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868 terms

All The Vocab You Need To Know For The Bio Regents

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abdomen
posterior part of an arthropod's body
abiotic factor
physical, or nonliving, factor that shapes an ecosystem
abscission layer
layer of cells at the petiole that seals off a leaf from the vascular system
accessory pigment
compound other than chlorophyll that absorbs light at different wavelengths than chlorophyll
acellular slime mold
slime mold that passes through a stage in which its cells fuse to form large cells with many nuclei
acetylcholine
neurotransmitter that diffuses across a synapse and produces an impulse in the cell membrane of a muscle cell
acid
compound that forms hydrogen ions (H+) in solution
acid rain
rain containing nitric and sulfuric acids
acoelomate
animal lacking a coelom, or body cavity
actin
a protein that mainly makes up the thin filaments in striations in skeletal muscle cells
action potential
reversal of charges across the cell membrane of a neuron; also called a nerve impulse
activation energy
energy needed to get a reaction started
active immunity
immunity produced by exposure to an antigen, as a result of the immune response
active transport
energy-requiring process that moves material across a cell membrane against a concentration difference
adaptation
inherited characteristic that increases an organism's chance of survival
adaptive radiation
process by which a single species or small group of species evolves into several different forms that live in different ways; rapid growth in the diversity of a group of organisms
addiction
uncontrollable dependence on a drug
adenosine triphosphate (ATP)
one of the principal chemical compounds that living things use to store and release energy
adhesion
attraction between molecules of different substances; in plants, attraction between unlike molecules
aerobic
process that requires oxygen
age-structure diagram
graph of the numbers of males and females within different age groups of a population
aggression
threatening behavior that one animal uses to gain control over another
agriculture
the practice of farming
air sac
one of several sacs attached to a bird's lungs into which air moves when a bird inhales; allows for the one-way flow of air through the respiratory system
algal bloom
an immediate increase in the amount of algae and other producers that results from a large input of a limiting nutrient
allele
one of a number of different forms of a gene
allergy
overreaction of the immune system to antigens
alternation of generations
process in which many algae switch back and forth between haploid and diploid stages of their life cycles
alveolus
tiny air sac at the end of a bronchiole in the lungs that provides surface area for gas exchange to occur
amino acid
compound with an amino group (−NH2) on one end and a carboxyl group (−COOH) on the other end
amniotic egg
egg composed of shell and membranes that create a protected environment in which the embryo can develop out of the water
amoeboid movement
type of locomotion used by amoebas
amphibian
vertebrate that, with some exceptions, lives in water as a larva and on land as an adult, breathes with lungs as an adult, has moist skin that contains mucus glands, and lacks scales and claws
amylase
enzyme in saliva that breaks the chemical bonds in starches
anaerobic
process that does not require oxygen
anal pore
region of the cell membrane of a ciliate where waste-containing food vacuoles fuse and are then emptied into the environment
anaphase
the third phase of mitosis, during which the chromosome pairs separate and move toward opposite poles
angiosperm
flowering plant; bears its seeds within a layer of tissue that protects the seed
Animalia
kingdom of multicellular eukaryotic heterotrophs whose cells do not have cell walls
annual
flowering plant that completes a life cycle within one growing season
anther
flower structure in which haploid male gametophytes are produced
antheridium
male reproductive structure in some algae and plants
anthropoid
primate group made up of humans, apes, and most monkeys
antibiotic
compound that blocks the growth and reproduction of bacteria
antibody
protein that helps destroy pathogens
anticodon
group of three bases on a tRNA molecule that are complementary to an mRNA codon
antigen
substance that triggers an immune response
anus
opening through which wastes leave the digestive tract
aorta
large blood vessel in mammals through which blood travels after it leaves the left ventricle
aphotic zone
permanently dark layer of the oceans below the photic zone
apical dominance
phenomenon in which the closer a bud is to the stem's tip, the more its growth is inhibited
apical meristem
group of undifferentiated cells that divide to produce increased length of stems and roots
appendage
structure, such as a leg or antenna, that extends from the body wall
aquaculture
the raising of aquatic organisms for human consumption
Archaea
domain of unicellular prokaryotes that have cell walls that do not contain peptidoglycan
Archaebacteria
kingdom of unicellular prokaryotes whose cell walls do not contain peptidoglycan
archaeocyte
specialized cell in a sponge that makes spicules
archegonium
female reproductive structure in some plants, including mosses and liverworts
artery
large blood vessel that carries blood from the heart to the tissues of the body
artificial selection
selection by humans for breeding of useful traits from the natural variation among different organisms
ascospore
haploid spore produced within the ascus of ascomycetes
ascus
structure within the fruiting body of an ascomycete in which two nuclei of different mating types fuse
asexual reproduction
process by which a single parent reproduces by itself
asthma
chronic respiratory disease in which the air passageways become narrower than normal
atherosclerosis
condition in which fatty deposits called plaque build up on the inner walls of the arteries
atom
basic unit of matter
ATP synthase
large protein that uses energy from H+ ions to bind ADP and a phosphate group together to produce ATP
atrium
upper chamber of the heart that receives and holds blood that is about to enter the ventricle
autosome
chromosome that is not a sex chromosome
autotroph
organism that can capture energy from sunlight or chemicals and use it to produce its own food from inorganic compounds; also called a producer
auxin
substance produced in the tip of a seedling that stimulates cell elongation
axon
long fiber that carries impulses away from the cell body of a neuron
bacillus
rod-shaped prokaryote
bacteria
domain of unicellular prokaryotes that have cell walls containing peptidoglycans
bacteriophage
virus that infects bacteria
bark
tree structure that includes all tissues outside the vascular cambium, including phloem, the cork cambium, and cork
base
compound that produces hydroxide ions (OH+) in solution
base pairing
principle that bonds in DNA can form only between adenine and thymine and between guanine and cytosine
basidiospore
spore in basidiomycetes that germinates to produce haploid primary mycelia
basidium
spore-bearing structure of a basidiomycete
behavior
the way an organism reacts to changes in its internal condition or external environment
behavioral isolation
form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding
benthos
organisms that live attached to or near the ocean floor
biennial
flowering plant that completes its life cycle in two years
bilateral symmetry
body plan in which only a single, imaginary line can divide the body into two equal halves; characteristic of worms, arthropods, and chordates
binary fission
"type of asexual reproduction in which an organism replicates its DNA and divides in half, producing two identical daughter cells
binocular vision
ability to merge visual images from both eyes, which provides depth perception and a three-dimensional view of the world
binomial nomenclature
classification system in which each species is assigned a two-part scientific name
biodiversity
biological diversity; the sum total of the variety of organisms in the biosphere
biogeochemical cycle
process in which elements, chemical compounds, and other forms of matter are passed from one organism to another and from one part of the biosphere to another
biological magnification
increasing concentration of a harmful substance in organisms at higher trophic levels in a food chain or food web
biology
science that seeks to understand the living world
biomass
total amount of living tissue within a given trophic level
biome
group of ecosystems that have the same climate and dominant communities
biosphere
part of Earth in which life exists including land, water, and air or atmosphere
biotic factor
biological influence on organisms within an ecosystem
bipedal
term used to refer to two-footed locomotion
bird
endothermic animal that has an outer covering of feathers, two legs covered with scales that are used for walking or perching, and front limbs modified into wings
blade
thin, flattened section of a plant leaf that collects sunlight
blastula
hollow ball of cells formed when a zygote undergoes a series of divisions
bone marrow
soft tissue inside the cavities within bones
book lung
organ that has layers of respiratory tissue that is used by some terrestrial arthropods for the exchange of gases
Bowman's capsule
cup-shaped structure in the upper end of a nephron that encases the glomerulus
brain stem
structure that connects the brain and spinal cord; includes the medulla oblongata and the pons
bronchus
passageway leading from the trachea to a lung
bryophyte
nonvascular plant; examples are mosses and their relatives
bud
plant structure containing undeveloped tissue that can produce new stems and leaves
budding
