descendants of a common ancestor. Also called a paraphyletic group.
    grade (35)
  325. See hominids.
    great apes (35)
  326. One of the three main regions of the vertebrate brain, responsible for balance and sometimes hearing; includes the cerebellum and medulla oblongata. Compare with forebrain and midbrain.
    hindbrain (35)
  327. Members of the family Hominidae, which includes humans and extinct related forms, chimpanzees, gorillas, and orangutans. Distinguished by large body size, no tail, and an exceptionally large brain. Also called great apes.
    hominids (35)
  328. Any extinct or living species of bipedal apes, such as Australopithecus africanus, Homo erectus, and Homo sapiens.
    hominins (35)
  329. Any member of the genus Homo, which includes modern humans (Homo sapiens) and several extinct species.
    human (35)
  330. (verb: lactate) Production of milk to feed offspring, from mammary glands of mammals.
    lactation (35)
  331. Fish with fins supported by bony elements that extend down the length of the structure.
    lobe-finned fish (35)
  332. One of the two lineages of amniotes (vertebrates that produce amniotic eggs) distinguished by hair (or fur) and mammary glands. Includes the monotremes (platypuses), marsupials, and eutherians (placental mammals).
    mammals (35)
  333. Specialized exocrine glands that produce and secrete milk for nursing offspring. A diagnostic feature of mammals.
    mammary glands (35)
  334. A lineage of mammals (Marsupiala) that nourish their young in an abdominal pouch after a very short period of development in the uterus.
    marsupials (35)
  335. In vertebrates, a region of the brain stem that along with the cerebellum forms the hindbrain.
    medulla oblongata (35)
  336. One of the three main regions of the vertebrate brain; includes sensory integrating and relay centers. Compare with forebrain and hindbrain.
    midbrain (35)
  337. A lineage of mammals (Monotremata) that lay eggs and then nourish the young with milk. Includes just five living species: the platypus and four species of echidna, all with leathery beaks or bills.
    monotremes (35)
  338. A recently extinct European species of hominin, Homo neanderthalensis, closely related to but distinct from modern humans.
    Neanderthal (35)
  339. In chordate animals, a hollow bundle of nerves extending from the brain along the dorsal (back) side of the animal, with cerebrospinal fluid inside a central channel. One of the defining features of chordates.
    nerve cord (35)
  340. The hypothesis that modern humans (Homo sapiens) evolved in Africa and spread to other continents, replacing other Homo species without interbreeding with them.
    out-of-Africa hypothesis (35)
  341. Any action by which an animal expends energy or assumes risks to benefit its offspring (e.g., nest building, feeding of young, defense).
    parental care (35)
  342. A set of parallel openings from the throat to the outside that function in both feeding and gas exchange. A diagnostic trait of chordates.
    pharyngeal gill slits (35)
  343. A secondary jaw in the back of the throat; found in some fishes, it aids in food processing. Derived from modified gill arches.
    pharyngeal jaw (35)
  344. A structure that forms in the pregnant uterus from maternal and fetal tissues. Delivers oxygen to the fetus, exchanges nutrients and wastes between mother and fetus, anchors the fetus to the uterine wall, and produces some hormones. Occurs in most mammals and in a few other vertebrates.
    placenta (35)
  345. See eutherians.
    placental mammals (35)
  346. The lineage of mammals that includes prosimians (lemurs, lorises, etc.), monkeys, and great apes (including humans).
    primates (35)
  347. One of the two major lineages of primates, a paraphyletic group including lemurs, pottos, and lorises. Compare with anthropoids.
    prosimians (35)
  348. Members of the Actinopterygii, a diverse group of fishes with fins supported by bony rods arranged in a ray pattern.
    ray-finned fishes (35)
  349. One of the two lineages of amniotes (vertebrates that produce amniotic eggs) distinguished by adaptations for life and reproduction on land. Living reptiles include turtles, snakes and lizards, crocodiles and alligators, and birds. Except for birds, all are ectotherms.
    reptiles (35)
  350. A gas-filled organ of many ray-finned fishes that regulates buoyancy.
    swim bladder (35)
  351. Any member of the lineage that includes all vertebrates with two pairs of limbs (amphibians, mammals, and reptiles, including birds).
