8th grade Science vocabulary answers

Check yourself on the meanings of these words.  Click on "8th grade Science vocabulary answers" and/or "Chapters" to go back to the Science page.

Unit 1

                                                              

Chapter 1

Lesson 1

  1. science: process used to investigate the world an provide some possible answers to scientific problems.
  2. scientific method: approaches taken to try and solve a problem; recognize a problem, form a hypothesis, test hypothesis, analyze data, draw conclusion.
  3. hypothesis: prediction about a problem that can be tested; based on observations, new information, and personal experience, and often written as an if-and-the statement.
  4. theory: explanation backed by results received from repeated tests or experiments.
  5. law: well-tested description of how something in nature works.
  6. control: standard used for comparison in an experiment.
  7. independent variable: factor that is changed in a controlled experiment.
  8. dependent variable: factor being measured or observed in a controlled experiment.
  9. constant: variable that stays the same in an experiment.
  10. graph: diagram that shows the relationship of one variable to another and that makes it easier to interpret and analyze data.

Lesson 2

  1. technology: application of what has been learned through science.
  2. sequence: arrangement of things or events in a certain order.
  3. inference: attempt at an explanation based on observation.

                                                              

Chapter 2

Lesson 1

  1. element: substance that cannot be broken down into simpler substances and whose atoms are exactly alike.
  2. electron: tiny, negatively charged particle that is present in all atoms and that has almost no mass.
  3. proton: positively charged, heavy particle contained in the nucleus of all atoms.
  4. neutron: electrically neutral particle that is present in the nucleus  of all atoms; same mass as proton. 
  5. electron cloud: region surrounding the nucleus of an atom, where electrons are more likely to be found.

Lesson 2

  1. atomic number: number of protons in the nucleus of an atom of a specific element.
  2. isotope: atoms of the same element that have different numbers of neutrons in their nuclei.
  3. mass number: number of neutrons plus the number of protons in the nucleus of an atom.
  4. radioactive decay: release of nuclear particles and energy from unstable atomic nuclei.
  5. half-life: time needed for one-half the mass of a sample of a radioactive isotope to decay;  can vary from fractions of a second to billions of years.

                                                              

Chapter 3

Lesson 1

  1. period: horizontal row of elements in the periodic table whose properties change gradually and predictably.
  2. group: family of elements with similar physical or chemical properties that occupies the same column in the periodic table.
  3. metal: element that is a good conductor of electricity and heat, is usually a solid at room temperature and is shiny, ductile, and malleable.  
  4. nonmetal: element that is a poor conductor of heat and electricity and may be a gas or a brittle solid at room temperature.
  5. metalloid: element that shares some properties with metals and some with nonmetals.

Lesson 2

  1. alloy: mixture made of 2 or more elements, one of which is a metal.
  2. semiconductor: element that doesn't conduct electricity as well as a metal but does conduct electricity better than a nonmetal.

                                                              

Chapter 4

Lesson 1

  1. electron dot diagram: shows the chemical symbol for an element surrounded by as many dots as there are electrons in its outer energy level. 
  2. chemical bond: force that hold 2 atoms together.

Lesson 2

  1. ion: atom that is no longer neutral because it has gained or last an electron.
  2. ionic bond: chemical bond that is created when one atom loses one or more electrons and another atom gains one or more electrons.
  3. compound: pure substance that contains 2 or more elements.
  4. covalent bond: chemical bond that forms between atoms when they share electrons.
  5. molecule: neutral particle that is formed when atoms share electrons.
  6. formula: combination of chemical symbols that tells what elements are in molecules and how many atoms of each element are present.

                                                              

Chapter 5

Lesson 1

  1. chemical reaction: energy-requiring process in which chemical changes occur; formation of new substances that have different properties than the original substances.
  2. reactant: substance that exists before a chemical reaction begins; in a chemical equation, the reactant is listed on the left side of the arrow.
  3. product: substance that is formed by a chemical reaction; in a chemical equation, the product is placed on the right side of the arrow.
  4. endothermic reaction: chemical reaction in which energy is absorbed, such as the reaction that breaks water down into hydrogen and oxygen.
  5. exothermic reaction: chemical reaction that releases energy, such as occurs when propane is burned in a gas grill.

