Biology Unit 2 Vocabulary

Vocabulary flashcards covering key definitions from sections 2.1 to 2.5 on atoms, chemical bonds, properties of water, carbon-based molecules, chemical reactions, and enzymes.

Atom

The smallest basic unit of matter.

Element

One particular type of atom that cannot be broken down into a simpler substance by ordinary chemical means.

Compound

A substance made of atoms of different elements bonded together in a certain ratio.

Ion

An atom that has gained or lost one or more electrons.

Ionic bond

A chemical bond that forms through the electrical force between oppositely charged ions.

Covalent bond

A chemical bond that forms when atoms share a pair of electrons.

Molecule

Two or more atoms held together by covalent bonds.

Hydrogen bond

An attraction between a slightly positive hydrogen atom and a slightly negative atom, often oxygen or nitrogen.

Cohesion

The attraction among molecules of a substance.

Adhesion

The attraction among molecules of different substances.

Solution

A mixture of substances that is the same throughout; it is a homogeneous mixture.

Solvent

The substance that is present in the greater amount and that dissolves another substance.

Solute

A substance that dissolves in a certain amount of solvent.

Acid

A compound that releases a proton—a hydrogen ion ($H^+$)—when it dissolves in water.

PH

A solution's acidity, or $H^+$ ion concentration.

Monomer

Small carbon-based molecule subunits in an entire molecule, which are linked like a chain with each subunit in the complete molecule.

Polymer

A large molecule, or macromolecule, made of many monomers bonded together.

Carbohydrates

Molecules composed of carbon, hydrogen, and oxygen, which include sugars and starches.

Lipids

Nonpolar molecules that include fats, oils, and cholesterol.

Fatty acids

Chains of carbon atoms bonded to hydrogen atoms.

Protein

A polymer made of monomers called amino acids.

Amino acids

Molecules that contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.

Nucleic acids

Polymers that are made up of monomers called nucleotides.

Chemical reactions

Processes that change substances into different substances by breaking and forming chemical bonds.

Reactants

The substances changed during a chemical reaction.

Products

The substances made by a chemical reaction.

Bond energy

The amount of energy that will break a bond between two atoms.

Equilibrium

The state reached when both the reactants and products are made at the same rate.

Activation energy

The amount of energy that needs to be absorbed for a chemical reaction to start.

Exothermic

A type of chemical reaction that releases more energy than it absorbs.

Endothermic

A type of chemical reaction that absorbs more energy than it releases.

Catalyst

A substance that decreases the activation energy needed to start a chemical reaction and, as a result, also increases the rate of the chemical reaction.

Enzymes

Catalysts for chemical reactions in living things.

Substrates

The specific reactants that an enzyme acts on.