Glossary

abiotic: nonliving
abscission: shedding of leaves; falling off
acetylation: addition of an acetyl group, CH₃-CHOO-
acidic: having an excess of H⁺ ions and a low pH
acinus: one of the small divisions of a fruit such as a raspberry
action potential: wave of ionic movement down the length of a nerve cell
active site: surface region of an enzyme where it catalyzes its reaction
adaptive radiation: diversification of a group of organisms into several different forms that adapt to different environments
adhesion: attachment; sticking to the surface of
ADP: adenosine diphosphate, the low-energy form of ATP
adventitious: growing from a nonstandard location
aerobe: organism that needs oxygen
aerobic: with oxygen, or requiring it
aestivating: remaining dormant for the summer
affinity: attraction
aflatoxin: toxic compound produced by a mold fungus
agar: gel derived from algae
agnosia: "not knowing"; loss of ability to recognize familiar objects
agroecosystem: agricultural ecosystem
alkaline: chemically basic, with an excess of OH-ions
allele: a particular form of a gene
allelopathy: inhibition of one plant's growth by another plant
amino acid: a building block of protein
amoeba: a single-celled protist that moves by crawling

amoeboid: like an amoeba, especially in movement via extension of portions of the membrane
AMP: adenosine monophosphate, form of ATP after removal of two phosphate groups
amphipathic: having both polar and nonpolar regions
anabolic: characteristic of a reaction that builds complex molecules from simpler ones, and requires energy
anadromous: describes fish that return to the rivers where they were born in order to breed
anaerobe: organism not needing oxygen
anaerobic: without oxygen, or not requiring oxygen
anemia: lack of oxygen-carrying capacity in the blood
aneurysm: bulging of the wall of a blood vessel
antagonism: working against
antagonist muscle: muscle that works against the action undertaken
anterior: toward the front
anterograde: forward
anthocyanins: colored compounds made by plants
anthropogenic: of, or relating to, the influence of human beings or nature
antibody: immune system protein that binds to foreign molecules
antigen: foreign substance that provokes an immune response
antioxidant: substance that prevents damage from oxidation
antitoxin: molecule used to inactivate a toxin
aphasia: loss of the ability to form ideas into words
apical: at the tip
apical meristem: growing tip from which all plant tissues arise
appendage: attached organ or structure
aqueous: watery or water-based
areolar: related to a small space within a tissue
aromatic: compound including a double-bonded carbon ring
arterioles: any of the small, terminal twigs of an artery that ends in capillaries
arthropods: organisms with jointed appendages and exoskeletons, including insects, spiders, and crustaceans
asymptomatic: without symptoms
ATP: adenosine triphosphate, a high-energy nucleotide used by cells to power most energy-requiring reactions

atria: two upper chambers of the heart (singular, atrium)
attenuation: lessening over time
autoimmune disease: disease in which the immune system attacks the body's own tissues
autonomic: independent; regulating involuntary actions
autonomic nervous system: one of the branches of the motor system, controlling involuntary muscles and glands
autosomal dominant: pattern of inheritance in which inheritance of a single allele from either parent results in expression of the trait
avian: concerning birds
axon: long extension of a nerve cell down which information flows
B lymphocyte: white blood cell that makes antibodies
B.C.E.: before the Common Era, equivalent to B.C.
basal: lowest level
base pair: two nucleotides (either DNA or RNA) linked by weak bonds
basic: having an excess of OH^- ions and a high pH
bilaterally symmetric: symmetric, or similar, across a central line
bilayer: composed of two layers
bioaccumulate: build up within organisms
bioluminescence: production of light by biochemical reactions
biopharmaceuticals: drugs produced by and harvested from living organisms
biosynthetic: forming a complex molecule from simpler ones
biotic: living
bolting: sudden spurt of growth
boreal: of, relating to, or located in northern regions
brood parasite: organism of one species that lays its eggs in the nest of another species
C4 and CAM plants: plants that employ accessory systems for trapping carbon for photosynthesis
cadherins: family of calcium-dependent adhesion proteins
carbohydrates: sugars, starches, and other molecules combining carbon, hydrogen, and oxygen and serving as fuel or structural components
cardiomyopathy: heart muscle disease
catalysis: aiding in the reaction of
catalyst: substance that aids in a reaction without being used up

