IB Biology New Glossary

A complete vocabulary glossary for IB Biology, covering terms from cellular structures to global ecological processes, featuring verbatim definitions and integrated LaTeX for scientific notation.

70S Ribosomes

Small ribosomes found in prokaryotic cells, as well as in the mitochondria and chloroplasts of eukaryotic cells, responsible for protein synthesis by translating messenger RNA (mRNA) into proteins.

80S Ribosomes

Larger ribosomes found in eukaryotic cells that synthesize proteins.

Abiogenesis

The origin of life from non-living matter, such as simple organic compounds.

Abiotic factors

Non-living components of the environment, such as temperature, light, water availability, salinity, and soil type, that influence organism survival and reproduction.

Absorption

The process by which digested nutrients are transported into the body, primarily occurring in the small intestine.

Absorption spectrum

A graph showing the percentage of light absorbed at each wavelength by a pigment or group of pigments.

Acetylcholine

A neurotransmitter found in many types of synapses, including neuromuscular junctions where nerves connect to muscles.

Acrosome reaction

The first step in fertilization that allows a sperm to penetrate the egg's protective glycoprotein layer, the zona pellucida, to reach the plasma membrane.

Action Potential

The rapid electrical signal generated when a neuron's membrane potential reaches a threshold.

Action spectrum

A graph showing the rate of photosynthesis at each wavelength of light.

Activation Energy

The minimum amount of energy required to start a chemical reaction.

Active site

A small region on an enzyme, formed by a specific sequence of amino acids within its three-dimensional structure, where the substrate binds.

Active transport

The movement of molecules or ions across a membrane against their concentration gradient (low to high), which requires energy.

Adaptations

Traits that increase an organismɹs fitness in response to environmental factors.

Adaptive radiation

The evolutionary process by which a single ancestral species rapidly diversifies into many species, each specialized for a different ecological niche.

Adhesion

The attraction between water molecules and other surfaces, enabling water to cling to them and move against gravity.

Adrenal gland

Small glands located above the kidneys responsible for producing hormones, including epinephrine.

Albedo ($\alpha$)

A measure of the reflectivity of a surface.

Allele

A variation of a gene.

Allelopathy

Occurs when plants release chemicals called allelochemicals into the soil to inhibit the growth of nearby plants.

Allopatric speciation

Occurs when populations are physically separated by a geographical barrier, such as a river, mountain range, or ocean.

Alternative splicing

A process that enables a single gene to produce multiple protein variants.

Amphipathic

A molecule, such as a phospholipid, that has both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions.

Anabolic Reactions

Metabolic processes in which smaller molecules are built into larger, more complex molecules using energy.

Analogous structures

Anatomical features in different species that serve similar functions but do not share a common evolutionary origin.

Antagonistic muscles

Pairs of muscles that work in opposition; when one contracts, the other relaxes.

Antibiotic resistance

Occurs when bacteria evolve mechanisms to survive exposure to antibiotics that would normally kill them.

Antigen

Foreign molecules, usually proteins or glycoproteins, that trigger an immune response by being recognized by the immune system.

Antigenic drift

The gradual accumulation of point mutations in surface proteins, creating new viral variants.

Antigenic shift

A sudden genetic reassortment occurring when two different viral strains infect the same host cell, producing a radically new subtype.

Aquaporin

Specialized proteins that facilitate water movement across cell membranes.

Assimilation

The process by which absorbed nutrients are transported to cells and used for growth, repair, and energy production.

ATP Synthase

The enzyme that uses energy from the proton gradient to catalyze the synthesis of ATP from ADP and inorganic phosphate.

Autotroph

An organism that uses external energy sources to synthesize carbon compounds from simple inorganic substances.

B lymphocytes (B cells)

White blood cells that recognize specific antigens and produce antibodies to neutralize pathogens.

Binomial name

A two-part Latinized name uniquely identifying a species, where the first word represents the genus and the second the species.

Biochemical Oxygen Demand (BOD)

Measures the oxygen required by microorganisms to decompose organic matter.

Biological Species Concept (BSC)

Defines a species as a group of organisms capable of interbreeding and producing fertile offspring.

Biomagnification

The increase in toxin concentration at each successive trophic level in a food chain.

Blood clotting

A coordinated response transforming liquid blood into a semi-solid gel to seal wounds and prevent pathogen entry.

Bohr Shift

Describes how haemoglobinɹs affinity for oxygen decreases in the presence of high levels of $CO_2$ or in acidic environments with lower pH.

C-value paradox

The lack of correlation between genome size and organismal complexity.

Calvin Cycle

A biochemical pathway that incorporates $CO_2$ into organic molecules using energy and electrons from ATP and NADPH.

Carbon sequestration

The process of capturing and storing $CO_2$ from the atmosphere to mitigate climate change effects.

Cell theory

A principle stating all organisms are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.

Cerebellum

The part of the brain responsible for coordinating voluntary muscle movements, balance, and motor control.

Chemiosmosis

The movement of protons ($H^+$) across a membrane, driven by a concentration gradient, to power ATP synthesis.

Chemosynthesis

The process by which organisms use energy from inorganic molecules like hydrogen sulfide to produce food in the absence of sunlight.

Chi-squared test

A statistical method used to assess whether the occurrences of two species in an area are due to chance or ecological association.

Circadian Rhythm

The $24 ext{-hour}$ biological cycle that regulates physiological processes, including sleep.

