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A
abiotic factors: nonliving physical features of the
environment, including soil, water,
temperature, air, light, wind, and minerals.
acid rain: rain or snow with a pH below 5.6; formed
when water vapor reacts with sulfur oxides
and nitrogen oxides in the air to form strong
acids.
active transport: movement of material through a
cell membrane with the use of energy.
adaptation: any characteristic of an organism that
makes it better able to survive in its
environment.
anaerobe: organism that can survive without
oxygen.
angiosperm: a flower-producing vascular plant in
which the seed is enclosed in a fruit, such as
an apple.
antibiotic: a substance produced by an organism
that is used to kill or inhibit another
organism.
antibiotic resistance: in bacteria, the evolutionary
change that occurs when bacterial strains
that are mostly killed by a specific drug
mutate into strains that are not affected by
that drug.
aerobe: organism that must have oxygen to survive.
antibody: a protein made by the body in response to
a specific antigen.
aggression: a forceful act used to dominate or
control another animal.
antigens: proteins and chemicals that are foreign to
the body.
algae: plantlike protists that contain chlorophyll and
make their own food; they have no roots,
stems, or leaves and live in or near water.
antiseptic: a substance that kills pathogens on living
tissue and helps prevent their regrowth.
allele: a different form a gene may have for a trait.
anus: an opening at the end of the digestive tract
through which solid wastes leave the body.
alternation of generations: in some protists and in
plants, a continuous cycle that alternates
between sporophyte and gametophyte
generations.
alveoli: in the lungs, clusters of tiny, thin walled air
sacs at the end of each bronchiole, where
oxygen and carbon dioxide are exchanged.
amino acids: the building blocks of proteins.
amniotic egg: in reptiles, the leathery egg that
provides a complete environment for the
developing embryo.
amniotic sac: a thin membrane that forms around
an embryo, filled with amniotic fluid (a clear
liquid that cushions the embryo).
amphibian: ectothermic vertebrate that spends part
of its life in water and part on land;
examples are frogs, toads, and salamanders.
appendage: a structure growing from the body, such
as an arm or a leg.
archaebacteria: prokaryotic, one-celled organisms
that live as anaerobes in extreme
environments, including salt ponds, hot
sulfur springs, and deep ocean thermal
vents.
artery: a thick, elastic-walled vessel that moves
blood away from the heart.
Arthropoda: largest animal phylum, classified by the
number of body segments and appendages;
includes insects, shrimp, spiders, and
centipedes.
ascus: the small, saclike structure in which sac fungi
produce spores.
asexual reproduction: a type of reproduction in
which a new organism is produced from one
parent.
bladder: the bag-shaped, elastic, muscular organ
that stores urine until it leaves the body;
can hold up to 500mL of urine.
atherosclerosis: a circulatory system disorder in
which fatty deposits form on artery walls
and restrict blood flow.
blood pressure: the force exerted by blood on the
walls of the vessels; pressure is highest in
the arteries and in young adults is normally
120 over 80.
atria: the two up[per chambers of the human heart.
auxin: a plant hormone that causes plant stems and
leaves to grow or bend toward light.
axon: neuron structure that carries messages away
from the cell body.
B
basidium: the club-shaped, spore-producing
structure of club fungi.
behavior: the way an organism acts toward its
environment.
bilateral symmetry: describes animals with body
parts arranged in the same way on both
sides of their body.
bog: low-lying, spongy, wet ground compressed
mainly of dead plants, whose decay has
been slowed by lack of oxygen.
brain stem: the part of the brain extending from the
cerebrum to the spinal cord; controls and
coordinates involuntary muscle movements
such as heartbeats.
bronchi: two short tubes that branch off the trachea
and carry air into the lungs (singular:
bronchus).
budding: a type of asexual reproduction in which a
new organism grows off the side of its
parent.
