10Th Chem R

Front 1

radar radio detection and ranging, a system that uses reflected radio waves to determine the velocity and location of objects

Back 1

radar

Front 2

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

Back 2

radial canal

Front 3

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

Back 3

radial canal

Front 4

radial symmetry a body plan in which the parts of an animal’s body are organized in a circle around a central axis

Back 4

radial symmetry

Front 5

radian an angle whose arc length is equal to the radius of the circle, which is approximately equal to 57.3°

Back 5

radian

Front 6

radiation the energy that is transferred as electromagnetic waves, such as visible light and infrared waves

Back 6

radiation

Front 7

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

Back 7

radiation fog

Front 8

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

Back 8

radiative zone

Front 9

radicals an organic group that has one or more electrons available for bonding

Back 9

radicals

Front 10

radicle in plants, the embryonic, or primary, root

Back 10

radicle

Front 11

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

Back 11

radioactive decay

Front 12

radioactive decay an isotope that has an unstable nucleus and that emits radiation

Back 12

radioactive decay

Front 13

radioactive nuclide a nuclide that contains isotopes that decay and that emit radiation

Back 13

radioactive nuclide

Front 14

radioactive tracer a radioactive material that is added to a substance so that its distribution can be detected later

Back 14

radioactive tracer

Front 15

radioactivity the pro radioactive tracer cess by which an unstable nucleus emits one or more particles or energy in the form of electromagnetic radiation

Back 15

radioactive tracer

Front 16

radiolarian a member of a group of marine protozoans that develop a siliceous skeleton that radiates from a spherical cell body

Back 16

radiolarian

Front 17

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

Back 17

radiometric dating

Front 18

Radiosonde a package of instruments that is carried aloft by balloons to measure upper atmosphere conditions, including temperature, dew point, and wind velocity

Back 18

radiosonde

Front 19

radula a rasping, tongue like organ that is covered with chitinous teeth and that is used for feeding by many mollusks

Back 19

radula

Front 20

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)

Back 20

random-access memory

Front 21

rarefaction the portion of a sound wave in which medium compression is minimum

Back 21

rate-determining step

Front 22

rate-determining step in a multistep chemical reaction, the step that has the lowest velocity, which determines the rate of the overall reaction

Back 22

rate-determining step

Front 23

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

Back 23

rate law

Front 24

ray a bright streak radiating from an impact crater; composed of rock material that was displaced by the impact

Back 24

ray

Front 25

reabsorption the process in the kidneys by which materials return to the blood from the nephrons

Back 25

reabsorption

Front 26

reactant a substance or molecule that participates in a chemical reaction

Back 26

reactant

Front 27

reaction mechanism the way in which a chemical reaction takes place; expressed in a series of chemical equations

Back 27

reaction mechanism

Front 28

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

Back 28

reaction rate

Front 29

reactivity the capacity of a substance to combine chemically with another substance

Back 29

reactivity

Front 30

read-only memory a memory device that contains data that can be read but cannot be changed (abbreviation, ROM)

Back 30

read-only memory

Front 31

real gas a gas that does not behave completely like a hypothetical ideal gas because of the interactions between the gas molecules

Back 31

real gas

Front 32

real image an image of an object that forms when rays of light go through a lens and intersect at a single point

Back 32

real image

Front 33

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

Back 33

realized niche

Front 34

reasoning the act of drawing a conclusion from facts or assumption

Back 34

reasoning

Front 35

receptacle the enlarged tip of a flower stalk to which the flower is attached

Back 35

receptacle

Front 36

receptor a specialized sensory nerve that responds to specific types of stimuli

Back 36

receptor

Front 37

receptor protein a protein that binds specific signal molecules, which causes the cell to respond

Back 37

receptor protein

Front 38

receptor site the part of a cell that combines with outside molecules and that functions as an antibody

Back 38

receptor site

Front 39

recessive describes a trait or an allele that is expressed only when two recessive alleles for the same characteristic are inherited