catalyze: aid in the reaction of
caudate: toward the tail
C.E.: Common Era; equivalent to AD
cell cycle: sequence of growth, replication, and division that produces new cells
cellulose: carbohydrate made by plants and some other organisms; part of the cell wall
central nervous system: brain and spinal cord
centromere: region of the chromosome linking chromatids
cerebral cortex: outermost wrinkled portion of the brain
chemiosmosis: use of proton gradients to make ATP
chitin: nitrogen-containing carbohydrate found in arthropod exoskeletons and fungus cell walls
chromatid: a replicated chromosome before separation from its copy
chromatin: complex of DNA, histones, and other proteins making up chromosomes
chromosomal analysis: staining, banding, and other techniques for detection of chromosomal abnormalities
chromosome: "colored body" in the cell nucleus; made of DNA and protein, and divided functionally into genes and non-gene regions
cilia: short, hairlike cell extensions of the cell membrane formed by the cytoskeleton
ciliated: possessing cilia, which are short, hairlike extensions of the cell membrane
circadian: related to a day or daylength
clavicle: collar bone
cloaca: common exit cavity for intestinal, genital, and urinary tracts
codon: sequence of three mRNA nucleotides coding for one amino acid
cognition: mental processes of thought and awareness
cognitive: related to thought or awareness
communicable: transmissible from person to person
complementary: matching opposite
complex carbohydrate: molecules formed by linking simpler carbohydrates such as sugars
condensation: compaction of chromosome strands into a tight structure
conformation: three-dimensional shape
congenital: present at birth; inherited

conjunctiva: eye membrane that helps seal the eye socket
connective tissue: one of four types of body tissue, characterized by few cells and extensive extracellular material
consanguineous: descended from the same ancestor
constitutive: at a constant rate or continually
contiguous: adjacent to or touching
continental shelf: submerged offshore area demarcated by land on one side and deep sea on the other
coralloid: resembling coral
coronary artery: artery supplying blood to the heart
cortical: related to the cortex, or outer portion
cotyledon: seed leaf, which stores food and performs photosynthesis after germination
cranial: related to the cranium, or brain cavity
cryptobiosis: when a plant or animal becomes so inactive that its life processes nearly come to a stop
cutaneous: related to the skin
cutaneous respiration: gas exchange through the skin
cytology: study of cells
cytoplasm: material in a cell, excluding the nucleus
cytoskeleton: internal scaffolding in a cell, composed of protein
cytosol: fluid portion of a cell, not including the organelles
Darwinian fitness: capacity to survive and reproduce
deciduous: trees that shed their leaves in the fall
deciliter: one-tenth of a liter; a unit of volume
dementia: neurological illness characterized by impaired thought or awareness
desiccation: drying out
desynchronized: not happening at the same time
deuterostome: "mouth second"; referring to the early development of the anal pore during gut tube formation
dialysis: cleansing by partial filtration
dicot: plant having two cotyledons, or seed leaves
dikaryotic cell: cell with a pair of nuclei
dilation: expansion or swelling
dimer: polymer formed from two molecules of a simple compound

dimerizes: forms a pair
diploid: having pairs of chromosomes in the nucleus
dissociate: break apart
distal: away from
diurnal: active during the daytime
dorsal: to the back of
ecosystem: an ecological community and its environment
effector: organ at the end of a nerve, such as a muscle or gland
efferent: conducting outward or directing away from
electrolytes: ions in body fluids
electromagnetic radiation: light, X rays, and other forms of radiant energy
electron transport system: membrane-bound system of proteins that extracts energy from high-energy electrons, found in mitochondria and chloroplasts
electrophoresis: technique that uses electricity to separate molecules based on size and electric charge
electrophoresis gel: porous medium through which molecules can be separated using an electric current
embalming: treating a dead body to protect it from decay
embryology: development of the embryo
emulsify: suspend in solution through interaction with soap or similar molecules
endocrine: related to the system of hormones and glands that regulate body function
endogenous: caused by factors inside the organism
endometriosis: disorder of the endometrium, the lining of the uterus
endoplasmic reticulum: network of membranes within the cell
endosperm: nutritive tissue within a seed
endosymbiosis: symbiosis in which one partner lives within the other
endothermic: characterized by regulation of body temperature through metabolic activity
Enlightenment: eighteenth-century philosophical movement stressing rational critique of previously accepted doctrines in all areas of thought
enzymatic: related to the function of an enzyme
enzyme: protein that controls a reaction in a cell
epidemic: rapid spread of disease through a population, or a disease that spreads in this manner