Lesson 2

  1. rate of reaction: measure of how quickly a chemical reaction occurs, which can be influenced by temperature, particle size, the amount of activation energy that starts the reaction.
  2. inhibitor: substance, such as butyl hydroxy toluene (BHT), that doesn't totally stop a chemical reaction but slows it down.
  3. catalyst: substance, such as an enzyme, that speeds up a chemical reaction but is not used up or permanently changed. 

Unit 2

                                                              

Chapter 6

Lesson 1

  1. speed: rate of change of an object's position.
  2. displacement: measures the change in position of an object, using the starting point and ending point and noting the direction.
  3. velocity: rate of change of displacement; both speed and direction.
  4. acceleration: rate of change of velocity; act in the direction of motion, at an angle, or opposite to the direction of motion.

Lesson 2

  1. mass: quantity of matter in an object and a measure of the object's inertia; unit is the kilogram.
  2. inertia: measures an object's tendency to remain at rest or to stay in constant motion.
  3. momentum: product of mass and velocity; quantity of motion for an object.
  4. law of conservation of momentum: if not outside forces act on a group of objects, the momentum of the group will not change.

Lesson 3

  1. energy: ability to cause change; cannot be destroyed or created, only transferred from one form to another.
  2. kinetic energy: energy an object has due to its motion; depends on the object's mass and velocity.
  3. law of conservation of energy: energy cannot be destroyed or created but it is only transformed from one form to another.
  4. gravitational potential energy: energy an object could potentially gain if it falls, depending on its mass and the height it can fall.

                                                              

Chapter 7

Lesson 1

  1. force: push or a pull exerted on an object.
  2. net force: sum of the forces acting on an object.
  3. balanced forces: 2 or more forces acting on an object that cancel each other out and do not cause a change in the object's motion.
  4. unbalanced forces: 2 or more unequal forces acting on an object that cause the object to accelerate. 
  5. Newton's first law of motion: an object at rest or moving at a constant speed in a straight path continues to do so until a net force acts on it. 
  6. friction: rubbing force that acts against motion between 2 touching surfaces.

Lesson 2

  1. Newton's second law of motion: an object acted upon by a net force will accelerate in the direction of this force according to the following equation a-fnet/m where a is the acceleration, fnet is the net force, and m is the mass.
  2. normal force: outward force a surface supplies to support an object.

Lesson 3

  1. Newton's third law of motion: forces always act in equal but opposite pairs.

Unit 3

                                                              

Chapter 8

Lesson 1

  1. fault: surface along which rocks break and move.
  2. earthquake: vibrations caused by breaking rocks along faults; most result form plates moving over, under, and past each other.
  3. normal fault: break in rock due to tension forces, where rock above the fault surface moves downward in relation to rock below the fault surface.
  4. reverse fault: break in rock due to compression forces, where rocks above the fault surface move upward and over the rocks below the fault surface.
  5. strike-slip fault: break in rock due to shearing forces, where rocks on either side of the fault surface move past each other with little upward or downward movement.

Lesson 2

  1. seismic wave: energy waves that are produced at and travel outward from the earthquake focus.
  2. focus: in an earthquake, the point beneath Earth's surface where energy release occurs.
  3. primary wave: wave that travels outward from an earthquake's focus and cause particles in rocks to move back and forth in the same direction the wave is moving.
  4. secondary wave: wave that travels outward from an earthquake's focus and move through Earth by causing particles in rocks to vibrate at right angles to the direction of the wave.
  5. epicenter: point on Earth's surface directly above an earthquake's focus. 
  6. surface waves: waves of energy that reach Earth's surface during an earthquake, travel outward from the epicenter, and move rock particles up and down and side to side.
  7. inner core: very dense, solid center of Earth that is made mostly of iron with smaller amounts of oxygen, silicon, sulfur, or nickel. 
  8. outer core: liquid core that surrounds Earth's solid inner core and that is made mostly of iron.
  9. mantle: largest layer inside Earth, lying directly above the outer core and that is made mostly of silicon, oxygen, magnesium, and iron.
  10. crust: Earth's outermost layer, which varies in thickness from about 5 km to 60 km and is separated from the mantle by the Moho discontinuity.