Cladistics

A method of classifying organisms into clades based on common ancestry determined by DNA or amino acid sequence analysis.

Coenocyte

A multinucleated cell-like structure formed by repeated nuclear divisions without cell division.

Collision theory

States that for a reaction to occur, molecules must collide with sufficient energy and in the correct orientation.

Companion cell

Specialized cells in phloem that provide metabolic support, including energy production, to sieve tube elements.

Competitive exclusion principle

States that two species cannot occupy the same ecological niche indefinitely if resources are limiting.

Conserved sequences

DNA or protein regions that remain unchanged across species or over time, indicating essential functional roles.

Cryo-EM

An advanced form of electron microscopy that studies biomolecules, especially proteins, in their natural, hydrated state.

Cyclins

A group of proteins that regulate the cell cycle by activating cyclin-dependent kinases (CDKs).

Cytokinesis

The process of dividing the cytoplasm of a parent cell into two daughter cells.

Degenerate

A property of the genetic code where multiple codons code for the same amino acid, reducing mutation impact.

Dichotomous Key

A tool for identifying organisms through a series of paired statements describing contrasting traits.

Differentiation

The process where pluripotent, unspecialized cells develop into specialized cells with unique structures and functions.

DNA methylation

The addition of a methyl group ($-CH_3$) to a cytosine base in DNA to regulate gene expression.

Double circulation

A circulatory system where blood passes through the heart twice in one cycle, via pulmonary and systemic circuits.

Ectotherm

Organisms that rely on external environmental conditions to regulate their body temperature.

Emergent properties

Capabilities created by interactions between subsystems that individual parts cannot achieve alone.

Endosymbiosis

Endotherm

Organisms that maintain a constant internal body temperature through metabolic heat production.

Environmental DNA (eDNA)

Genetic material shed by organisms into surroundings (skin, mucus, feces) enabling detection without direct observation.

Eutrophication

Enrichment of water bodies with nutrients causing excessive plant and algae growth.

Facultative anaerobes

Organisms that can adapt to both oxic (oxygen-rich) and anoxic (oxygen-free) environments.

Feedback Inhibition

Process where the end product of a metabolic pathway inhibits an enzyme involved in its own synthesis.

Globular protein

Compact, spherical proteins typically soluble in water, formed by tightly packed polypeptide folding.

Glycolysis

Metabolic pathway in the cytoplasm that breaks down one glucose molecule ($6C$) into two pyruvate molecules ($3C$), yielding $2$ ATP and $2$ NADH.

Great Oxidation Event

A dramatic increase in atmospheric oxygen that transformed Earthɹs environment and paved the way for complex life.

Haemophilia

A disorder where blood fails to clot properly due to a deficiency in a clotting factor.

Hematopoietic stem cells

Immature cells that can develop into all types of blood cells.

Holozoic nutrition

The process by which animals obtain nutrients by consuming other organisms or organic matter involving ingestion, digestion, absorption, assimilation, and egestion.

Homeostasis

The maintenance of a stable internal environment ensuring optimal conditions for cellular processes.

Horizontal Gene Transfer

Direct exchange of genetic material between unrelated organisms, bypassing parent-offspring inheritance, common in prokaryotes.

Human chorionic gonadotropin (hCG)

A hormone essential for early pregnancy that maintains progesterone production for the uterine environment.

In vitro fertilization (IVF)

A medical procedure allowing fertilization to occur outside the body.

Kleptoplasty

Process where marine mixotrophs "steal" chloroplasts from consumed algae for photosynthesis.

LUCA (Last Universal Common Ancestor)

The last universal common ancestor of all present-day organisms, representing the root of the tree of life.

Mechanism-based inhibition

Also called suicide inhibition, where an inhibitor binds irreversibly to an enzymeɹs active site, permanently deactivating it.

Microplastics

Plastic fragments smaller than $5.0\,mm$ in size.

Molecular Clock

The use of gradual mutation accumulation to infer when species diverged from a common ancestor.

Naked DNA

DNA that is not enclosed in a nucleus or bound to histones, found in prokaryotes or external environments.

Non-Disjunction

Failure of homologous chromosomes or sister chromatids to separate properly during meiosis.

Obligate Anaerobes

Organisms to which oxygen is toxic; they thrive in anoxic environments like deep ocean sediments or animal guts.

Osmosis

Passive net movement of water molecules across a semi-permeable membrane from lower solute concentration (hypotonic) to higher solute concentration (hypertonic).

Pacemaker

Group of cells in the right atrium that regulates the heartbeat via electrical impulses.

Parthenogenesis

A form of asexual reproduction where an egg develops into an individual without fertilization.

Peristalsis

Wave-like contraction of smooth muscles pushing food through the digestive tract.

Phenotypic plasticity

The ability of an organism to alter its phenotype in response to environmental changes.

Photolysis

Spliting water ($H_2O$) molecules into oxygen, protons ($H^+$), and electrons using light energy.

Plasmolysis

Process where the cell membrane pulls away from the cell wall due to water loss.

Pneumocytes

Specialized alveolar cells in the lungs responsible for exchanging oxygen and $CO_2$.

Polyploidy

The duplication of an organismɹs entire chromosome set.

Prokaryote

A single-celled organism lacking a nucleus and membrane-bound organelles with DNA in a circular molecule in the nucleoid.