TOEFL · Natural Sciences · Intermediate

• organism

  n. an individual living thing

  Every organism needs water to live.

• ecosystem

  n. a community of living things and their environment

  A pond is a small ecosystem.

• photosynthesis

  n. the process plants use to make food from light

  Photosynthesis turns sunlight into sugar.

• molecule

  n. the smallest unit of a chemical compound

  A water molecule has two hydrogen atoms.

• atom

  n. the basic unit of a chemical element

  Everything is made of tiny atoms.

• compound

  n. a substance made of two or more elements

  Salt is a common chemical compound.

• element

  n. a pure substance that cannot be broken down

  Oxygen is an element in the air.

• reaction

  n. a process where substances change into others

  The reaction produced a lot of heat.

• nutrient

  n. a substance that living things need to grow

  Plants take nutrients from the soil.

• evolution

  n. the gradual change of species over time

  Evolution explains the variety of life.

• adaptation

  n. a feature that helps a species survive

  Thick fur is an adaptation to cold.

• extinction

  n. the dying out of a species

  Hunting caused the extinction of the bird.

• fossil

  n. the preserved remains of an ancient organism

  The fossil was millions of years old.

• glacier

  n. a large slow-moving mass of ice

  The glacier carved out the valley.

• erosion

  n. the gradual wearing away of land

  Wind causes erosion of the rocks.

• sediment

  n. small particles that settle at the bottom

  River sediment built up over years.

• orbit

  n. the curved path of an object in space

  The Earth follows an orbit around the Sun.

• galaxy

  n. a huge system of stars in space

  Our galaxy contains billions of stars.

• radiation

  n. energy that travels as waves or particles

  The Sun gives off harmful radiation.

• density

  n. the amount of mass in a given space

  Lead has a high density.

• mass

  n. the amount of matter in an object

  The mass of the rock was two kilograms.

• velocity

  n. the speed of something in a direction

  The car increased its velocity quickly.

• friction

  n. the force that slows moving surfaces

  Friction makes the tires grip the road.

• acceleration

  n. the rate of change of speed

  The rocket gained speed through acceleration.

• electron

  n. a tiny negatively charged particle

  An electron moves around the nucleus.

• nucleus

  n. the central core of an atom or cell

  The nucleus holds the cell's genes.

• tissue

  n. a group of similar cells in the body

  Muscle tissue helps the body move.

• membrane

  n. a thin layer that covers a cell or organ

  The membrane controls what enters the cell.

• enzyme

  n. a protein that speeds up reactions in the body

  An enzyme helps break down food.

• hormone

  n. a chemical that controls body functions

  A hormone controls how we grow.

• digestion

  n. the process of breaking down food

  Digestion begins in the mouth.

• respiration

  n. the process of using oxygen to release energy

  Respiration provides energy for cells.

• circulation

  n. the movement of blood around the body

  Exercise improves blood circulation.

• immune

  adj. able to resist infection or disease

  A strong immune system fights germs.

• infection

  n. the spread of harmful germs in the body

  The cut led to a small infection.

• vaccine

  n. a substance that protects against a disease

  The vaccine prevents the flu.

• chromosome

  n. a thread of DNA that carries genes

  Humans have forty-six chromosomes.

• heredity

  n. the passing of traits from parents to children

  Eye color is determined by heredity.

• trait

  n. a feature that an organism has

  Tall height is an inherited trait.

• diversity

  n. the variety of living things

  The rainforest has great diversity.

• balance

  n. a state where forces are equal

  Nature keeps a delicate balance.

• cycle

  n. a series of events that repeat

  The water cycle moves rain and rivers.

• carbon

  n. a common element found in all living things

  Carbon is the basis of life on Earth.

• nitrogen

  n. a gas that makes up most of the air

  Plants need nitrogen to grow.

• hydrogen

  n. the lightest chemical element

  Hydrogen burns very easily.

• particle

  n. a very small piece of matter

  Dust is made of tiny particles.

• substance

  n. a particular kind of matter

  Sugar is a sweet substance.

• property

  n. a quality that something has

  Hardness is a property of diamonds.

• volume

  n. the amount of space something takes up

  The bottle has a volume of one liter.