Lesson 3

  1. seismologist: scientist who studies earthquakes and seismic waves.
  2. seismograph: device used by seismologists to record primary, secondary, and surface waves from earthquakes.
  3. magnitude: measure of the energy released by an earthquake.
  4. tsunami: powerful seismic sea wave that can travel thousands of kilometers in all directions and that begins over an earthquake focus.

                                                              

Chapter 9

Lesson 1

  1. volcano: opening in Earth's surface that often forms a mountain when layers of lava and volcanic ash erupt an build up; occurs where Earth's plates are moving apart or together and at hot spots.
  2. vent: opening on Earth's surface where magma is forced up and flows out as lava.
  3. crater: steep-walled depression around a volcano's vent.
  4. hot spot: location in the mantle that is hotter than other areas and that melts rock, which is forced up toward the crust as magma.

Lesson 2

  1. shield volcano: broad volcano with gently sloping sides formed when hot, fluid lava flows from one or more vents.
  2. tephra: bits of rock or solidified lava dropped from the air during an explosive volcanic eruption.
  3. cinder cone: steep-sided volcano made of loosely packed tephra.
  4.  composite volcano: volcano formed by alternating layers of tephra and lava and that is found mostly where Earth's plates come together. 

Lesson 3

  1. batholiths: largest intrusive igneous rock bodies that form when magma cools underground before reaching Earth's surface.
  2. dike: intrusive igneous rock body formed when magma is squeezed into a vertical crack that cuts across rock layers and hardens.
  3. sill: intrusive igneous rock body that forms when magma is squeezed into a horizontal crack between rock layers and hardens.
  4. volcanic neck: solid, igneous core of a volcano left behind when a volcano stops erupting and the softer cone erodes away. 
  5. calderas: large openings formed when the top of a volcano collapses.

                                                              

Chapter 10

Lesson 1

  1. continental drift: hypothesis proposed by Alfred Wegener that states that continents have moved slowly to their current location on Earth.
  2. Pangaea: single large land-mass made up of all the continents connected together that broke apart about 200 million years ago.

Lesson 2

  1. seafloor spreading: magma from below Earth's crust is force upward toward the surface at a midocean ridge, flows from the cracks as the seafloor spreads apart and becomes solid as it cools, forming new seafloor.

Lesson 3

  1. plate tectonics: Earth's crust and upper mantle are broken into sections that move around on a plasticlike layer of the mantle.
  2. plate: section of Earth's lithosphere that is composed of oceanic crust, continental crust, and rigid upper mantle and that moves around on a plasticlike layer of the mantle.
  3. lithosphere: rigid, outer-most layer of Earth that is about 100 km thick, and is composed of the crust and part of the upper mantle.
  4. asthenosphere: plasticlike layer below the lithosphere.
  5. convection current: cycle of heating, rising, cooling, and sinking that is thought to be the force behind plate tectonics.

Unit 4

                                                              

Chapter 11

Lesson 1

  1. fossil: remains or traces of once-living organism preserved in rock.
  2. petrified remains: fossils that form when some or all of the original materials that made up the organisms are replaced with minerals.
  3. carbonaceous film: fossil formed when the remains of a once-living organism are subjected to heat and pressure, leaving only a thin film of carbon behind.
  4. mold: fossil formed when an organism is buried, decays and leaves behind a hollow place in the rock.
  5. cast: fossil formed when sediments fill a mold and harden into rock.
  6. index fossil: fossils of species that existed on Earth for only a short time, were abundant, and were widespread geographically; used by scientists to determine the age of rock layers.

Lesson 2

  1. principle of superposition: undisturbed layers of rocks, older rocks lie underneath younger and younger rocks.
  2. relative dating: method to determine the order of events and relative age of the rocks by examining the position of rocks in a sequence.
  3. unconformity: gap in the rock layers due to erosion, nondeposition, or both.

Lesson 3

  1. absolute dating: process that uses the properties of atoms in rocks and other objects to determine their exact ages, in years.
  2. radioactive decay: release of nuclear particles and energy from unstable atomic nuclei.
  3. half-life: time needed for one-half the mass of a sample of a radioactive isotope to decay; varies from fractions of a second to billions of years.
  4. radiometric dating: process to determine the absolute ages of rocks by measuring the amounts of parent and daughter materials in a rock and by knowing the half-life of the parent.
  5. uniformitarianism: Earth processes happening today are similar to those that happened in the past.

