Comprehensive Biology Glossary Review (A–Z)

150 key vocabulary flashcards covering fundamental terms from the provided biology glossary (A–Z). Each card gives a concise definition suitable for exam review.

Adaptive Evolution

Process in which survival- or reproduction-enhancing traits increase in frequency, improving the match between organisms and their environment.

Adaptive Immunity

Vertebrate-specific defense mediated by B and T lymphocytes that exhibits specificity, memory, and self–nonself recognition.

Adaptive Radiation

Period of evolutionary change in which related organisms form many new species adapted to different ecological niches.

Addition Rule (Probability)

Rule stating that the probability of one of several mutually exclusive events occurring is the sum of their individual probabilities.

Adenylyl Cyclase

Enzyme that converts ATP to cyclic AMP (cAMP) in response to an extracellular signal.

Adhesion

Clinging of one substance to another, as when water molecules stick to plant cell walls by hydrogen bonding.

Adipose Tissue

Connective tissue that stores fat, insulates the body, and serves as a fuel reserve.

Adrenal Gland

Endocrine gland atop the kidney; cortex secretes steroid hormones, medulla secretes epinephrine and norepinephrine.

Aerobic Respiration

Catabolic pathway using O₂ as final electron acceptor, producing ATP most efficiently in eukaryotes and many prokaryotes.

Age Structure

Relative number of individuals of each age in a population.

Aggregate Fruit

Fruit that develops from a single flower with multiple carpels.

Alcohol Fermentation

Glycolysis followed by reduction of pyruvate to ethanol, regenerating NAD⁺ and releasing CO₂.

Acclimatization

Physiological adjustment to a change in an environmental factor.

Acetyl CoA

Entry compound for the citric acid cycle, formed from a two-carbon fragment of pyruvate and coenzyme A.

Acid

Substance that increases the hydrogen-ion concentration of a solution.

Acrosomal Reaction

Release of hydrolytic enzymes from sperm’s acrosome when contacting an egg.

Actin

Globular protein that forms microfilaments; important in muscle contraction and cell movement.

Action Potential

All-or-none electrical signal that travels along membranes of neurons or other excitable cells.

Activation Energy

Energy reactants must absorb before a chemical reaction can start; free energy of activation.

Activator (Genetics)

Protein that binds DNA and stimulates transcription; in eukaryotes, usually binds enhancers.

Active Immunity

Long-lasting immunity produced by action of B and T cells; develops after infection or vaccination.

Active Site

Specific region of an enzyme where the substrate binds and catalysis occurs.

Active Transport

Energy-requiring movement of substances across membranes against concentration or electrochemical gradients.

Adaptation

Inherited characteristic that enhances an organism’s survival and reproduction in a specific environment.

5′ Cap

Modified guanine nucleotide added to 5′ end of pre-mRNA for stability and ribosome binding.

ABC Hypothesis

Model of flower formation describing how three classes of organ identity genes specify four floral organs.

Abiotic

Nonliving; referring to physical and chemical properties of an environment.

Abscisic Acid (ABA)

Plant hormone that slows growth, promotes seed dormancy, and aids drought tolerance.

Absorption Spectrum

Range and graph of a pigment’s light-absorption versus wavelength.

Anaphase

Fourth stage of mitosis in which sister chromatids separate and move to opposite poles.

Anchorage Dependence

Requirement that a cell must be attached to a substrate to divide.

Androgen

Steroid hormone (e.g., testosterone) stimulating male reproductive system development and maintenance.

Aneuploidy

Chromosomal aberration with extra or missing chromosomes (not complete sets).

Angiosperm

Flowering plant that forms seeds inside a protective ovary.

Anhydrobiosis

Dormant state involving loss of almost all body water.

Animal Pole

End of egg with least yolk, opposite vegetal pole.

Antibody

Y-shaped protein produced by B cells that binds specific antigens; also called immunoglobulin.

Anticodon

tRNA nucleotide triplet that base-pairs with complementary mRNA codon.

Antidiuretic Hormone (ADH)

Posterior-pituitary peptide hormone promoting water retention by kidneys; also called vasopressin.

Antigen

Substance that elicits immune response by binding receptors on B or T cells.

Antiparallel

Refers to opposite 5′→3′ orientations of DNA double-helix backbones.

Apical Meristem

Region at tips of roots and shoots where cells divide, enabling primary growth.

Apoptosis

Programmed cell death involving activation of enzymes that dismantle the cell.

Aquaporin

Membrane channel protein that facilitates water transport (osmosis).

Archaea

One of two prokaryotic domains, distinct from Bacteria.

Archegonium

Female gametangium of plants, a moist chamber where gametes develop.