Back 39

recessive

Front 40

recessive trait a trait that is apparent only when two recessive alleles for the same characteristic are inherited

Back 40

recessive trait

Front 41

recharge zone an area in which water travels downward to become part of an aquifer

Back 41

recharge zone

Front 42

reclamation the process of returning land to its original condition after mining is completed

Back 42

reclamation

Front 43

DNA molecules that are artificially created by combining DNA from different sources

Back 43

recombinant DNA

Front 44

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

Back 44

rectal gland

Front 45

recycling the process of recovering valuable or useful materials from waste or scrap; the process of reusing some items

Back 45

recycling

Front 46

red blood cell a disc-shaped cell that has no nucleus, that contains hemoglobin, and that transports oxygen in the circulatory system

Back 46

red blood cell

Front 47

red giant a large, reddish star late in its life cycle

Back 47

red giant

Front 48

red shift an apparent shift toward longer wavelengths of light that is caused when a luminous object moves away from the observer

Back 48

red shift

Front 49

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

Back 49

red tide

Front 50

reduced describes a substance that has gained electrons, lost an oxygen atom, or gained a hydrogen atom

Back 50

reduced

Front 51

reducing agent a substance that has the potential to reduce another substance

Back 51

reducing agent

Front 52

reduction a chemical change in which electrons are gained, either by the removal of oxygen, the addition of hydrogen, or the addition of electrons

Back 52

reduction

Front 53

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

Back 53

reduction potential

Front 54

reflecting telescope a telescope that uses a curved mirror to gather and focus light from distant objects

Back 54

reflecting telescope

Front 55

reflection the bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through

Back 55

reflection

Front 56

reflex an involuntary and almost immediate movement in response to a stimulus

Back 56

reflex

Front 57

reforestation the reestablishment and development of trees in a forest land

Back 57

reforestation

Front 58

refracting telescope a telescope that uses a set of lenses to gather and focus light from distant objects

Back 58

refracting telescope

Front 59

refraction the bending of a wavefront as the wavefront passes between two substances in which the speed of the wave differs

Back 59

refraction

Front 60

refraction the process by which ocean waves bend directly toward the coastline as they approach shallow water

Back 60

refraction

Front 61

refractory period a short period of time after the stimulation of a nerve during which the nerve cannot be stimulated

Back 61

refractory period

Front 62

refrigerant a material used to cool an area or an object to a temperature that is lower than the temperature of the environment

Back 62

refrigerant

Front 63

regeneration the re growth of missing tissues or organs

Back 63

regeneration

Front 64

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

Back 64

regional metamorphism

Front 65

regolith the layer of material, including soils, sediments, and rock fragments, that forms the surface of the land

Back 65

regolith

Front 66

regulator gene a genetic unit that regulates or suppresses the activity of one or more structural genes

Back 66

regulator gene

Front 67

rejuvenated describes a river that goes back to a more youthful stage of development because of erosion

Back 67

rejuvenated

Front 68

relative age the age of an object in relation to the ages of other objects

Back 68

relative age

Front 69

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

Back 69

relative age

Front 70

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

Back 70

relative humidity

Front 71

release-inhibiting hormone a hormone that is secreted by the hypothalamus and that inhibits the release of a specific hormone

Back 71

release-inhibiting hormone

Front 72

releasing hormone a hormone that is secreted by the hypothalamus and that stimulates the anterior pituitary to release a specific hormone

Back 72

releasing hormone

Front 73

relief the difference between the highest and lowest elevations in a given area; the variations in elevation of a land surface

Back 73

relief

Front 74

rem the quantity of ionizing radiation that does as much damage to human tissue as 1 roentgen of high-voltage X rays does

Back 74

rem

Front 75

remote sensing the process of gathering and analyzing information about an object without physically being in touch with the object

Back 75

remote sensing

Front 76

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

Back 76

renal pelvis

Front 77

renal tubule the long, tubular portion of a nephron that produces and that takes urine to the renal pelvis of a kidney