C
binomial nomenclature: the two-word naming
system that provides every organism with its
own scientific name.
cambium: vascular plant tissue that produces new
xylem and phloem cells.
biological indicator: species whose health reflects
the health of its ecosystem.
cancer: a major chronic disease resulting from
uncontrolled cell growth.
biomass: organic material from plants or animals
that is used for energy.
capillary: a microscopic blood vessel that connects
arteries and veins; nutrients, oxygen, and
wastes are exchanged through their onecell-thick walls.
biomes: large geographic areas that have similar
climates and ecosystems.
biosphere: all parts of Earth where life exists,
including air, land, and water.
biotechnology: a method of improving crops by
moving DNA directly from one organism to
another.
biotic factors: living organisms in the environment,
such as plants and animals.
captive breeding: the breeding of an endangered
species in captivity.
carbohydrate: a nutrient that provides move of the
body’s energy; made up of carbon,
hydrogen, and oxygen.
cardiac muscle: involuntary muscle tissue found
only in the heart.
carnivore: an animal that eats only other animals.
carrying capacity: the largest number of individuals
that an environment can support and
maintain over time.
cartilage: a thick, tough, smooth flexible tissue that
is harder than flesh but softer than bone
(like your ears); it covers the ends of bones
to allow movement and cushion shock.
cell: the smallest unit of an organism that can
perform life functions.
cell membrane: the selectively permeable outer
boundary of a cell that allows food and
oxygen to move into the cell and wastes to
leave it.
cell theory: a major theory of life science: the cell is
the basic unit of life; organisms are made up
of one or more cells; and all cells come from
other cells.
cell wall: in plants, the rigid structure made of
cellulose that surrounds a plant cell
membrane and supports and protects it.
central nervous system: part of the body’s control
system, including the brain and spinal cord;
sorts and interprets information from
stimuli.
cerebellum: the part of the brain that coordinates
voluntary muscle movements: maintains
balance and muscle tone.
cerebrum: the part of the brain that interprets
impulses from the senses, stores memory,
and controls the work of voluntary muscles.
chemical digestion: chemical breakdown of food by
fluids in the mouth, stomach, and small
intestine; breaks down large molecules into
smaller ones that can be absorbed by cells.
chemotherapy: the use of chemicals to destroy
cancer cells.
chloroplasts: plant cell organelles in which light
energy is changed into chemical energy in
the form of sugar during the process of
photosynthesis.
chordate: a member of the animal phylum Chordata
that has a notochord, a dorsal hollow nerve
cord, and gill slits at some time in its life
cycle.
chromatin: hereditary material in a cell’s nucleus;
chromatin coils into the form of
chromosomes when a cell divides.
chromosome: threadlike strands of DNA and protein
in a cell nucleus that carry the code for the
cell characteristics of an organism.
chronic disease: a noncommunicable disease, such
as diabetes or cancer, that lasts a long time.
cilia: short, hairlike structures that extend from the
cell membrane and help tiny organisms
move; found in respiratory passages.
circadian rhythm: behavior on a 24-hour cycle.
class: third highest taxonomic category, below
phylum (animals) or division(plants).
classify: to group ideas, information, or objects
based on their similarities.
climax community: the final stage of a community’s
ecological succession; it is stable, with a
balance of abiotic and biotic factors.
clinical trial: a test performed on volunteers,
typically to test medicines, before the
products are made available to the public.
clone: an individual that is genetically identical to
one of its parents.
closed circulatory system: a type of bloodcirculation system in which vessels transport
blood to the internal organs, as in humans.
cnidarians: a phylum of hollow-bodied animals with
stinging cells.
collar cells: in sponges, the lining cells that help
water move through the sponge by the
beating of flagella.
dermis: the inner layer of skin; it contains many
blood vessels, nerves, and sweat and oil
glands.
commensalism: a symbiotic relationship that
benefits one partner but not the other.
desert: the driest biome on Earth; supports little
plant life and receives less than 25 cm of rain
yearly.
communicable disease: a disease that is transmitted
from one organism to another by pathogenic
bacteria, viruses, and fungi.
communication: an exchange of information among
animals by means of cries, movements,
touch, speech, pheromones, and so on.
