AP Biology Units 1 & 2: Chemistry of Life, Cell Structure, and Transport

Comprehensive vocabulary flashcards covering the key terms, molecular structures, cellular organelles, and transport concepts from AP Biology Units 1 and 2.

Polar Covalent Bond

A covalent bond formed between atoms with different electronegativities, causing electrons to be shared unequally and creating partial positive and partial negative charges.

Hydrogen Bond

A weak intermolecular attraction formed when the partial negative charge on an electronegative atom (such as oxygen) in one molecule is attracted to the partial positive charge on a hydrogen atom in another molecule.

Cohesion

The property of water molecules being attracted to one another due to hydrogen bonding, giving water a high surface tension.

Adhesion

The attraction of water molecules to other polar or charged surfaces, assisting in capillary action.

Capillary Action

The ability of water to move upward through narrow tubes, such as plant xylem, driven by the combined effects of cohesion and adhesion against the pull of gravity.

Specific Heat

The amount of energy required to change the temperature of a substance; water has a high specific heat because substantial energy is required to break hydrogen bonds between water molecules.

Hydration Shell

A surrounding sphere of oriented water molecules that forms around dissolved ions or polar molecules due to electrostatic attractions with water's partial charges.

pH

A logarithmic measure of the concentration of $H^+$ ions in a solution; a pH less than $7$ is acidic, equal to $7$ is neutral, and greater than $7$ is basic.

Buffer

A substance or chemical system in living cells that helps maintain a relatively constant pH level by absorbing or releasing $H^+$ ions in response to fluctuating pH.

Carbonic Acid–Bicarbonate System

A critical blood plasma buffering system in which dissolved carbon dioxide reacts with water to form carbonic acid ($H_2CO_3$), which dissociates into bicarbonate ions ($HCO_3^-$) and hydrogen ions ($H^+$) to neutralize excess acid or base.

Dehydration Synthesis

A chemical reaction that links monomer building blocks together to form polymers by removing a water molecule and creating a covalent bond.

Hydrolysis

A chemical reaction that breaks down biological macromolecules into smaller monomers through the addition of a water molecule.

Carbohydrate

A biological macromolecule composed of sugar monomers joined in linear or branched chains, functioning in energy storage (such as starch and glycogen) or structural support (such as cellulose).

Saturated Fatty Acid

A fatty acid hydrocarbon chain containing the maximum number of single $C\text{--}H$ bonds and no $C=C$ double bonds; it forms straight chains, packs tightly, is solid at room temperature, and usually originates in animals.

Unsaturated Fatty Acid

A fatty acid containing at least one $C=C$ double bond that creates kinks in the hydrocarbon chain, preventing tight packing and making it liquid at room temperature; usually originates in plants.

Phospholipid

An amphipathic lipid composed of a glycerol molecule bonded to two hydrophobic fatty acid tails and one hydrophilic phosphate head, forming the cell membrane bilayer.

Steroid

A class of nonpolar lipids characterized by a structure of four carbon-based fused rings, often synthesized by modifying cholesterol (e.g., estradiol, testosterone, cortisol, and vitamin D).

Amino Acid

The monomer subunit of proteins, consisting of a central carbon atom bonded to an amino group, a carboxylic acid group, a hydrogen atom, and a unique variable side chain (R-group).

Peptide Bond

The covalent bond formed through dehydration synthesis between the carboxyl group of one amino acid and the amino group of another amino acid.

Primary Protein Structure

The unique linear sequence of amino acids in a polypeptide chain held together by covalent peptide bonds, extending from the amino ($NH_2$) terminus to the carboxyl ($COOH$) terminus.

Secondary Protein Structure

Localized folding patterns within a polypeptide chain, such as alpha helices and beta-pleated sheets, driven by hydrogen bonding between backbone atoms of adjacent amino acids.

Tertiary Protein Structure

The overall three-dimensional shape of a single polypeptide, stabilized by interactions among variable R-groups, including hydrophobic interactions, hydrogen bonds, ionic bonds, and disulfide bridges.

Quaternary Protein Structure

The structure resulting from the assembly and functional association of two or more individual polypeptide chains or subunits, such as the four subunits of hemoglobin or the three of collagen.

Protein Denaturation

The loss of a protein's native three-dimensional conformation and biological function caused by external stress, such as extreme pH or temperature, which disrupts noncovalent bonds and interactions.

Nucleotide

The monomer building block of nucleic acids, consisting of a five-carbon sugar (ribose or deoxyribose), a nitrogenous base, and a phosphate group covalently linked to the $5'$ carbon.

Pyrimidine

A class of single-ring nitrogenous bases that includes cytosine, thymine (in DNA), and uracil (in RNA).

Purine

A class of double-ring nitrogenous bases that includes adenine and guanine.

Antiparallel Strands

The complementary orientation of the two strands in a DNA double helix, where the $5'$ phosphate end of one strand runs opposite to the $3'$ hydroxyl end of the complementary strand.

