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154 Cards in this Set

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radar radio detection and ranging, a system that uses reflected radio waves to determine the velocity and location of objects
radial canal one of the canals of a sea star's water-vascular system that branch from the central ring and run to the tip of each arm
radial canal
radial cleavage the type of cleavage in which the division of a fertilized egg (zygote) and subsequent embryonic cells occurs parallel to or at right angles to the longitudinal axis of the fertilized egg
radial canal
radial symmetry a body plan in which the parts of an animal’s body are organized in a circle around a central axis
radial symmetry
radian an angle whose arc length is equal to the radius of the circle, which is approximately equal to 57.3°
radiation the energy that is transferred as electromagnetic waves, such as visible light and infrared waves
radiation fog a type of fog that forms when the Earth's surface cools down at night, which lowers the temperature of the air that is near the ground until the air condenses
radiation fog
radiative zone the zone of the sun’s interior that is between the core and the convection zone and in which energy moves by radiation
radiative zone
radicals an organic group that has one or more electrons available for bonding
radicle in plants, the embryonic, or primary, root
radioactive decay the disintegration of an unstable atomic nucleus into one or more different nuclides, accompanied by the emission of radiation, the nuclear capture or ejection of electrons, or fission
radioactive decay
radioactive decay an isotope that has an unstable nucleus and that emits radiation
radioactive decay
radioactive nuclide a nuclide that contains isotopes that decay and that emit radiation
radioactive nuclide
radioactive tracer a radioactive material that is added to a substance so that its distribution can be detected later
radioactive tracer
radioactivity the pro radioactive tracer cess by which an unstable nucleus emits one or more particles or energy in the form of electromagnetic radiation
radioactive tracer
radiolarian a member of a group of marine protozoans that develop a siliceous skeleton that radiates from a spherical cell body
radiometric dating a method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope
radiometric dating
Radiosonde a package of instruments that is carried aloft by balloons to measure upper atmosphere conditions, including temperature, dew point, and wind velocity
radula a rasping, tongue like organ that is covered with chitinous teeth and that is used for feeding by many mollusks
random-access memory a storage device that allows a computer user to write and read data; it is the amount of data that the memory chips can hold at one time (abbreviation, RAM)
random-access memory
rarefaction the portion of a sound wave in which medium compression is minimum
rate-determining step
rate-determining step in a multistep chemical reaction, the step that has the lowest velocity, which determines the rate of the overall reaction
rate-determining step
rate law the expression that shows how the rate of formation of product depends on the concentration of all species other than the solvent that take part in a reaction
rate law
ray a bright streak radiating from an impact crater; composed of rock material that was displaced by the impact
reabsorption the process in the kidneys by which materials return to the blood from the nephrons
reactant a substance or molecule that participates in a chemical reaction
reaction mechanism the way in which a chemical reaction takes place; expressed in a series of chemical equations
reaction mechanism
reaction rate the rate at which a chemical reaction takes place; measured by the rate of formation of the product or the rate of disappearance of the reactants
reaction rate
reactivity the capacity of a substance to combine chemically with another substance
read-only memory a memory device that contains data that can be read but cannot be changed (abbreviation, ROM)
read-only memory
real gas a gas that does not behave completely like a hypothetical ideal gas because of the interactions between the gas molecules
real gas
real image an image of an object that forms when rays of light go through a lens and intersect at a single point
real image
realized niche the range of resources that a species uses, the conditions that the species can tolerate, and the functional roles that the species plays as a result of competition in the species' fundamental niche
realized niche
reasoning the act of drawing a conclusion from facts or assumption
receptacle the enlarged tip of a flower stalk to which the flower is attached
receptor a specialized sensory nerve that responds to specific types of stimuli
receptor protein a protein that binds specific signal molecules, which causes the cell to respond
receptor protein
receptor site the part of a cell that combines with outside molecules and that functions as an antibody
receptor site
recessive describes a trait or an allele that is expressed only when two recessive alleles for the same characteristic are inherited
recessive trait a trait that is apparent only when two recessive alleles for the same characteristic are inherited
recessive trait
recharge zone an area in which water travels downward to become part of an aquifer
recharge zone
reclamation the process of returning land to its original condition after mining is completed
DNA molecules that are artificially created by combining DNA from different sources
recombinant DNA
rectal gland in fishes, a gland that is located at the end of the intestine and that regulates the water and salt concentration of body fluids
rectal gland
recycling the process of recovering valuable or useful materials from waste or scrap; the process of reusing some items
red blood cell a disc-shaped cell that has no nucleus, that contains hemoglobin, and that transports oxygen in the circulatory system
red blood cell
red giant a large, reddish star late in its life cycle
red giant
red shift an apparent shift toward longer wavelengths of light that is caused when a luminous object moves away from the observer
red shift
