AP Biology Vocabulary

Abiotic factors

Nonliving chemical and physical components of an environment, such as temperature, light, water, and minerals.

Example: "Sunlight, temperature, and soil pH are all          that influence which organisms can survive in an ecosystem."

Absorption spectrum

A graph showing the wavelengths of light that a pigment absorbs; each pigment has a characteristic absorption spectrum.

Example: "The          of chlorophyll a shows peak absorption in the blue-violet and red regions of visible light."

Acetyl-CoA

A two-carbon molecule attached to coenzyme A that enters the citric acid cycle during cellular respiration; formed by oxidation of pyruvate.

Example: "After glycolysis, pyruvate is converted to          before entering the Krebs cycle in the mitochondrial matrix."

Acid

A substance that increases the hydrogen ion (H+) concentration of a solution, resulting in a pH below 7.

Example: "Hydrochloric acid in the stomach acts as an         , lowering the pH to help digest proteins."

Action potential

A rapid, temporary change in electrical potential across a neuron's membrane caused by the flow of ions through voltage-gated channels.

Similar definitions: nerve impulse

Example: "When a neuron is sufficiently stimulated, an          propagates along the axon toward the synaptic terminal."

Activation energy

The minimum amount of energy required to initiate a chemical reaction; enzymes lower this energy barrier.

Example: "Enzymes speed up reactions by lowering the          needed for the reaction to proceed."

Active site

The specific region of an enzyme where the substrate binds and the catalytic reaction occurs.

Example: "The substrate fits into the enzyme's          like a key fitting into a lock, though the shape may change upon binding."

Active transport

The movement of molecules across a cell membrane against their concentration gradient, requiring energy (usually ATP).

Example: "The sodium-potassium pump uses          to move Na+ out of and K+ into the cell."

Adaptive immunity

A vertebrate-specific defense system that develops targeted responses to specific pathogens and retains memory for future encounters.

Similar definitions: acquired immunity, specific immunity

Example: "After being vaccinated, a person develops          that enables a faster response upon re-exposure to the pathogen."

Adaptive radiation

The rapid diversification of a single ancestral species into many new species that fill different ecological niches.

Example: "Darwin's finches are a classic example of         , with each species evolving a beak shape suited to a different food source."

Adenine

A purine nitrogenous base found in DNA and RNA that pairs with thymine in DNA and uracil in RNA.

Example: "In DNA,          always forms two hydrogen bonds with thymine according to Chargaff's rules."

Adenosine triphosphate (ATP)

The primary energy-carrying molecule in cells, consisting of adenine, ribose, and three phosphate groups; energy is released when a phosphate bond is hydrolyzed.

Example: "Cells use          as their main energy currency to power metabolic processes."

Adhesion

The attraction between molecules of different substances, such as water molecules clinging to the walls of a xylem vessel.

Example: "         between water molecules and the xylem walls helps water travel upward in plants."

Aerobic respiration

A metabolic process that uses oxygen as the final electron acceptor to break down glucose and produce ATP through glycolysis, the citric acid cycle, and oxidative phosphorylation in eukaryotic mitochondria.

Example: "During         , a single molecule of glucose can yield up to 30-32 ATP."

Allele

An alternative form of a gene that arises by mutation and occupies a specific locus on a chromosome.

Example: "A pea plant may carry a dominant          for purple flowers and a recessive one for white flowers."

Allele frequency

The proportion of a specific allele relative to all alleles at that locus in a population's gene pool.

Example: "If 60 out of 100 alleles in a population are dominant, the          for the dominant allele is 0.6."

Allopatric speciation

The formation of new species when populations are geographically separated by a physical barrier, preventing gene flow.

Example: "A mountain range dividing a population of squirrels can lead to          over many generations."

Alternative splicing

A process by which the exons of a pre-mRNA are joined in different combinations, allowing a single gene to encode multiple proteins.

Example: "         explains how the human genome can produce far more proteins than the number of genes it contains."

Amino acid

An organic molecule containing an amino group, a carboxyl group, and a variable R group; the monomer of proteins.

Example: "There are 20 different          types that can be linked by peptide bonds to form polypeptides."

Amylase

An enzyme that catalyzes the hydrolysis of starch into simpler sugars; found in saliva and pancreatic secretions.

Example: "Salivary          begins the chemical digestion of carbohydrates in the mouth."

Anaerobic respiration

A metabolic process that generates ATP without oxygen, using an alternative electron acceptor (such as sulfate or nitrate) in the electron transport chain; distinct from fermentation, which does not use an electron transport chain.

