GCSE Biology Key Terms Glossary¶

Use this glossary to look up a term, then follow its topic link for the explanation, examples and related ideas. Definitions are grouped under the chapters where they are taught.

How To Use This Glossary¶

Use the linked topic page when you need a process explanation or an example.
Compare connected topics to see how the same idea applies in different systems.
Practise recalling a definition, then explain how it helps account for a biological observation.

Cell Biology¶

Cell Structure ¶

Eukaryotic cell: a cell with genetic material enclosed in a nucleus.
Prokaryotic cell: a smaller cell without a nucleus, such as a bacterium.
Differentiation: the process by which a cell becomes specialised for a particular function.
Magnification: how many times larger the image appears than the real object.
Resolution: the ability to distinguish two close points as separate.
Aseptic technique: methods used to prevent contamination when culturing microorganisms.
Nucleoid: the region in a bacterial cell where the main DNA chromosome is located.
Plasmid: a small circular loop of DNA in bacteria, separate from the main chromosome.
Flagellum: a whip-like structure that helps bacteria move.
Peptidoglycan: the material that makes up bacterial cell walls.
Vesicle: a fluid-filled sac that transports molecules within or out of a cell.

Cell Division ¶

Chromosome: a structure made of DNA that carries genes.
Gene: a short section of DNA that codes for a particular characteristic or protein.
Mitosis: nuclear division that produces two genetically identical nuclei.
Cell cycle: the sequence of growth, DNA replication and division in a cell.
Interphase: the stage of the cell cycle during which the cell grows, replicates DNA and produces organelles.
Cytokinesis: the final stage where the cytoplasm and cell membrane divide to form two separate cells.
Stem cell: an unspecialised cell that can divide and become specialised.
Pluripotent: able to differentiate into almost any cell type (describing embryonic stem cells).
Multipotent: able to differentiate into a limited range of cell types (describing adult stem cells).
Meristem: plant tissue containing cells that can divide and differentiate.

Transport in Cells ¶

Diffusion: the net movement of particles from high concentration to low concentration.
Osmosis: the movement of water through a partially permeable membrane from dilute to concentrated solution.
Partially permeable membrane: a membrane that lets some substances pass through but not others.
Concentration gradient: the difference in concentration between two regions.
Water potential: a measure of the tendency of water to move from one region to another.
Active transport: movement against a concentration gradient using energy from respiration.
ATP: a molecule that transfers energy between reactions in cells.
Turgid: firm state of a plant cell after water enters by osmosis.
Flaccid: wilted and limp state of a plant cell after water loss by osmosis.
Plasmolysis: the separation of the cell membrane from the cell wall due to water loss.
Turgor pressure: the pressure of water inside a plant cell pushing on the cell wall.
Facilitated diffusion: passive transport using membrane proteins, following the concentration gradient.

Organisation¶

Principles of Organisation ¶

Cell: the basic building block of a living organism.
Tissue: a group of specialised cells working together to perform a function.
Organ: a structure made from different tissues working together.
Organ system: a group of organs that work together to carry out a major function.

Animal Tissues, Organs and Organ Systems ¶

Villus: a finger-like projection in the small intestine that increases the surface area for absorption.
Artery: a blood vessel that carries blood away from the heart.
Vein: a blood vessel that returns blood to the heart.
Capillary: a tiny blood vessel with thin walls for exchange of substances.
Haemoglobin: the iron-containing protein in red blood cells that binds oxygen.
Coronary artery: blood vessel that supplies oxygen to the heart muscle itself.
Coronary heart disease: disease caused by fatty deposits in the coronary arteries reducing blood flow to the heart muscle.
Atherosclerosis: the buildup of fatty deposits (plaque) in arteries, narrowing them.
Benign tumour: a non-cancerous tumour that stays in one place.
Malignant tumour: a cancerous tumour that can invade tissues and spread in the body.
Metastasis: the spread of cancer from one part of the body to another.
Double circulatory system: separate circuits to the lungs and body, allowing higher blood pressure and more efficient oxygen distribution.