• pressure

  n. the force pressing on a surface

  High pressure can crush the can.

• magnet

  n. an object that attracts iron

  The magnet picked up the nails.

• voltage

  n. the force that pushes electric current

  A battery supplies a steady voltage.

• circuit

  n. a path that electricity flows around

  The lamp lights when the circuit is closed.

• frequency

  n. how often a wave repeats per second

  High frequency sounds are very sharp.

• spectrum

  n. the range of colors or waves

  Rainbows show the spectrum of light.

• magnitude

  n. the size or strength of something

  The earthquake had a large magnitude.

• altitude

  n. the height above sea level

  The air is thin at high altitude.

• latitude

  n. distance north or south of the equator

  Cold regions lie at high latitude.

• equator

  n. the imaginary line around the middle of Earth

  Countries near the equator are hot.

• humidity

  n. the amount of water vapor in the air

  High humidity makes the day feel hot.

• moisture

  n. small amounts of water in the air or soil

  Plants absorb moisture from the ground.

• evaporate

  v. to change from liquid into vapor

  Water evaporates in the hot sun.

• condense

  v. to change from gas into liquid

  Steam condenses on the cold glass.

• dissolve

  v. to mix completely into a liquid

  Sugar dissolves easily in water.

• expand

  v. to become larger in size

  Metal expands when it is heated.

• contract

  v. to become smaller in size

  The metal contracts as it cools.

• vibrate

  v. to move quickly back and forth

  The string vibrates to make sound.

• conduct

  v. to allow heat or electricity to pass

  Metals conduct electricity well.

• generate

  v. to produce energy or something new

  Dams generate electricity from water.

• emit

  v. to send out light, heat, or gas

  The fire emits a warm glow.

• conserve

  v. to keep and protect from waste

  We should conserve clean water.

• reproduce

  v. to produce offspring

  Many fish reproduce in spring.

• inherit

  v. to receive traits from parents

  Children inherit genes from their parents.

• classify

  v. to arrange into groups by type

  Scientists classify animals into groups.

• analyze

  v. to examine something in detail

  They analyze the water for pollution.

• estimate

  v. to make a rough calculation

  Scientists estimate the age of the rock.

• predict

  v. to say what will happen in the future

  Models predict tomorrow's weather.

• contaminate

  v. to make something dirty or impure

  Oil can contaminate the river.

• decay

  v. to break down and rot

  Dead leaves decay on the ground.

• fertile

  adj. able to produce many plants or young

  Fertile soil grows healthy crops.

• toxic

  adj. poisonous and harmful to life

  The factory released toxic waste.

• soluble

  adj. able to dissolve in liquid

  Salt is soluble in water.

• solar

  adj. relating to the Sun

  Solar panels collect energy from the Sun.

• flexible

  adj. able to bend without breaking

  Rubber is a flexible material.

• microscopic

  adj. too small to see without a microscope

  Microscopic germs cover the skin.

• abundant

  adj. present in large amounts

  Water is abundant on Earth.

• scarce

  adj. available in small amounts

  Clean water is scarce in deserts.

• stable

  adj. not likely to change or move

  The chemical is stable at room temperature.

• visible

  adj. able to be seen

  The stars are visible at night.

• artificial

  adj. made by people, not natural

  Artificial light replaces sunlight indoors.

• organic

  adj. relating to living matter

  Organic material enriches the soil.

• genetic

  adj. relating to genes and heredity

  The disease has a genetic cause.

• fluid

  n. a liquid or gas that flows

  Blood is a fluid in the body.

• vapor

  n. a gas made from a liquid

  Water vapor rises into the sky.

• crust

  n. the hard outer layer of the Earth

  The Earth's crust is made of rock.

• core

  n. the central part of the Earth

  The Earth's core is extremely hot.

• layer

  n. a sheet of material covering a surface

  A thick layer of ice covered the pond.

• specimen

  n. an example used for study

  The scientist studied a leaf specimen.

• hypothesis

  n. an idea that can be tested by experiment

  Her hypothesis was proven by the test.

• laboratory

  n. a room used for scientific work

  They mixed the chemicals in the laboratory.

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