Lewis/Life - Glossary

S

saccule SAK-yul A pouch in the vestibule of the inner ear, containing a jellylike fluid and lined with hair cells that contain calcium carbonate granules that move in response to changes in velocity, firing action potentials. 655

salivary amylase SAL-eh-vare-ee AM-eh-lase An enzyme produced in the mouth that begins chemical digestion of starch. 760

salt A molecule composed of cations and anions. 38

saltatory conduction SAL-teh-tore-ee kon-DUK-shun Jumping of an action potential between nodes of Ranvier in myelinated axons. 614

sample size The number of individuals in an experiment. 24

saprobes SA-probez and saprophytes sa-pro-FITES Organisms that obtain nutrients from dead plants and animals through absorption. 445, 476

sapwood SAP-wood Wood nearest the vascular cambium that transports water and dissolved nutrients within a plant. 551

sarcomere SAR-ko-mere A pattern of repeated bands in skeletal muscle. 695

sarcoplasmic reticulum SAR-ko-PLASZ-mik reh-TIK-u-lum The endoplasmic reticulum of a skeletal muscle cell. 694

satellite The end of a chromosome attached to the rest of the chromosome by a bridge. 296

saturated (fat) A triglyceride with single bonds between the carbons of its fatty acid tails. 45

savanna sa-VAN-ah A grassland. 877

scale A pinecone subunit that bears two ovules. 560

scavenger SKAV-en-jer Animal that eats the remains of other animals' meals. 862

scent glands Sweat gland derivatives that occur in different body regions in different species and produce fluids that evaporate to yield a distinctive odor. 603

Schwann cell SHWAN sel A type of neuroglia that forms a sheath around certain neurons. 597, 612

scientific method A systematic approach to interpreting observations, involving reasoning, predicting, testing, and drawing conclusions, and then putting them into perspective with existing knowledge. 18

sclera SKLER-ah The outermost white layer of the human eye. 648

sclereids SKLER-ridz Plant cells with a gritty texture found in pears and peanut hulls. 536

sclerenchyma sklah-REN-kah-mah Elongated supportive plant cells with thick, nonstretchable secondary cell walls. 536

scolex SKO-lex The holdfast organ of a tapeworm. 518

scramble competition When members of a population compete directly for a resource. 843

scrotum SKRO-tum The sac of skin containing the testes. 197

sebaceous glands se-BAY-shis GLANDS Glands in human skin that secrete a mixture of oils that soften hair and skin. 603

secondary consumer Carnivores, which form trophic levels beyond the second level. 862

secondary growth Thickening of a plant due to cell division in lateral meristems. 534

secondary immune response The immune system's response to subsequent encounters with a foreign antigen. 795

secondary nutrient deficiency Too little of a particular nutrient due to an inborn metabolic condition. 757

secondary oocyte SEC-un-derry OO-site A haploid cell that is an intermediate in ovum formation. 204

secondary spermatocyte SEC-un-derry sper-MAT-o-site A haploid cell that is an intermediate in sperm formation. 204

secondary (2_) structure The shape a protein assumes when amino acids close together in the primary structure chemically attract. 49

secondary succession Return of life to a devastated area. 856

second filial generation SEK-und FIL-e-al jen-er-A-shun (F2) The third generation in a genetics problem. 265

second messenger A biochemical activated by an extracellular signal that transmits a message inside a cell. 103

secretion seh-KREE-shun A cell's release of a biochemical. Adding substances to the material in a kidney tubule. 778

secretory vacuole SEK-re-tore-ee VAK-u-ole An enzyme-containing sac in a protozoan. 459

seed A temporarily dormant sporophyte within a protective coat. 561

seed coat A tough outer layer that protects a dormant plant embryo and its food supply in a seed. 569

segmentation SEG-men-TAY-shun Localized muscle contractions in the small intestine that provide mechanical digestion. 761

selectively permeable sah-LEK-tive-lee PERM-ee-ah-bul A biological membrane that admits only some substances. 612

semicircular canal SEM-ee-SIR-ku-ler kah-NAL Fluid-filled structure in the inner ear that provides information on the position of the head. 653

semiconservative replication sem-ee-con-SERV-a-tive rep-li-KAY-shun Mode of DNA replication. Each double helix has one parental and one new strand. 317

semilunar valve SEM-ee-LOON-er VALV Tissue flaps in the artery just outside each ventricle that maintain one-way blood flow. 720

seminal fluid SEM-in-el FLEW-id Secretions that carry sperm. 197

seminal vesicles SEM-in-el VES-eh-kels In the human male, the paired structures that add fructose and prostaglandins to sperm. 197

seminiferous tubule sem-i-NIF-er-us TUBE-yule Tubule within the testis where sperm form and mature. 196