epistasis: supression of a characteristic of one gene by the action of another gene
epithelium: one of four tissue types found in the body, characterized by thin sheets and usually serving a protective or secretory function
esophagus: tube connecting the throat to the stomach
eudicot: "true dicot"; plants with two seed leaves that originated from the earliest of flowering plants
eukaryotic cell: a cell with a nucleus
eutrophication: process by which waters become enriched in dissolved nutrients that promote plant growth which results in depletion of dissolved oxygen
evapotranspiration: loss of water from a plant by evaporation within the leaf
evidentiary DNA profile: analyzed DNA from a sample used as evidence
excrete: deposit outside of
exocrine gland: gland that secretes substances to an external or internal surface rather than into the bloodstream
exoskeleton: external skeleton
extensibility: ability to expand or grow larger
fallopian tubes: tubes through which eggs pass to the uterus
fecundity: ability to reproduce
feedback: process in which the output or result influences the rate of the process
fertilization: union of sperm and egg
fibroblast: undifferentiated cell normally giving rise to connective tissue cells
filtrate: material passing through a filter
focal: at a point
follicle: a vesicle that contains a developing egg surrounded by a covering of cells
food web: set of feeding relations in an ecosystem
forb: broad-leaved herbaceous plant
forensic: related to legal proceedings
fulcrum: pivot point of a lever
fungi: major group of parasitic, lower plants that obtain their food from the products of organic decay (e.g. molds, smuts, etc.)
gamete: reproductive cell, such as sperm or egg
gametophyte: a haploid plant that makes gametes by mitosis
ganglia: cluster of nerve cell bodies

gastroenteritis: inflammation of the gastrointestinal tract, often from infection
gene: portion of DNA that codes for a protein or RNA molecule
gene expression: use of a gene to create the corresponding protein
genetic code: relationship between triples of RNA nucleotides and the amino acids they code for during protein synthesis
genitalia: reproductive organs
genome: total genetic material in a cell or organism
germ line: cells creating eggs or sperm
gestation: period of fetal development within the mother
glial: supporting tissue of the elements of nervous tissue, including the brain, spinal cord, and ganglia
glucose: simple sugar that provides energy to animal cells; it is the building block of cellulose in plants
glycogen: complex carbohydrate used as storage in animals and some other organisms
glycolysis: initial stages of sugar breakdown in a cell
gradient: difference in concentration between two places
grafting: attachment and fusing of parts from different plants
guard cells: paired cells on leaves that control gas exchange and water loss
gymnosperms: "naked seed" plants, including conifers
hallucination: altered sensory experience resulting in the perception of objects that are not real
haploid: having single, nonpaired chromosomes in the nucleus
hectare: 10,000 square meters (2.47 acres)
heme: the deep red, iron containing, nonprotein portion of hemoglobin and myglobin
hemicellulose: complex carbohydrate related to cellulose and found in cell walls of plants and some other organisms
hemoglobin: oxygen-carrying protein complex in red blood cells
herbarium: a collection of dried plant specimens systematically arranged for reference
hermaphrodite: organism possessing both male and female reproductive structures
heterodimer: complex molecule composed of two different parts
heterogeneous: composed of, or containing, different parts or types
heterozygous: characterized by possession of two different forms (alleles) of a particular gene