Artery

Blood vessel that carries blood away from the heart to organs.

Artificial Selection

Selective breeding to promote desirable traits in domesticated species.

ATP (Adenosine Triphosphate)

Primary energy currency of the cell; hydrolysis releases energy for endergonic reactions.

ATP Synthase

Protein complex that uses proton gradient energy to make ATP from ADP and Pi.

Autotroph

Organism that makes organic molecules from CO₂ or inorganic substances; self-feeder.

Auxin

Class of plant hormones (e.g., IAA) promoting cell elongation, root formation, and other growth responses.

Axon

Long neuronal extension that transmits impulses to target cells.

B Cell

Lymphocyte completing development in bone marrow; mediates humoral immunity.

Batesian Mimicry

Harmless species resembles harmful one to deter predators.

Benthic Zone

Bottom surface of an aquatic environment.

Binary Fission

Asexual reproduction where cell grows double size then divides into two; common in prokaryotes.

Bioenergetics

Study of energy flow and transformation in organisms.

Biogeochemical Cycle

Movement of elements through biotic and abiotic components of ecosystems.

Biological Species Concept

Defines species as groups capable of interbreeding and producing fertile offspring.

Biomagnification

Increase in concentration of substances in organisms at successively higher trophic levels.

Biome

Major ecosystem type characterized by vegetation (terrestrial) or physical environment (aquatic).

Biosphere

Sum of all Earth’s ecosystems; regions inhabited by life.

Biotechnology

Manipulation of organisms or their components to make useful products.

Blastula

Hollow ball of cells marking end of animal cleavage stage.

Bohr Shift

Decrease in hemoglobin affinity for O₂ with lowered pH, facilitating oxygen release to tissues.

Brown Alga

Large multicellular marine stramenopile with brown carotenoid pigments (e.g., kelp).

Buffer

Solution containing weak acid/base that minimizes pH changes.

Calvin Cycle

Second stage of photosynthesis that fixes CO₂ into carbohydrate using ATP and NADPH.

CAM Plant

Plant using crassulacean acid metabolism: night CO₂ fixation, day Calvin cycle; water-efficient.

Capsid

Protein shell enclosing viral genome.

Carbohydrate

Sugar or polymer of sugars; includes monosaccharides, disaccharides, polysaccharides.

Carbon Fixation

Incorporation of CO₂ into organic molecules during photosynthesis.

Carotenoid

Accessory pigment (yellow/orange) broadening spectrum for photosynthesis and providing photoprotection.

Carrying Capacity (K)

Maximum population size environment can sustain.

Catabolic Pathway

Metabolic pathway that breaks complex molecules into simpler ones, releasing energy.

Catalyst

Chemical agent that speeds reaction without being consumed.

Cation

Positively charged ion.

Cell Cycle

Ordered sequence of events in cell life from formation to division into two daughter cells.

Cell Theory

All living things are composed of cells; cell is basic unit; cells arise from pre-existing cells.

Cellulose

Structural polysaccharide of plant cell walls composed of β-glucose monomers.

Central Nervous System (CNS)

Brain and spinal cord where signal integration occurs.

Centromere

Region where sister chromatids are most closely attached; site of kinetochore assembly.

Chaperonin

Protein complex assisting proper folding of other proteins.

Chemical Bond

Attractive force holding atoms together via electron sharing or charge attraction.

Chemiosmosis

Energy-coupling mechanism using proton gradient to drive cellular work like ATP synthesis.

Chitin

Structural polysaccharide in fungal cell walls and arthropod exoskeletons.

Chlorophyll a

Primary photosynthetic pigment directly participating in light reactions.

Chloroplast

Organelle in plants/algae where photosynthesis occurs; contains thylakoids and stroma.

Chromatin

DNA-protein complex composing eukaryotic chromosomes.

Chromosome Theory of Inheritance

Genes have specific loci on chromosomes; chromosome behavior during meiosis accounts for inheritance patterns.

Cis-Trans Isomer

Compound with same formula/covalent bonds but differing in spatial arrangement around double bond.

Clade

Evolutionary branch including ancestor and all its descendants; monophyletic group.

Climate

Long-term prevailing weather conditions in an area.

Cohesion

Attraction between molecules of same substance, notably water via hydrogen bonds.

Commensalism

+/0 interaction where one species benefits and the other is neither harmed nor helped.

Competitive Exclusion

Concept that two species competing for identical resources cannot coexist indefinitely.

Complement System

Group of ~30 blood proteins that enhance immune responses and can lyse pathogens.

Concentration Gradient

Region along which density of a substance increases or decreases.

Conjugation (Prokaryotes)

Direct DNA transfer between temporarily joined bacterial cells.