Example: "Certain bacteria perform          using sulfate or nitrate instead of oxygen as the final electron acceptor."

Analogous structures

Body structures in different organisms that have similar functions but evolved independently, not from a common ancestor.

Similar definitions: convergent structures

Example: "The wings of birds and the wings of insects are          because they serve the same purpose but arose independently."

Anaphase

The stage of mitosis (or meiosis) during which chromosomes are pulled toward opposite poles of the cell. In mitosis and meiosis II, sister chromatids separate; in meiosis I, homologous chromosomes separate.

Example: "During         , the spindle fibers shorten and sister chromatids separate toward opposite ends of the cell."

Aneuploidy

A chromosomal condition in which a cell has an abnormal number of chromosomes due to nondisjunction during cell division.

Example: "Down syndrome is caused by         , specifically trisomy of chromosome 21."

Angiosperm

A flowering plant that produces seeds enclosed within a fruit; the most diverse group of land plants.

Similar definitions: flowering plant

Example: "An apple tree is an          because it produces flowers and encloses its seeds within a fleshy fruit."

Animal cell

A eukaryotic cell that lacks a cell wall and chloroplasts but contains centrioles and lysosomes; the basic unit of animal tissues.

Example: "Unlike plant cells, an          divides by forming a cleavage furrow rather than a cell plate."

Antibiotic resistance

The ability of bacteria to survive and reproduce in the presence of antibiotics, typically arising through natural selection of resistant variants.

Example: "Overuse of antibiotics accelerates the evolution of          in bacterial populations."

Antibody

A Y-shaped protein produced by B cells that binds to a specific antigen, marking it for destruction by the immune system.

Similar definitions: immunoglobulin

Example: "Each          has a unique variable region that allows it to recognize and bind a particular antigen."

Anticodon

A three-nucleotide sequence on tRNA that is complementary to a codon on mRNA, ensuring the correct amino acid is added during translation.

Example: "The tRNA carrying methionine has the          UAC, which pairs with the start codon AUG on the mRNA."

Antigen

A foreign molecule that is recognized by the immune system and triggers an immune response, often a protein on the surface of a pathogen.

Example: "Vaccines work by exposing the immune system to a harmless form of an          so that memory cells are produced."

Apical meristem

A region of undifferentiated cells at the tips of roots and shoots in plants that is responsible for primary growth in length.

Example: "Cell division in the          allows a plant stem to grow taller and roots to grow deeper."

Apoptosis

Programmed cell death, a genetically controlled process in which a cell self-destructs in an orderly fashion without triggering inflammation.

Similar definitions: programmed cell death

Example: "During embryonic development,          eliminates the webbing between fingers and toes."

Aposematic coloration

Bright, conspicuous coloring of an organism that warns predators of toxicity or unpalatability; a form of antipredator adaptation.

Example: "The bright orange and black pattern of a monarch butterfly is an example of          that warns birds of its toxicity."

Aquaporin

A channel protein embedded in cell membranes that facilitates the rapid passive transport of water molecules.

Example: "Kidney cells have many          proteins to efficiently reabsorb water from the filtrate."

Archaea

A domain of single-celled prokaryotes that are genetically and biochemically distinct from bacteria; many thrive in extreme environments.

Example: "Methanogens and thermophiles are examples of          that inhabit environments like hot springs and deep-sea vents."

Artificial selection

The selective breeding of organisms by humans to promote desirable traits over successive generations.

Similar definitions: selective breeding

Example: "Dog breeds are a product of         , in which humans chose individuals with specific traits to reproduce."

Asexual reproduction

A mode of reproduction involving a single parent that produces genetically identical offspring without the fusion of gametes.

Example: "Bacteria reproduce through          via binary fission, creating clones of the parent cell."

ATP synthase

A membrane-embedded enzyme complex that uses the flow of H+ ions down their concentration gradient to synthesize ATP from ADP and inorganic phosphate.

Example: "During chemiosmosis, protons pass through          to generate most of the ATP produced in cellular respiration."

Autosome

Any chromosome that is not a sex chromosome; humans have 22 pairs of autosomes.

Example: "A trait encoded on an          is inherited independently of the sex of the individual."

Autotroph

An organism that produces its own organic molecules from inorganic sources, using light energy or chemical energy.

Similar definitions: producer

Example: "Plants are classified as          because they use photosynthesis to convert CO2 and water into glucose."