asexual process by which yeasts increase in number; process of attaching a bud to a plant to produce a new branch
buffer
weak acid or base that can react with strong acids or bases to help prevent sharp, sudden changes in pH
Calorie
term used by scientists to measure the energy stored in foods; 1000 calories
calorie
amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius
Calvin cycle
reactions of photosynthesis in which energy from ATP and NADPH is used to build high-energy compounds such as sugars
cancer
disorder in which some of the body's own cells lose the ability to control growth
canopy
dense covering formed by the leafy tops of tall rain forest trees
capillary
smallest blood vessel; brings nutrients and oxygen to the tissues and absorbs carbon dioxide and waste products
capillary action
tendency of water to rise in a thin tube
capsid
outer protein coat of a virus
carapace
in crustaceans, the part of the exoskeleton that covers the cephalothorax; in turtles and tortoises, the dorsal part of the shell
carbohydrate
compound made up of carbon, hydrogen, and oxygen atoms; major source of energy for the human body
carcinogen
chemical compound known to cause cancer
carnivore
organism that obtains energy by eating animals
carpel
innermost part of a flower that produces the female gametophytes
carrying capacity
largest number of individuals of a population that a given environment can support
cartilage
strong connective tissue that supports the body and is softer and more flexible than bone
Casparian strip
waterproof strip that surrounds plant endodermis cells
caste
group of individual insects specialized to perform particular tasks, or roles
catalyst
substance that speeds up the rate of a chemical reaction
cell
collection of living matter enclosed by a barrier that separates the cell from its surroundings; basic unit of all forms of life
cell body
largest part of a typical neuron; contains the nucleus and much of the cytoplasm
cell culture
group of cells grown in a nutrient solution from a single original cell
cell cycle
series of events that cells go through as they grow and divide
cell division
process by which a cell divides into two new daughter cells
cell fractionation
technique in which cells are broken into pieces and the different cell parts are separated
cell membrane
thin, flexible barrier around a cell; regulates what enters and leaves the cell
cell specialization
the process in which cells develop in different ways to perform different tasks
cell theory
idea that all living things are composed of cells, cells are the basic units of structure and function in living things, and new cells are produced from existing cells
cell wall
strong supporting layer around the cell membrane in plants, algae, and some bacteria
cell-mediated immunity
immunity against abnormal cells and pathogens inside living cells
cellular respiration
process that releases energy by breaking down glucose and other food molecules in the presence of oxygen
cellular slime mold
slime mold whose individual cells remain separated during every phase of the mold's life cycle
centriole
one of two tiny structures located in the cytoplasm of animal cells near the nuclear envelope
centromere
area where the chromatids of a chromosome are attached
cephalization
concentration of sense organs and nerve cells at the front of an animal's body
cephalothorax
region of a crustacean formed by the fusion of the head with the thorax
cerebellum
region of the brain that coordinates body movements
cerebral cortex
outer layer of the cerebrum of a mammal's brain; center of thinking and other complex behaviors
cerebrospinal fluid
fluid in the space between the meninges that acts as a shock absorber that protects the central nervous system
cerebrum
area of the brain responsible for all voluntary activities of the body
chelicerae
pair of mouthparts in chelicerates that contain fangs and are used to stab and paralyze prey
cheliped
one of the first pair of legs of decapods
chemical bond
link that holds together atoms in compounds
chemical reaction
process that changes one set of chemicals into another set of chemicals
chemoautotroph
organism that makes organic carbon molecules from carbon dioxide using energy from chemical reactions
chemoheterotroph
organism that must take in organic molecules for both energy and carbon
chemosynthesis
process by which some organisms, such as certain bacteria, use chemical energy to produce carbohydrates
chitin
complex carbohydrate that makes up the cell walls of fungi; also found in the external skeletons of arthropods
chlorophyll
principal pigment of plants and other photosynthetic organisms; captures light energy
chloroplast
organelle found in cells of plants and some other organisms that captures the energy from sunlight and converts it into chemical energy
choanocyte
specialized cell in sponges that uses a flagellum to move a steady current of water through the sponge
chordate
member of the phylum Chordata; animal that has, for at least some stage of its life, a dorsal hollow nerve cord, a notochord, pharyngeal pouches, and a muscular tail
chromatid
one of two identical "sister" parts of a duplicated chromosome
chromatin
granular material visible within the nucleus; consists of DNA tightly coiled around proteins
chromosome
"threadlike structure within the nucleus containing the genetic information that is passed from one generation of cells to the next
chyme
mixture of stomach fluids and food produced in the stomach by contracting stomach muscles
cilium
short hairlike projection similar to a flagellum; produces movement in many cells
circadian rhythm
behavioral cycle that occurs in a daily pattern
cladogram
diagram that shows the evolutionary relationships among a group of organisms
class
group of similar orders
classical conditioning
learning process in which an animal makes a mental connection between a stimulus and some kind of reward or punishment
climate
average, year-after-year conditions of temperature and precipitation in a particular region
clitellum
band of thickened, specialized segments in annelids that secretes a mucus ring into which eggs and sperm are released
cloaca
a muscular cavity at the end of the large intestine through which digestive wastes, urine, and eggs or sperm leave the body
clone
member of a population of genetically identical cells produced from a single cell
closed circulatory system
system in which blood is contained within a network of blood vessels
cnidocyte
stinging cell of cnidarians; used for defense and to capture prey
coastal ocean
marine zone that extends from the low-tide mark to the end of the continental shelf
coccus
spherical prokaryote
cochlea
fluid-filled part of the inner ear; sends nerve impulses to the brain through the cochlear nerve
codominance
situation in which both alleles of a gene contribute to the phenotype of the organism
codon
three-nucleotide sequence on messenger RNA that codes for a single amino acid
coelom
fluid-filled body cavity lined with mesoderm
coevolution
process by which two species evolve in response to changes in each other
cohesion
attraction between molecules of the same substance
collenchyma
type of ground tissue cell with a strong, flexible cell wall; helps support larger plants
commensalism
symbiotic relationship in which one member of the association benefits and the other is neither helped nor harmed
common descent
principle that all living things were derived from common ancestors
communication
passing of information from one organism to another
community
assemblage of different populations that live together in a defined area
companion cell
phloem cell that surrounds sieve tube elements
competitive exclusion principle
ecological rule that states that no two species can occupy the same exact niche in the same habitat at the same time
complete metamorphosis
type of insect development in which the larvae look and act nothing like their parents and also feed in completely different ways
compound
substance formed by the chemical combination of two or more elements in definite proportions
compound light microscope
microscope that allows light to pass through a specimen and uses two lenses to form an image
concentration
the mass of solute in a given volume of solution, or mass/volume
cone
in gymnosperms, a seed-bearing structure; in the retina of the eye, a photoreceptor that responds to light of different colors, producing color vision
conidium
tiny fungal spore that forms at the tips of specialized hyphae in ascomycetes
coniferous
term used to refer to trees that produce seed-bearing cones and have thin leaves shaped like needles
conjugation
form of sexual reproduction in which paramecia and some prokaryotes exchange genetic information
connective tissue
tissue that holds organs in place and binds different parts of the body together
conservation
wise management of natural resources, including the preservation of habitats and wildlife
consumer
organism that relies on other organisms for its energy and food supply; also called a heterotroph
contractile vacuole
cavity in the cytoplasm of some protists that collects water and discharges it from the cell
controlled experiment
a test of the effect of a single variable by changing it while keeping all other variables the same
controlled variable
factor in an experiment that a scientist purposely keeps the same
convergent evolution
process by which unrelated organisms independently evolve similarities when adapting to similar environments
coral reef
diverse and productive environment named for the coral animals that make up its primary structure
cork cambium
lateral meristematic tissue that produces the outer covering of stems
corpus luteum
name given to a follicle after ovulation because of its yellow color
cortex
spongy layer of ground tissue just inside the epidermis of a root
cotyledon
first leaf or first pair of leaves produced by the embryo of a seed plant