                                                              

Chapter 12

Lesson 1

  1. species: group of similar organisms that can successfully reproduce among themselves in their natural environment.
  2. evolution: changes in the inherited features of a species over time; can occur slowly (gradualism) or rapidly (punctuated equilibrium).
  3. natural selection: Darwin's theory of evolution that  organisms with traits best suited to their environments are more likely to survive and reproduce.
  4. variation: an inherited trait that makes an individual different from other members of the same species; can be beneficial, harmful, or neutral in a population.
  5. gradualism: model of evolution that shows a slow change of some species to another, new species through continued mutations and variations over time.
  6. punctuated equilibrium: model of evolution that shows the rapid change of a species caused by the mutation of just a few genes, resulting in the appearance of a new species.

Lesson 2

  1. sedimentary rock: rock formed by compaction and cementation of sediments or when minerals precipitate out of solutions or are left behind when a solution evaporates; rock type formed from particles of preexisting rocks contains the most fossils.
  2. radioactive element: element that gives off radiation due to an unstable nucleus.
  3. homologous: body structures that are similar in origin and show that 2 or more species may share common ancestors.
  4. vestigial structure: body structure with no obvious use, which may once have functioned in an ancestor.
  5. embryology: study of development in organisms.

Lesson 3

  1. primates: group of mammals that includes monkeys, apes, and humans, and that shares several characteristics, such as opposable thumbs and binocular vision.
  2. hominids: humanlike primates that walked upright on 2 feet and ate both meat and vegetables.
  3. Homo sapiens:  human species thought to have evolved about 400,000 years ago.

                                                              

Chapter 13

Lesson 1

  1. geologic time scale: record of events in Earth's history based on major evolutionary changes and geologic events; major subdivisions are eras, periods, and epochs.
  2. era: major subdivision of the geologic time scale based on differences n life-forms.
  3. period: next-smaller division of the geologic time scale after the era.
  4. epoch: division of geologic time smaller than a period.
  5. trilobite: organism that lived hundreds of millions of years ago and is considered an index fossil of the Paleozoic era.

Lesson 2

  1. Precambrian time: longest geologic time unit in Earth's history; poor fossil record.
  2. cyanobacteria: one of the earliest life-forms on Earth; evolved during Precambrian time.
  3. Paleozoic era: geologic era marked by the first appearance of life-forms with hard parts.
  4. amphibian: animals that live on land and breathe air but return to water to reproduce.
  5. reptile: egg-laying, scaly-skinned animals that do not need to return to water to reproduce and probably evolved from the same ancestor as amphibians.

Lesson 3

  1. Mesozoic era: geologic era in which Pangaea broke up, the present-day continents were formed, and whose dominant land life-forms were reptiles and gymnosperms.
  2. gastrolith: stones swallowed by dinosaurs and by modern birds to help with digestion. 
  3. Cenozoic era: geologic era in which we live; began with the extinction of dinosaurs and many other life-forms.

Unit 5

                                                              

Chapter 14

Lesson 1

  1. organic compound: compound that contains carbon.
  2. hydrocarbon: compound that contains only carbon and hydrogen atoms--for example methane, CH4, and ethane, C2H6.
  3. saturated hydrocarbon: hydrocarbon with only single bonds--for example propane, C3H8, and butane, C4H10.
  4. unsaturated hydrocarbon: hydrocarbon that has one or more double or triple bonds--for example ethylene, C2H4, and propylene, C3H6
  5. isomer: compound with the same chemical formula but different structures and different chemical and physical properties.

Lesson 2

  1. hydroxyl group: consists of one oxygen atom and one hydrogen atom joined together by a covalent bond; formula is -OH; when substituted for hydrogen in a hydrocarbon, forms an alcohol.
  2. carboxyl group: consists of one carbon atom, 2 oxygen atoms, and one hydrogen atom; formula is -COOH; when substituted for hydrogen in a hydrocarbon, forms a carboxylic acid.
  3. amino group: consists of a nitrogen atom joined by covalent bonds to 2 hydrogen atoms; formula is -NH2; when substituted for hydrogen in a hydrocarbon, forms an amine.
  4. amino acid: building block of proteins; contains both an amino group and a carboxyl group substituted on the same carbon atom.