Back 77

renal tubule

Front 78

renewable energy energy from sources that are constantly being formed

Back 78

renewable energy

Front 79

renewable resource a natural resource that can be replaced at the same rate at which the resource is consumed

Back 79

renewable resource

Front 80

replication the duplication of a DNA molecule

Back 80

replication

Front 81

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

Back 81

replication fork

Front 82

repression the blockage of transcription or translation caused by the binding of a repressor protein to a portion of a DNA or mRNA molecule

Back 82

repression

Front 83

repressor a regulatory protein that binds to an operator and blocks transcription of the genes of an operon

Back 83

repressor

Front 84

reproductionthe process of producing offspring

Back 84

reproduction

Front 85

reproductive isolation the inability of members of a population to successfully interbreed with members of another population of the same or a related species

Back 85

reproductive isolation

Front 86

reproductive potential the maximum number of offspring that a given organism can produce

Back 86

reproductive potential

Front 87

reservoir an artificial body of water that usually forms behind a dam

Back 87

reservoir

Front 88

resistance in biology, the ability of an organism to tolerate a chemical or disease-causing agent

Back 88

resistance

Front 89

resistance in physical science, the opposition presented to the current by a material or device

Back 89

resistance

Front 90

resolution in microscopes, the ability to form images with fine detail

Back 90

resolution

Front 91

resolving power the ability of an optical instrument to form separate images of two objects that are close together

Back 91

resolving power

Front 92

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

Back 92

resonance

Front 93

resource an available supply of a material or mineral

Back 93

resource

Front 94

resource partitioning the pattern in which species that may compete with each other for shared resources use different portions of the shared resources

Back 94

resource partitioning

Front 95

the process of transforming wastes into useful products, such as fuel and oil, for recycling

Back 95

resource recovery

Front 96

respiration in biology, the exchange of oxygen and carbon dioxide between living cells and their environment; includes breathing and cellular respiration

Back 96

respiration

Front 97

respiration in chemistry, the process by which cells produce energy from carbohydrates; atmospheric oxygen combines with glucose to form water and carbon dioxide

Back 97

respiration

Front 98

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

Back 98

respiration

Front 99

resting potential the electric potential across the cell membrane of a nerve cell or muscle cell when the cell is not active

Back 99

resting potential

Front 100

restoration biology the science of rehabilitating, replacing, or acquiring the equivalent of any natural resources that have been injured, destroyed, or lost

Back 100

restoration biology

Front 101

an enzyme that destroys foreign DNA molecules by cutting them at specific sites

Back 101

restriction enzyme

Front 102

resultant a vector that represents the sum of two or more vectors

Back 102

resultant

Front 103

reticular formation the network of nerve fibers that run from the spinal cord through the brain stem and the diencephalon; it influences wakefulness

Back 103

reticular formation

Front 104

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

Back 104

retina

Front 105

retrograde rotation the clockwise spin of a planet or moon as seen from above the planet’s North Pole

Back 105

retrograde rotation

Front 106

retrovirus a virus that contains single-stranded RNA and produces a reverse transcriptase, which converts RNA to DNA

Back 106

retrovirus

Front 107

reverse fault a fault in which the hanging wall moves up in relation to the footwall

Back 107

reverse fault

Front 108

reverse transcriptase an enzyme that catalyzes the formation of DNA from an RNA template

Back 108

reverse transcriptase

Front 109

reversible reaction a chemical reaction in which the products re-form the original reactants

Back 109

reversible reaction

Front 110

revolution the motion of a body that travels around another body in space; one complete trip along an orbit

Back 110

revolution

Front 111

rheumatoid arthritis a chronic immune-system disorder that causes stiff and painful joints

Back 111

rheumatoid arthritis

Front 112

Rh factor one of several blood-group antigens carried on the surface of red blood cells

Back 112

Rh factor

Front 113

rhizoid a rootlike structure in nonvascular plants, such as mosses or liverworts, that holds the plants in place and aids in absorption