Bacteriophage

A virus that infects and replicates within bacteria, often used as a tool in molecular biology research.

Similar definitions: phage

Example: "The Hershey-Chase experiment used a          to demonstrate that DNA, not protein, is the genetic material."

Barr body

A condensed, inactivated X chromosome visible as a dense spot in the nucleus of female mammalian cells.

Example: "In females, one X chromosome is randomly inactivated in each cell and appears as a          along the nuclear envelope."

Base

A substance that reduces the hydrogen ion (H+) concentration of a solution, resulting in a pH above 7.

Example: "Sodium hydroxide is a strong          that dissociates completely in water, raising the pH."

Base pair

Two complementary nitrogenous bases held together by hydrogen bonds in double-stranded DNA (A-T, G-C) or DNA-RNA hybrids.

Example: "The human genome contains approximately 3 billion          of DNA."

Batesian mimicry

A form of mimicry in which a harmless species evolves to resemble a harmful or toxic species, gaining protection from predators.

Example: "The viceroy butterfly exhibits          by resembling the toxic monarch butterfly."

Binary fission

A form of asexual reproduction in prokaryotes in which a cell divides into two genetically identical daughter cells.

Example: "Under optimal conditions, E. coli can undergo          every 20 minutes, rapidly increasing the population."

Biodiversity

The variety of life in an area, including diversity within species, between species, and among ecosystems.

Example: "Tropical rainforests have the highest          of any biome on Earth."

Biological fitness

The ability of an organism to survive and reproduce in its environment, measured by its relative contribution of alleles to the next generation; the central measure of evolutionary success.

Similar definitions: Darwinian fitness, reproductive fitness, relative fitness

Example: "An organism that produces more viable offspring than others in the population has higher         ."

Biological magnification

The process by which toxins become increasingly concentrated in organisms at higher trophic levels of a food chain.

Similar definitions: biomagnification

Example: "DDT accumulating in bald eagles' tissues is a well-known example of         ."

Biomass

The total mass of organic matter in organisms or an ecosystem at a given time.

Example: "An ecological pyramid of          shows that producers generally have the greatest mass in a terrestrial ecosystem."

Biome

A large-scale community of organisms defined primarily by its dominant vegetation and characterized by regional climate conditions.

Example: "The tundra is a          characterized by permafrost, low temperatures, and minimal tree growth."

Biosphere

The global sum of all ecosystems; the zone of life on Earth, extending from the deep ocean to the lower atmosphere.

Example: "The          includes every environment on Earth where living organisms are found."

Biotechnology

The use of living organisms or their components to develop products and technologies, such as genetic engineering and PCR.

Example: "Producing human insulin in bacteria through recombinant DNA techniques is an application of         ."

Biotic factors

Living components of an environment that influence other organisms, including predators, competitors, and pathogens.

Example: "Predators, parasites, and competing species are all          that can affect a population's size."

Bottleneck effect

A type of genetic drift that occurs when a population is drastically reduced in size by a catastrophic event, reducing genetic diversity.

Example: "The cheetah population shows very low genetic variation, likely due to a past         ."

Buffer

A substance that minimizes changes in pH by accepting or donating hydrogen ions when acids or bases are added to a solution.

Example: "Bicarbonate acts as a          in human blood, helping maintain a pH near 7.4."

C3 plant

A plant that uses only the Calvin cycle for carbon fixation, producing a three-carbon compound (3-PGA) as the first stable product; susceptible to photorespiration in hot, dry conditions.

Example: "Rice and wheat are          plants that may experience reduced photosynthetic efficiency on hot days due to photorespiration."

C4 plant

A plant that minimizes photorespiration by first fixing CO2 into a four-carbon compound in mesophyll cells before passing it to bundle-sheath cells for the Calvin cycle.

Example: "Corn and sugarcane are          plants that are more efficient at photosynthesis in hot climates."

Calvin cycle

The set of light-independent reactions in photosynthesis that uses ATP and NADPH to fix CO2 into G3P in the chloroplast stroma.

Similar definitions: light-independent reactions, C3 cycle

Example: "The          uses the enzyme RuBisCO to incorporate carbon dioxide into organic molecules."

CAM plant

A plant adapted to arid conditions that opens stomata at night to fix CO2 into organic acids, which are then used in the Calvin cycle during the day when stomata are closed.

Example: "Cacti and pineapples are          plants that conserve water by separating carbon fixation and the Calvin cycle temporally."

cAMP (cyclic AMP)

A cyclic nucleotide derived from ATP that serves as a second messenger in many signal transduction pathways within cells.