Lesson 3

  1. polymer: large natural or synthetic molecule made of many small organic molecules that link together to form a long chain.
  2. protein: polymer made of individual amino acids linked together in a chain; catalyzes many cell reactions and provides the structural material for many parts of the body.
  3. carbohydrate: energy-supplying organic compounds that are broken down into simple sugars in the body; contain only carbon, hydrogen, and oxygen.
  4. lipid: energy-supplying and energy-storing organic compounds composed of  3 long-chain carboxylic acids bonded to glycerol; commonly called fats and oils and can be saturated or unsaturated.

                                                              

Chapter 15

Lesson 1

  1. stomata: openings on leaf surfaces o leaflike structures through which gases like carbon dioxide and water vapor may enter and leave a plant.
  2. transpiration: loss of water vapor through the stomata of a leaf.
  3. photosynthesis: food-making process that takes place in the chloroplasts of plant cells, where carbon dioxide from the air, water in the soil, and light energy react to form glucose and oxygen.
  4. respiration: series of chemical reactions by which all living cells break down food to release energy.

Lesson 2

  1. tropism: response of a plant to an outside stimulus such as gravity or light.
  2. auxin: type of plant hormone that can cause plants to show positive phototropism.
  3. photoperiodism: response of a plant to the number of hours of daylight and darkness it receives each day.
  4. long-day plant: plant that needs less than 10-12 hours of darkness to begin the flowering process.
  5. short-day plant: plant that needs 12 or more hours of darkness to begin the flowering process.
  6. day-neutral plant: plant that does not have a specific photoperiod and whose flowering process can begin over a wide range of hours of darkness.

                                                              

Chapter 16

Lesson 1

  1. gametophytes stage: plant life cycle stage in which all plant structures are made of cells with a haploid number (n) of chromosomes.
  2. sporophyte stage: plant life cycle stage in which all plant structures are made of cells with a diploid number (2n) of chromosomes.
  3. alternation of generations: occurs when a plant's life cycle alternates between a sex-cell-producing stage and a spore-producing stage.
  4. frond: leaf of a fern that grows from a rhizome.
  5. rhizome: underground stem of a fern, from which fronds and roots grow.
  6. sori: spore-producing structures on the undersides of fern fronds.
  7. prothallus: fern gametophyte, which can make its own food, absorb water and nutrients, and has both male and female reproductive structures.

 

Lesson 2

  1. ovule: in a seed plant, the structure that contains an egg cell, food0storage tissue, and a sticky fluid.
  2. pollen grain: produced by the male reproductive organs of seed plants; 2 sperm develop in each pollen grain.
  3. stamen: male reproductive organ inside the flower of an angiosperm; consists of a filament and an anther.
  4. pistil: female reproductive organ inside the flower of an angiosperm; consists of a stick stigma, a style, and an ovary.
  5. ovary: in angiosperms, the swollen base of the pistil where ovules are formed.
  6. pollination: transfer of pollen grains from the stamen to the stigma.

Unit 6

                                                              

Chapter 17

Lesson 1

  1. biosphere: part of Earth that supports organisms, is the highest level of biological organization, and is made up of all Earth's ecosystem.
  2. ecology: study of the interactions that take place among organisms and between organisms and the physical features of the environment.
  3. abiotic factor: all the nonliving, physical features of the environment, including light, soil, water, and temperature, that help determine which species can survive in an area.
  4. biotic factor: living or once-living organisms in the environment.
  5. population: all the individuals of one species that live in the same area at the same time and compete with each other for food, water, mates, and space.
  6. community: consists of groups of populations that interact with each other in a given area and depend on each other for food, shelter, and for other needs.
  7. ecosystem: consists of a biotic community and the abiotic factors that affect it.