Plant Tissues, Organs and Systems ¶

Xylem: plant tissue that transports water and mineral ions from the roots.
Phloem: plant tissue that transports dissolved sugars around the plant.
Transpiration: the loss of water vapour from plant leaves.
Translocation: the movement of dissolved sugars through the phloem.
Transpiration stream: the continuous upward movement of water from roots through xylem to leaves, driven by transpiration.
Meristem: plant tissue containing cells that can divide and differentiate.
Stoma: a pore in the leaf surface through which gases and water vapour move.
Guard cell: specialized cell pair controlling the opening and closing of stomata.
Palisade mesophyll: columnar photosynthetic tissue in the upper leaf.
Spongy mesophyll: loosely arranged tissue in the lower leaf for gas exchange.
Root hair cell: epidermal cell with large surface area for water and ion absorption.
Vascular bundle: group of xylem and phloem tissues in roots, stems and leaves.

Infection and Response¶

Communicable Diseases ¶

Pathogen: a microorganism or agent that causes disease.
Communicable disease: a disease that can be passed from one organism to another.
Vaccination: introducing antigens safely so the immune system can prepare memory cells.
Antibody: a protein produced by white blood cells that binds to a specific antigen.
Antitoxin: a protein that neutralises a specific bacterial toxin.
Phagocytosis: the process by which white blood cells engulf and digest pathogens.
Antibiotic: a drug that kills bacteria or stops them reproducing.
Antiviral: a drug that inhibits viral replication.
Pathogenic: capable of causing disease.
Clinical trial: careful testing of a treatment on people to assess safety and effectiveness.

Monoclonal Antibodies ¶

Monoclonal antibody: an antibody produced from a single clone of cells and therefore all identical.
Polyclonal antibody: a mixture of different antibodies, each targeting different parts of an antigen.
Hybridoma: a cell formed by fusing a lymphocyte with a tumour cell.
Lymphocyte: a type of white blood cell that produces antibodies.
Specificity: the property of binding to one particular target and not others.
Antigen: a molecule recognised by the immune system as foreign or targetable.
Epitope: a specific part of an antigen that an antibody binds to.
Pregnancy test: a test that uses monoclonal antibodies to detect a hormone (hCG) linked to pregnancy.

Plant Disease ¶

Pathogen: a microorganism or agent that causes disease.
Deficiency symptom: a sign caused by shortage of a mineral ion rather than infection.
Cuticle: a waxy layer on the leaf surface that helps reduce water loss and pathogen entry.
Cellulose cell wall: a rigid outer layer that strengthens plant cells and helps resist damage.
Testing kit: a diagnostic tool used to help identify the cause of plant disease.
Chlorosis: yellowing of plant leaves caused by insufficient chlorophyll, often the result of magnesium deficiency.
Nitrate deficiency: a shortage of nitrate ions in the soil, leading to stunted growth because the plant cannot make enough protein.
Magnesium deficiency: a shortage of magnesium ions, leading to chlorosis because the plant cannot synthesise chlorophyll.
Crown gall disease: a bacterial infection that causes tumour-like growths on stems and roots, restricting water flow through the plant.
Tobacco mosaic virus (TMV): a viral disease of plants that creates a mosaic pattern of discolouration on leaves and reduces photosynthesis.
Black spot: a fungal disease, commonly affecting rose plants, visible as dark spots on leaves.
Antibacterial chemical: a substance produced by some plants that kills or inhibits bacterial pathogens.
Thorn: a sharp outgrowth from a plant stem that acts as a mechanical defence against herbivores.

