AP Biology Study Guide — Chapters 2, 3 & 4

Comprehensive vocabulary flashcards covering key chemical concepts, water properties, and carbon chemistry from Chapters 2, 3, and 4 of Campbell Biology (12th Edition).

Matter

Anything that occupies space and has mass.

Element

A substance that cannot be broken down into other substances by chemical reactions.

Compound

A substance consisting of two or more different elements combined in a fixed ratio, exhibiting properties distinct from those of its constituent elements.

Essential elements

Elements required by an organism for health and survival; oxygen, carbon, hydrogen, and nitrogen make up approximately $96\%$ of living matter.

Trace elements

Elements indispensable for life but required in only minute quantities, such as iron and iodine.

Proton

A subatomic particle with a single positive electrical charge ($+1$) found in the nucleus of an atom that determines the element's identity and atomic number.

Neutron

An electrically neutral subatomic particle (charge of $0$) located in the atomic nucleus that contributes to mass and changes the isotope of an element.

Electron

A subatomic particle with a single negative charge ($-1$) found in the electron cloud around the nucleus that controls bonding and chemical behavior.

Atomic number ($Z$)

The number of protons in the nucleus of an atom, which uniquely identifies an element and equals the number of electrons in an electrically neutral atom.

Mass number ($A$)

The total sum of protons and neutrons in the nucleus of an atom ($A = \text{protons} + \text{neutrons}$).

Isotopes

Different atomic forms of the same element that possess identical numbers of protons but different numbers of neutrons, resulting in different mass numbers.

Radioactive isotope

An unstable isotope whose nucleus decays spontaneously, releasing detectable particles and energy.

Valence shell

The outermost occupied electron shell of an atom.

Valence electrons

Electrons residing in the outermost occupied shell of an atom that dictate its chemical reactivity and bonding capacity.

Orbital

A three-dimensional space where an electron is found $90\%$ of the time; each individual orbital holds a maximum of two electrons.

Nonpolar covalent bond

A type of chemical bond formed when electrons are shared equally or nearly equally between two atoms of similar electronegativity, producing no strong bond dipole.

Polar covalent bond

A covalent bond between atoms that differ in electronegativity, causing unequal sharing of electrons and generating partial electrical charges ($\delta^+$ and $\delta^-$).

Electronegativity

The attraction of a particular atom for the shared electrons of a covalent bond.

Ionic bond

A chemical attraction between oppositely charged ions formed after the transfer of one or more valence electrons.

Hydrogen bond

A noncovalent attraction between a partially positive hydrogen atom ($\delta^+$) and an electronegative atom ($\delta^-$), such as between neighboring water molecules.

Van der Waals interactions

Weak, transient attractions between molecules or parts of molecules that occur when temporary asymmetrical electron distributions create brief dipoles.

Dynamic chemical equilibrium

The state in a reversible chemical reaction where the forward and reverse reactions proceed at equal rates, keeping reactant and product concentrations constant over time.

Cohesion

The linking together of like molecules, primarily through hydrogen bonding among water molecules.

Adhesion

The clinging of one substance to another, such as water molecules forming hydrogen bonds with polar cell walls in plants.

Surface tension

A measure of how difficult it is to stretch or break the surface of a liquid, caused by the strong cohesive hydrogen bonding at the liquid-air interface.

Specific heat

The amount of heat that must be absorbed or lost for $1\,\text{g}$ of a substance to change its temperature by $1^\circ\text{C}$.

Heat of vaporization

The quantity of heat a liquid must absorb for $1\,\text{g}$ of it to be converted from the liquid state to the gaseous state.

Evaporative cooling

The process in which the surface of a liquid cools down during evaporation because the molecules with the highest kinetic energy escape as gas.

Hydration shell

The sphere of water molecules surrounding each dissolved ion, oriented according to partial electrical charges.

Hydrophilic

Having an affinity for water; typically ionic or polar substances that interact favorably with or dissolve in water.

Hydrophobic

Having no affinity for water; nonpolar and nonionic substances that do not dissolve readily in water.

Molarity ($\text{M}$)

A concentration unit defined as the number of moles of solute dissolved in one liter of solution ($\text{moles of solute} \div \text{liters of solution}$).

Acid

A substance that donates hydrogen ions ($\text{H}^+$) to a solution, thereby increasing the hydrogen ion concentration.

Base

A substance that reduces the hydrogen ion ($\text{H}^+$) concentration of a solution by accepting $\text{H}^+$ or by releasing $\text{OH}^-$.

pH

A measure of the hydrogen ion concentration of an aqueous solution, defined as $-\log_{10}[\text{H}^+]$.

Buffer

A substance that minimizes changes in the concentrations of $\text{H}^+$ and $\text{OH}^-$ in a solution by accepting excess $\text{H}^+$ or donating $\text{H}^+$.

Ocean acidification

The process whereby excess atmospheric $\text{CO}_2$ dissolves into seawater to form carbonic acid ($\text{H}_2\text{CO}_3$), releasing $\text{H}^+$, lowering ocean pH, and depleting carbonate ions ($\text{CO}_3^{2-}$) required for calcification.

Vitalism

The historical belief that organic compounds could only be synthesized within living organisms due to a distinct life force.

Stanley Miller's experiment

A 1953 laboratory experiment that demonstrated organic compounds can form abiotically under conditions simulating early Earth using simple gases, water, and electrical discharges.

Hydrocarbon

An organic molecule consisting exclusively of carbon and hydrogen atoms, characterized by nonpolar and hydrophobic properties.

Structural isomers

Compounds that have the same molecular formula but differ in the covalent arrangements of their carbon skeletons or double-bond locations.

Cis-trans isomers

Molecules that share the same covalent bonds but differ in their spatial arrangements around an inflexible, rigid double bond.

Enantiomers

Isomers that are non-superimposable mirror images of each other, typically occurring when a carbon atom is bonded to four different groups.

Asymmetric carbon

A carbon atom covalently bonded to four different atoms or groups of atoms, forming a chiral center capable of producing enantiomers.

Hydroxyl group

A chemical group consisting of a hydrogen atom bonded to an oxygen atom ($\text{–OH}$); polar, capable of hydrogen-bonding with water, and characteristic of alcohols.

Carbonyl group

A chemical group featuring a carbon atom double-bonded to an oxygen atom ($>\text{C=O}$); forms ketones within a skeleton or aldehydes at the end of a skeleton.

Carboxyl group

A functional group consisting of a single carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group ($\text{–COOH}$); acts as an acid by donating $\text{H}^+$.

Amino group

A functional group consisting of a nitrogen atom bonded to two hydrogen atoms ($\text{–NH}_2$); acts as a base by accepting $\text{H}^+$.

Sulfhydryl group

A chemical group composed of a sulfur atom bonded to a hydrogen atom ($\text{–SH}$); two groups can interact to form covalent disulfide cross-links that stabilize protein structure.

Phosphate group

A phosphorus atom covalently bonded to four oxygen atoms ($\text{–OPO}_3^{2-}$); carries a negative charge and plays a central role in energy storage and transfer.

Methyl group

A nonpolar, unreactive chemical group consisting of a carbon atom bonded to three hydrogen atoms ($\text{–CH}_3$); can alter molecular shape and influence gene expression.

Adenosine triphosphate (ATP)

An organic molecule consisting of adenosine attached to three phosphate groups that releases usable cellular energy upon reaction with water to form ADP and inorganic phosphate.