community: all the populations of different species
that live in the same place at the same time
and interact with each other.
compound light microscope: an instrument that
uses light and convex lenses to magnify
objects.
consumers: organisms that can’t make their own
food.
contour feathers: on birds, the strong, lightweight
feathers that are used for flight and that give
birds their coloring and sleek shape.
control: in an experiment, the standard for
comparison.
coronary circulation: the flow of blood to heart
tissues.
crop: in an earthworm, a sac in the digestive system
that stores soil.
cuticle: a waxy protective layer on the stems and
leaves of land plants that helps the plant
conserve water.
cytoplasm: the gel-like substance inside the cell
membrane that contains structures that
carry out life processes.
D
dendrite: neuron structure that receives messages
and sends them to the cell body.
development: all the changes undergone by living
things as they grow.
diaphragm: a muscle beneath the lungs that helps
move air in and out of the body.
dichotomous key: a detailed list of traits used to
identify a specific organism.
diffusion: the movement of molecules from areas of
greater concentration to areas of lesser
concentration.
digestion: the process that breaks down food into
small molecules that can be moved into the
blood and used by the cell.
disinfectant: a substance that kills pathogens on
non-living objects.
division: second-highest taxonomic category in the
plant and fungi kingdoms.
DNA: deoxyribonucleic acid; a chemical in the
nuclei of cells that codes and stores genetic
information; consists of strands of
molecules that control cell activities using
coded instructions.
dominant: the form of a trait that appears to
dominate or mask another form of the same
trait.
dorsal hollow nerve cord: a tubular bundle of nerves
that lies above the notochord in a chordate
animal; the spinal cord in most vertebrates.
down feathers: on birds, the soft, fluffy insulating
feathers that cover their skin.
E
echinoderm: a spiny skinned invertebrate that lives
on the bottom of the ocean and that moves
by means of a water-vascular system.
endocytosis: a process by which cells transport a
large body, such as a large protein molecule,
through a cell membrane into the
cytoplasm.
ecological pyramid: a model used to describe the
transfer of energy through a community.
endoplasmic reticulum (ER): a cell organelle
consisting of folded membranes that move
materials around within the cell.
ecological succession: the process of gradual change
from one community of organisms to
another.
endoskeleton: the internal skeleton of an organism
that supports and protects the internal
organs and provides a frame for muscle.
ecology: the study of relationships between
organisms and between organisms and their
physical environment.
endospore: a tick walled structure that some
bacteria produce around themselves,
especially for protection from heat and
drought.
ecosystem: a community interacting with the nonliving (abiotic) parts of its environment.
ectotherm: vertebrate animal whose internal body
temperature changes with its environment.
egg: in organisms that reproduce sexually, the sex
cell (gamete) from the female parent.
electron microscope: an instrument that bends
beams of electrons in a magnetic field;
magnifies objects too small to be seen with a
light microscope.
embryo: a fertilized egg during early growth; in
humans, an unborn child during the first two
months of pregnancy.
embryology: the study of the development of
embryos, which are the earliest stage of an
organism’s development.
emphysema: a respiratory disease in which the
alveoli in the lungs lose their ability to
expand and contract, mostly caused by
smoking.
endangered species: a species with so few
individuals left that it is in danger of
extinction.
endotherm: vertebrate animal that maintains a
constant body temperature.
enzyme: a protein that speeds chemical reactions in
cells without being changed itself.
epidermis: the surface or outer layer of our skin.
equilibrium: condition in which molecules of
substance are spread evenly throughout a
space.
erosion: the wearing away of soil by wind, water,
and ice.
estivation: an adaptation for survival in hot, dry
weather during which an animal becomes
inactive and all body processes slow down.
estuary: the areas where a freshwater river or
stream meets the ocean.
ethics: the process that applies right and wrong to
people and their actions.
eubacteria; prokaryotic, one-celled organisms found
everywhere; reproduce by fission; include
pathogenic bacteria and cyanobacteria.
evidence: information that is gathered by direct
observation.
evolution: changes that occur over time in the
hereditary features of a species of
organisms.
flagellum: a whiplike tail on bacteria and some
protists that helps them move through a
moist environment.
exocytosis: a process by which a cell moves large
molecules out through the cell membrane.
food chain: a model used to show how energy from
food passes from one organism to another.
exoskeleton: on all arthropods, the hard, lightweight
external covering that shields, supports, and
protects the body.
food web: a model used to describe a series of
overlapping food chains.
extinction: the dying out of an entire species.