Lesson 2

  1. population density: size of a population that occupies an area of limited size.
  2. limiting factor: any biotic or abiotic factor that restricts the number of individuals in a population.
  3. carrying capacity: largest number of individuals an environment can support and maintain over a long period of time.
  4. symbiosis: any close relationship between 2 or more different species.
  5. habitat: physical location where an organism lives.
  6. niche: role of an organism in the ecosystem, including what it eats, how it interacts with other organisms, and hot it gets food.

Lesson 3

  1. food chain: model that describes the feeding relationships in a community, usually has 3 or 4 links, and shows how energy in the form of food passes from one organism to another.
  2. food web: model used to describe a series of overlapping food chains and that shows the many organisms that feed on more than one level in an ecosystem. 
  3. ecological pyramid: model used to describe the transfer of energy from the producers of an ecosystem through successive levels of organisms in the food chain.
  4. water cycle: constant journey of water molecules on Earth as they rise into the atmosphere, fall to land or the ocean as rain, or snow, and flow into rivers and oceans through the processes of evaporation, condensation, and precipitation.
  5. nitrogen cycle: transfer of nitrogen from the atmosphere to plants and back to the atmosphere or directly into plants again.

                                                              

Chapter 18

Lesson 1

  1. ecological succession: process of gradual change from one community of organisms to another.   
  2. primary succession: ecological succession that begins in a place that does not have soil.
  3. pioneer community: first community of organisms to move into a new environment. 
  4. secondary succession: ecological succession that begins in a place that already has soil and was once the home of living organisms.
  5. climax community: community that has reached the final stage of ecological succession. 

Lesson 2

  1. biome: large geographic areas with similar climates and ecosystems; 6 most common are tundra, taiga, temperate forest, tropical rain forest, grassland, and desert.
  2. tundra: cold, dry ,treeless biome located at latitudes surrounding the north pole and that has winters 6 to 9 months long.
  3. taiga: cold region of cone-bearing evergreen trees that lies just below the tundra and is the world's largest terrestrial biome.
  4. temperate deciduous forest: biome that lies at latitudes below about 50 degrees in both the northern and southern hemispheres, usually has 4 distinct seasons, and supports a wide variety of plants and animals.
  5. tropical rain forest: hot, wet, equatorial biome that contains the largest number of species.
  6. grassland: temperate and tropical regions that receive between 25 cm and 75 cm of precipitation each year ad are dominated by climax communities of grasses.
  7. desert: driest biome on Earth; receives less than 25 cm of rain each year and supports little plant life.

Lesson 3

  1. plankton: microscopic algae, plants and other organisms that float in warm, sunlit waters near the surface of freshwater lakes and ponds.
  2. estuary: area where a river meets the ocean that contains a mixture of freshwater and salt water and serves as nursery for many species of ocean fish. 
  3. intertidal zone: portion of the shoreline that is covered with water at high tide and exposed to the air at low tide.

                                                              

Chapter 19

Lesson 1

  1. natural resource: material found in nature that is useful or necessary for living organisms.
  2. renewable resource: natural resource, such as water, that is recycled or replaced by ongoing natural processes.
  3. nonrenewable resource: natural resource, such as petroleum, that is available in limited amounts and cannot be replace or is only replaced slowly.
  4. fossil fuel: nonrenewable energy source, such as natural gas, that formed from the bodies of organisms that died hundreds of millions of years ago.
  5. photovoltaic (PV) cell: device made of silicon that turns sunlight directly into electric current.
  6. hydroelectric power: electricity produced by the energy of flowing water.
  7. geothermal energy: heat energy from below the surface of Earth.
  8. nuclear energy: energy produced when the nuclei of uranium atoms split apart in a nuclear fission reaction.

Lesson 2

  1. soil depletion: removal of soil nutrients from land used for agriculture due to the replacement of native plants with crops that do not decay and replenish the soil.  
  2. erosion: wearing away of soil by wind and water.
  3. soil management: use of plowing methods to prevent or reduce soil depletion and erosion.
  4. extinction: dying out of an entire species either naturally or through the actions of humans.
  5. endangered species: species that is in danger of becoming extinct unless action is taken to protect it.
  6.  recycling: process that reduces the use of natural resources by reusing an item after it has been changed or reprocessed.