courtship
type of behavior in which an animal sends out stimuli—such as sounds, visual displays, or chemicals—in order to attract a member of the opposite sex
covalent bond
bond formed by the sharing of electrons between atoms
crop
in earthworms, part of the digestive system in which food can be stored; in birds, structure at the lower end of the esophagus in which food is stored and moistened
crossing-over
process in which homologous chromosomes exchange portions of their chromatids during meiosis
cuticle
in plants, a thick waxy layer on exposed outer surfaces of cells that protects them against water loss and injury
cyclin
one of a family of closely related proteins that regulate the cell cycle in eukaryotic cells
cytokinesis
division of the cytoplasm during cell division
cytokinin
plant hormone produced in growing roots and in developing fruits and seeds
cytoplasm
"material inside the cell membrane—not including the nucleus
cytoskeleton
network of protein filaments within some cells that helps the cell maintain its shape and is involved in many forms of cell movement
data
evidence; information gathered from observations
deciduous
term used to refer to a tree that sheds its leaves during a particular season each year
decomposer
organism that breaks down and obtains energy from dead organic matter
deforestation
destruction of forests
demographic transition
change in a population from high birth and death rates to low birth and death rates
demography
scientific study of human populations
dendrite
extension of the cell body of a neuron that carries impulses from the environment or from other neurons toward the cell body
denitrification
conversion of nitrates into nitrogen gas
density-dependent limiting factor
limiting factor that depends on population size
density-independent limiting factor
limiting factor that affects all populations in similar ways, regardless of population size
deoxyribonucleic acid (DNA)
nucleic acid that contains the sugar deoxyribose
dependent variable
factor in an experiment that a scientist wants to observe, which may change because of the manipulated variable; also known as a responding variable
depressant
drug that decreases the rate of functions regulated by the brain
derived character
characteristic that appears in recent parts of a lineage, but not in its older members
dermis
inner layer of the skin
descent with modification
principle that each living species has descended, with changes, from other species over time
desertification
in areas with dry climates, a process caused by a combination of poor farming practices, overgrazing, and drought that turns productive land into desert
detritivore
organism that feeds on plant and animal remains and other dead matter
detritus
particles of organic material that provide food for organisms at the base of an estuary's food web
deuterostome
"animal whose anus is formed from the blastopore of a blastula
diabetes mellitus
condition that occurs when the pancreas produces too little insulin, resulting in an increase in the level of blood glucose
diaphragm
large, flat muscle at the bottom of the chest cavity that helps with breathing
dicot
angiosperm whose seeds have two cotyledons
differentiation
process in which cells become specialized in structure and function
diffusion
process by which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated
diploid
term used to refer to a cell that contains both sets of homologous chromosomes
directional selection
form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve
disease
any change, other than an injury, that disrupts the normal functions of the body
disruptive selection
form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle
DNA fingerprinting
analysis of sections of DNA that have little or no known function, but vary widely from one individual to another, in order to identify individuals
DNA polymerase
enzyme involved in DNA replication that joins individual nucleotides to produce a DNA molecule
domain
most inclusive taxonomic category; larger than a kingdom
dormancy
period of time during which a plant embryo is alive but not growing
double fertilization
fertilization in angiosperms, in which two distinct fertilization events take place between the male and female gametophytes
drug
any substance, other than food, that causes a change in the structure or function of the body
drug abuse
intentional misuse of any drug for nonmedical purposes
ecological pyramid
diagram that shows the relative amounts of energy or matter within each trophic level in a food chain or food web
ecological succession
gradual change in living communities that follows a disturbance
ecology
scientific study of interactions among organisms and between organisms and their environment
ecosystem
collection of all the organisms that live in a particular place, together with their nonliving environment
ecosystem diversity
variety of habitats, living communities, and ecological processes in the living world
ectoderm
outermost germ layer of most animals; gives rise to outer layer of the skin, sense organs, and nerves
ectotherm
animal that relies on interactions with the environment to help it control body temperature
electron
variety of habitats, living communities, and ecological processes in the living world
electron microscope
microscope that forms an image by focusing beams of electrons onto a specimen
electron transport chain
a series of proteins in which the high-energy electrons from the Krebs cycle are used to convert ADP into ATP
element
substance consisting entirely of one type of atom
embryo
organism in its early stage of development
embryo sac
female gametophyte within the ovule of a flowering plant
emigration
movement of individuals out of an area
emphysema
disease in which the tissues of the lungs lose elasticity, making breathing very difficult
endangered species
species whose population size is rapidly declining and will become extinct if the trend continues
endocrine gland
gland that releases its secretions directly into the bloodstream
endocytosis
process by which a cell takes material into the cell by infolding of the cell membrane
endoderm
innermost germ layer of most animals; develops into the linings of the digestive tract and much of the respiratory system
endodermis
layer of cells that completely encloses vascular tissue
endoplasmic reticulum
internal membrane system in cells in which lipid components of the cell membrane are assembled and some proteins are modified
endoskeleton
structural support located inside the body of an animal
endosperm
food-rich tissue that nourishes a seedling as it grows
endospore
type of spore formed when a bacterium produces a thick internal wall that encloses its DNA and a portion of its cytoplasm
endosymbiotic theory
theory that eukaryotic cells formed from a symbiosis among several different prokaryotic organisms
endotherm
animal that generates its own body heat and controls its body temperature from within
enzyme
protein that acts as a biological catalyst
epidermal cell
cell that makes up the dermal tissue, which is the outer covering of a plant
epidermis
outer layer of the skin
epididymis
structure in the male reproductive system in which sperm fully mature and are stored
epiphyte
plant that is not rooted in soil but instead grows directly on the body of another plant
epithelial tissue
tissue that covers the surface of the body and lines internal organs
equilibrium
when the concentration of a solute is the same throughout a solution
era
one of several subdivisions of the time between the Precambrian and the present
esophagus
food tube connecting the mouth to the stomach
estuary
wetlands formed where rivers meet the ocean
ethylene
plant hormone that stimulates fruits to ripen
Eubacteria
kingdom of unicellular prokaryotes whose cell walls are made up of peptidoglycan
Eukarya
domain of all organisms whose cells have nuclei, including protists, plants, fungi, and animals
eukaryote
organism whose cells contain nuclei
evaporation
process by which water changes from a liquid into an atmospheric gas
evolution
change in a kind of organism over time; process by which modern organisms have descended from ancient organisms
evolutionary classification
method of grouping organisms together according to their evolutionary history
exocrine gland
gland that releases its secretions through tubelike structures called ducts
exocytosis
process by which a cell releases large amounts of material
exon
expressed sequence of DNA; codes for a protein
exoskeleton
external skeleton; tough external covering that protects and supports the body of many invertebrates
exponential growth
growth pattern in which the individuals in a population reproduce at a constant rate
external fertilization
process in which eggs are fertilized outside the female's body
extinct
term used to refer to a species that has died out
extinction
disappearance of a species from all parts of its geographical range
extracellular digestion
process in which food is broken down outside the cells in a digestive tract
eyespot
group of cells that can detect changes in the amount of light in the environment
facilitated diffusion
movement of specific molecules across cell membranes through protein channels
facultative anaerobe
organism that can survive with or without oxygen
Fallopian tube
one of two fluid-filled tubes in human females through which an egg passes after its release from an ovary
family
group of genera that share many characteristics
fat
lipid; made up of fatty acids and glycerol; protects body organs, insulates body, and stores energy in the body
feather
structure made mostly of protein that develops from a pit in a bird's skin
feedback inhibition
process in which the product or result stops or limits the process
fermentation
process by which cells release energy in the absence of oxygen