hexamer: a structure composed of six parts
histogenesis: origin or production of tissues
histology: study of tissues
histone: protein around which DNA wraps to form chromosomes
homologous: similar in structure
homologous chromosomes: chromosomes carrying similar genetic information
homologous recombination: exchange of DNA segments between chromosomes
homozygous: containing two identical copies of a particular gene
hormone: molecule released by one cell to influence another
hybrid: combination of two different types
hydrocarbon: molecule or group composed only of C and H
hydrogen bond: weak bond between the H of one molecule or group and a nitrogen or oxygen of another
hydrolyze: to split apart using water
hydrophilic: "water loving"
hydrophobic: "water hating," such as oils
hydroponics: growing of plants without soil
hydroxyl: chemical group consisting of -OH
hypersalinity: very high level of salt
hypersecretion: excess secretion
hypersensitivity reaction: immune reaction characterized by rapid and severe response, often with swelling of airways
hyphae: threadlike part of the vegetative portion of the fungus
hyposecretion: lack of secretion
hypothermia: subnormal temperature of the body
ice-out: a thawing of ice covering a lake or other body of water
immunoglobulin: an immune protein, also called an antibody
immunosuppressant: inhibition of the immune response
in utero: inside the uterus
in vitro: "in glass"; in lab apparatus, rather than within a living organism
inbred: repeatedly bred with close relatives, creating organisms with very little genetic variation

inducible: able to be switched on
inflorescence: characteristic arrangement of flowers on a stalk
infrastructure: roads, phone lines, and other utilities that allow commerce
inorganic: not bonded to carbon
insectivorous: insect-eating
integrins: a family of transmembrane linking proteins
interferons: signaling molecules of the immune system
intermediate filament protein: one type of cytoskeleton protein
interspecific: between different species
interstitial space: space between cells in a tissue
intracellular: within a cell
intraocular: within the eyeball
intrinsic to: intimate part of; within
intron: untranslated portion of a gene that interrupts coding regions
ion: an electrically charged particle
ionic: based on or functioning by means of ions
ionizing radiation: high-energy radiation that destroys chemical bonds
isometric: relating to contraction without movement
isotopes: forms of an atom that differ by the number of neutrons in the nucleus
keratin: a major structural protein
kilobase: one thousand DNA bases; a measure of size of a piece of DNA
kilobasepair: one thousand DNA base pairs; a measure of size of a piece of DNA
kinase: enzyme that adds a phosphate group to another molecule, usually a protein
Krebs cycle: central metabolic pathway in mitochondria
lactation: production of milk by the mammary glands
laparoscopic surgery: surgery in which an instrument is inserted through a very small incision, usually guided by some type of imaging technique
larynx: "voice box"; muscles at the top of the trachea that control pitch and loudness
lateral: side-to-side
lethargy: lack of excitability; torpor
lignified: hardened by impregnation with lignin, a compound formed in plants

lignin: organic molecule used in plant cell walls to add stiffness to cellulose
lineage: ancestral line
lipid: fat or waxlike molecule, insoluble in water
lipoprotein: combination of protein and lipid, or fatlike molecule
locus: site on a chromosome (plural, loci)
lotic: of, relating to, or living in actively moving water
lymph: pale fluid that circulates in the lymphatic system, principally composed of blood plasma and cell fluid
lymphatic system: network of tubes that permeates the body for transport of lymph and combat of infection
lymphocyte: white blood cell found in lymph nodes
lyse: break apart
lysine: an amino acid
lysing: disintegration or dissolution of cells
macromolecules: large molecules such as proteins, carbohydrates, and nucleic acids
marsupials: kangaroos and other mammals that gestate young in an external pouch
materialism: the belief that life is due entirely to biochemical interactions, without the intervention of supernatural forces
matrix: a network, usually of threadlike fibers
medium: nutrient source
meiosis: cell division that forms eggs or sperm
membrane potential: electrical and chemical differences across a membrane leading to storage of energy and excitability
metabolism: chemical reactions within a cell
metabolite: molecule involved in a metabolic pathway
metamorphosis: development process that includes a larval stage with a different form from the adult
metaphase: intermediate stage in cell division, in which chromosomes line up before separating
metastasis: breaking away of cancer cells from a solid tumor to travel elsewhere in the body
metazoans: animals other than sponges
methylation: addition of the methyl group CH ₃
micron: one-millionth of a meter; also called a micrometer
mid-dorsal: middle of the back