    tetrapod (35)
  352. One of the many small, mobile, fluid-filled extensions of the water vascular system of echinoderms; the part extending outside the body is called a podium, while the bulb within the body is the ampulla. Used in locomotion, feeding, and respiration.
    tube foot (35)
  353. One of the three major chordate lineages (Urochordata), comprising sessile or floating, filter-feeding animals that have a polysaccharide covering (tunic) and two siphons through which water enters and exits; include tunicates and salps. Compare with cephalochordates and vertebrates.
    urochordates (35)
  354. (singular: vertebra) The cartilaginous or bony elements that form the backbones of vertebrate animals.
    vertebrae (35)
  355. In echinoderms, a system of fluid-filled tubes and chambers that functions as a hydrostatic skeleton.
    water vascular system (35)
  356. Not alive (e.g., air, water, and some components of soil). Compare with biotic.
    abiotic (52)
  357. The total mass of living plants in an area, excluding roots.
    aboveground biomass (52)
  358. Deep water receiving no sunlight. Compare with photic zone.
    aphotic zone (52)
  359. The area along the bottom of an aquatic environment.
    benthic zone (52)
  360. The total mass of all organisms in a given population or geographical area; usually expressed as total dry weight.
    biomass (52)
  361. A large terrestrial or marine region characterized by distinct abiotic characteristics and dominant types of vegetation.
    biome (52)
  362. The thin zone surrounding the Earth where all life exists; the sum of all terrestrial and aquatic ecosystems.
    biosphere (52)
  363. Living, or produced by a living organism. Compare with abiotic.
    biotic (52)
  364. A freshwater wetland that has no or almost no water flow, resulting in very low oxygen levels and acidic conditions.
    bog (52)
  365. The prevailing, long-term weather conditions in a particular region.
    climate (52)
  366. All of the species that interact with each other in a certain area.
    community (42)
  367. The effort to study, preserve, and restore threatened genetic diversity, populations, communities, and ecosystems.
    conservation biology (52)
  368. The portion of a geologic plate that extends from a continent under seawater.
    continental shelf (52)
  369. A large assemblage of colonial marine corals that usually serves as shallow-water, sunlit habitat for many other species as well.
    coral reef (52)
  370. The movement of individuals from their place of origin (birth, hatching) to a new location.
    dispersal (52)
  371. The study of how organisms interact with each other and with their surrounding environment.
    ecology (52)
  372. Any plants in an aquatic habitat that extend above the surface of the water.
    emergent vegetation (52)
  373. A nonnative species that is introduced into a new area. Exotic species often are competitors, pathogens, or predators of native species.
    exotic species (52)
  374. An atmospheric cycle of large-scale air movement in which warm equatorial air rises, moves north or south, and then descends at approximately 30° N or 30° S latitude.
    Hadley cell (52)
  375. The region between the low-tide and high-tide marks on a seashore.
    intertidal zone (52)
  376. An exotic (nonnative) species that, upon introduction to a new area, spreads rapidly and competes successfully with native species.
    invasive species (52)
  377. Open water (not near shore) that receives enough sunlight to support photosynthesis.
    limnetic zone (52)
  378. Shallow water near shore that receives enough sunlight to support photosynthesis. May be marine or freshwater; often flowering plants are present.
    littoral zone (52)
  379. A wetland dominated by grasses and other nonwoody plants.
    marsh (52)
  380. Shallow marine waters beyond the intertidal zone, extending down to about 200 meters, where the continental shelf ends.
    neritic zone (52)
  381. The waters of the open ocean beyond the continental shelf.
    oceanic zone (52)
  382. A permanently frozen layer of icy soil found in most tundra and some taiga.
    permafrost (52)
  383. In an aquatic habitat, water that is shallow enough to receive some sunlight (whether or not it is enough to support photosynthesis). Compare with aphotic zone.
    photic zone (52)
  384. The dry region on the side of a mountain range away from the prevailing wind.
    rain shadow (52)
  385. The geographic distribution of a species.
    range (52)
  386. The proportion of solutes dissolved in water in natural environments, often designated in grams of solute per kilogram of water (cited as parts per thousand).
    salinity (52)
  387. A wetland that has a steady rate of water flow and is dominated by trees and shrubs.
    swamp (52)
  388. A vast forest biome throughout subarctic regions, consisting primarily of short coniferous trees. Characterized by intensely cold winters, short summers, and high annual variation in temperature.