fertilization
process in sexual reproduction in which male and female reproductive cells join to form a new cell
fetal alcohol syndrome
group of birth defects caused by the effects of alcohol on a fetus
fetus
name given to a human embryo after eight weeks of development
fever
elevated body temperature that occurs in response to infection
fibrous root
part of a root system in which roots branch to such an extent that no single root grows larger than the rest
filament
in algae, a long threadlike colony formed by many green algae; in plants, a long, thin structure that supports an anther
filtration
process by which a liquid or gas passes through a filter to remove wastes
fish
aquatic vertebrate characterized by paired fins, scales, and gills
fission
form of asexual reproduction in which an organism splits into two, and each half grows new parts to become a complete organism
fitness
ability of an organism to survive and reproduce in its environment
flame cell
specialized cell that filters and removes excess water from the body of a flatworm
flower
seed-bearing structure of an angiosperm
follicle
cluster of cells surrounding a single egg in the human female reproductive system
food chain
series of steps in an ecosystem in which organisms transfer energy by eating and being eaten
food vacuole
small cavity in the cytoplasm of protists that temporarily stores food
food web
network of complex interactions formed by the feeding relationships among the various organisms in an ecosystem
foot
muscular part of a mollusk
fossil
preserved remains or evidence of an ancient organism
fossil record
information about past life, including the structure of organisms, what they ate, what ate them, in what environment they lived, and the order in which they lived
founder effect
change in allele frequencies as a result of the migration of a small subgroup of a population
frameshift mutation
mutation that shifts the "reading" frame of the genetic message by inserting or deleting a nucleotide
frond
large leaf of a fern
fruit
wall of tissue surrounding an angiosperm seed
fruiting body
slender reproductive structure that produces spores and is found in some funguslike protists; reproductive structure of fungus that develops from a mycelium
Fungi
kingdom composed of heterotrophs; many obtain energy and nutrients from dead organic matter
gametangium
gamete-producing structure found in black bread mold
gamete
specialized cell involved in sexual reproduction
gametophyte
haploid, or gamete-producing, phase of an organism
ganglion
group of nerve cells
gastrovascular cavity
digestive chamber with a single opening, in which cnidarians, flatworms, and echinoderms digest food
gastrulation
process of cell migration by which a third layer of cells is formed within the cavity of a blastocyst
gel electrophoresis
procedure used to separate and analyze DNA fragments by placing a mixture of DNA fragments at one end of a porous gel and applying an electrical voltage to the gel
gemma
small cup-shaped structure in liverworts that contains many haploid cells; used for asexual reproduction
gemmule
group of archaeocytes surrounded by a tough layer of spicules; produced by some sponges
gene
sequence of DNA that codes for a protein and thus determines a trait
gene map
diagram showing the relative locations of each known gene on a particular chromosome
gene pool
"combined genetic information of all the members of a particular population
genetic diversity
sum total of all the different forms of genetic information carried by all organisms living on Earth today
genetic drift
random change in allele frequencies that occurs in small populations
genetic engineering
process of making changes in the DNA code of living organisms
genetic equilibrium
situation in which allele frequencies remain constant
genetic marker
gene that makes it possible to distinguish bacteria that carry a plasmid with foreign DNA from those that don't
genetics
scientific study of heredity
genotype
genetic makeup of an organism
genus
group of closely related species, and the first part of the scientific name in binomial nomenclature
geographic isolation
form of reproductive isolation in which two populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water
geologic time scale
scale used by paleontologists to represent evolutionary time
germ theory of disease
idea that infectious diseases are caused by microorganisms, or germs
germination
early growth stage of a plant embryo
gibberellin
growth-promoting substance produced by plants
gill
filamentous organ in aquatic animals specialized for the exchange of gases with water
gizzard
in earthworms, part of the digestive system in which food is ground into smaller pieces; in birds, a muscular organ that helps in the mechanical breakdown of food
global warming
increase in the average temperatures on Earth
glomerulus
small network of capillaries encased in the upper end of a nephron; where the filtration of blood takes place
glycolysis
first step in releasing the energy of glucose, in which a molecule of glucose is broken into two molecules of pyruvic acid
Golgi apparatus
stack of membranes in the cell that modifies, sorts, and packages proteins from the endoplasmic reticulum
grafting
use of a stem as a scion
gravitropism
response of a plant to the force of gravity
green revolution
the development of highly productive crop strains and the use of modern agricultural techniques to increase yields of food crops
greenhouse effect
natural situation in which heat is retained in Earth's atmosphere by carbon dioxide, methane, water vapor, and other gases
guard cell
specialized cell in the epidermis of plants that controls the opening and closing of stomata by responding to changes in water pressure
gullet
indentation in one side of a ciliate that allows food to enter the cell
gymnosperm
seed plant that bears its seeds directly on the surfaces of cones
habitat
the area where an organism lives, including the biotic and abiotic factors that affect it
habitat fragmentation
splitting of ecosystems into small fragments
habituation
learning process by which an animal decreases or stops its response to a repetitive stimulus that neither rewards nor harms it
hair follicle
tubelike pocket of epidermal cells that extends into the dermis; cells at the base of hair follicles produce hair
half-life
length of time required for half of the radioactive atoms in a sample to decay
haploid
term used to refer to a cell that contains only a single set of chromosomes and therefore only a single set of genes
Hardy-Weinberg principle
principle that allele frequencies in a population will remain constant unless one or more factors cause the frequencies to change
Haversian canal
one of a network of tubes running through compact bone that contains blood vessels and nerves
heartwood
older xylem near the center of a woody stem that no longer conducts water
hemoglobin
iron-containing protein in red blood cells that transports oxygen from the lungs to the tissues of the body
herbicide
compound that is toxic to plants
herbivore
organism that obtains energy by eating only plants
hermaphrodite
individual that has both male and female reproductive organs
heterotroph
organism that obtains energy from the foods it consumes; also called a consumer
heterozygous
term used to refer to an organism that has two different alleles for the same trait
histamine
chemical released by activated mast cells that increases the flow of blood and fluids to the surrounding area
histone
protein molecule around which DNA is tightly coiled in chromatin
homeostasis
process by which organisms maintain a relatively stable internal environment
hominid
primate that walks upright, has opposable thumbs, and possesses a large brain; only living members are humans
hominoid
anthropoid group that includes apes and humans
homologous
term used to refer to chromosomes that each have a corresponding chromosome from the opposite-sex parent
homologous structures
structures that have different mature forms in different organisms but develop from the same embryonic tissues
homozygous
term used to refer to an organism that has two identical alleles for a particular trait
hormone
substance produced in one part of an organism that affects another part of the same organism
hox genes
series of genes that controls the differentiation of cells and tissues in an embryo
humoral immunity
immunity against antigens and pathogens in the body fluids
humus
material formed from decaying leaves and other organic matter
hybrid
offspring of crosses between parents with different traits
hybridization
breeding technique that involves crossing dissimilar individuals to bring together the best traits of both organisms
hydrostatic skeleton
layers of circular and longitudinal muscles, together with the water in the gastrovascular cavity, that enable movement
hypertonic
when comparing two solutions, the solution with the greater concentration of solutes
hypha
tiny filament that makes up a multicellular fungus or a water mold
hypothalamus
brain structure that acts as a control center for recognition and analysis of hunger, thirst, fatigue, anger, and body temperature
hypothesis
possible explanation for a set of observations or possible answer to a scientific question
hypotonic
when comparing two solutions, the solution with the lesser concentration of solutes
immigration
movement of individuals into an area occupied by an existing population
immune response
the body's specific defenses that attack a disease-causing agent
immunity
ability of the body to resist a specific pathogen
implantation
process in which a blastocyst attaches itself to the wall of the uterus
imprinting
learning based on early experience; once imprinting has occurred, the behavior cannot be changed
inbreeding
continued breeding of individuals with similar characteristics to maintain the desired characteristics of a line of organisms
