AP Bio Vocab

Vocabulary for AP Biology, with words and definitions coming from the Campbell BIOLOGY 11e, AP® Edition textbook chapters 2-26, 40, 43, 45, 48, 51, and 53-55.

5' cap

A modified form of guanine nucleotide added onto the nucleotide at the 5' end of a pre-mRNA molecule.

A site

One of a ribosome's three binding sites for tRNA during translation. It holds the tRNA carrying the next amino acid to be added to the polypeptide chain.

absorption spectrum

The range of a pigment's ability to absorb various wavelengths of light; also a graph of such a range.

acclimatization

Physiological adjustment to a change in an environmental factor.

acetyl CoA

Acetyl coenzyme A; the entry compound for the citric acid cycle in cellular respiration, formed from a two-carbon fragment of pyruvate attached to a coenzyme.

acetylcholine

One of the most common neurotransmitters; functions by binding to receptors and altering the permeability of the postsynaptic membrane to specific ions, either depolarizing or hyperpolarizing the membrane.

acid

A substance that increases the hydrogen ion concentration of a solution.

acquired immunideficiency syndrome (AIDS)

The symptoms and signs present during the late stages of HIV infection, defined by a specified reduction in the number of T cells and the appearance of characteristic secondary infections.

actin

A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.

action potential

An electrical signal that propagates (travels) along the membrane of a neuron or other excitable cell as a nongraded (all-or-none) depolarization.

action spectrum

A graph that profiles the relative effectiveness of different wavelengths of radiation in driving a particular process.

activation energy

The amount of energy that reactants must absorb before a chemical reaction will start; also called free energy of activation.

activator

A protein that binds to DNA and stimulates gene transcription. In prokaryotes, activators bind in or near the promoter; in eukaryotes, activators generally bind to control elements in enhancers.

active immunity

Long-lasting immunity conferred by the action of B cells and T cells and the resulting B and T memory cells specific for a pathogen. Active immunity can develop as a result of natural infection or immunization.

active site

The specific region of an enzyme that binds the substrate and that forms the pocket in which catalysis occurs.

active transport

The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy.

adaptation

Inherited characteristic of an organism that enhances its survival and reproduction in a specific environment.

adaptive evolution

Evolution that results in a better match between organisms and their environment.

adaptive immunity

A vertebrate-specific defense that is mediated by B lymphocytes (B cells) and T lymphocytes (T cells) and that exhibits specificity, memory, and self-nonself recognition; also called acquired immunity.

adaptive radiation

Period of evolutionary change in which groups of organisms form many new species whose adaptations allow them to fill different ecological roles in their communities.

addition rule

A rule of probability stating that the probability of any one of two or more mutually exclusive events occurring can be determined by adding their individual probabilities.

adenylyl cyclase

An enzyme that converts ATP to cyclic AMP in response to an extracellular signal.

adhesion

The clinging of one substance to another, such as water to plant cell walls by means of hydrogen bonds.

adrenal gland

One of two endocrine glands located adjacent to the kidneys in mammals. Endocrine cells in the outer portion (cortex) respond to adrenocorticotropic hormone (ACTH) by secreting steroid hormones that help maintain homeostasis during long-term stress. Neurosecretory cells in the central portion (medulla) secrete epinephrine and norepinephrine in response to nerve signals triggered by short-term stress.

aerobic respiration

A catabolic pathway for organic molecules, using oxygen (O2) as the final electron acceptor in an electron transport chain and ultimately producing ATP. This is the most efficient catabolic pathway and is carried out in most eukaryotic cells and many prokaryotic organisms.

age structure

The relative number of individuals of each age in a population.