middle lamella: layer of material between two plant cells that holds them together
minerals: iron, calcium, sodium, and other elements needed by living organisms
missense mutation: nucleotide change that causes a change in the amino acid normally added to the protein
mitochondria: subcellular organelle that creates ATP used for energyrequiring processes in a cell
mitogen: substance that stimulates mitosis
mitosis: separation of replicated chromosomes
molecular hybridization: base-pairing among DNAs or RNAs of different origins
monocot: any of various flowering plants, such as grasses and orchids, that have a single cotyledon in the seed
monoculture: cultivation of a single type of crop in a large area
monomer: "single part"; monomers are joined to form a polymer
monophyletic: a group that includes an ancestral species and all its descendants
montane: mountainous region
morphology: related to shape and form
motile: able to move
motor neuron: nerve cell that controls a muscle or gland
mucous membrane: outer covering designed to secrete mucus, often found lining cavities and internal surfaces
multimer: composed of many similar parts
multinucleate: having many nuclei within a single cell membrane
muscle tone: low level, constant muscle contraction
mutualism: symbiosis between two organisms in which both benefit
mycorrhizae: symbiosis between soil fungus and plant root to maximize absorption
myxedema: thyroid disorder characterized by dry skin, swelling in the face, and mental deterioration
nanometer: 10 ^-9 meters; one-billionth of a meter
natural selection: process by which organisms best suited to their environments achieve greater reproductive success thus creating more "fit" future generations
nematode: worm of the Nematoda phylum, many of which are parasitic
nephron: functional unit of the kidney that performs filtration, reabsorption, and excretion

neritic: zone near the shore
neural: related to nerve cells or the nervous system
neurologist: doctor who treats brain disorders
neuron: nerve cell
neurotransmitters: molecules released by one neuron to stimulate or inhibit another neuron or cell
niche: the habitat supplying the right environment for a particular species
nm: nanometer; one-billionth of a meter
nocturnal: characterized by activity at night, or related to the night
nondisjunction: failure of separation of homologous chromosomes during meiosis
nuclear envelope: double membrane surrounding the cell nucleus
nucleated: having a nucleus
nucleotide: the building block of RNA or DNA
nucleus: membrane-bound portion of cell containing the chromosomes
obligate: required or necessary, especially referring to a metabolic process or mode of nutrition
octomer: composed of eight parts
oligosaccharide: chain of several sugar molecules
oncogene: gene that causes cancer
oocyte: unfertilized egg
opportunistic: caused by a microorganism that is usually harmless but which causes infection in an immunosuppressed person
organelle: membrane-bound cell compartment
organic: composed of carbon, or derived from living organisms; also, a type of agriculture stressing soil fertility and avoidance of synthetic pesticides and fertilizers
osmosis: passage of water through a membrane in response to concentration differences
osseous: related to bone
outcross: fertilization between two different plants
ovipary: production of eggs that hatch outside the body
ovovivipary: production of eggs that hatch within the female's body
ovule: multicellular structure that develops into a seed after fertilization
oxidation: reaction characterized by loss of electrons, or reaction with oxygen