incomplete dominance
situation in which one allele is not completely dominant over another
incomplete metamorphosis
type of insect development characterized by a similar appearance throughout all stages of the life cycle
independent assortment
independent segregation of genes during the formation of gametes
independent variable
factor in an experiment that a scientist purposely changes; also known as a responding variable
index fossil
distinctive fossil used to compare the relative ages of fossils
inference
logical interpretation based on prior knowledge and experience
inflammatory response
nonspecific defense reaction to tissue damage caused by injury or infection
innate behavior
instinct, or inborn behavior; behavior that appears in a fully functional form the first time it is performed
insight learning
also called reasoning; learning process in which an animal applies something it has already learned to a new situation without a period of trial and error
interferon
one of a group of proteins that help cells resist viral infection
internal fertilization
process in which eggs are fertilized inside the female's body
internode
region between nodes on plant stems
interphase
period of the cell cycle between cell divisions
intracellular digestion
process in which food is digested inside cells
intron
sequence of DNA that is not involved in coding for a protein
invasive species
plants and animals that have migrated to places where they are not native
invertebrate
animal that does not have a backbone or vertebral column
ion
atom that has a positive or negative charge
ionic bond
bond formed when one or more electrons are transferred from one atom to another
isotonic
when the concentration of two solutions is the same
isotope
atom of an element that has a number of neutrons different from that of other atoms of the same element
joint
place where one bone attaches to another
karyotype
photograph of chromosomes grouped in order in pairs
kelp forest
coastal ocean community named for its dominant organism—kelp, a giant brown alga
keratin
tough, fibrous protein found in skin
kidney
organ that removes urea, excess water, and other waste products from the blood and passes them to the ureter
kingdom
large taxonomic group, consisting of closely related phyla
Koch's postulates
series of guidelines used to identify the microorganism that causes a specific disease
Krebs cycle
second stage of cellular respiration, in which pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions
language
system of communication that combines sounds, symbols, or gestures according to a set of rules about word order and meaning
large intestine
colon; organ that removes water from the undigested materials that pass through it
larva
immature stage of an organism that looks different from the adult form
larynx
structure in the throat containing the vocal cords
lateral bud
meristematic area on the side of a stem that gives rise to side branches
lateral line system
sensitive receptor system that enables fish to detect gentle currents and vibrations in the water
leaf
photosynthetic organ that contains one or more bundles of vascular tissue
learning
alterations in behavior as a result of experience; also called acquired behavior
lens
transparent object behind the iris that changes shape to help adjust the eye's focus to see near or distant objects
lichen
symbiotic association between a fungus and a photosynthetic organism
ligament
strip of tough connective tissue that holds bones together at a joint
light-dependent reactions
reactions of photosynthesis that use energy from light to produce ATP and NADPH
lignin
substance in vascular plants that makes cell walls rigid
limiting factor
factor that causes the growth of a population to decrease
limiting nutrient
single nutrient that either is scarce or cycles very slowly, limiting the growth of organisms in an ecosystem
lipid
macromolecule made mainly from carbon and hydrogen atoms; includes fats, oils, and waxes
lipid bilayer
double-layered sheet that forms the core of nearly all cell membranes
liver
large organ just above the stomach that produces bile, a fluid loaded with lipids and salts
logistic growth
growth pattern in which a population's growth rate slows or stops following a period of exponential growth
long-day plant
plant that flowers when days are long
loop of Henle
section of the nephron tubule that conserves water and minimizes the volume of urine
lymph
fluid lost by the blood into surrounding tissue
lymphocyte
type of white blood cell that produces antibodies that help destroy pathogens
lysogenic infection
process by which a virus embeds its DNA into the DNA of the host cell and is replicated along with the host cell's DNA
lysosome
cell organelle filled with enzymes needed to break down certain materials in the cell
lytic infection
process in which a virus enters a cell, makes a copy of itself, and causes the cell to burst
macroevolution
large-scale evolutionary changes that take place over long periods of time
macronucleus
the larger of a ciliate's two nuclei, contains multiple copies of most of the genes that the cell needs in its day-to-day existence
madreporite
sievelike structure through which the water vascular system of an echinoderm opens to the outside
Malpighian tubule
saclike organ in most terrestrial arthropods that extracts wastes from the blood, adding them to feces that move through the gut
mammary gland
gland in mammals that produces milk to nourish the young
mandible
mouthpart adapted for biting and grinding food
mangrove swamp
coastal wetland dominated by mangroves, salt-tolerant woody plants
manipulated variable
factor in an experiment that a scientist purposely changes; also known as independent variable
mantle
thin layer of tissue that covers most of a mollusk's body
marsupial
mammal which bears live young that complete their development in an external pouch
mass extinction
event in which many types of living things become extinct at the same time
medulla oblongata
area of the brain that controls the functioning of many internal organs
medusa
motile stage of the life cycle of a cnidarian that has a bell-shaped body
meiosis
process by which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell
melanin
dark-brown pigment found in skin
meninges
three layers of connective tissue in which the brain and spinal cord are wrapped
menstrual cycle
cycle during which an egg develops and is released from an ovary and the uterus is prepared to receive a fertilized egg
menstruation
phase of the menstrual cycle during which the lining of the uterus, along with blood and the unfertilized egg, is discharged through the vagina
meristem
cluster of tissue that is responsible for continuing growth throughout a plant's lifetime
meristematic tissue
plant tissue found only in the tips of shoots and roots; responsible for plant growth
mesoderm
middle germ layer of most animals; gives rise to muscles and much of the circulatory, reproductive, and excretory systems
mesophyll
specialized ground tissue that makes up the bulk of most leaves; performs most of a plant's photosynthesis
messenger RNA (mRNA)
RNA molecule that carries copies of instructions for the assembly of amino acids into proteins from DNA to the rest of the cell
metabolism
set of chemical reactions through which an organism builds up or breaks down materials as it carries out its life processes
metaphase
second phase of mitosis, during which the chromosomes line up across the center of the cell
metric system
decimal system of measurement based on certain physical standards and scaled on multiples of 10
microclimate
climate within a small area that differs significantly from the climate of the surrounding area
microfossil
microscopic fossil
micronucleus
the smaller of a ciliate's two nuclei; contains a "reserve copy" of all of the cell's genes
microscope
device that produces magnified images of structures that are too small to see with the unaided eye
migration
periodic movement and return of animals from one place to another
mineral
inorganic nutrient the body needs, usually in small amounts
mitochondrion
cell organelle that converts the chemical energy stored in food into compounds that are more convenient for the cell to use
mitosis
part of eukaryotic cell division during which the cell nucleus divides
mixture
material composed of two or more elements or compounds that are physically mixed together but not chemically combined
molecular clock
model that uses DNA comparisons to estimate the length of time that two species have been evolving independently
molecule
smallest unit of most compounds
molting
process in which an arthropod sheds its exoskeleton and manufactures a larger one to take its place
monocot
angiosperm whose seeds have one cotyledon
monoculture
farming strategy in which large fields are planted with a single crop, year after year
monomer
small unit that can join together with other small units to form polymers
monosaccharide
single sugar molecule
monotreme
egg-laying mammal
multiple alleles
three or more alleles of the same gene
muscle tissue
"tissue that controls the internal movement of materials in the body, as well as external movement
mutation
change in a DNA sequence that affects genetic information
mutualism
symbiotic relationship in which both species benefit from the relationship
mycelium
many hyphae tangled together into a thick mass; comprises the bodies of multicellular fungi
mycorrhiza
symbiotic association of plant roots and fungi
myelin sheath
insulating membrane surrounding the axon in some neurons
myocardium
thick middle muscle layer of the heart; pumps blood through the circulatory system
myosin
protein that makes up the thick filaments in striations in skeletal muscle cells
NAD+ (nicotinamide adenine dinucleotide)
electron carrier involved in glycolysis
