Biology Unit 2 Test Terms

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A substance that donates hydrogen ions to solutions (lower on pH scale)


Water is attracted to other like, polar substances. (Property of Water)


The smallest unit of matter that retains the properties of an element.

atomic mass

Protons added to neutrons.

atomic number

The number of protons in each atom of a particular element.


A substance that reduces the hydrogen ion concentration of a solution (higher on a pH scale)


A chemical substance that minimizes changes in pH by accepting hydrogen ions from or donating hydrogen ions to solutions.

chemical bond

An attraction between two atoms resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells.

chemical reaction

The making and breaking of chemical bonds, leading to changes in the composition of matter


The sticking together of molecules of the same kind, often by hydrogen bonds.


A substance containing two or more elements in a fixed ratio. For example, table salt (NaCl) consists of one atom of the element sodium (Na) for every atom of chlorine (Cl).

covalent bond

A type of strong chemical bond in which two atoms share one or more pairs of valence electrons.


A subatomic particle with a single negative electrical charge.

electron shell

A level of electrons at a characteristic average distance from the nucleus of an atom


The attraction of a given atom for the electrons of a covalent bond


A substance that cannot be broken down to other substances by chemical means.

evaporative cooling

The process in which the surface of an object becomes cooler during evaporation, a result of the molecules with the greatest energy changing from the liquid to the gaseous state


Thermal energy in transfer from one body of matter to another

hydrogen bond

A type of weak chemical bond formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule (or in another region of the same molecule)


An atom or group of atoms that has gained or lost one or more electrons, thus acquiring an electrical charge.

ionic bond

A chemical bond resulting from the attraction between oppositely charged ions.


One of several atomic forms of an element, each with the same number of protons but a different number of neutrons.

mass number

The sum of the number of protons and neutrons in an atom’s nucleus


Anything that occupies space and has mass


Two or more atoms held together by covalent bonds


A subatomic particle having no electrical charge, found in the nucleus of an atom

nonpolar covalent bonds

A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity.


An atom’s central core, containing protons and neutrons

pH scale

A measure of the acidity of a solution, ranging in value from 0 (most acidic) to 14 (most basic)

polar covalent bond

A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive.

polar molecule

A molecule containing polar covalent bonds and having an unequal distribution of charges


A subatomic particle with a single positive electrical charge, found in the nucleus of an atom.


A substance that is dissolved in a solution


A liquid that is a homogeneous mixture of two or more substances


The dissolving agent of a solution.

surface tension

A measure of how difficult it is to stretch or break the surface of a liquid

trace element

An element that is essential for life but required in extremely minute amounts

amino acid

An organic molecule containing a carboxyl group and an amino group; serves as the monomer of proteins

amino group

A chemical group consisting of a nitrogen atom bonded to two hydrogen atoms


Member of the class of biological molecules consisting of single-monomer sugars (monosaccharides), two-monomer sugars (disaccharides), and polymers (polysaccharides)


A structural polysaccharide of plant cell walls composed of glucose monomers


A structural polysaccharide found in many fungal cell walls and in the exoskeletons of arthropods.


A steroid that is an important component of animal cell membranes and that acts as a precursor molecule for the synthesis of other steroids, such as hormones

dehydration reaction

A chemical reaction in which two molecules become covalently bonded to each other with the removal of a water molecule


A process in which a protein unravels, losing its specific structure and hence function; can be caused by changes in pH or salt concentration or by high temperature

deoxyribonucleic acid (DNA)

A double-stranded helical nucleic acid molecule consisting of nucleotide monomers with deoxyribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T)


A sugar molecule consisting of two monosaccharides linked by a dehydration reaction

double helix

The form of native DNA, referring to its two adjacent polynucleotide strands interwound into a spiral shape


macromolecule, usually a protein, that serves as a biological catalyst, changing the rate of a chemical reaction without being consumed by the reaction