F
fossil fuel: a fuel created over time from the bodies
of once-living organisms; coal, oil, and
natural gas.
fossils: remains of life from an earlier time.
family: the fifth-highest taxonomic category, below
an order.
fat: a nutrient that provides energy; also cushions
organs and helps the body absorb some
vitamins.
free-living: describes an organism that finds its own
food and place to live without depending on
another organism; the opposite of a
parasite.
function: the specific task something does.
fermentation: a form of respiration that converts
energy from glucose when the supply of
oxygen is not sufficient; yeast and some
bacteria use alcohol fermentation to release
energy and carbon dioxide.
fertilization: in organisms that reproduce sexually,
the fusion of an egg and sperm.
fetus: a developing embryo.
filter feeder: an organism that obtains food and
oxygen by filtering it from the water from
which it lives.
fin: fanlike structure on most fish; adapted for
steering, balancing, and moving through the
water.
fish: a ectothermic vertebrate whose gills, fins, and
scales adapt it to living in water.
fission: a type of asexual reproduction used by
bacteria in which one bacterium divides to
form two cells with identical genetic
material.
G
gametophyte: the sex cell-producing stage of a
plants life cycle.
gene: the segment of DNA on a chromosome that
directs the making of a specific protein, thus
controlling traits that are passed to
offspring.
genetic engineering: biological and chemical
methods to change a cell’s DNA sequence to
produce desirable traits or eliminate
undesirable traits.
genetics: the science of how traits are inherited
through alleles passed from one generation
to another.
genome: a map of the location of individual genes
on every chromosome of an individual.
genotype: the genetic makeup of an organism for a
trait.
genus: a group of different organisms with similar
characteristics; can have one or more
species.
geothermal energy: heat energy from below Earth’s
surface.
gestation period: the time between fertilization and
birth, during which the embryo develops in
the uterus.
gill: organ that exchanges carbon dioxide with
water.
gill slits: pair openings in the throat; in fish, they
develop into gills for breathing underwater.
gizzard: in an earthworm, a muscular digestive
structure that grinds soil.
H
habitat: the physical location where an organism
lives.
hazardous waste: harmful or poisonous waste
material.
heart murmur: a defect in the heart caused by an
improperly functioning valve.
hemoglobin: a chemical in red blood cells that
carries oxygen to tissues, carries carbon
dioxide to lungs, and gives blood its red
color.
global warming: the potential warming of Earth due
to an increase in greenhouse gases in the
atmosphere.
herbivore: an animal that eats only plants.
Golgi bodies: cell organelles consisting of stacks of
membrane-covered sacs that package and
move proteins to the outside of the cell.
hermaphrodite: an animal that produces both
sperm and eggs.
gradualism: a model of evolution, showing a steady,
slow, and continuous change of one species
into new species.
grassland: a biome dominated by climax
communities of grasses but that, due to a
dry season, does not have forests.
greenhouse effect: the process by which heat
radiated from Earth’s surface is trapped and
reflected back to Earth by gases in the
atmosphere, causing worldwide
temperatures to increase.
groundwater: water in the soil or trapped in
underground rock pockets.
guard cells: in a plant leaf, cells that surround the
stomata to open and close them.
gymnosperm: a vascular plant that produces seeds
on the scales of female cones, such as
pinecones.
heredity: passing of traits from parent to offspring.
heterozygous: an organism that has two different
alleles for a trait.