Lesson 3

  1. pollutant: any substance that contaminates the environment and causes pollution.
  2. smog: air pollution that forms when sunlight reacts with pollutant chemicals produced by burning fossil fuels.
  3. acid rain: rain or snow with a pH below 5.6; results from the mixture of water vapor and air pollutants in the atmosphere.
  4. ozone depletion: thinning of Earth's protective ozone layer, primarily from chlorofluorocarbons reacting with and destroying ozone molecules.
  5. greenhouse effect: warming of Earth due to a blanket of gases in the atmosphere that prevents heat from radiating back into space.
  6. global warming: increase in the average yearly temperature of Earth.
  7. hazardous waste: waste materials, such as pesticides and nuclear waste, that are harmful to human health or poisonous to living organisms and that must be properly disposed of.
  8. groundwater: water contained in the soil or trapped in underground pockets formed by nonporous rock; comes from rainfall and runoff that soaks through the soil.

Unit 7

                                                              

Chapter 20

Lesson 1

  1. electromagnetic spectrum: arrangement of electromagnetic radiation according to wavelength.
  2. refracting telescope: optical telescope that uses a double convex lens to focus light and form an image at the focal point.
  3. reflecting telescope: optical telescope that uses a mirror to focus light an produce an image at the focal point.
  4. observatory: specially designed building, often with a dome-shaped roof that opens up to admit light; used to house optical telescopes.
  5. radio telescope: type of telescope that uses a large, curved dish to collect and record radio waves traveling through space and that can be used during the day or at night and during bad weather.

Lesson 2

  1. satellite: any object that revolves around another object; can be natural (Earth's moon) or artificial.
  2. orbit: curved path of a satellite as it revolves around an abject in space.
  3. space probe: instrument that travels out into the solar system to gather information and sends the data back to Earth.
  4. Project Mercury: 1st step in the US effort to reach the moon, in which a piloted spacecraft successfully orbited around Earth and returned safely.
  5. Project Gemini: 2nd stage in the US program to reach the moon, in which a team of astronauts met and connected with another spacecraft while in orbit.
  6. Project Apollo: final stage in the US effort to reach the moon--on July 20, 1969, Neil Armstrong was the 1st human to set foot on the lunar surface.

Lesson 3

  1. space shuttle: reusable spacecraft that carries astronauts, satellites, and other materials to and from space.
  2. space station: large artificial satellite that provides support systems, living quarters, and equipment so that humans can live and work in space and conduct research not possible on Earth.

                                                              

Chapter 21

Lesson 1

  1. sphere: round, 3-dimensional object whose surface at all points is the same distance from its center.
  2. axis: imaginary line around which Earth spins.
  3. rotation: spinning of Earth on its axis, which causes day and night to occur.
  4. revolution: yearly orbit of Earth around the sun.
  5. ellipse: elongated, closed curve that describes Earth's orbit.
  6. equinox: twice-yearly time when the sun is directly above Earth's equator and the number of nighttime hours equals the number of daylight hours worldwide.
  7. solstice: point at which the sun reaches its greatest distance north or south of the equator.

Lesson 2

  1. moon phase: changing appearance of the moon as seen from earth, which depends on the relative positions of the moon, Earth, and sun.
  2. new moon: moon phase that occurs when the lighted half of the moon faces the sun and the dark side faces Earth.
  3. waxing: occurs shortly after a new moon, when more and more of the moon's lighted side becomes visible.
  4. first quarter: moon phase in which one-quarter of the moon's surface that faces Earth is lit up; occurs about a week after a new moon.
  5. full moon: moon phase in which all of the moon's surface that faces Earth is lit up.
  6. waning: occurs after a full moon, when the amount of the moon's lighted side that can be seen becomes smaller.
  7. third quarter: moon phase in which only half of the lighted side of the moon is visible.
  8. solar eclipse: eclipse that occurs when the moon moves directly between the sun and Earth and casts a shadow on part of Earth.
  9. lunar eclipse: eclipse that occurs when Earth's shadow falls on the moon.
  10. maria: dark-colored, relatively flat areas of the moon that were formed when ancient lava filled basins on the moon's surface.

Lesson 3

  1. mascon: concentration of mass on the moon located beneath an impact basin.