    taiga (52)
  389. Having a climate with pronounced annual fluctuations in temperature (i.e., warm summers and cold winters) but typically neither as hot as the tropics nor as cold as the poles.
    temperate (52)
  390. A steep gradient (cline) in environmental temperature, such as occurs in a thermally stratified lake or ocean.
    thermocline (52)
  391. The treeless biome in polar and alpine regions, characterized by short, slow-growing vegetation, permafrost, and a climate of long, intensely cold winters and very short summers.
    tundra (52)
  392. Cloudiness of water caused by sediments and/or microscopic organisms.
    turbidity (52)
  393. In lake ecology, the complete mixing of upper and lower layers of water of different temperatures; occurs each spring and fall in temperate-zone lakes.
    turnover (52)
  394. A line in the Indonesian region that demarcates two areas, each of which is characterized by a distinct set of animal species.
    Wallace line (52)
  395. The specific short-term atmospheric conditions of temperature, moisture, sunlight, and wind in a certain area.
    weather (52)
  396. Any behavior that has a fitness cost to the individual (lowered survival and/or reproduction) and a fitness benefit to the recipient. See reciprocal altruism.
    altruism (53)
  397. Any action by an organism, often in response to a stimulus.
    behavior (53)
  398. The study of how organisms respond to particular abiotic and biotic stimuli from their environment.
    behavioral ecology (53)
  399. An internal mechanism found in most organisms that regulates many body processes (sleep–wake cycles, hormonal patterns, etc.) in a roughly 24-hour cycle.
    circadian clock (53)
  400. A measure of how closely two individuals are related. Calculated as the probability that an allele in two individuals is inherited from the same ancestor.
    coefficient of relatedness (r) (53)
  401. In ecology, any process in which a signal from one individual modifies the behavior of another individual.
    communication (53)
  402. A type of navigation in which movement occurs in a specific direction.
    compass orientation (53)
  403. Decisions or analyses that weigh the fitness costs and benefits of a particular action.
    cost–benefit analysis (53)
  404. A complex social structure in which workers sacrifice most or all of their direct reproduction to help rear the queen's offspring. Common in insects such as ants, bees, wasps, and termites.
    eusociality (53)
  405. Highly stereotyped behavior pattern that occurs in a certain invariant way in a certain species. A form of innate behavior.
    fixed action pattern (FAP) (53)
  406. Searching for food.
    foraging (53)
  407. The proposition that an allele for altruistic behavior will be favored by natural selection only if Br C, where B = the fitness benefit to the recipient, C = the fitness cost to the actor, and r = the coefficient of relatedness between recipient and actor.
    Hamilton's rule (53)
  408. The combination of (1) direct production of offspring (direct fitness) and (2) extra production of offspring by relatives in response to help provided by the individual in question (indirect fitness).
    inclusive fitness (53)
  409. Behavior that is inherited genetically, does not have to be learned, and is typical of a species.
    innate behavior (53)
  410. A form of natural selection that favors traits that increase survival or reproduction of an individual's kin at the expense of the individual.
    kin selection (53)
  411. (1) In ecology, a seasonal movement of large numbers of organisms from one geographic location or habitat to another.
    (2) In population genetics, movement of individuals from one population to another.
    migration (53)
  412. The concept that animals forage in a way that maximizes the amount of usable energy they take in, given the costs of finding and ingesting their food and the risk of being eaten while they're at it.
    optimal foraging (53)
  413. A type of navigation in which animals use familiar landmarks to find their way.
    piloting (53)
  414. Altruistic behavior that is exchanged between a pair of individuals at different times (i.e., sometimes individual A helps individual B, and sometimes B helps A).
    reciprocal altruism (53)
  415. In behavioral ecology, any information- containing behavior or characteristic.
    signal (53)
  416. The type of navigation by which an animal can reach a specific point on Earth's surface. Also called map orientation.