hibernation: an adaption for winter survival during
which an animal becomes inactive and all
body processes slow down.
homeostasis: the regulation of steady, lifemaintaining conditions inside an organism or
cell, despite changes in its environment.
homologous: body parts in different species that are
similar in origin and structure.
homozygous: an organism that has two identical
alleles for a trait.
hormones: chemicals secreted from endocrine
glands that control specific body activities.
host cell: a living cell in which a virus reproduces.
hydroelectric power: energy source that uses the
power of flowing water to produce
electricity.
hyphae: the mass of many-celled, threadlike tubes
that form the body of a fungus.
hypothesis: a prediction that can be tested.
I
immune system: a complex group of defenses that
the body uses to fight disease.
incomplete dominance: the production of a
phenotype in an offspring that is
intermediate to the phenotypes of its two
homozygous parents.
inference: a logical conclusion based on your
observations.
informed consent: a form volunteers sign that states
that they have been told about the risks and
that they agree to participate in the trial.
insulin: substance produced by the islets of
Langerhans to help body cells use glucose in
the blood for energy.
interneurons: nerve cells throughout the brain and
spinal cord that transmit impulses from
sensory neurons to motor neurons.
intertidal zone: the part of the shoreline that is
submerged at high tide and exposed to air at
low tide.
invertebrate: animal without a backbone.
involuntary muscle: a muscle that can’t be
consciously controlled, such as heart and
digestive muscle.
islets of Langerhans: cells in the pancreas that
produce insulin.
J
kingdom: the highest and largest of the taxonomic
categories; kingdoms include all other
categories.
L
larva: young organism that develops between egg
and adult stages.
larynx: airway to which the vocal cords are
attached; the structure between the
pharynx and trachea.
lichen: an organism made up of a fungus and green
algae living in a mutualistic relationship.
life span: the length of time an organism is expected
to live.
ligament: a tough band of tissue that holds bones
together at joints.
limiting factor: any biotic or abiotic factor that
restricts the number of individuals in a
population.
lymph: fluid in body tissues made up of water,
dissolved substances, and lymphocytes.
lymph nodes: bean-shaped structures throughout
the body that filter microorganisms and
foreign material from lymph before it
returns to blood.
lymphatic system: collects fluid from body tissues
and returns it to the blood.
lymphocyte: a type of white blood cell that fights
disease-causing antigens by engulfing and
digesting them.
joint: any place where two or more bones meet;
may be movable or immovable.
lysosome: a cytoplasmic organelle that contains
chemicals and digests wastes and worn-out
cell parts.
K
M
kidney: the major organ of the urinary system;
filters blood to produce waste liquid called
urine.
mammal: a endothermic vertebrate with insulating
hair and mammary glands.
mammary glands: glands in female mammals that
produce mild for feeding young.
multiple alleles: having more than two alleles that
control a trait.
mantle: in a mollusk, the thin layer of tissue that
covers the soft body; it secretes chemicals
that become a shell or protects the body if
no shell exists.
muscle: an organ that can relax and contract to
allow movement.
marsupial: a mammal with a pouch on its abdomen
for carrying and nursing its young.
mechanical digestion: physical breakdown of food
into smaller particles by chewing (in the
mouth) and by churning (in the stomach).
medusa: a bell-shaped cnidarians that is free
swimming.
meiosis: the division of the cell nucleus to produce
sex cells.
metabolism: all of the chemical activities of an
organism that enable it to live, grow, and
reproduce.
mutation: any permanent change in an organism’s
genetic material (DNA).
mutualism: a symbiotic relationship that benefits
both partners.