Melting Temperature ($T_m$)

The temperature at which $50\%$ of double-stranded DNA molecules dissociate into single strands; higher GC content elevates $T_m$ because GC base pairs share three hydrogen bonds compared to two in AT pairs.

Nucleoid Region

The non-membrane-enclosed central area in a prokaryotic cell where the circular chromosomal DNA is located.

Plasmid

A small, circular, extra-chromosomal piece of DNA found in bacteria that can replicate independently of the bacterial chromosome.

Ribosome

A non-membrane-bound subcellular complex composed of ribosomal RNA (rRNA) and proteins that carries out protein synthesis during translation.

Rough Endoplasmic Reticulum

A compartmentalized network of flattened membrane channels studded with bound ribosomes, specialized for the synthesis and structural modification of proteins.

Smooth Endoplasmic Reticulum

A tubular membrane network lacking ribosomes that functions in lipid synthesis and the detoxification of harmful substances and metabolic byproducts.

Golgi Complex

A series of flattened membrane sacs called cisternae with internal lumens that modifies, packages, and sorts proteins into transport vesicles.

Lysosome

A membrane-bound organelle filled with hydrolytic enzymes that digests macromolecules, recycles worn-out organelles, destroys pathogens, and participates in apoptosis.

Vacuole

A membrane-bound sac that functions in water regulation, cellular storage, waste containment, and the generation of internal turgor pressure in plant cells.

Mitochondrion

A double-membraned organelle containing an enzyme-rich fluid matrix and a highly folded inner membrane (cristae) for ATP synthesis; contains its own circular DNA and ribosomes.

Chloroplast

A double-membraned photosynthetic organelle in plants and algae consisting of thylakoid discs stacked into grana and surrounded by stroma; contains its own circular DNA and ribosomes.

Amyloplast

A specialized organelle in plant cells, particularly in roots and starchy tubers, that stores excess glucose in the form of starch granules.

Endomembrane System

A coordinated intracellular system comprising the nuclear envelope, endoplasmic reticulum, Golgi complex, lysosomes, vacuoles, vesicles, and plasma membrane that processes and transports cellular products.

Endosymbiosis Hypothesis

The evolutionary theory stating that eukaryotic membrane-bound organelles (mitochondria and chloroplasts) originated from free-living prokaryotes engulfed by ancestral host cells.

Surface Area to Volume Ratio

A mathematical relationship ($\frac{\text{SA}}{V}$) that dictates a cell's exchange efficiency with its environment; as cell radius increases, this ratio decreases, constraining maximum cell size.

Fluid Mosaic Model

A model describing the structural arrangement of the plasma membrane as a dynamic phospholipid bilayer embedded with laterally diffusing proteins, glycoproteins, glycolipids, and steroids.

Passive Transport

The net movement of molecules down their concentration gradient from an area of higher concentration to an area of lower concentration without the expenditure of cellular energy.

Facilitated Diffusion

A saturable form of passive transport where polar or charged molecules move down their concentration gradient across a membrane using specific channel or carrier proteins.

Aquaporin

A specialized transmembrane channel protein that facilitates the rapid, large-scale passive transport of water molecules across the cell membrane.

Active Transport

The movement of ions or molecules across a cellular membrane against their concentration gradient (from low to high concentration), requiring cellular energy input such as ATP.

Sodium-Potassium ($Na^+/K^+$) Pump

An active transport membrane protein that hydrolyzes ATP to export three $Na^+$ ions out of the cell and import two $K^+$ ions into the cell, establishing an electrochemical membrane potential.

Endocytosis

An energy-requiring active transport process by which the cell internalizes external fluids or macromolecules through the invagination and pinching off of the plasma membrane into vesicles.

Exocytosis

An energy-dependent form of bulk active transport in which intracellular vesicles fuse with the plasma membrane to secrete macromolecules into the extracellular space.

Water Potential ($\Psi$)

The measure of the potential energy of water per unit volume in a system relative to pure water, calculated as $\Psi = \Psi_s + \Psi_p$; water always moves from higher to lower water potential.

Solute Potential ($\Psi_s$)

The component of water potential that is directly dependent on solute concentration, calculated by $\Psi_s = -iCRT$; it is $0\,\text{bars}$ for pure water and becomes increasingly negative as solute is added.

Pressure Potential ($\Psi_p$)

The physical hydrostatic pressure exerted on or by a solution; it equals $0\,\text{bars}$ in open containers at atmospheric equilibrium and can be positive (turgor) or negative (tension).

Hypertonic Solution

A solution that has a higher concentration of solute (and therefore a lower water potential) compared to another reference solution.

Hypotonic Solution

A solution that has a lower concentration of solute (and therefore a higher water potential) compared to another reference solution.

Isotonic Solution

A solution that has an equal solute concentration (and equal water potential) relative to another solution, resulting in zero net movement of water.

Osmolarity

The total molar concentration of all solute particles dissolved in a given volume of solution.

Contractile Vacuole

A specialized osmoregulatory organelle in freshwater unicellular organisms that accumulates and periodically pumps out excess incoming water to prevent cell swelling and lysis.