    true navigation (53)
  417. All the individuals of a specific age in a population.
    age class (54)
  418. The proportion of individuals in a population that are of each possible age.
    age structure (54)
  419. The average number of female offspring produced by a female in a certain age class.
    age-specific fecundity (54)
  420. The maximum population size of a certain species that a given habitat can support.
    carrying capacity (K) (54)
  421. A group of individuals that are the same age and can be followed through time.
    cohort (54)
  422. The study of factors that determine the size and structure of populations through time.
    demography (54)
  423. In population ecology, referring to any characteristic that varies depending on population density.
    density dependent (54)
  424. In population ecology, referring to any characteristic that does not vary with population density.
    density independent (54)
  425. The migration of individuals away from one population to other populations. Compare with immigration.
    emigration (54)
  426. The accelerating increase in the size of a population that occurs when the growth rate is constant and density independent. Compare with logistic population growth.
    exponential population growth (54)
  427. The average number of female offspring produced by a single female in the course of her lifetime.
    fecundity (54)
  428. The average number of surviving children that each woman has during her lifetime.
    fertility (54)
  429. The rate of increase of a population over a given period of time. Calculated as the ending population size divided by the starting population size. Compare with intrinsic rate of increase.
    finite rate of increase (λ) (54)
  430. The average time between a mother's first offspring and her daughter's first offspring.
    generation (54)
  431. The migration of individuals into a particular population from other populations. Compare with emigration.
    immigration (54)
  432. The rate at which a population will grow under optimal conditions (i.e., when birthrates are as high as possible and death rates are as low as possible). Compare with finite rate of increase.
    intrinsic rate of increase (rmax) (54)
  433. The sequence of events in an individual's life from birth to reproduction to death, including how an individual allocates resources to growth, reproduction, and activities or structures that are related to survival.
    life history (54)
  434. A data set that summarizes the probability that an individual in a certain population will survive and reproduce in any given year over the course of its lifetime.
    life table (54)
  435. The density-dependent decrease in growth rate as population size approaches the carrying capacity. Compare with exponential population growth.
    logistic population growth (54)
  436. A population made up of many small, physically isolated populations connected by migration.
    metapopulation (54)
  437. The growth rate of a population per generation; equivalent to the average number of female offspring that each female produces over her lifetime.
    net reproductive rate (R0) (54)
  438. The number of individuals of a population per unit area.
    population density (54)
  439. Changes in the size and other characteristics of populations through time and space.
    population dynamics (54)
  440. The study of how and why the number of individuals in a population changes over time and space.
    population ecology (54)
  441. The number of offspring each female must produce over her entire life to "replace" herself and her mate, resulting in zero population growth. The actual number is slightly more than 2 because some offspring die before reproducing.
    replacement rate (54)
  442. On average, the proportion of offspring that survive to a particular age.
    survivorship (54)
  443. A graph depicting the percentage of a population that survives to different ages.
    survivorship curve (54)
  444. A state of stable population size due to fertility staying at the replacement rate for at least one generation.
    zero population growth (ZPG) (54)
  445. Ecological competition between two species in which one species suffers a much greater fitness decline than the other. Compare with symmetric competition.
    asymmetric competition (55)
  446. A type of mimicry in which a harmless or palatable species resembles a dangerous or poisonous species. Compare with Müllerian mimicry.
    Batesian mimicry (55)
  447. The evolutionary tendency for the traits of similar species that occupy overlapping ranges to change in a way that reduces interspecific competition.
    character displacement (55)
  448. The stable, final community that develops from ecological succession.
    climax community (55)
  449. A series of adaptations and counter-adaptations observed in species that interact closely over time and affect each other's fitness.
    coevolutionary arms race (55)
  450. In ecology, the interaction of two species or two individuals trying to use the same limited resource (e.g., water, food, living space). May occur between individuals of the same species (intraspecific competition) or different species (interspecific competition).
    competition (55)
  451. The principle that two species cannot coexist in the same ecological niche in the same area because one species will outcompete the other.
    competitive exclusion principle (55)
  452. A defensive trait that is always manifested even in the absence of a predator or pathogen. Also called standing defense. Compare with inducible defenses.
    constitutive defense (55)
  453. Predation or herbivory.
    consumption (55)
  454. In ecology, any strong, short-lived disruption to a community that changes the distribution of living and/or nonliving resources.
    disturbance (55)
  455. The characteristic disturbances that affect a given ecological community.
    disturbance regime (55)
  456. In ecological succession, the phenomenon in which early-arriving species make conditions more favorable for later-arriving species. Compare with inhibition and tolerance.