red tide a population explosion of certain marine dinoflagellates that causes the water to turn a red or red-brown color and to contain poisonous alkaloids produced by the dinoflagellates
red tide
reduced describes a substance that has gained electrons, lost an oxygen atom, or gained a hydrogen atom
reducing agent a substance that has the potential to reduce another substance
reducing agent
reduction a chemical change in which electrons are gained, either by the removal of oxygen, the addition of hydrogen, or the addition of electrons
reduction potential the decrease in voltage that takes place when a positive ion becomes less positive or neutral or when a neutral atom becomes negative ion
reduction potential
reflecting telescope a telescope that uses a curved mirror to gather and focus light from distant objects
reflecting telescope
reflection the bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through
reflex an involuntary and almost immediate movement in response to a stimulus
reforestation the reestablishment and development of trees in a forest land
refracting telescope a telescope that uses a set of lenses to gather and focus light from distant objects
refracting telescope
refraction the bending of a wavefront as the wavefront passes between two substances in which the speed of the wave differs
refraction the process by which ocean waves bend directly toward the coastline as they approach shallow water
refractory period a short period of time after the stimulation of a nerve during which the nerve cannot be stimulated
refractory period
refrigerant a material used to cool an area or an object to a temperature that is lower than the temperature of the environment
regeneration the re growth of missing tissues or organs
regional metamorphism a change in the texture, structure, or chemical composition of a rock due to changes in temperature and pressure over a large area, generally as a result of tectonic forces
regional metamorphism
regolith the layer of material, including soils, sediments, and rock fragments, that forms the surface of the land
regulator gene a genetic unit that regulates or suppresses the activity of one or more structural genes
regulator gene
rejuvenated describes a river that goes back to a more youthful stage of development because of erosion
relative age the age of an object in relation to the ages of other objects
relative age
relative age a method ofdetermining whether an event or object, such as a fossil, is older or younger than other events or objects without referring to the object's age in years
relative age
relative humidity the ratio of the amount of water vapor in the air to the amount of water vapor needed to reach saturation at a given temperature
relative humidity
release-inhibiting hormone a hormone that is secreted by the hypothalamus and that inhibits the release of a specific hormone
release-inhibiting hormone
releasing hormone a hormone that is secreted by the hypothalamus and that stimulates the anterior pituitary to release a specific hormone
releasing hormone
relief the difference between the highest and lowest elevations in a given area; the variations in elevation of a land surface
rem the quantity of ionizing radiation that does as much damage to human tissue as 1 roentgen of high-voltage X rays does
remote sensing the process of gathering and analyzing information about an object without physically being in touch with the object
remote sensing
renal pelvis the funnel-shaped part of the kidney in which urine produced by the nephrons collects and from which urine passes into the ureter
renal pelvis
renal tubule the long, tubular portion of a nephron that produces and that takes urine to the renal pelvis of a kidney
renal tubule
renewable energy energy from sources that are constantly being formed
renewable energy
renewable resource a natural resource that can be replaced at the same rate at which the resource is consumed
renewable resource
replication the duplication of a DNA molecule
replication fork a Y-shaped point that results when the two strands of a DNA double helix separate so that the DNA molecule can be replicated
replication fork
repression the blockage of transcription or translation caused by the binding of a repressor protein to a portion of a DNA or mRNA molecule
repressor a regulatory protein that binds to an operator and blocks transcription of the genes of an operon
reproductionthe process of producing offspring
reproductive isolation the inability of members of a population to successfully interbreed with members of another population of the same or a related species
reproductive isolation
reproductive potential the maximum number of offspring that a given organism can produce
reproductive potential
reservoir an artificial body of water that usually forms behind a dam
resistance in biology, the ability of an organism to tolerate a chemical or disease-causing agent
resistance in physical science, the opposition presented to the current by a material or device
resolution in microscopes, the ability to form images with fine detail
resolving power the ability of an optical instrument to form separate images of two objects that are close together
resolving power
resonance a phenomenon that occurs when two objects naturally vibrate at the same frequency; the sound produced by one object causes the other object to vibrate
resource an available supply of a material or mineral
resource partitioning the pattern in which species that may compete with each other for shared resources use different portions of the shared resources
resource partitioning
the process of transforming wastes into useful products, such as fuel and oil, for recycling
resource recovery
respiration in biology, the exchange of oxygen and carbon dioxide between living cells and their environment; includes breathing and cellular respiration
respiration in chemistry, the process by which cells produce energy from carbohydrates; atmospheric oxygen combines with glucose to form water and carbon dioxide
respirationa collection of organs whose primary function is to take in oxygen and expel carbon dioxide; the organs of this system include the lungs, the throat, and the passageways that lead to the lungs
resting potential the electric potential across the cell membrane of a nerve cell or muscle cell when the cell is not active