AIDS (acquired immunodeficiency syndrome)

The symptoms and signs present during the late stages of HIV infection, defined by a specified reduction in the number of T cells and the appearance of characteristic secondary infections.

alcohol fermentation

Glycolysis followed by the reduction of pyruvate to ethyl alcohol, regenerating NAD+ and releasing carbon dioxide.

alkaline vent

A deep-sea hydrothermal vent that releases water that is warm (40-90°C) rather than hot and that has a high pH (is basic). These vents consist of tiny pores lined with iron and other catalytic minerals that some scientists hypothesize might have been the location of the earliest abiotic synthesis of organic compounds.

allele

Any of the alternative versions of a gene that may produce distinguishable phenotypic effects.

allopatric speciation

The formation of new species in populations that are geographically isolated from one another.

allopolyploid

A fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosomes.

allosteric regulation

The binding of a regulatory molecule to a protein at one site that affects the function of the protein at a different site.

alternation of generations

A life cycle in which there is both a multicellular diploid form, the sporophyte, and a multicellular haploid form, the gametophyte; characteristic of plants and some algae.

alternative RNA splicing

A type of eukaryotic gene regulation at the RNA-processing level in which different mRNA molecules are produced from the same primary transcript, depending on which RNA segments are treated as exons and which as introns.

altruism

Selflessness; behavior that reduces an individual's fitness while increasing the fitness of another individual.

amino acid

An organic molecule possessing both a carboxyl and an amino group. They serve as the monomers of polypeptides.

aminoacyl-tRNA synthetase

An enzyme that joins each amino acid to the appropriate tRNA.

amniocentesis

A technique associated with prenatal diagnosis in which amniotic fluid is obtained by aspiration from a needle inserted into the uterus. The fluid and the fetal cells it contains are analyzed to detect certain genetic and congenital defects in the fetus.

amphipathic

Having both a hydrophilic region and a hydrophobic region.

anabolic pathway

A metabolic pathway that consumes energy to synthesize a complex molecule from simpler compounds.

analogous

Having characteristics that are similar because of convergent evolution, not homology.

analogy

Similarity between two species that is due to convergent evolution rather than to descent from a common ancestor with the same trait.

anaphase

The fourth stage of mitosis, in which the chromatids of each chromosome have separated and the daughter chromosomes are moving to the poles of the cell.

anatomy

The structure of an organism.

anchorage dependence

The requirement that a cell must be attached to a substratum in order to initiate cell division.

androgen

Any steroid hormone, such as testosterone, that stimulates the development and maintenance of the male reproductive system and secondary sex characteristics.

aneuploidy

A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.

anion

A negatively charged ion.

anterior pituitary

A portion of the pituitary gland that develops from nonneural tissue; consists of endocrine cells that synthesize and secrete several tropic and nontropic hormones.

antibody

A protein secreted by plasma cells (differentiated B cells) that binds to a particular antigen; also called immunoglobulin. All antibodies have the same Y-shaped structure and in their monomer form consist of two identical heavy chains and two identical light chains.

anticodon

A nucleotide triplet at one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule.

antidiuretic hormone (ADH)

A peptide hormone, also called vasopressin, that promotes water retention by the kidneys. Produced in the hypothalamus and released from the posterior pituitary, ADH also functions in the brain.

antigen

A substance that elicits an immune response by binding to receptors of B or T cells.

antigen presentation

The process by which an MHC molecule binds to a fragment of an intracellular protein antigen and carries it to the cell surface, where it is displayed and can be recognized by a T cell.

antigen receptor

The general term for a surface protein, located on B cells and T cells, that binds to antigens, initiating adaptive immune responses. The antigen receptors on B cells are called B cell receptors, and the antigen receptors on T cells are called T cell receptors.

antigen-presenting cell

A cell that upon ingesting pathogens or internalizing pathogen proteins generates peptide fragments that are bound by class II MHC molecules and subsequently displayed on the cell surface to T cells. Macrophages, dendritic cells, and B cells are the primary antigen-presenting cells.

antiparallel

Referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite 5′ S 3′ directions).

apoptosis

A type of programmed cell death, which is brought about by activation of enzymes that break down many chemical components in the cell.

aposematic coloration

The bright warning coloration of many animals with effective physical or chemical defenses.

aquaporin

A channel protein in a cellular membrane that specifically facilitates osmosis, the diffusion of free water across the membrane.

aqueous solution

A solution in which water is the solvent.

artificial selection

The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.

asexual reproduction

The generation of offspring from a single parent that occurs without the fusion of gametes. In most cases, the offspring are genetically identical to the parent.

associative learning

The acquired ability to associate one environmental feature (such as a color) with another (such as danger).

atom

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

atomic mass

The total mass of an atom, numerically equivalent to the mass in grams of 1 mole of the atom.

atomic nucleus

An atom's dense central core, containing protons and neutrons.

atomic number

The number of protons in the nucleus of an atom, unique for each atom and designated by a subscript.