    facilitation (55)
  457. The complex network of interactions among species in an ecosystem formed by the transfer of energy and nutrients among trophic levels. Consists of many food chains.
    food web (55)
  458. The total theoretical range of environmental conditions that a species can tolerate. Compare with realized niche.
    fundamental niche (55)
  459. The practice of eating plant tissues.
    herbivory (55)
  460. An individual that has been invaded by an organism such as a parasite or a virus, or that provides habitat or resources to a commensal organism.
    host (55)
  461. A defensive trait that is manifested only in response to the presence of a consumer (predator or herbivore) or pathogen. Compare with constitutive defense.
    inducible defense (55)
  462. In ecological succession, the phenomenon in which early-arriving species make conditions less favorable for the establishment of certain later-arriving species. Compare with facilitation and tolerance.
    inhibition (55)
  463. In agriculture or forestry, systems for managing insects or other pests that include carefully controlled applications of toxins, introduction of species that prey on pests, planting schemes that reduce the chance of a severe pest outbreak, and other techniques.
    integrated pest management (55)
  464. Competition between members of different species for the same limited resource. Compare with intraspecific competition.
    interspecific competition (55)
  465. Competition between members of the same species for the same limited resource. Compare with interspecific competition.
    intraspecific competition (55)
  466. A species that has an exceptionally great impact on the other species in its ecosystem relative to its abundance.
    keystone species (55)
  467. A comparative analysis of the results of many smaller, previously published studies.
    meta-analysis (55)
  468. A phenomenon in which one species has evolved (or learns) to look or sound like another species. See Batesian mimicry and MŸllerian mimicry.
    mimicry (55)
  469. (adjective: mutualistic) A symbiotic relationship between two organisms (mutualists) that benefits both. Compare with commensalism and parasitism.
    mutualism (55)
  470. The evolutionary change in resource use by competing species that occurs as the result of character displacement.
    niche differentiation (55)
  471. Those species that appear first in recently disturbed areas.
    pioneering species (55)
  472. The killing and eating of one organism (the prey) by another (the predator).
    predation (55)
  473. The gradual colonization of a habitat of bare rock or gravel, usually after an environmental disturbance that removes all soil and previous organisms. Compare with secondary succession.
    primary succession (55)
  474. The portion of the fundamental niche that a species actually occupies given limiting factors such as competition with other species. Compare with fundamental niche.
    realized niche (55)
  475. Gradual colonization of a habitat after an environmental disturbance (e.g., fire, windstorm, logging) that removes some or all previous organisms but leaves the soil intact. Compare with primary succession.
    secondary succession (55)
  476. The variety and relative abundance of the species present in a given ecological community.
    species diversity (55)
  477. The number of species present in a given ecological community.
    species richness (55)
  478. In ecology, the gradual colonization of a habitat after an environmental disturbance (e.g., fire, flood), usually by a series of species. See primary and secondary succession.
    succession (55)
  479. Ecological competition between two species in which both suffer similar declines in fitness. Compare with asymmetric competition.
    symmetric competition (55)
  480. In ecological succession, the phenomenon in which early-arriving species do not affect the probability that subsequent species will become established. Compare with facilitation and inhibition.
    tolerance (55)
  481. An underground layer of porous rock, sand, or gravel that is saturated with water.
    aquifer (56)
  482. The pattern of circulation of an element or molecule among living organisms and the environment.
    biogeochemical cycle (56)
  483. In animal tissues, an increase in the concentration of particular molecules that may occur as those molecules are passed up a food chain.
    biomagnification (56)
  484. An ecological network of detritus, decomposers that eat detritus, and predators and parasites of the decomposers.
    decomposer food chain (56)
  485. A relatively simple pathway of energy flow through a few species, each at a different trophic level, in an ecosystem. Might include, for example, a primary producer, a primary consumer, a secondary consumer, and a decomposer. A subset of a food web.
    food chain (56)
  486. The global sum of all the local changes in temperature and precipitation patterns that accompany global warming (or in some past events, global cooling).