                                                              

Chapter 22

Lesson 1

  1. solar system: system of 9 planets that orbit the sun; objects that orbit the sun.
  2. inner planet: 4 solid, rocky planets that are closest to the sun--Mercury, Venus, Earth, and Mars.
  3. outer planet: 5 planets that are the farthest away from the sun--Jupiter, Saturn, Uranus, Neptune, and Pluto.

Lesson 2

  1. Mercury: planet closest to the sun; has many craters, low gravitational pull, and is the 2nd smallest planet in our solar system.
  2. Venus: 2nd planet from the sun; has a dense atmosphere of carbon dioxide and sulfuric acid.
  3. Earth: 3rd planet from the sun; surface temperatures allow water to exist as a solid, liquid, and gas and atmosphere protects life from the sun's radiation.
  4. Mars: 4th planet from the sun; appears red due to the iron oxide content in its weathered rocks.
  5. astronomical unit: average distance from Earth to the sun (150 million km), which is used to measure distances to objects in the solar system.

Lesson 3

  1. Jupiter:  largest planet and 5th planet from the sun; composed mostly of hydrogen and helium; has continuous storms of high-pressure gas.
  2. Uranus: large, gaseous planet and 7th planet from the sun; has a magnetic pole tilted 60 degrees and rotates on an axis nearly parallel to the plane of its orbit.
  3. Neptune: large, gaseous planet similar to Uranus; usually the 8th planet form the sun.
  4. Pluto: smallest planet and considered the 9th planet from the sun; has a thin, changing atmosphere and icy-rock surface.    
  5. Saturn: 6th planet from the sun; has a complex ring system made of hundreds of ringlets.
  6. Great Red Spot: high-pressure storm generated by huge thunderstorms in Jupiter's atmosphere.

Lesson 4

  1. comet: mass of dust and rock particles mixed in with frozen water, ammonia, and methane; consists of a nucleus, a coma, and a tail.
  2. Oort Cloud: cloud of comets that completely surrounds the solar system and that is located beyond the orbit of Pluto.
  3. meteor: meteoroid that burns up in Earth's atmosphere.
  4. meteorite: meteoroid that does not completely burn up in Earth's atmosphere and strikes Earth.
  5. asteroid: piece of rock usually found in the asteroid belt between the orbits of Mars and Jupiter.

                                                              

Chapter 23

Lesson 1

  1. constellation: group of stars that forms a pattern that looks like a familiar object, animal, or character.   
  2. absolute magnitude: measure of the amount of light a star actually emits.
  3. apparent magnitude: measure of the amount of light that is received on Earth from a star.
  4. parallax: apparent shift in position of an object when it is viewed from 2 different positions.
  5. light-year: distance that light travels in one year (9.5 trillion km), which is used to measure distances in space.

Lesson 2

  1. photosphere: lowest layer of the sun's atmosphere and the layer that gives off light.
  2. chromospheres: layer of the sun's atmosphere above the photosphere and below the corona.
  3. corona: largest layer of the sun's atmosphere that extends millions of miles into space.
  4. sunspot: dark, relatively cool areas on the surface of the sun.
  5. binary system: system in which 2 stars orbit each other.

Lesson 3

  1. main sequence: in an H-R diagram, the diagonal band of stars that runs from hot, bright stars in the upper-left corner of the diagram to cool, faint stars in the lower-right corner.
  2. nebula: large cloud of gas and dust that can fragment into smaller pieces, each of which will collapse and form stars.
  3. giant: stage in a star's life cycle where hydrogen in the cores is used up, the core contracts, and temperatures inside the star increase, causing the outer layers of the star to expand.
  4. white dwarf: late stage in a star's life cycle where its core uses up its supply of helium, it contracts, and its outer layers escape into space, leaving behind the hot dense core.
  5. supergiant: late stage in the life cycle of a massive star where the core reaches very high temperatures, heavy elements form by fusion, and the star expands.
  6. neutron star: collapsed core of a supernova that shrinks to about 10km to 15 km in diameter and has only neutrons in the dense core.
  7. black hole: remnant of a star that is so dense that nothing can escape its gravity.

Lesson 4

  1. galaxy: large group of stars, gas, and dust held together by gravity.
  2. big bang theory: approximately 15 billion years ago, the universe began expanding out of an enormous explosion.