center of an atom; contains neutrons and protons. In eukaryotic cells, the central membrane-bound organelle that manages cellular functions and contains DNA
pure substance composed of only one type of atom; cannot be broken down into another substance by physical or chemical means
atom that is negatively or positively charged because it have lost or gained one or more electrons.
energy-requiring process by which atoms or groups of atoms in substances are changed into different substances
substance that exists before a chemical reaction starts; located on the left side of the arrow in a chemical reaction.
substance formed by a chemical reaction; located on the right side of the arrow in a chemical equation.
protein that speeds up a biological reaction by lowering the activation energy needed to start the reaction
combination of two or more different substances in which each substance keeps its individual characteristics; can have a uniform composition (homogeneous) or have distinct areas of substances (heterogeneous).
homogeneous mixture formed when a substance (the solute) is dissolved in another substance (the solvent).
substance that releases hydrogen ions (H+) when dissolved in water; an acidic solution has a pH less than 7.
substance that releases hydroxide ions (OH-) when dissolved in water; a basic solution has a pH greater than 7.
large molecule formed from smaller repeating units or identical, or nearly identical, compounds linked by covalent bonds.
organic compound containing carbon, hydrogen, and oxygen in a ratio of on oxygen and two hydrogen atoms for each carbon atom.
hydrophobic biological molecule composed mostly or carbon and hydrogen; fats, oils, and waxes are lipids
organic compound made of amino acids joined by peptide bonds; primary building block of organisms.