NADP+ (nicotinamide adenine dinucleotide phosphate)
one of the carrier molecules that transfers high-energy electrons from chlorophyll to other molecules
natural selection
process by which individuals that are better suited to their environment survive and reproduce most successfully; also called survival of the fittest
nematocyst
stinging structure within each cnidocyte of a cnidarian that is used to poison or kill prey
nephridium
excretory organ of an annelid that filters fluid in the coelom
nephron
"blood-filtering unit in the renal cortex of the kidney
nerve net
loosely organized network of nerve cells that together allow cnidarians to detect stimuli
nervous tissue
tissue that receives messages from the body's external and internal environment, analyzes the data, and directs the response
neuromuscular junction
point of contact between a motor neuron and a skeletal muscle cell
neuron
cell that carries messages throughout the nervous system
neurotransmitter
chemical used by a neuron to transmit an impulse across a synapse to another cell
neurulation
development of the nervous system
niche
full range of physical and biological conditions in which an organism lives and the way in which the organism uses those conditions
nicotine
stimulant drug in tobacco that increases heart rate and blood pressure
nictitating membrane
movable transparent membrane in amphibians located inside the regular eyelid; protects the surface of the eye from damage under water and keeps it moist on land
nitrogen fixation
process of converting nitrogen gas into ammonia
node
point on a stem where a leaf is attached
nondisjunction
error in meiosis in which homologous chromosomes fail to separate
nonrenewable resource
resource that cannot be replenished by natural processes
notochord
long supporting rod that runs through a chordate's body just below the nerve cord
nuclear envelope
layer of two membranes that surrounds the nucleus of a cell
nucleic acid
macromolecule containing hydrogen, oxygen, nitrogen, carbon, and phosphorus
nucleolus
small, dense region within most nuclei in which the assembly of proteins begins
nucleotide
monomer of nucleic acids made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base
nucleus
the center of the atom which contains the protons and neutrons; in cells, structure that contains the cell's genetic material (DNA) and controls the cell's activities
nutrient
chemical substance that an organism requires to live
nymph
immature form that lacks functional sex organs and other adult structures
obligate aerobe
organism that requires a constant supply of oxygen in order to live
obligate anaerobe
organism that cannot live in the presence of oxygen
observation
use of one or more of the senses—sight, hearing, touch, smell, and sometimes taste—to gather information
omnivore
organism that obtains energy by eating both plants and animals
oogonium
specialized structure formed by hyphae that produces female nuclei
open circulatory system
system in which blood is not always contained within a network of blood vessels
operant conditioning
learning process in which an animal learns to behave in a certain way through repeated practice, in order to receive a reward or avoid punishment; also called trial-and-error learning
operational definition
description of how a particular variable is to be measured or how a term is to be defined
operator
region of chromosome in an operon to which the repressor binds when the operon is "turned off"
operon
group of genes operating together
opposable thumb
thumb that enables grasping objects and using tools
order
group of similar families
organ
group of tissues that work together to perform closely related functions
organ system
group of organs that work together to perform a specific function
organelle
specialized structure that performs important cellular functions within a eukaryotic cell
osculum
large hole at the top of the sponge through which water leaves the sponge
osmosis
diffusion of water through a selectively permeable membrane
ossification
process of bone formation, during which cartilage is replaced by bone
ovary
in plants, a flower structure that contains one or more ovules from which female gametophytes are produced; in animals, the female gonad that produces eggs
oviparous
term used to refer to animals whose eggs hatch outside the mother's body
ovoviviparous
term used to refer to animals whose young are born alive after developing in eggs inside the mother's body
ovulation
process in which an egg is released from the ovary
ovule
structure in seed cones in which female gametophytes develop
ozone layer
atmospheric layer in which ozone gas is relatively concentrated
pacemaker
small group of cardiac muscle cells in the right atrium that "set the pace" for the heart as a whole; also known as the sinoatrial node
paleontologist
scientist who studies fossils
palisade mesophyll
layer of tall, column-shaped mesophyll cells just under the upper epidermis of a leaf
pancreas
gland that produces hormones that regulate blood sugar; produces enzymes that break down carbohydrates, proteins, lipids, and nucleic acids; and produces sodium bicarbonate, a base that neutralizes stomach acid
parasite
organism that lives within or on another organism and harms that organism by feeding on it
parasitism
symbiotic relationship in which one organism lives in or on another organism (the host) and consequently harms it
parenchyma
type of ground-tissue cell with a thin cell wall and large central vacuole
passive immunity
short-term immunity caused when antibodies produced by other animals for a pathogen are injected into the body
pathogen
disease-causing agent
pedigree
chart that shows the relationships within a family
pedipalps
pair of mouthparts in chelicerates that are usually modified to grab prey
pellicle
cell membrane in euglenas
penis
external male reproductive organ
perennial
flowering plant that lives for more than two years
period
unit of time into which eras are subdivided
periosteum
tough layer of connective tissue surrounding a bone
peristalsis
rhythmic muscular contractions that squeeze food through the esophagus into the stomach
permafrost
layer of permanently frozen subsoil in the tundra
petal
brightly colored structure just inside the sepals; attracts insects and other pollinators to a flower
petiole
thin stalk by which a leaf blade is attached to a stem
pH scale
measurement system used to indicate the concentration of hydrogen ions (H+) in solution; ranges from 0 to 14
phagocyte
white blood cell that engulfs and digests foreign cells
phagocytosis
process in which extensions of cytoplasm surround and engulf large particles and take them into the cell
pharyngeal pouch
one of a pair of structures in the throat (pharynx) region of a chordate
pharynx
muscular tube at the end of the gastrovascular cavity, or throat, that connects the mouth with the rest of the digestive tract and serves as a passageway for air and food
phenotype
physical characteristics of an organism
pheromone
specific chemical messenger that affects the behavior or development of other individuals of the same species
phloem
vascular tissue responsible for the transport of nutrients and the carbohydrates produced by photosynthesis
photic zone
well-lit upper layer of the oceans
photoautotroph
organism that uses energy from sunlight to convert carbon dioxide and water to carbon compounds
photoheterotroph
organism that is photosynthetic but needs organic compounds as a carbon source
photoperiodism
response of plants to periods of light and darkness
photosynthesis
process by which plants and some other organisms use light energy to convert water and carbon dioxide into oxygen and high-energy carbohydrates such as sugars and starches
photosystem
light-collecting units of the chloroplast
phototropism
tendency of plants to grow toward a source of light
phycobilin
accessory pigment found in red algae that is especially good at absorbing blue light
phylogeny
the study of evolutionary relationships among organisms
phylum
group of closely related classes
phytochrome
plant pigment responsible for photoperiodism
phytoplankton
population of algae and other small, photosynthetic organisms found near the surface of the ocean and forming part of plankton
pigment
light-absorbing molecule
pinocytosis
process by which a cell takes in liquid from the surrounding environment
pioneer species
first species to populate an area during primary succession
pith
parenchyma cells inside the ring of vascular tissue in dicot stems
pituitary gland
gland in the base of the skull that secretes nine hormones that directly regulate many body functions and control the actions of several other endocrine glands
placenta
organ in placental mammals through which nutrients, oxygen, carbon dioxide, and wastes are exchanged between embryo and mother
plankton
tiny, free-floating organisms that occur in aquatic environments
Plantae
kingdom of multicellular photosynthetic autotrophs that have cell walls containing cellulose
plasma
straw-colored fluid that makes up about 55 percent of blood
plasmid
small circular piece of DNA
plasmodium
structure with many nuclei formed by acellular slime molds
plastron
ventral part of a turtle's or tortoise's shell
platelet
cell fragment released by bone marrow that helps in blood clotting
point mutation
gene mutation involving changes in one or a few nucleotides
polar zone
cold climate zone where the sun's rays strike Earth at a very low angle
pollen cone
cone in gymnosperms that produces male gametophytes in the form of pollen grains
pollen grain
male gametophyte in seed plants
pollen tube
structure grown by a pollen grain; contains two haploid sperm nuclei
pollination
transfer of pollen from the male reproductive structure to the female reproductive structure
pollutant
harmful material that can enter the biosphere through the land, air, or water