    global climate change (56)
  487. A sustained increase in Earth's average surface temperature.
    global warming (56)
  488. The ecological network of herbivores and the predators and parasites that consume them.
    grazing food chain (56)
  489. An atmospheric gas that absorbs and reflects infrared radiation, so that heat radiated from Earth is retained in the atmosphere instead of being lost to space.
    greenhouse gas (56)
  490. In an ecosystem, the total amount of carbon fixed by photosynthesis (or more rarely, chemosynthesis), including that used for cellular respiration, over a given time period. Compare with net primary productivity.
    gross primary productivity (56)
  491. Any water below the land surface.
    groundwater (56)
  492. The decayed organic matter in soils.
    humus (56)
  493. In an ecosystem, the total amount of carbon fixed by photosynthesis over a given time period minus the amount oxidized during cellular respiration. Compare with gross primary productivity.
    net primary productivity (NPP) (56)
  494. The timing of events during the year, in environments where seasonal changes occur.
    phenology (56)
  495. An herbivore; an organism that eats plants, algae, or other primary producers. Compare with secondary consumer.
    primary consumer (56)
  496. A decomposer (detritivore) that consumes detritus from plants.
    primary decomposer (56)
  497. A carnivore; an organism that eats herbivores. Compare with primary consumer.
    secondary consumer (56)
  498. Organic (carbon-containing) compounds found in soil.
    soil organic matter (56)
  499. In a food chain or food web, organisms that feed on secondary consumers. Compare with primary consumer and secondary consumer.
    tertiary consumers (56)
  500. The hypothesis that population size is limited by predators or herbivores (consumers).
    top-down control (56)
  501. A series of changes in the abundance of species in a food web, usually caused by the addition or removal of a key predator.
    trophic cascade (56)
  502. A feeding level in an ecosystem.
    trophic level (56)
  503. The upper limit of the underground layer of soil that is saturated with water.
    water table (56)
  504. The area drained by a single stream or river.
    watershed (56)
  505. The use of well-characterized gene sequences to identify species.
    bar coding (57)
  506. The diversity of life considered at three levels: genetic diversity (variety of alleles and/or genes in a population, species, or group of species); species diversity (variety and relative abundance of species present in a certain area); and ecosystem diversity (variety of communities and abiotic components in a region).
    biodiversity (57)
  507. A region that is extraordinarily rich in species.
    biodiversity hotspot (57)
  508. The effort to find commercially useful compounds by studying organisms—especially species that are poorly studied to date.
    bioprospecting (57)
  509. The variety of biotic components in a region along with abiotic components, such as soil, water, and nutrients.
    ecosystem diversity (57)
  510. The sum of biological and chemical processes that are characteristic of a given ecosystem—such as primary production, nitrogen cycling, and carbon storage.
    ecosystem function (57)
  511. All of the benefits that humans derive, directly or indirectly, from ecosystem functions.
    ecosystem services (57)
  512. Tourism that is based on observing wildlife or experiencing other aspects of natural areas.
    ecotourism (57)
  513. A species whose numbers have decreased so much that it is in danger of extinction throughout all or part of its range.
    endangered species (57)
  514. A species that lives in one geographic area and nowhere else.
    endemic species (57)
  515. Preserving species outside of natural areas (e.g., in zoos, aquaria, or botanical gardens).
    ex situ conservation (57)
  516. The diversity of alleles or genes in a population, species, or group of species.
    genetic diversity (57)
  517. Human-caused destruction of a natural habitat, replaced by an urban, suburban, or agricultural landscape.
    habitat destruction (57)
  518. The breakup of a large region of a habitat into many smaller regions, separated from others by a different type of habitat.
    habitat fragmentation (57)
  519. Unsustainable removal of wildlife from the natural environment for use by humans.
    overexploitation (57)
  520. A measure of how quickly a community recovers following a disturbance.
    resilience, community (57)
  521. A measure of how much a community is affected by a disturbance.
    resistance, community (57)
  522. A repository where seeds, representing many different varieties of domestic crops or other species, are preserved.
    seed bank (57)
  523. The mathematical relationship between the area of a certain habitat and the number of species that it can support.
    species–area relationship (57)
  524. The planned use of environmental resources at a rate no faster than the rate at which they are naturally replaced.
    sustainability (57)
  525. Strips of wildlife habitat connecting populations that otherwise would be isolated by human-made development.
    wildlife corridor (57)