sensory adaptation Lessening of sensation with prolonged exposure to the stimulus. 644

sensory neuron A neuron that brings information toward the central nervous system, with a short axon and long dendrites that transmit the message from the stimulated body part to a cell body near the spinal cord. 611

sensory receptors Specialized neurons in the skin and sense organs that transmit messages in response to environmental stimuli. 597, 640

sepals SEE-pelz Leaflike structures that enclose and protect inner floral parts. 563

septate SEP-tate Structures that partition fungal hyphae. 478

setae SEE-tay Bristles on the sides of earthworms. 521, 645

sex chromosome A chromosome that carries genes that determine sex. 198

sex hormone Hormone that controls development of secondary sexual characteristics and prepares an animal for sexual reproduction. 670

sex-linked A gene on the X chromosome or a trait that results from activity of such a gene. 291

sex pilus SEX PILL-us A bacterial cell outgrowth that exchanges genetic material. 194, 449

sex ratio The proportion of males to females in a population. 838

sexual dimorphism SEX-u-al di-MOR-fiz-um The difference in appearance between males and females of the same species. 830

sexual reproduction The combination of genetic material from two individuals to create a third individual. 10, 192

sexual selection Natural selection of traits that increase an individual's reproductive success. 382

shoot part of seedling aboveground. 534

short-day seedling Plant that requires light periods shorter than some critical length to flower. 583

sieve cells SIV SELZ Less specialized conducting cells in phloem. 539

sieve plate SIV PLATE End walls of aligned sieve tubes in phloem. 539

sieve tube members SIV TOOB MEM-berz More complex and specialized conducting cells in phloem that form long sieve tubes. 539

signal transduction The biochemical transmission of a message from outside the cell to inside. 85, 103

signature sequence DNA sequence unique to the members of specific taxonomic groups. 442

simple epithelium SIM-pel ep-eh-THEEL-ee-um A single layer of epithelium. 594

sinoatrial (SA) node SI-no-A-tree-al NODE Specialized cells in the wall of the right atrium that set the pace of the heartbeat. The pacemaker. 720

skeletal muscle cell Single, multinucleated cells that contract when actin and myosin filaments slide. They make up voluntary, striated muscle. 598

sliding filament model Sliding of protein myofilaments past each other to shorten skeletal muscle cells, leading to contraction. 695

slime molds Organisms that form acellular or cellular mobile masses that enable cells to collectively migrate to locate food. 458

smooth muscle cells Cells that make up involuntary, nonstriated contractile tissue that lines the digestive tract and other organs. 598

sodium-potassium pump A mechanism that uses energy released from splitting ATP to transport Na{pos} out of cells and K{pos} into cells. 92, 612

softwood Wood of gymnosperms. 551

solute SOL-yoot A chemical that dissolves in another, forming a solution. 40, 87

solution A homogenous mixture of a substance (the solute) dissolved in water (the solvent). 40

solvent SOL-vent A chemical in which others dissolve, forming a solution. 40, 87

somatic mutation so-MAT-ik mew-TAY-shun A mutation in a body cell. 341

somatic nervous system so-MAT-ik NER-ves SIS-tum Part of the motor pathways of the peripheral nervous system that leads to skeletal muscles. 622

somatostatin so-MAT-owe-STAT-in A pancreatic hormone that controls the rate of nutrient absorption into the bloodstream. 672

sori SOR-ee Dark spots on the undersides of most ferns that are collections of spore-producing structures. 498

speciation SPE-she-AY-shun Appearance of a new type of organism. 375

species A group of similar individuals that breed in nature only among themselves. 9

specific rate of population growth The number of births and deaths divided by the number of individuals in a population during a specific time period. 840

sperm The male sex cell. 196

spermatid sper-ma-TID An intermediate stage in sperm development. 204

spermatogenesis sper-MAT-o-JEN-eh-sis The differentiation of a sperm cell from a diploid spermatogonium, to primary spermatocyte, to two haploid secondary spermatocytes, to spermatids, and finally to mature spermatozoa. 203

spermatogonium sper-mat-o-GOWN-e-um A diploid cell that divides, yielding progeny cells that become sperm cells. 203

spermatozoa sper-mat-o-ZO-a Mature sperm. 204

S phase The synthesis phase of interphase, when DNA replicates and microtubules assemble from tubulin. 170

sphincter SFINK-ter Muscular ring that controls passage of a substance from one part of the body to another. 760

spicules SPIK-yools Glassy or limy material that make up sponge skeletons. 516

spines Modified leaves that protect plants from predators and excess sunlight. 544

spiracles SPEER-a-kulls Openings in the body wall of arthropods used for breathing. 522