oxidation-reduction: oxidation is loss of electrons, and reduction is gain of electrons
oxidative: characterized by oxidation, or loss of electrons
oxidative phosphorylation: use of oxygen to make ATP
oxidize: to react or make react with oxygen
palatine bone: bone of the hard palate at the roof of the mouth
paleoanthropology: study of ancient humans
palindromic: reading the same forward and backward
pandemic: disease spread throughout an entire population
papillate: small, nipplelike projection
parasite: organism living in close association with another from which it derives most of its nutrition
parasitology: study of parasites
parasympathetic nervous system: branch of the nervous system promoting nutrient absorption and other maintenance activities
pathogen: disease-causing organism
pathogenesis: pathway leading to disease
pathologic: related to disease
pectin: carbohydrate in plants that forms crosslinks to stabilize cell walls
peptide bond: bond between two amino acids
peptidoglycans: polymer that is composed of polysaccharides and peptic chains
perianth: combined sepals and petals
peripheral: outside the central nervous system (brain and spinal cord)
pH: measure of acidity or alkalinity; numbers below 7 are acid, above are basic
phage: short for bacteriophage
phagocytosis: engulfing of cells or large fragments by another cell, including immune system cells
pharynx: throat
phase-contrast microscopy: technique that manipulates passage of light through transparent specimens to reveal internal features
phenotype: observable characteristics of an organism
pheromone: molecule released by one organism to influence another organism's behavior
phloem: plant tissue that conducts sugars from leaves to roots and other tissues

phosphodiester: the link between two nucleotides in DNA or RNA
phosphorylate: add a phosphate group to
phosphorylation: addition of the phosphate group PO ₄^3-
phyletic gradualism: the belief that evolutionary change is slow and steady
phylogenetic: related to phylogeny, the evolutionary development of a species
phylum: taxonomic level below kingdom, e.g., arthropod or chordate
physiology: branch of biology that deals with the functions and activities of living matter
phytoplankton: microscopic floating creatures that photosynthesize
pinnate: featherlike
pinocytosis: introduction of fluids into a cell by enclosing it and pinching off the plasma membrane
pipette: lab instrument for precise measurement and transfer of small volumes of liquids
pistil: female reproductive organ of a flower
placental: related to mammals that nourish the fetus with a placenta, an exchange organ in the uterus
plankton: microscopic floating organisms
plant hybridization: creation of offspring by union of two different types of plants, such as wheat and rye
plasmid: small ring of DNA found in many bacteria
plasticity: change form
plate tectonics: the movement of large plates of Earth's crust
polar: partially charged, and usually soluble in water
polar covalent: bond in which electrons are unevenly shared
polymer: molecule composed of many similar parts
polymerase: enzyme complex that synthesizes DNA or RNA from individual nucleotides
polymerization: linking together of similar parts to form a polymer
polypeptide: chain of amino acids
polysaccharide: carbohydrate composed of many individual units of sugar
posterior: toward the back
postmortem: after death
prebiotic: before the origin of life
Precambrian: before the Cambrian era; before 600 million years ago

primer: short nucleotide sequence that helps begin DNA replication
progeny: offspring
prokaryote: single-celled organism without a nucleus
promoter: DNA sequence to which RNA polymerase binds to begin transcription
prostaglandins: hormonelike molecules released by one cell that affect nearby cells, including smooth muscle
prostrate: face downward
protein: complex molecule made from amino acids; used in cells for structure, signaling, and controlling reactions
proteolysis: breakdown of proteins
protoecology: early ecology
protoplasm: fluid portion of a plant cell within the cell wall
protostome: "mouth first"; referring to the early development of the oral pore during gut tube formation
protozoa: any of a phylum of minute protoplasmic animals present in almost every kind of habitat, some of which pose serious threats to humans and animals
pseudopod: "false foot"; an extension of the plasma membrane during locomotion by an amoeba or similar crawling cell
psychosis: severe mental disorder characterized by diminished connection with reality
psychotropic: affecting consciousness, thought, or emotion
punctuated equilibrium: pattern of evolution in which long periods of relatively little change are punctuated by rapid change
pyruvate: the ionized form of pyruvic acid, a key intermediate in cell metabolism
quarternary: fourth level
radially symmetric: symmetric, or similar, about a central point (a wheel is radially symmetric)
reproductive isolation: isolation of a population from other populations of the same species due to inability to successfully reproduce; an early stage in species formation
respire: use oxygen to burn cellular fuel
restriction enzyme: enzyme that cuts DNA at a particular sequence
restriction fragments: fragments of DNA created by restriction enzymes
reticular: netlike
retrograde: backward