N
natural resources: parts of the environment that
organisms need for survival, such as air,
water, soil, and food.
natural selection: Darwin’s theory of evolution,
which says that organisms best adapted to
their environment are more likely to survive
and pass their traits to their offspring.
nephron: the tiny filtering unit of the kidney.
metamorphosis: the changes in body form during
the life cycle.
nerves: takes in information and sends it
throughout the body.
mitochondria: cell organelles that break down food
molecules and release energy.
nervous system: controls the body’s response to
information.
mitosis: the process by which a nucleus divides into
two identical cells, each containing the same
number and type of chromosomes as the
parent cell.
neuron: nerve cell that carries impulses throughout
the body; the basic unit of the nervous
system.
mollusk: a soft-bodied invertebrate that usually has
a hard shell.
molting: the periodic shedding and replacing of the
old, outgrown body covering, such as skin or
an exoskeleton.
monotreme: a mammal that lays eggs having a
tough leathery shell.
motor neuron: nerve cell that conducts impulses
from the brain or spinal cord to muscles or
glands throughout the body.
niche: the role of an organism in the ecosystem.
noncommunicable disease: a disease that cannot be
spread from one organism to another; may
be caused by genetics, chemicals, poor diet,
or uncontrolled cell division.
nonrenewable resource: a natural resource that is
available only in limited amounts and that
cannot be replaced by nature in a short
period of time.
nonvascular plant: a plant lacking vascular tissue; it
absorbs water directly through its cell
membranes.
notochord: a flexible, rodlike structure along the
dorsal side of a chordate animal; the
backbone in vertebrates.
nuclear energy: energy produced from the splitting
apart of uranium nuclei by a nuclear fission
reaction.
nucleus: the structure inside a cell that directs the
cell’s activities; contains chromatin;
chromosomes in a dividing cell.
nutrient: a substance in food that produces energy
and materials for life activities.
O
observation: to describe something using one of
your senses.
omnivore: an animal that eats both plants and
animals.
open circulatory system: a type of blood-circulation
system that lacks vessels but instead bathes
internal organs in blood, such as in mollusks.
order: the fourth-highest taxonomic category,
below a class.
organ: a structure made up of different types of
tissues that work together to do a specific
job; for example the heart.
organelles: in eukaryotic cells, the structures within
the cytoplasm that break down food, moves
wastes, and store materials.
organism: a living thing that is made of one or more
cells, uses energy, moves, responds to its
environment, adjusts, reproduces, adapts,
and has a life span.
organ system: a group of organs working together.
osmosis: the diffusion of water through a cell
membrane.
ozone depletion: the thinning of Earth’s ozone layer.
P
parasitism: a symbiotic relationship that benefits
the parasite but harms the parasite’s
partner.
passive transport: movement of material across a
cell membrane without the use of energy.
pasteurization: heating food long enough to kill
most bacteria.
pathogen: any organism that produces a disease.
pedigree: a diagram that shows the occurrence of a
trait in a family.
peripheral nervous system: part of the control
system, including cranial nerves and spinal
nerves that connect the brain and spinal
cord to other body parts.
peristalsis: muscular contractions that move food
through the digestive system.
pesticide: a chemical that kills undesirable plants or
animal pests.
pharynx: a tubelike passageway for both food and
air, located between the nasal cavity and the
esophagus.
phenotype: a physical trait that shows as a result of
an organism’s particular genotype.
phloem: vascular plant tissue made up of tubular
cells that move food from leaves and stems
to other parts of the plant for use or storage.
photosynthesis: chemical reaction used by
producers, such as green plants, to produce
food; light energy is used to produce
chemical energy, converting carbon dioxide
and water into sugar and oxygen.
phylogeny: the evolutionary history of an organism.
phylum: the second-highest taxonomic category in
the animal kingdom.
pioneer community: the first community to inhabit
a new environment.
pioneer species: the first plants to grow in a new or
disturbed area.
pistil: the female reproductive organ of a flower.
placebo: a control that simulates a medicine but
doesn’t have the active ingredient.
plankton: microscopic algae, plants, and other
organisms that float in lakes, ponds, oceans,
and other bodies of water.
plasma: the liquid part of blood, made mostly of
water but also containing dissolved
nutrients, minerals, and oxygen.
pollen grain: the male reproductive part of a plant
that contains the sperm.
pollination: the process that transfers pollen grains
from the stamen to the stigmas.
