(1) a hard, external, shieldlike plate; in vertebrates scuta may be composed of horn or bone; in invertebrates they are generally chitinous; (2) the largest of the four parts covering the upper surface of the thorax of an insect. second messenger A molecule that relays a message — carried by a hormone from elsewhere in the body to the surface of a cell — to some point within the cell. Any solid material that settles out of a suspending liquid or a gas. sedimentary rock /sed-ə-MENT-er-ee, British: sed-ə-MEN-tree/ n. Expressed sequence tags (ESTs) are STSs derived from c DNAs. CODONS | MOLECULAR STRUCTURE | SERINE BIOSYNTHESIS serous fluid /SIR-əs/ n. Specifically: the three membranes lining the pleural, pericardial, and peritoneal cavities. single nucleotide polymorphism (SNP) /pawl-ee-MORE-fiz-əm/ n. DNA sequence variations that occur when a single nucleotide (A, T, C, or G) in the genome sequence is altered. When this occurs, each forms a duplicate of itself and the resulting two structures, called sister chromatids, are joined at the centromere. An instrument used to accurately administer small amounts of fluid; when a needle is attached to a syringe it can be used to make injections. systematist One who engages in the practice of systematics. On the Origins of New Forms of Life Mammalian Hybrids Cat-rabbit Hybrids: Fact or fiction? In external secretion the substance is not emitted into the blood, whereas in internal secretion it is — secretory /SEEK-rə-tore-ee, see-KREE-tə-ree/ sediment /SED-ə-mənt/ n. sedimentation coefficient (S) /sed-ə-men-TAY-shən co-ə-FISH-ənt/ n. A value indicating the rate at which a particular type of molecule moves through a solution during centrifugation as it settles toward its equilibrium position in the centrifugation gradient. An encapsulated plant embryo in an arrested state of development and, usually, surrounded by endosperm. This is the opposite view from that taken in the theoretical portion of this website, which argues that evolution is typically a matter of selection among distinct, stable types of organisms. STSs are useful for correlating mapping and sequence data reported from different laboratories since they are unique and detectable by polymerase chain reaction. READ ABOUT THE DIET OF SNAKES sessile /SESS-əl/ adj. The first coral reefs formed in the oceans, and fish with movable jaws made their appearance and eurypterids were abundant. single-gene disorder Hereditary disorder caused by a mutant allele of a single gene (e.g., Duchenne muscular dystrophy, retinoblastoma, sickle cell disease). A block of genes occurring in the same order in two different types of organisms. During the eukaryotic cell cycle, a substage of interphase when each of the chromosomes replicate. systematics (also taxonomy) The study of the classification of living things.
saliva (common names: spit, spittle) /sə-LIE-və/ n. Its capacity for contraction is the essential trait that makes muscles work. Any fraction of DNA that forms a separate band from the main body of DNA during isopycnic Cs CL gradient centrifugation ("satellite" refers to the subordinate or minor status of such bands). Certain aspects of their worldview, based on religious dogmas, have carried over into modern biological thought, for example, their ideas concerning continuity, gradualism, and ideal forms. The outermost coat of the eyeball, extending from the optic nerve to the edges of the cornea. The first of these two types is the primary spermatocyte, which is a mature sex cell that develops from the spermatogonium without division. During spermatogenesis, one of the primordial, undifferentiated sex cells that give rise, via maturation and growth, first to a primary spermatocyte, then via division, to two secondary spermatocytes that in turn divide to form four spermatids, which then mature without further division into four fully functional spermatozoa — spermatogonial /sperm-awd-ə-GŌ-nee-əl/ spermatozoon (pl spermatozoa) /sper-mat-ə-ZŌ-ən; pl: -ZŌ-ə/ n. An angular bend in the large intestine between the transverse and descending colons.
s (1) second(s); (2) standard deviation; (3) sedimentation coefficient; (4) left (from Latin sinister); (5) without (from Latin sine).
S (1) Silurian Period; (2) sulfur; (3) serine; (4) S phase; (5) Svedberg unit.
MORE INFORMATION Sitophilus /sigh-TAWF-ə-ləs, sə-/ n. An economically important genus of weevils, which are highly destructive of grains. The study of nutrition and dietetics — sitologist /sigh-TAWL-ə-jist, -jəst/ sitosterol (also β-sitosterol) /SIDE-ō-STAIR-awl/ n. Chemical element; atomic number 11, atomic weight 22.98976928. The sticky tip of a carpel; the stigmata are the parts of a flower that receive pollen. Microscopic pores in the epidermis of plants; stomata allow gas exchange with the atmosphere. A baglike, elastic portion of the digestive tract following the esophagus. It secretes acidic gastric juices that convert proteins into peptones. stratum corneum /STRAT-əm KORN-ee-əm/ (pl strata cornea /STRAT-ə KORN-ee-ə/) The outermost, horny layer of the skin. superoxide dismutase (SOD) /SOO-pər-AWK-sīd DIS-myoo-tāz/ n. An enzyme that catalyzes the conversion of superoxide into hydrogen peroxide and oxygen. suture (1) a line of union forming an immovable joint (as in the skull or between the segments of a gastropod shell) SUTURES OF HUMAN SKULL | SUTURES IN A DEER SKULL (2) surgical stitches uniting two parts (or the line of union so formed).
sister chromatids The two identical nucleoprotein strands of a single replicated chromosome, which are joined at the centromere. A class of complex cyclic alcohols with a tetracyclic structure (MOLECULAR STRUCTURE), which occur in plants, animals, and fungi. stigma (pl stigmata or stigmas) /STIG-mə, stig-MAWT-ə/ n. stratum /STRAT-əm/ (pl strata /STRAT-ə/) (1) 1n geology: a layer of rock or earth, with a characteristic composition and fossil content, lying between other layers differing from it with respect to composition and content; (2) in biology: a layer of an organ or other living structure. An operation; (2) the branch of medicine dealing with such procedures; (3) the room in which such procedures are carried out (4) (British) the room where a doctor sees patients. syndrome The group or recognizable pattern of symptoms or abnormalities that indicate a particular trait or disease. Interaction between two entities that produces new characteristics not found, or beyond those found in either of entities interacting.