spiral cleavage SPY-ral CLEEV-edge Pattern of early cleavage cells in protostomes, which resembles a spiral. 513

spleen Abdominal organ that produces and stores lymphocytes and red blood cells. 728

spongin SPUNJ-in Organic material in sponge skeletons. 516

spongocoel SPUNJ-o-seel The central cavity of a sponge. 515

spongy bone Flat bones and tips of long bones that have many large spaces between a web of bony struts. 689

spongy mesophyll cells SPUN-gee MEZ-o-fil SELZ Irregularly shaped chlorenchyma cells separated by large spaces that are beneath the palisade layer in leaves. 543

spontaneous generation The idea, proven untrue, that life can arise from nonliving matter. 353

spontaneous mutation A change in DNA sequence not caused by a mutagen, usually resulting from a DNA replication error. 339

sporophyte SPOR-o-fite Diploid stage of the plant life cycle. 192

spring turnover The rising of nutrient-rich lower layers of a lake and sinking of oxygen-rich layers from the top, often causing algal blooms. 880

squamous SKWAY-mus Flat, as in epithelium. 594

S-shaped curve A leveling off of a population growth curve. 843

stabilizing selection When extreme phenotypes are less adaptive than an intermediate phenotype. 411

stable isotope tracing STA-bull ICE-o-tope TRAYS-ing A method to chemically trace which species eat which species. 862

stamens STA-menz Male reproductive structures in flowers that consist of stalklike filaments that bear pollen-producing anthers at their tips. 563

stapes STAY-peez A small bone in the middle ear. 653

statocyst STAT-o-sist A fluid-filled cavity that contains minerals and sensory hairs that control balance and equilibrium. 645

statolith STAT-o-lith A mineral that functions as a mechanoreceptor. 645

stem cell An undifferentiated cell that divides to give rise to specialized cells. 178

steroid hormone STAIR-oid HOR-moan A lipid hormone that can cross a target cell membrane and enter the cell's nucleus. 662

stigma STIG-mah A pollen receptacle at the tip of a style in a flower. 563

stipe STYp Stemlike region of a brown alga. 467

stolon STOL-on Stem that grows along the soil surface. 541

stoma STO-mah Pore in a plant's cuticle through which water and gases exchange between the plant and the atmosphere. 159

storage leaves Fleshy leaves that store nutrients. 544

stratified epithelium STRAT-eh-fyed ep-eh-THEEL-ee-um Layered epithelium. 594

stroma STRO-ma The nonmembranous inner region of the chloroplast. 151

style A stalk that forms from an ovary in a flower. 563

subapical region sub-APE-eh-kel REE-jen The region behind the root cap, which is divided into zones of cellular division, cellular elongation, and cellular maturation. 547

subcutaneous layer sub-kew-TAYN-ee-us lay-r In human skin, the layer of fat beneath the dermis. 599

suberin SU-ber-in A waxy, waterproof biochemical in the interior of a root's cortex. 548

substrate SUB-strate A reactant an enzyme acts upon. 50

substrate-level phosphorylation SUB-strate LEV-ell fos-for-i-LAY-shun ATP formation from transferring a phosphate group to ADP. 129

succulent stems SUK-ku-lent STEMZ Fleshy plant tissues that store water. 541

superior vena cava su-PEER-ee-er VEE-nah KAY-vah The upper branch of the largest vein that leads to the heart. 720

supernormal releaser A model that exaggerates a releaser and elicits a stronger response than does the natural object. 814

survivorship The fraction of a group of individuals that survive to a particular age. 842

suspension feeders Animals that capture food particles suspended in the water. 515

sweat glands Epidermal invaginations that produce sweat. 602

symbiosis sim-bi-O-sis A biological relationship of one type of organism living in or on another. 434

sympathetic nervous system Part of the autonomic nervous system that mobilizes the body to respond to environmental stimuli. 622

synapse, synaptic cleft sin-APSE, sin-AP-tik CLEFT A space between two neurons. 616

synapsis sin-AP-sis The gene-by-gene alignment of homologous chromosomes during prophase of meiosis I. 198

synaptic integration sin-AP-tik in-teg-RAY-shun A cell's overall response to many incoming neural messages. 617

syncytium sin-SIK-tee-um A mass of multinucleated cells. 175

synovial joint sin-OV-ee-el JOYNT A capsule of fluid-filled fibrous connective tissue between freely movable bones. 700

synovial membrane sin-OV-ee-el MEM-brane Lining of the interior of a joint capsule, which secretes lubricating synovial fluid. 700

synteny SIN-ten-ee Comparison of gene order on chromosomes between species. 396

systematics sis-te-MAT-ix Study of the evolutionary relationships among species. 427

systole SIS-toll-ee The heart's contraction. 720

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