reverse transcriptase: enzyme that copies RNA into DNA
reverse transcription: creation of DNA from an RNA template
ribonucleoprotein: combination of RNA and protein
ribosome: protein-RNA complex in cells that synthesizes protein
rickettsia: (pl. -sias or siae) any of a family of polymorphic microorganisms that cause various diseases
RNA polymerase: enzyme complex that creates RNA from DNA template
saline: of, or relating to, salt
saprophyte: plant that feeds on decaying parts of other plants
savanna: open grassland with sparse trees
sclerophyll: small, tough evergreen leaves
secretion: material released from the cell
secretory pathway: series of events within a cell by which molecules are brought to the plasma membrane for release from the cell
sepals: whorls of flower organs outside of the petals, usually green and serving to protect the flower before it opens
serotinous: developing late in the season
serotype: identity of an organism or virus based on reaction to an antibody
sessile: attached and remaining in one place
silviculture: cultivation of forest trees
sleep apnea: difficulty breathing while asleep
solenoid: cylindrical coiled structure
solute: dissolved substance
solvation: the process of dissolving
somatic: nonreproductive; not an egg or sperm
somatostatin: hormone produced by the hypothalamus that influences growth
spasticity: of, or relating to, spasms
spectroscopy: process using light or other emitted radiation to determine properties of a sample
sphincter: ring of muscle regulating passage of material through a tube such as the gastrointestinal tract
spontaneous generation: the theory that life began from nonliving matter
stasis: state of no change
steroid hormone: group of hormones that includes estrogen, testosterone, and progesterone

steroids: hormones such as testosterone or estrogens that control many aspects of physiology
stomata: openings in leaves for gas exchange, surrounded and regulated by guard cells
strong bond: high-energy arrangement between two atoms involving electron-sharing; strong bonds require more energy to break than weak bonds
subcutaneous: below the skin
substrate: the molecule acted on by an enzyme; also a surface for attachment
succession: series of changes seen in some plant communities over time, in which low-growing, rapidly reproducing species are replaced by taller and more slowly reproducing ones
superficial: on the surface; not deep
symbiont: organism living in close association with another organism
symbiosis: close relationship between two species in which at least one benefits
sympathetic nervous system: branch of the nervous system that promotes heightened awareness, increased nutrient consumption, and other changes associated with "fight or flight"
synaptic transmission: passage of chemicals between nerve cells to send messages or alter neuron firing
synchronously: at the same time
synergism: working together to create a larger product rather than a simple sum
systemic: throughout the body
T cell: white blood cell that controls the immune response
taxon: a level of classification, such as kingdom or phylum
tectonic plate: large segment of Earth's crust that moves in relation to other similar plates
template: master copy
teratogens: substances that cause birth defects
tertiary: third level
thermoregulation: temperature regulation
transcribe: creation of an RNA copy of a DNA gene
transcription: messenger RNA formation from a DNA sequence
transcription factor: protein that increases the rate of transcription of a gene
transduction: conversion of a signal of one type into another type

transgenic: characterized by presence of one or more genes from a different organism
translation: synthesis of protein using mRNA code
translocation: movement of sugars and other nutrients throughout a plant
transverse: situated or lying across
trimer: a structure composed of three parts
triploid: possessing three sets of chromosomes
trophic: related to feeding
trophic level: feeding level in an ecosystem
true breeding: giving only offspring identical to the parents
turgor: internal pressure
ubiquitous: found everywhere
ultrasonography: use of sound waves to produce an image
ungulate: hoofed mammals such as cattle
uninucleate: possessing one nucleus
vas deferens: tube through which sperm travel from testes to urethra
vector: carrier
ventral to: toward the belly side
ventricle: fluid-filled chamber
venule: any of the minute veins connecting the capillaries with the larger systemic veins
vesicle: membrane-bound sac
vestigial: no longer functional
visceral: related to the viscera, or internal organs
viscous: thick
vivipary: production of live young
volatile: easily vaporized
vulva: external female genitalia
weak bond: low-energy arrangement between two atoms involving electronsharing; weak bonds require less energy to break than strong bonds
X-ray crystallography: use of X rays to determine the structure of a molecule
xylem: water-transporting system in plants
zygote: fertilized egg