Back 113

rhizoid

Front 114

rhizome a horizontal, underground stem that provides a mechanism for asexual reproduction

Back 114

rhizome

Front 115

ribose a five-carbon sugar present in RNA

Back 115

ribose

Front 116

ribosome a cell organelle composed of RNA and protein; the site of protein synthesis

Back 116

ribosome

Front 117

ribozyme a type of RNA that can act as an enzyme

Back 117

ribozyme

Front 118

Richter scale a scale that expresses the magnitude of an earthquake

Back 118

Richter scale

Front 119

riftingthe process by which Earth's crust breaks apart; can occur within continental crust or oceanic crust

Back 119

rifting

Front 120

rift zone an area of deep cracks that forms between two tectonic plates that are pulling away from each other

Back 120

rifting

Front 121

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

Back 121

right ascension

Front 122

rille a long, narrow valley on the surface of the moon

Back 122

rille

Front 123

ring canal in echinoderms, a circular canal that is near the mouth and that is part of the water-vascular system

Back 123

ring canal

Front 124

rip current a strong, seaward flow of water that has accumulated close to the shore by the action of waves and wind

Back 124

rip current

Front 125

risk the probability of an unwanted outcome

Back 125

risk

Front 126

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

Back 126

risk assessment

Front 127

river system a flowing network of rivers and streams draining a river basin

Back 127

river system

Front 128

rms current the value of alternating current that gives the same heating effect that the corresponding value of direct current does

Back 128

rms current

Front 129

RNA ribonucleic acid, a natural polymer that is present in all living cells and that plays a role in protein synthesis

Back 129

RNA

Front 130

rRNA ribosomal RNA, an organelle that contains most of the RNA in the cell and that is responsible for ribosome function

Back 130

rRNA

Front 131

RNA polymerase an enzyme that starts (catalyzes) the formation of RNA by using a strand of a DNA molecule as a template

Back 131

RNA polymerase

Front 132

roche moutonnée a rounded knob of rock produced by glacial erosion

Back 132

roche moutonnée

Front 133

rock a solid mixture of one or more minerals or organic matter

Back 133

rock

Front 134

rock cycle the series of processes in which rock forms, changes from one type to another, is destroyed, and forms again by geologic processes

Back 134

rock cycle

Front 135

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

Back 135

rocket

Front 136

rock fall the rapid mass movement of rock down a steep slope or cliff

Back 136

rock fall

Front 137

a mineral that is one of the main constituents of a rock and that determines the rock's classification

Back 137

rock-for rod ming mineral

Front 138

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

Back 138

rod

Front 139

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

Back 139

roentgen

Front 140

root the mainly underground organ of vascular plants that holds plants in place and absorbs and stores water and minerals from the soil

Back 140

root

Front 141

root cap the protective layer of cells that covers the tip of a root

Back 141

root cap

Front 142

root hair an extension of the epidermis of a root that increases the root's surface area for absorption

Back 142

root hair

Front 143

rotation the spin of a body on its axis

Back 143

rotation

Front 144

the energy of an object that is due to the object's rotational motion

Back 144

rotation

Front 145

rotational motion the motion of a body that spins about its axis

Back 145

rotational motion

Front 146

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

Back 146

rotifer

Front 147

rough endoplasmic reticulum the portion of the endoplasmic reticulum to which ribosomes are attached

Back 147

rough endoplasmic reticulum

Front 148

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

Back 148

roundworm

Front 149

royal jelly a high-protein substance secreted by worker bees and fed to a queen bee and female larvae that develop into queen bees

Back 149

royal jelly

Front 150

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

Back 150

r-strategist

Front 151

rumen the first of the four compartments in the stomach of a ruminant mammal

Back 151

rumen

Front 152

ruminant a cud-chewing mammal that has a three- or four-chambered stomach; examples include sheep, goats, and cattle

Back 152

ruminant

Front 153

runoff precipitation that flows over the land and into streams and rivers

Back 153

runoff

Front 154

rural describes an area of open land that is often used for farming

Back 154

rural