pollutant: any substance that contaminates the
environment; mostly made up of waste
products from burning fossil fuels.
polygenic inheritance: occurs when groups of gene
pairs act together to produce a specific trait.
polyp: a vase-shaped cnidarians that usually is
sessile.
population: organisms of one species that live in the
same place at the same time and that can
produce offspring.
primary succession: the development of new
communities in areas that do not have any
soil.
producers: green plants that make their own food
by photosynthesis.
protein: a nutrient made up of amino acids; used
throughout the body for growth and to
replace and repair cells.
protists: members of the Kingdom Protista; some
are plantlike, others are animal-like, and
others are fungus-like; simple one cells or
many celled organisms.
protozoa: one cells animal like protists; many are
parasites.
pseudopod: a footlike cytoplasmic extension used
by some organisms to move and to trap
food.
pulmonary circulation: the path of blood from the
heart, to the lungs, and back to the heart.
pulse: the number of contractions of the heart in a
specific time.
punctuated equilibrium: a model of evolution,
showing the rapid change of a species
caused by the mutation of just a few genes.
Punnett square: a tool that shows how genes can
combine; used to predict the probability of
types of offspring.
Q
population density: the number of individuals per
unit of living space.
qualitative: describing the general characteristics of
something.
precipitation: the amount of moisture that
condenses and falls as rain, sleet, hair, or
snow, or that forms as fog.
quantitative: describing something using exact
measurements.
predation: the feeding of one organism on another
organism.
preening: a behavior of birds in which a bird uses its
beak to rub oil over its feathers to condition
them and help make them water repellant.
R
radial symmetry: describes animals with body parts
arranged in a circle around a central point,
similar to a bicycle wheel.
radula: in gastropods, a tongue-like organ with tows
of teeth that scrape and tear food.
saprophyte: any organism that uses dead material
as a food and energy source.
recessive: the form of a trait that seems to
disappear in a population but can reappear
depending on the way the alleles combine.
scales: hard, thin, overlapping plates that cover and
protect a fish’s body.
recycling: the reusing of an item or resource after it
has been changed or reprocessed.
red tide: an algal population explosion that causes
the water to look red and can cause fish kills
and illness.
regeneration: the ability of an organism to replace
body parts; a type of asexual reproduction
in which a whole new organism grows from
just a part of the parent organism.
relative dating: estimating the age of a fossil by
comparing it to younger fossils in the rock
layers above and to older fossils in the rock
layers below.
renewable resource: a natural resource that is
constantly being recycled or replaced by
nature.
reptile: an ectothermic vertebrate that has dry,
scaly skin and that lays eggs covered with a
leathery shell.
respiration: the process by which organism break
down food to release energy.
response: the reaction of an organism to a stimulus.
ribosome: a cell organelle on which protein is made.
RNA: ribonucleic acid; carries codes for making
proteins.
S
saliva: the watery substance produced in the mouth
that begins the chemical digestion of food.
sample size: the amount of people or thing being
tested.
scientific methods: problem solving procedures
used by scientists; define the problem,
make a hypothesis, test the hypothesis,
analyte the results, and draw conclusion.
secondary succession: a type of ecological
succession that occurs in a place that has soil
and was once the home of living organisms.
sensory neuron: nerve cell that transmits stimuli
from receptors to the brain or spinal cord.
sessile: describes organisms, such as trees, that
remain attached to one place during their
lifetime.
setae: in a segmented worm, bristle-like structures
on the outside of the body that help it grip
soil and move.
sex-linked gene: an allele inherited on a sex
chromosome.
sexual reproduction: a type of reproduction in
which a new organism is produced by
combining sex cells from two parents.
simulation: an experience that is meant to mimic, or
be like, another experiment.
skeletal muscles: voluntary muscles that work in
pairs and move bones.
skeletal system: the body’s network of bones, which
forma rigid frame to support the body,
protect internal organs, generate red blood
cells, and store calcium and phosphorus.