Example: "When a hormone binds to a G-protein-coupled receptor, adenylyl cyclase converts ATP to         , which activates protein kinase A."

Carbohydrate

An organic macromolecule composed of carbon, hydrogen, and oxygen, typically in a 1:2:1 ratio; includes sugars, starches, and cellulose.

Example: "Glucose is a simple          that serves as a primary source of energy for cells."

Carbon cycle

The biogeochemical cycle by which carbon is exchanged among the biosphere, atmosphere, oceans, and geosphere through processes like photosynthesis and respiration.

Example: "Burning fossil fuels releases stored carbon into the atmosphere, disrupting the natural         ."

Carbon fixation

The process by which inorganic carbon dioxide is incorporated into organic molecules, primarily by the enzyme RuBisCO during the Calvin cycle.

Example: "         is the first step of the Calvin cycle, in which CO2 is attached to RuBP."

Carrier protein

A membrane protein that changes shape to transport specific molecules across the cell membrane, used in both passive and active transport.

Example: "Glucose enters many cells via a          that undergoes a conformational change during facilitated diffusion."

Carrying capacity

The maximum population size of a species that an environment can sustain indefinitely given available resources.

Example: "When a population exceeds the          of its environment, resources become scarce and the growth rate declines."

Catalyst

A substance that speeds up a chemical reaction without being consumed or permanently altered in the process.

Example: "Enzymes function as biological          by lowering the activation energy of metabolic reactions."

Cell cycle

The ordered sequence of events in a cell's life from one division to the next, consisting of interphase and the mitotic phase.

Example: "Checkpoints in the          ensure that DNA is properly replicated before the cell proceeds to mitosis."

Cell membrane

A selectively permeable phospholipid bilayer that forms the outer boundary of all cells and controls the movement of substances in and out.

Similar definitions: plasma membrane

Example: "The          is described by the fluid mosaic model, with proteins embedded in a flexible lipid bilayer."

Cell plate

A structure that forms during cytokinesis in plant cells, developing into a new cell wall that divides the cell in two.

Example: "Unlike animal cells, plant cells form a          at the center of the dividing cell during cytokinesis."

Cell signaling

The process by which cells communicate with each other through chemical signals (ligands) that bind to receptors, triggering intracellular responses. Types include autocrine, paracrine, and endocrine signaling.

Example: "         allows cells in a multicellular organism to coordinate growth, immune responses, and homeostasis."

Cell theory

The fundamental biological concept stating that all living things are composed of cells, cells are the basic units of life, and all cells arise from pre-existing cells.

Example: "         is one of the unifying principles of biology, first articulated by Schleiden, Schwann, and Virchow."

Cell wall

A rigid outer layer surrounding the cell membrane of plants, fungi, bacteria, and some protists, providing structural support and protection.

Example: "The          of a plant cell is made primarily of cellulose and gives the cell a fixed shape."

Cellular respiration

The metabolic process by which cells break down glucose and other organic molecules to produce ATP, using oxygen in aerobic pathways.

Example: "         consists of glycolysis, the citric acid cycle, and oxidative phosphorylation."

Cellulose

A structural polysaccharide made of beta-glucose monomers that forms the primary component of plant cell walls.

Example: "Humans cannot digest          because they lack the enzyme cellulase needed to break its beta-1,4 glycosidic bonds."

Central dogma

The principle that genetic information flows from DNA to RNA to protein through the processes of transcription and translation.

Example: "The          of molecular biology describes the unidirectional flow of genetic information in cells."

Centriole

A cylindrical organelle composed of microtubule triplets found in animal cells; involved in organizing the mitotic spindle during cell division.

Example: "During mitosis, pairs of          migrate to opposite poles of the cell and help organize the spindle fibers."

Centromere

The constricted region of a chromosome where sister chromatids are joined and where the kinetochore forms for spindle fiber attachment.

Example: "Spindle fibers attach to the          of each chromosome to pull sister chromatids apart during anaphase."

Channel protein

A transmembrane protein that forms a hydrophilic pore allowing specific ions or small molecules to pass through the membrane by passive transport.

Example: "Potassium ions leave the neuron through a          during the repolarization phase of an action potential."

Chemiosmosis

The process by which ATP is produced using the energy of a proton gradient across a membrane, as H+ ions flow through ATP synthase.

Example: "         occurs in both mitochondria during cellular respiration and chloroplasts during photosynthesis."

