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.129sex pili In a bacterium, elongated, hollow appendage used to transfer DNA to other cells.51sexual selection Changes in males and females, often due to male competition and female selectivity, leading to increased fitness.236shoot system Aboveground portion of a plant consisting of the stem, leaves, and flowers.338short-day plant Plant that flowers when day length is shorter than a critical length e.g., cocklebur, poinsettia, and chrysanthemum.360shoulder (pectoral) girdle Portion of the vertebrate skeleton that provides support and attachment for the upper (fore) limbs; consists of the scapula and clavicle on eachside of the body.503sickle cell disease Hereditary disease in which red blood cells are narrow and curved so that they are unable to pass through capillaries and are destroyed; causes chronicanemia.203sieve-tube member Member that joins with others in the phloem tissue of plants as a means of transport for nutrient sap.342signal Molecule that stimulates or inhibits an event in the cell cycle.119signal transduction pathway Activation and inhibition of intracellular targets after binding of growth factors.187simple diffusion Movement of molecules or ions from a region of higher to lower concentration; it requires no energy and tends to lead to an equal distribution.77simple goiter Condition in which an enlarged thyroid produces low levels of thyroxine.486sinus Cavity or hollow space in an organ such as the skull.422sister chromatid One of two genetically identical chromosomal units that are the result of DNA replication and are attached to each other at the centromere.113skeletal muscle Striated, voluntary muscle tissue that comprises skeletal muscles; also called striated muscle.384skeletal system System of bones, cartilage, and ligaments that works with the muscular system to protect the body and provide support for locomotion and movement.387sliding filament model An explanation for muscle contraction based on the movementof actin filaments in relation to myosin filaments.505slime mold Protists that decompose dead material and feed on bacteria by phagocytosis; vegetative state is mobile and amoeboid.279small intestine In vertebrates, the portion of the digestive tract that precedes the large intestine; in humans, consists of the duodenum, jejunum, and ileum.418smooth ER Membranous system of tubules, vesicles, and sacs in eukaryotic cells; lacks attached ribosomes.58smooth (visceral) muscle Nonstriated, involuntary muscles found in the walls of internal organs.384sodium-potassium pump Carrier protein in the plasma membrane that moves sodium ions out of and potassium ions into animal cells; important in nerve and musclecells.79solute Substance that is dissolved in a solvent, forming a solution.77solution Fluid (the solvent) that contains a dissolved solid (the solute).77solvent Liquid portion of a solution that serves to dissolve a solute.77somatic cell Body cell; excludes cells that undergo meiosis and become sperm or egg.120somatic system Portion of the peripheral nervous system containing motor neurons that control skeletal muscles.481speciation Origin of new species due to the evolutionary process of descent with modification.220, 246species Group of similarly constructed organisms capable of interbreeding and producing fertile offspring; organisms that share a common gene pool; the taxon at thelowest level of classification.4, 6, 256species richness List of difference species in a community.553specific epithet In the binomial system of taxonomy, the second part of an organism s name; it may be descriptive.256spermatogenesis Production of sperm in males by the process of meiosis and maturation.129spinal cord In vertebrates, the nerve cord that is continuous with the base of the brain and housed within the vertebral column.478spinal nerves Nerves that arises from the spinal cord.481spindle Microtubule structure that brings about chromosomal movement during nuclear division.115spindle equator Disk formed during metaphase in which all of a cell s chromosomes lie in a single plane at right angles to the spindle fibers [ Pobierz całość w formacie PDF ]