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coupled with that of a given gene; e.g., red-green color blindness and
hemophilia in humans. Traits located on the X-chromosome.
sexual reproduction A system of reproduction in which two haploid sex cells
(gametes) fuse to produce a diploid zygote.
shoot The plant stem; provides support for the leaves and þowers; one of the
three major plant organs; also referred to as the shoot system.
short-day plants Plants that þower during early spring or fall when nights are
relatively long and days are short; e.g., poinsettia and dandelions.
sickle cell anemia Human autosomal recessive disease that causes production of
abnormal red blood cells that collapse (or sickle) and cause circulatory problems.
sieve cells Conducting cells in the phloem of vascular plants. See sieve elements
sieve elements Tubular, thin-walled cells that form a system of tubes
extending from the roots to the leaves in the phloem of plants; lose their nuclei
and organelles at maturity, but retain a functional plasma membrane.
sieve plates Pores in the end walls of sieve elements that connect the sieve
elements together. The end walls of sieve tube cells that are perforated (sieves).
sieve tube members Phloem cells that form long sieve tubes. See sieve elements.
silica Silicon dioxide.
Silurian Period The geological time period of the Paleozoic Era following the
Ordovician, between 435 and 395 million years ago, when plants colonized the
land.
simple leaf A leaf in which the blade does not form leaflets.
sink A body or process that acts as a storage device or disposal mechanism;
e.g., plants and the oceans act as sinks absorbing atmospheric carbon dioxide.
Also, a location in a plant where sugar is being consumed, either in metabolism
or by conversion to starch.
sinoatrial (SA) node A region of modiÞed muscle cells in the right atrium that
sends timed impulses to the heart's other muscle cells, causing them to contract;
the heart's pacemaker.
sister chromatids Chromatids joined by a common centromere and carrying
identical genetic information (unless crossing-over has occurred).
sleep movement In legumes, the movement of the leaves in response to daily
rhythms of dark and light. The leaves are horizontal in daylight and folded
vertically at night.
skeletal muscle Muscle that is generally attached to the skeleton and causes
body parts to move; consists of muscle Þbers. Voluntary muscle cells that have a
striated appearance. These muscles control skeletal movements and are
normally under conscious control.
skeletal system One of eleven major body organ systems in animals; supports
the body, protects internal organs, and, with the muscular system, allows
movement and locomotion.
skin One of eleven major body organ systems in animals; the outermost layer
protecting multicellular animals from the loss or exchange of internal þuids and
from invasion by foreign microorganisms; composed of two layers: the
epidermis and dermis.
sliding filament model Model of muscular contraction in which the actin
Þlaments in the sarcomere slide past the myosin Þlaments, shortening the
sarcomere and therefore the muscle. | | |
slime molds Protistans that may represent a transition between protistans and
fungi.
small intestine A coiled tube in the abdominal cavity that is the major site of
chemical digestion and absorption of nutrients; composed of the duodenum,
jejunum, and ileum.
smog A local alteration in the atmosphere caused by human activity; mainly an
urban problem that is often due to pollutants produced by fuel combustion.
smooth muscle Muscle that lacks striations; found around circulatory system
vessels and in the walls of such organs as the stomach, intestines, and bladder.
Involuntary, not striated cells that control autonomic functions such as digestion
and artery contraction.
social behavior Behavior that takes place in a social context and results from
the interaction between and among individuals.
societies The most highly organized type of social organization; consist of
individuals that show varying degrees of cooperation and communication with
one another; often have a rigid division of labor.
sodium-potassium pump The mechanism that uses ATP energy to reset the
sodium and potassium ions after transmission of a nerve impulse.
soil Weathered rocks and minerals combined with air, water and organic matter
that can support plants.
somatic Relating to the non-gonadal tissues and organs of an organism's body.
somatic cell A cell that is not or will not become a gamete; the cells of the
body.
somatic senses All senses except vision, hearing, taste, and smell; include
pain, temperature, and pressure.
somatic nervous system The portion of the peripheral nervous system consisting
of the motor neuron pathways that innervate skeletal muscles.
somatostatin Pancreatic hormone that controls the rate of nutrient absorption
into the bloodstream.
somites Mesodermal structures formed during embryonic development that
give rise to segmented body parts such as the muscles of the body wall.
special senses Vision, hearing, taste, and smell. [ Pobierz całość w formacie PDF ]