smog: a brown colored air pollution that occurs
when sunlight reacts with waste products
released by the burning of fuels.
smooth muscles: involuntary muscles that move
many internal organs.
soil depletion: the removal of soil nutrients due to
the taking away of mature plants form
where they were grown.
taxonomy: the science of classifying and naming
organisms.
soil management: the use of plowing methods to
prevent soil depletion and erosion.
temperate deciduous forest: climax communities of
deciduous trees, which lose their leaves in
the fall.
solid wastes: unwanted, solid materials that can be
recycled, burned, buried, or dumped.
tendon: a thick band of tissue that attaches a
muscle to a bone.
species: a group of organism whose members
successfully reproduce among themselves.
tentacles: the armlike structures that surround the
mouths of some organisms and help them to
capture food.
species diversity: the great variety of plants,
animals, and other organisms on Earth.
spontaneous generation: the theory that nonliving
things produce living things.
spore: a reproductive cell that forms new organism
without fertilization.
sporophyte: the spore forming stage of a plant’s life
cycle.
stamen: the male reproductive organ of a flower.
stimulus: anything an organism responds to, such as
sound, light, heat, vibration, odor,
movement, hunger, thirst, and so on.
stomata: small pores in the surface of a plant leaf
that allow carbon dioxide, water, and oxygen
to enter and leave.
symbiosis: a close relationship between two
organisms that live together.
synapse: the small gap between two neurons across
which impulses can travel.
systematic circulation: the flow of blood from the
heart to all the body tissues (except lungs
and heart) and back to the heart.
territory: an area that an animal defends from other
members of the same species.
tissues: groups of similar cells that do the same sort
of work.
touch receptors: nerve endings that detect pressure
in your skin.
toxin: a poison produced by disease causing
organisms.
trachea: a cartilage reinforced tube that carries air
to the bronchi.
trade-off: something given up in selecting one
alternative over another.
transgenic crop: a crop of plants that has new DNA
inserted into it to improve yield, disease
resistance, and so on.
transpiration: in plants, loss of water vapor through
the stomata of a leaf.
tropical rain forest: hot, humid, equatorial biome: it
contains the largest number of species.
tropism: the response of a plant to a stimulus.
T
tube feet: in echinoderms, the structures connected
to the water-vascular system that help them
move and feed.
taiga: a cold biome below the tundra; it has
coniferous forests and is warmer and wetter
than the tundra.
tumor: an abnormal growth of tissue.
tundra: a very cold, dry, treeless biome where the
sun is barely visible during the six to nine
months of winter.
U
urethra: a tube that carries urine from the bladder
to the outside of the body.
urinary system: a system of excretory organs that
tides blood of wastes, excess water, and
excess salts.
coat; it infects host cells in order to
reproduce.
voluntary muscle: a muscle you can control, such as
arm and leg muscles.
W
water cycle: the continuous movement of water in
the biosphere through evaporation,
condensation, and precipitation.
urine: waste liquid collected by the kidneys;
contains water, salts, and other wastes.
water-vascular system: in echinoderms, the network
of water filled canals to which thousands of
tube feet are connected.
V
Z
vaccination: administration of a weakened virus to
develop immunity against a disease.
zygote: in organisms that reproduce sexually, the
cell that forms in fertilization.
vaccine: a solution made from damaged virus or
bacteria particles or from killed or weakened
viruses or bacteria; can prevent, but not
cure, many viral and bacterial diseases.
valve: helps blood flow in one direction.
variable: in an experiment, the factor tested.
variation: the occurrence of an inherited trait that
makes an individual different from other
members of the same species.
vascular plant: a plant containing vascular tissue
made up of tube-like cells that transport
food and water through the plant.
vein: a vessel with one-way valves that moves blood
toward the heart, carrying wastes.
ventricles: the two lower chambers of the human
heart.
vertebrate: animal with a backbone.
villi: tiny, fingerlike projections on the inner surface
of the small intestine.
virus: a microscopic particle made of either a DNA
or an RNA core and covered with a protein