ATP (adenosine triphosphate)

An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.

ATP synthase

A complex of several membrane proteins that functions in chemiosmosis with adjacent electron transport chains, using the energy of a hydrogen ion (proton) concentration gradient to make ATP. ATP synthases are found in the inner mitochondrial membranes of eukaryotic cells and in the plasma membranes of prokaryotes.

autocrine

Referring to a secreted molecule that acts on the cell that secreted it.

autoimmune disease

An immunological disorder in which the immune system turns against self.

autopolyploid

An individual that has more than two chromosome sets that are all derived from a single species.

autosome

A chromosome that is not directly involved in determining sex; not a sex chromosome.

autotroph

An organism that obtains organic food molecules without eating other organisms or substances derived from other organisms. Autotrophs use energy from the sun or from oxidation of inorganic substances to make organic molecules from inorganic ones.

axon

A typically long extension, or process, of a neuron that carries nerve impulses away from the cell body toward target cells.

B cells

The lymphocytes that complete their development in the bone marrow and become effector cells for the humoral immune response.

bacteriophage

A virus that infects bacteria; also called a phage.

balancing selection

Natural selection that maintains two or more phenotypic forms in a population.

Barr body

A dense object lying along the inside of the nuclear envelope in cells of female mammals, representing a highly condensed, inactivated X chromosome.

basal body

A eukaryotic cell structure consisting of a ""9 + 0"" arrangement of microtubule triplets. It may organize the microtubule assembly of a cilium or flagellum and is structurally very similar to a centriole.

basal metabolic rate (BMR)

The metabolic rate of a resting, fasting, and nonstressed endotherm at a comfortable temperature.

basal taxon

In a specified group of organisms, a taxon whose evolutionary lineage diverged early in the history of the group.

base

A substance that reduces the hydrogen ion concentration of a solution.

Batesian mimicry

A type of mimicry in which a harmless species resembles an unpalatable or harmful species to which it is not closely related.

behavior

Individually, an action carried out by muscles or glands under control of the nervous system in response to a stimulus; collectively, the sum of an animal's responses to external and internal stimuli.

behavioral ecology

The study of the evolution of and ecological basis for animal behavior.

benign tumor

A mass of abnormal cells with specific genetic and cellular changes such that the cells are not capable of surviving at a new site and generally remain at the site of the tumor's origin.

beta oxidation

A metabolic sequence that breaks fatty acids down to two-carbon fragments that enter the citric acid cycle as acetyl CoA.

bicoid

A maternal effect gene that codes for a protein responsible for specifying the anterior end in Drosophila melanogaster.

binary fission

A method of asexual reproduction in single-celled organisms in which the cell grows to roughly double its size and then divides into two cells. In prokaryotes, binary fission does not involve mitosis, but in single-celled eukaryotes that undergo binary fission, mitosis is part of the process.

binomial

A common term for the two-part, latinized format for naming a species, consisting of the genus and specific epithet; also called a binomen.

bioenergetics

(1) The overall flow and transformation of energy in an organism. (2) The study of how energy flows through organisms.

biogeochemical cycle

Any of the various chemical cycles, which involve both biotic and abiotic components of ecosystems.

biogeography

The scientific study of the past and present geographic distributions of species.

bioinformatics

The use of computers, software, and mathematical models to process and integrate biological information from large data sets.

biological augmentation

An approach to restoration ecology that uses organisms to add essential materials to a degraded ecosystem.

biological species concept

Definition of a species as a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but do not produce viable, fertile offspring with members of other such groups.

biomanipulation

An approach that applies the top-down model of community organization to alter ecosystem characteristics. For example, ecologists can prevent algal blooms and eutrophication by altering the density of higher-level consumers in lakes instead of by using chemical treatments.