Chemoautotroph

An organism that obtains energy by oxidizing inorganic chemicals and uses that energy to fix carbon dioxide into organic molecules.

Similar definitions: chemolithoautotroph

Example: "Bacteria near deep-sea hydrothermal vents are          that derive energy from hydrogen sulfide."

Chemotroph

An organism that obtains energy by oxidizing chemical compounds, either organic (chemoorganotroph) or inorganic (chemolithotroph).

Example: "Animals and fungi are          because they obtain energy from the chemical bonds in food molecules."

Chi-square test

A statistical test used to determine whether observed data differ significantly from expected values, commonly applied in genetics to test whether inheritance patterns match predicted ratios.

Example: "A          was used to determine whether the observed 3:1 phenotype ratio matched the expected Mendelian ratio."

Chitin

A structural polysaccharide made of modified glucose units that forms the exoskeletons of arthropods and the cell walls of fungi.

Example: "The hard outer shell of a crab is composed of         , which provides both protection and structural support."

Chlorophyll

A green photosynthetic pigment found in chloroplasts that absorbs light energy, primarily in the blue and red wavelengths, to drive photosynthesis.

Example: "         reflects green light, which is why most plant leaves appear green."

Chloroplast

A membrane-bound organelle in plant and algal cells where photosynthesis takes place, containing thylakoids and stroma.

Example: "The light reactions of photosynthesis occur in the thylakoid membranes of the         ."

Chromatid

One of the two identical copies of a replicated chromosome that are joined at the centromere; each becomes a separate chromosome after division.

Similar definitions: sister chromatid

Example: "After DNA replication, a chromosome consists of two sister          connected at the centromere."

Chromatin

The complex of DNA and histone proteins that makes up chromosomes; it can be loosely or tightly packed depending on the stage of the cell cycle.

Example: "During interphase, DNA exists as loosely packed         , which allows genes to be transcribed."

Chromosome

A threadlike structure of DNA and associated proteins in the nucleus that carries genetic information; visible during cell division.

Example: "Humans have 46          in each somatic cell, organized into 23 pairs."

Citric acid cycle

A cyclic series of reactions in the mitochondrial matrix that oxidizes acetyl-CoA, producing CO2, NADH, FADH2, and GTP.

Similar definitions: Krebs cycle, tricarboxylic acid (TCA) cycle

Example: "The          completes the oxidation of glucose and supplies electron carriers to the electron transport chain."

Clade

A group of organisms that includes an ancestor and all of its descendants, forming a single branch on a phylogenetic tree.

Similar definitions: monophyletic group

Example: "Mammals form a          because they all share a common ancestor that possessed mammary glands."

Cladistics

A method of classifying organisms based on shared derived characteristics to construct evolutionary relationships and cladograms.

Example: "         uses shared derived traits rather than overall similarity to determine how organisms are related."

Cladogram

A branching diagram that depicts the evolutionary relationships among groups of organisms based on shared derived characteristics.

Similar definitions: phylogenetic tree

Example: "By analyzing DNA sequences, scientists can construct a          showing the most likely pattern of evolutionary divergence."

Codominance

A pattern of inheritance in which both alleles are fully and simultaneously expressed in the heterozygote, with neither being dominant.

Example: "In         , a cow with both red and white alleles has a roan coat displaying patches of both colors."

Codon

A sequence of three nucleotides on mRNA that specifies a particular amino acid or a stop signal during translation.

Example: "The          AUG signals the start of translation and codes for the amino acid methionine."

Coenzyme

A small organic molecule, often derived from vitamins, that assists an enzyme by transferring chemical groups or electrons during a reaction.

Example: "NAD+ is a          that accepts electrons during glycolysis and the citric acid cycle."

Coevolution

The process by which two or more species reciprocally influence each other's evolution over time through close ecological interactions.

Example: "The relationship between flowering plants and their pollinators is an example of         ."

Cofactor

A non-protein chemical compound or metal ion that is required for an enzyme's activity; can be inorganic ions or organic coenzymes.

Example: "Zinc acts as a          for many enzymes, including DNA polymerase, by stabilizing the enzyme's structure."

Cohesion

The attraction between molecules of the same substance, such as the hydrogen bonding between water molecules.

Example: "         among water molecules creates surface tension, allowing small insects to walk on water."

Commensalism

A symbiotic relationship in which one organism benefits while the other is neither helped nor harmed.

Example: "Barnacles growing on a whale's skin is an example of         ; the barnacles gain access to food while the whale is unaffected."