scanning electron microscope (SEM) -- n. A special kind of microscope that scans samples with a high-energy beam of electrons to produce a high-resolution, detailed, three-dimensional image. An SEM can magnify a sample up to 250 times that of the best light microscopes.
secondary growth -- Growth in a plant which does not occur at the tips of the stems or roots. Secondary growth produces wood and bark in seed plants.
sedentary -- Living in a fixed location, as with most plants, tunicates, sponges, etc. Contrast with motile.
sedimentary rock -- Any rock resulting from the consolidation of sediment.
seed -- A structure produced by seed plants which encapsulates the embryo. The seed often provides nourishment during germination, but may lie dormant for many years first.
segmentation -- In many animals, the body is divided into repeated subunits called segments, such as those in centipedes, insects, and annelids. Segmentation is the state of having or developing a body plan in this way.
selection -- Process which favors one feature of organisms in a population over another feature found in the population. This occurs through differential reproductionthose with the favored feature produce more offspring than those with the other feature, such that they become a greater percentage of the population in the next generation.
sepal -- The outermost structures of a flower. More info?
sexual reproduction -- A type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited through the gametes of the two parents. Sexual reproduction involves meiosis and syngamy.
siderite -- Also called ironstone, that is a concretion of iron carbonate. Common in the Mazon Creek fossil beds.
skeleton -- Support structure in animals, against which the force of muscles acts. Vertebrates have a skeleton of bone or cartilage; arthropods have one made of chitin; while many other invertebrates use a hydrostatic skeleton, which is merely an incompressible fluid-filled region of their body.
soil -- Unconsolidated materials above bedrock.
specialist -- Organism which has adopted a lifestyle specific to a particular set of conditions. Contrast with generalist.
spermatophyte -- A seed plant.
spicule -- Crystalline or mineral deposits found in sponges, sea cucumbers, or urochordates. They are structural components in many sponges, and may serve a protective function in other organisms.
spongin -- proteinacous compound of which the spicules in Demospongiae are composed.
spongocoel -- Central body cavity of sponges. More Info?
sporangium -- A chamber inside of which spores are produced through meiosis.
spore -- n. A single cell that is dispersed as a reproductive unit, or that encapsulates a cell during unfavorable environmental conditions; in organisms with an alternation of generations; the products of meiosis are spores.
sporophyte -- The diploid stage in the life cycle of an organism undergoing an alternation of generations. The sporophyte is multicellular and develops from a zygote. The mature sporophyte meiotically produces haploid spores that later generate the gametophyte generation.
stamen -- Part of a flower, the tip of which produces pollen and is called the anther. More info?
stigma -- The sticky tip of a pistil. Or, the dense region of pigments found in many photosynthetic protists which is sensitive to light, and thus functions somewhat like a miniature eye.More info?
stipules -- Paired appendages found at the base of the leaves of many flowering plants.
stratum -- A layer of sedimentary rock; plural is strata.
strike -- The direction or trend of a bedding plane or fault, as it intersects the horizontal.
subduction -- n. A geologic process in which one edge of one crustal plate is forced below the edge of another; subduct– v.; subduction zone- n. A long narrow area in which subduction is taking place, e.g. the Peru-Chile trench, where the Pacific Plate is being subducted under the South American Plate.
substrate -- "Supporting surface" on which an organism grows. The substrate may simply provide structural support, or may provide water and nutrients. A substrate may be inorganic, such as rock or soil, or it may be organic, such as wood.
symbiosis -- n. A relationship between two organisms that live in intimate contact with each other; includes mutualism (both organisms benefit, they rely on each other for survival), parasitism (one organism benefits at its host's expense) and commensalism (one partner benefits and the other is neither benefitted nor harmed); symbiotic- adj.
syncline -- A fold of rock layers that is convex downwards. Antonym of anticline.
syncytic -- see Hexactinellida