Biology Holt McDougal Chapter 2

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atom

smallest basic unit of matter

compound

substance made of atoms of different elements that are bonded together in a set ratio

covalent bond

chemical bond formed when two atoms share one or more pairs of electrons

element

substance made of only one type of atom that cannot be broken down by chemical means

ion

atom that has gained or lost one or more electron

ionic bond

chemical bond formed between oppositely charged ions

molecule

two or more atoms held together by covalent bonds, not necessarily a compound

hydrogen bond

attraction between a slightly positive hydrogen atom and a slightly negative atom

cohesion

attration between molecules of the same substance

adhesion

attractions between molecules of different substances

solution

mixture that is consistant throughout: also called a homogeneous mixture

solute

substance that dissolves in a solvent and is present at a lower concentration than the solvent

solvent

substance in which solutes dissolve and that is present in greatest concentration in a solution

acid

substance that gives up a proton (H+) when dissolved in a solution

base

compound that takes up a proton (H+) when dissolved in a solution

pH

measurement of acidity; related to the concentration of free hydrogen in a solution

monomer

molecular subunit of a polymer

polymer

large, carbon-based molecule formed by the smaller sub-units called monomers

carbohydrate

molecule made of carbon of carbon, hydrogen, and oxygen; includes sugers and starches

fatty acid

hydrocarbon chain often bonded to glycerol in a lipid

protein

polymer made up of amino acids linked by peptide bonds; folds into a particular structure depending on bonds between amino acids

lipid

nonpolar molecule made up of carbon, hydrogen, and oxygen; includes fats and oils

nucleic acid

polymer of nucleotides; the genetic material of organisms

chemical reaction

process by which substances turn into different substances through the making and breaking of chemical bonds

reactant

substance that is changed by a chemical reation

product

substance formed by a chemical reation

bond energy

amount of energy needed to break a bond between two particular atons; or the amount of energy released when a bond forms between two particular atoms

equilibrium

condition in which reactants and products of a chemical reaction are formed at the same rate

activation energy

the lowest amount of energy needed to start a chemical reaction

exothermic

chemical reaction that yields a net release of energy in the form of heat

endothermic

chemical reaction that requires a net input of energy

amino acid

molecule that makes up proteins; made of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur

catalyst

substance that decreases activation energy and increases reaction rate in a chemical reaction

enzyme

protein that catalyzes chemical reactions in organisms

substrate

reactant in a chemical reaction upon which an enzyme acts

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