polygenic trait
trait controlled by two or more genes
polymer
large compound formed from combinations of many monomers
polymerase chain reaction (PCR)
technique that allows molecular biologists to make many copies of a particular gene
polyp
usually sessile stage of the life cycle of a cnidarian that has a cylindrical body with armlike tentacles
polyploidy
condition in which an organism has extra sets of chromosomes
polysaccharide
large macromolecule formed from monosaccharides
population
group of individuals of the same species that live in the same area
population density
number of individuals per unit of area
predation
interaction in which one organism captures and feeds on another organism
predator-prey relationship
mechanism of population control in which a population is regulated by predation
prehensile
term used to refer to a long tail that can grasp branches
pressure-flow hypothesis
hypothesis that considers plants in terms of where they produce and use materials from photosynthesis
primary growth
type of plant growth that occurs at the tips of roots and shoots
primary productivity
rate at which organic matter is created by producers in an ecosystem
primary succession
succession that occurs on surfaces where no soil exists
prion
infectious particle made up of protein rather than RNA or DNA
probability
likelihood that a particular event will occur
producer
organism that can capture energy from sunlight or chemicals and use it to produce food from inorganic compounds; also called an autotroph
product
element or compound produced by a chemical reaction
proglottid
one of the segments that make up most of a tapeworm's body
prokaryote
unicellular organism lacking a nucleus
promoter
region of DNA that indicates to an enzyme where to bind to make RNA
prophage
the viral DNA that is embedded in the host cell's DNA
prophase
first and longest phase of mitosis, during which the chromosomes become visible and the centrioles separate and take up positions on the opposite sides of the nucleus
prosimian
with few exceptions, small, nocturnal primate that has large eyes for seeing in the dark
prostaglandin
hormonelike modified fatty acid produced by a wide range of cells; generally affects only nearby cells and tissues
protein
macromolecule that contains carbon, hydrogen, oxygen, and nitrogen; needed by the body for growth and repair and to make up enzymes
proteinoid microsphere
tiny bubble, formed of large organic molecules, that has some characteristics of a cell
protist
any eukaryote that is not a plant, an animal, or a fungus
Protista
kingdom composed of eukaryotes that are not classified as plants, animals, or fungi
protonema
mass of tangled green filaments in mosses that forms during germination
protostome
animal whose mouth is formed from its blastopore
pseudocoelom
body cavity between the endoderm and mesoderm tissues that is partially lined with mesoderm tissue
pseudopod
temporary projection of cytoplasm, or a "false foot," used by some protists for feeding or movement
puberty
period of rapid growth and sexual maturation during which the reproductive system becomes fully functional
pulmonary circulation
pathway of circulation between the heart and the lungs
punctuated equilibrium
pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change
Punnett square
diagram showing the gene combinations that might result from a genetic cross
pupa
stage of metamorphosis in which an insect changes from a larva into an adult
pupil
small opening in the middle of the iris through which light enters the eye
radial symmetry
body plan in which body parts repeat around the center of the body; characteristic of sea anemones and sea stars
radioactive dating
technique in which scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains
radula
tongue-shaped structure used for feeding by snails and slugs
reabsorption
process in which liquid is taken back into a vessel
reactant
element or compound that enters into a chemical reaction
recombinant DNA
DNA produced by combining DNA from different sources
reflex
quick automatic response to a stimulus
reflex arc
sensory receptor, sensory neuron, motor neuron, and effector that are involved in a quick response to a stimulus
relative dating
method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock
relative frequency
number of times an allele occurs in a gene pool compared with the number of times other alleles occur
renewable resource
resource that can regenerate quickly and that is replaceable
replication
copying process by which a cell duplicates its DNA
reproductive isolation
separation of species or populations so that they cannot interbreed and produce fertile offspring
reptile
any vertebrate that has dry scaly skin, lungs, and terrestrial eggs with several protective membranes
resource
any necessity of life, such as water, nutrients, light, food, or space
responding variable
factor in an experiment that a scientist wants to observe, which may change in response to the manipulated variable; also known as a dependent variable
response
single, specific reaction to a stimulus
resting potential
electrical charge across the cell membrane of a resting neuron
restriction enzyme
enzyme that cuts DNA at a specific sequence of nucleotides
retina
innermost layer of the eye; contains photoreceptors
retrovirus
virus that contains RNA as its genetic information
rhizoid
in fungi, a rootlike hypha that penetrates the surface of an object; in mosses, a long, thin cell that anchors the moss to the ground and absorbs water and minerals from the surrounding soil
rhizome
creeping or underground stem in ferns
ribonucleic acid (RNA)
single-stranded nucleic acid that contains the sugar ribose
ribosomal RNA (rRNA)
type of RNA that makes up the major part of ribosomes
ribosome
small particle in the cell on which proteins are assembled; made of RNA and protein
risk factor
anything that increases the chance of disease or injury
RNA polymerase
enzyme similar to DNA polymerase that binds to DNA and separates the DNA strands during transcription
rod
photoreceptor in eye that is sensitive to light but not to colors
root
underground organ in plants that absorbs water and minerals
root cap
tough structure that protects a root as it forces its way through the soil
root hair
tiny projection from the outer surface, or epidermis, of a root
rumen
stomach chamber in cows and related animals in which newly swallowed plant food is stored and processed
salt marsh
temperate-zone estuary dominated by salt-tolerant grasses above the low-tide line and by seagrasses under water
saprobe
organism that obtains food from decaying organic matter
sapwood
area in plants that surrounds heartwood and is active in fluid transport
science
organized way of using evidence to learn about the natural world; also, the body of knowledge that scientists have built up after years of using this process
sclerenchyma
type of ground-tissue cell with an extremely thick, rigid cell wall that makes ground tissue tough and strong
scolex
head of an adult tapeworm; can contain suckers or hooks
scrotum
external sac containing the testes
secondary growth
pattern of plant growth in which stems increase in width
secondary succession
succession following a disturbance that destroys a community without destroying the soil
seed
embryo of a living plant that is encased in a protective covering and surrounded by a food supply
seed coat
structure that surrounds and protects a plant embryo and keeps it from drying out
seed cone
cone that produces female gametophytes
segregation
separation of alleles during gamete formation
selective breeding
method of breeding that allows only those individual organisms with desired characteristics to produce the next generation
semicircular canal
one of three structures within the inner ear that help monitor the position of the body
seminiferous tubule
one of hundreds of tiny tubules in the testes in which sperm are produced
sensory receptor
neuron that reacts to a specific stimulus, such as light or sound, by sending impulses to other neurons and eventually to the central nervous system
sepal
outermost circle of flower parts that encloses a bud before it opens and protects the flower while it is developing
septum
internal wall between the segments of an annelid's body
seta
bristle attached to the segments of many annelids
sex chromosome
one of two chromosomes that determine an individual's sex; females have two X chromosomes; males have one X chromosome and one Y chromosome
sex-linked gene
gene located on the X or Y chromosome
sexual reproduction
process by which cells from two different parents unite to produce the first cell of a new organism
sexually transmitted disease (STD)
disease spread from one person to another during sexual contact
shell
structure in mollusks made by glands in the mantle that secrete calcium carbonate
short-day plant
plant that flowers when daylight is short
sieve tube element
phloem cell that is joined end-to-end to similar cells to form a continuous sieve tube
single-gene trait
trait controlled by a single gene that has two alleles
siphon
tubelike structure through which water enters and leaves a mollusk's body
small intestine
digestive organ in which most chemical digestion takes place
smog
mixture of chemicals that occurs as a gray-brown haze in the atmosphere
society
group of closely related animals of the same species that work together for the benefit of the group
soil erosion
wearing away of surface soil by water and wind
solute
substance that is dissolved in a solvent to make a solution
solution
mixture of two or more substances in which the molecules of the substances are evenly distributed
solvent
substance in which a solute is dissolved to form a solution
sorus
cluster of sporangia on the underside of a fern frond
specialized cell