resting potential
restoration biology the science of rehabilitating, replacing, or acquiring the equivalent of any natural resources that have been injured, destroyed, or lost
restoration biology
an enzyme that destroys foreign DNA molecules by cutting them at specific sites
restriction enzyme
resultant a vector that represents the sum of two or more vectors
reticular formation the network of nerve fibers that run from the spinal cord through the brain stem and the diencephalon; it influences wakefulness
reticular formation
retina the light-sensitive inner layer of the eye, which receives images formed by the lens and transmits them through the optic nerve to the brain
retrograde rotation the clockwise spin of a planet or moon as seen from above the planet’s North Pole
retrograde rotation
retrovirus a virus that contains single-stranded RNA and produces a reverse transcriptase, which converts RNA to DNA
reverse fault a fault in which the hanging wall moves up in relation to the footwall
reverse fault
reverse transcriptase an enzyme that catalyzes the formation of DNA from an RNA template
reverse transcriptase
reversible reaction a chemical reaction in which the products re-form the original reactants
reversible reaction
revolution the motion of a body that travels around another body in space; one complete trip along an orbit
rheumatoid arthritis a chronic immune-system disorder that causes stiff and painful joints
rheumatoid arthritis
Rh factor one of several blood-group antigens carried on the surface of red blood cells
Rh factor
rhizoid a rootlike structure in nonvascular plants, such as mosses or liverworts, that holds the plants in place and aids in absorption
rhizome a horizontal, underground stem that provides a mechanism for asexual reproduction
ribose a five-carbon sugar present in RNA
ribosome a cell organelle composed of RNA and protein; the site of protein synthesis
ribozyme a type of RNA that can act as an enzyme
Richter scale a scale that expresses the magnitude of an earthquake
Richter scale
riftingthe process by which Earth's crust breaks apart; can occur within continental crust or oceanic crust
rift zone an area of deep cracks that forms between two tectonic plates that are pulling away from each other
right ascension a measure of how far east an object is from the point at which the sun appears on the first day of spring; celestial longitude, which is measured eastward from the vernal equinox along the celestial equator
right ascension
rille a long, narrow valley on the surface of the moon
ring canal in echinoderms, a circular canal that is near the mouth and that is part of the water-vascular system
ring canal
rip current a strong, seaward flow of water that has accumulated close to the shore by the action of waves and wind
rip current
risk the probability of an unwanted outcome
risk assessment the scientific assessment, study, and management of risk; a scientific estimation of the likelihood of negative effects that may result from exposure to a specific hazard
risk assessment
river system a flowing network of rivers and streams draining a river basin
river system
rms current the value of alternating current that gives the same heating effect that the corresponding value of direct current does
rms current
RNA ribonucleic acid, a natural polymer that is present in all living cells and that plays a role in protein synthesis
rRNA ribosomal RNA, an organelle that contains most of the RNA in the cell and that is responsible for ribosome function
RNA polymerase an enzyme that starts (catalyzes) the formation of RNA by using a strand of a DNA molecule as a template
RNA polymerase
roche moutonnée a rounded knob of rock produced by glacial erosion
roche moutonnée
rock a solid mixture of one or more minerals or organic matter
rock cycle the series of processes in which rock forms, changes from one type to another, is destroyed, and forms again by geologic processes
rock cycle
rocket a vehicle or device that contains all of the substances needed to burn fuel and that uses escaping gas from the burning of fuel to move
rock fall the rapid mass movement of rock down a steep slope or cliff
rock fall
a mineral that is one of the main constituents of a rock and that determines the rock's classification
rock-for rod ming mineral
rod one of the two types of light-detecting cells in the eye; rods can detect dim light and play a major role in noncolor and night vision
roentgen a unit of radiation dose of X rays or gamma rays that is equal to the amount of radiation that will produce 2.58 ¥ 10–4 of ions per kilogram of air at atmospheric pressure
root the mainly underground organ of vascular plants that holds plants in place and absorbs and stores water and minerals from the soil
root cap the protective layer of cells that covers the tip of a root
root cap
root hair an extension of the epidermis of a root that increases the root's surface area for absorption
root hair
rotation the spin of a body on its axis
the energy of an object that is due to the object's rotational motion
rotational motion the motion of a body that spins about its axis
rotational motion
rotifer a member of the phylum Rotifera, which consists of small, aquatic invertebrates whose ring of cilia around the mouth makes the animal look like a spinning wheel
rough endoplasmic reticulum the portion of the endoplasmic reticulum to which ribosomes are attached
rough endoplasmic reticulum
roundworm a member of the phylum Nematoda, which consists of animals that have smooth skin and a long, cylindrical, and unsegmented body that tapers at both ends
royal jelly a high-protein substance secreted by worker bees and fed to a queen bee and female larvae that develop into queen bees
royal jelly
r-strategist a species that is adapted for living in an environment where changes are rapid and unpredictable; characterized by rapid growth, high fertility, short life span, small body size, and exponential population growth
rumen the first of the four compartments in the stomach of a ruminant mammal
ruminant a cud-chewing mammal that has a three- or four-chambered stomach; examples include sheep, goats, and cattle
runoff precipitation that flows over the land and into streams and rivers
rural describes an area of open land that is often used for farming