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ACT Science Vocabulary

Key Concepts:

Terms in this set (61)

Absolute zero
Approximately -273° C; the lowest possible temperature
Acid
A compound that releases hydrogen ions when dissolved in water; has a pH of less than 7
Algae
Simple, one-celled plantlike organism found in water or damp places; includes seaweeds, pond scum, and so on
Alloy
A substance composed of two or more metals
Atmosphere
The layer of air surrounding Earth
Atmospheric pressure
The pressure exerted by the atmosphere on every part of Earth's surface; approximately 10 newtons per square centimeter
Atom
The smallest part of an element that is recognizable as that element
Barometer
An instrument that measures atmospheric pressure
Base
A compound that releases hydroxide ions in water; has a pH of more than 7; is sometimes called an alkali
Boiling point
The temperature at which additional thermal energy causes a substance to change from a liquid to a vapor
Calorie
A quantity of heat energy; the amount needed to raise the temperature of one gram of water 1° C
Carbohydrate
An organic compound-like sugar or starch that contains carbon, hydrogen, and oxygen in the ratio of 1:2:1; the human body's main source of energy
Carcinogen
A cancer-causing agent
Carnivore
Meat-eater
Catalyst
A substance that speeds up a chemical reaction without being changed by the reaction
Cell
The lowest-level structure of any living organism that can perform all the functions of life, including reproduction
Chlorophyll
The main pigment in plants that captures light energy during photosynthesis
Compound
A substance composed of two or more chemically bonded elements
Concentration
The exact amount of substance dissolved in a given amount of solvent; refers to a solution
Condensation
The process whereby a decrease in energy causes vapor particles to return to a liquid phase
Conductor
A material that allows heat or electricity to flow through it with minimal resistance
Control
A sample in which no variables are tested, thus serving as a basis for comparison
Control variable
A variable that stays constant in an experiment, allowing the effect of another variable to be measured
Convection
The circulation of fluid caused by warm fluid rising and cool fluid sinking
Density
In a physics sense, the amount of mass per unit volume; in a more general sense, the quantity per unit area or volume
Diffusion
The scattering of light; the spreading of a liquid or gas from areas of higher concentration to areas of lower concentration
DNA
Nucleic acid in the cells of an organism; contains the genes of an organism and transmits these to future generations
Ecological succesion
A sequence of changes in the plant and/or animal life of a region over time
Electron
A negatively charged fundamental atomic particle
Element
A substance consisting of exactly one type of atom
Erosion
Wearing away; typically the washing away of sand or rock by running water or wind
Evaporation
The changing of a fluid into gas
Fossil
The preserved remains of a very old organism
Frequency
The number of cycles per unit time of a repeating phenomenon
Glucose
A simple sugar that is broken down to provide energy to an organism
Habitat
The part of an ecosystem where a plant or animal naturally grows or lives
Herbivore
An animal that eats only plants
Hormone
A chemical substance secreted by a gland of the body that affects other parts of the body
Humidity
The amount of water vapor in the air
Hypothesis
A statement that is a proposed explanation of a scientific phenomenon
Infrared radiation
Electromagnetic waves whose wavelength is longer than that of visible light
Insulator
A substance that blocks the flow of heat or electricity
Ion
A molecule or atom that has become charged by either gaining or losing an electron
Isotope
A variety of an element with the same number of protons per atom but a different number of neutrons
Kinetic energy
The energy of an object due to its motion
Melting point
The temperature at which additional thermal energy breaks the chemical bonds holding a substance together and causes the substance to change from the solid to a liquid state
Molecule
The smallest unit of a chemical compound
Neutron
A fundamental atomic particle that has no charge
Ore
A piece of rock from which metal can be profitably extracted
Osmosis
The movement of liquid through a membrane
Parasite
An organism that invades another organism and feeds off it
pH
A numerical scale from 1-14 representing the acidity or alkalinity of a solution; 1 is very acidic, 14 is very alkaline, and 7 is neutral
Photosynthesis
The process in which plants use the sun's energy to convert carbon dioxide and water into glucose
Pressure
Force per unit area
Protein
A complex molecule composed of amino acids that carries out a variety of processes in cells
Proton
A positively charged fundamental atomic particle
Starch
A complex carbohydrate found in potatoes, rice, corn, and many other vegetables
Symbiosis
A close relationship between two organisms that is mutually beneficial
Ultraviolet radiation
Electromagnetic waves with wavelength shorter than that of visible light
Vapor
The gaseous form of a liquid
X ray
Electromagnetic radiation with wavelength shorter than ultraviolet radiation
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