cell that is uniquely suited to performing a particular function
speciation
formation of new species
species
group of similar organisms that can breed and produce fertile offspring
species diversity
number of different species in the biosphere
spicule
spike-shaped structure that makes up the skeletons of harder sponges; made of either chalklike calcium carbonate or glasslike silica
spindle
fanlike microtubule structure that helps separate the chromosomes during mitosis
spinneret
organ in spiders that contains silk glands
spiracle
small opening located along the side of the body through which air enters and leaves the body of many terrestrial arthropods
spirillum
spiral or corkscrew-shaped prokaryote
spongy mesophyll
loose tissue beneath the palisade layer of a leaf; has many air spaces between its cells
spontaneous generation
hypothesis (disproven) stating that life could arise from nonliving matter
sporangiophore
specialized hyphae where sporangia are found
sporangium
structure in ferns and some fungi that contains spores
spore
haploid reproductive cell
sporophyte
diploid, or spore-producing, phase of an organism
stabilizing selection
form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end
stamen
male part of the flower; made up of an anther and a filament
stem
supporting structure that connects roots and leaves and carries water and nutrients between them
stigma
sticky portion at the top of the style where pollen grains frequently land
stimulant
drug that speeds up the actions regulated by the nervous system
stimulus
a signal to which an organism responds
stolon
in fungi, a stemlike hypha that runs along the surface of an object; in plants, a long, trailing stem that produces roots when it touches the ground
stoma
opening in the underside of a leaf that allows carbon dioxide and oxygen to diffuse into and out of the leaf
stomach
large muscular sac that continues the mechanical and chemical digestion of food
stroma
region outside the thylakoid membranes in chloroplasts
struggle for existence
competition among members of a species for food, living space, and the other necessities of life
style
narrow stalk of the carpel in a flower
subcutaneous fat
layer of fat cells beneath the skin that helps conserve body heat
substrate
reactant of an enzyme-catalyzed reaction
survival of the fittest
process by which individuals that are better suited to their environment survive and reproduce most successfully; also called natural selection
suspension
mixture of water and nondissolved materials
sustainable development
using natural resources at a rate that does not deplete them
swim bladder
internal gas-filled organ in many bony fishes that adjusts their buoyancy
swimmerets
flipperlike appendages used by decapods for swimming
symbiosis
relationship in which two species live closely together
synapse
location at which a neuron can transfer an impulse to another cell
systemic circulation
pathway of circulation between the heart and the rest of the body except the lungs
taiga
biome in which the winters are cold but summers are mild enough to allow the ground to thaw
taproot
primary root found in some plants that grows longer and thicker than other roots
target cell
cell that has a receptor for a particular hormone
taste bud
sense organ that detects the flavor of a substance
taxon
group or level of organization into which organisms are classified
taxonomy
discipline of classifying organisms and assigning each organism a universally accepted name
telophase
fourth and final phase of mitosis, during which the chromosomes begin to disperse into a tangle of dense material
temperate zone
moderate climate zone between the polar zones and the tropics
temporal isolation
form of reproductive isolation in which two populations reproduce at different times
tendon
tough connective tissue that joins skeletal muscles to bones
territory
specific area occupied and protected by an animal or group of animals
testis
male gonad that produces sperm
tetrad
structure containing 4 chromatids that forms during meiosis
thalamus
brain structure that receives messages from the sense organs and relays the information to the proper region of the cerebrum for further processing
theory
well-tested explanation that unifies a broad range of observations
thigmotropism
response of plants to touch
thorax
body part of a crustacean that lies just behind the head and houses most of the internal organs
threshold
minimum level of a stimulus required to activate a neuron
thylakoid
saclike photosynthetic membrane found in chloroplasts
tissue
group of similar cells that perform a particular function
tolerance
organism's capacity to grow or thrive when subjected to an unfavorable environmental factor
trachea
windpipe; tube through which air moves
tracheal tube
one of many branching, air-filled tubes that extend throughout the bodies of many terrestrial arthropods
tracheid
hollow plant cell in xylem tissue with thick cell walls that resist pressure
trait
specific characteristic that varies from one individual to another
transcription
process in which part of the nucleotide sequence of DNA is copied into a complementary sequence in RNA
transfer RNA (tRNA)
type of RNA molecule that transfers amino acids to ribosomes during protein synthesis
transformation
process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria
transgenic
term used to refer to an organism that contains genes from other organisms
translation
decoding of a mRNA message into a polypeptide chain
transpiration
loss of water from a plant through its leaves
trichocyst
small, bottle-shaped structure used for defense by paramecia
trichome
tiny cellular projection on the surfaces of some leaves that helps protect the leaf and also gives it a fuzzy appearance
trochophore
free-swimming larval stage of an aquatic mollusk
trophic level
step in a food chain or food web
tropical zone
warm climate zone that receives direct or nearly direct sunlight year round
tropism
response of a plant to an external stimulus
true-breeding
term used to describe organisms that produce offspring identical to themselves if allowed to self-pollinate
tube foot
suction-cuplike structure attached to radial canals of echinoderms; used to walk and to open shells
tumor
mass of growing tissue
tympanic membrane
eardrum of amphibians inside the skull; vibrates in response to sound, allowing hearing
understory
layer in a rain forest formed by shorter trees and vines
ureter
tube that carries urine from the kidney to the urinary bladder
urethra
tube that carries urine from the bladder and releases it from the body; in males, tube through which semen is released from the body
urinary bladder
saclike organ in which urine is stored before being excreted
uterus
organ of the female reproductive system in which a fertilized egg can develop
vaccination
injection of a weakened or mild form of a pathogen to produce immunity
vaccine
a preparation of weakened or killed pathogens
vacuole
cell organelle that stores materials such as water, salts, proteins, and carbohydrates
vagina
in the human female reproductive system, a canal that leads from the uterus to the outside of the body
valve
flap of connective tissue between an atrium and a ventricle, or in a vein, that prevents backflow of blood
van der Waals forces
a slight attraction that develops between the oppositely charged regions of nearby molecules
variable
factor in an experiment that can change
vas deferens
tube that carries sperm from the epididymis to the urethra
vascular bundle
plant stem structure that contains xylem and phloem tissue
vascular cambium
lateral meristematic tissue that produces vascular tissues and increases the thickness of the stem over time
vascular cylinder
central region of a root that includes the vascular tissue—xylem and phloem
vascular tissue
type of plant tissue specialized to conduct water and nutrients throughout a plant
vector
animal that carries pathogens from person to person
vegetative reproduction
method of asexual reproduction used by many flowering plants
vein
in plants, a cluster of vascular tissue in leaves; in animals, a blood vessel that returns blood to the heart
ventricle
lower chamber of the heart that pumps blood out of the heart
vertebra
individual segment of the backbone; encloses and protects the spinal cord
vertebrate
animal that has a vertebral column, or backbone
vessel element
in angiosperms, xylem cell that forms part of a continuous tube through which water can move
vestigial organ
organ that serves no useful function in an organism
villus
folded projection that increases the surface area of the walls of the small intestine
viroid
single-stranded RNA molecule that has no surrounding capsids
virus
particle made up of nucleic acid, protein, and in some cases lipids that can replicate only by infecting living cells
visceral mass
area beneath the mantle of a mollusk that contains the internal organs
vitamin
organic molecule that helps regulate body processes
viviparous
term used to refer to animals that bear live young that are nourished directly by the mother's body as they develop
water vascular system
system of internal tubes in echinoderms that carries out essential functions such as feeding, respiration, circulation, and movement
weather
condition of Earth's atmosphere at a particular time and place
wetland
ecosystem in which water either covers the soil or is present at or near the surface of the soil for at least part of the year
xerophyte
plant that lives in the desert biome
xylem
vascular tissue that carries water upward from the roots to every part of a plant
zonation
prominent horizontal banding of organisms that live in a particular habitat
zooplankton
tiny animals that form part of the plankton
zoosporangium
spore case
zygospore
resting spore that contains zygotes formed during the sexual phase of a mold's life cycle
zygote
fertilized egg