Bioenergetics¶

Photosynthesis ¶

Photosynthesis: the process by which plants use light energy to make glucose from carbon dioxide and water.
Chlorophyll: the green pigment that absorbs light energy for photosynthesis.
Limiting factor: a factor in shortest supply that restricts the rate of a process.
Glucose: a simple sugar made during photosynthesis and used for respiration and growth.
Starch: an insoluble storage carbohydrate made from glucose in plants.
Endothermic reaction: a reaction that takes in energy from the surroundings; photosynthesis is endothermic because it absorbs light energy.
Chloroplast: the organelle in plant cells where photosynthesis takes place; contains chlorophyll.
Inverse square law: the rule that light intensity is inversely proportional to the square of the distance from the source (intensity ∝ 1/d²).
Hydrogencarbonate indicator: a pH-sensitive indicator used to detect changes in CO₂ concentration; orange at normal levels, yellow when CO₂ increases, purple when CO₂ decreases.
Optimum temperature: the temperature at which enzyme-controlled reactions, including photosynthesis, proceed at the fastest rate.

Respiration ¶

Respiration: the process that transfers energy from glucose in cells.
Aerobic respiration: respiration that uses oxygen and releases more energy per glucose molecule than anaerobic respiration.
Anaerobic respiration: respiration without oxygen that releases less energy per glucose molecule than aerobic respiration.
Lactic acid: a product of anaerobic respiration in animal muscles; accumulates during intense exercise.
Oxygen debt: the extra oxygen needed after exercise to break down accumulated lactic acid and restore normal conditions.
Metabolism: the sum of all the chemical reactions in a cell or body.
ATP: a molecule that transfers energy between reactions in cells.
Fermentation: anaerobic respiration in yeast and plants; produces ethanol and carbon dioxide.
Cardiac output: the volume of blood pumped from the heart per minute; calculated as heart rate × stroke volume.
Muscle fatigue: reduced ability of muscles to contract effectively after prolonged vigorous activity.

Homeostasis and Response¶

Homeostasis ¶

Homeostasis: the maintenance of a stable internal environment.
Set point: the ideal value or narrow range around which a control system keeps a condition.
Stimulus: a change in the internal or external environment detected by receptors.
Receptor: a structure that detects a stimulus or change.
Coordination centre: a part of the body that receives and processes information from receptors.
Effector: a muscle or gland that brings about a response.
Negative feedback: control in which a change triggers responses that oppose it and restore the normal range.

The Human Nervous System ¶

Reflex arc: the pathway taken by impulses in a rapid automatic response.
Sensory neurone: a neurone that carries impulses from receptors to the central nervous system.
Relay neurone: a neurone within the CNS that connects sensory and motor neurones.
Motor neurone: a neurone that carries impulses from the central nervous system to effectors.
Synapse: the junction between two neurones; impulses cross by neurotransmitter diffusion.
Neurotransmitter: a chemical released at a synapse that carries the signal across the synaptic cleft.
Accommodation: the process by which the lens changes shape to focus on near or distant objects.
Vasodilation: widening of blood vessels near the skin surface to increase heat loss.
Vasoconstriction: narrowing of blood vessels near the skin surface to reduce heat loss.
Myelin sheath: the insulating fatty layer around a neurone's axon that speeds impulse transmission.
Retina: the layer at the back of the eye containing rod and cone cells that detect light.
Fovea: the region of the retina with the highest concentration of cone cells; gives the sharpest colour vision.
Ciliary muscles: muscles in the eye that change the shape of the lens for accommodation.
Suspensory ligaments: fibres that hold the lens in position in the eye.
Myopia: short-sightedness; corrected by a concave lens.
Hyperopia: long-sightedness; corrected by a convex lens.
Cerebral cortex: the region of the brain responsible for conscious thought, intelligence, memory and language.
Cerebellum: the region of the brain that coordinates movement and balance.
Medulla oblongata: the region of the brain that controls unconscious processes such as heart rate and breathing.

Hormonal Coordination in Humans ¶

Hormone: a chemical messenger released by a gland and carried in the blood.
Endocrine gland: a gland that releases hormones directly into the bloodstream.
Insulin: a hormone that lowers blood glucose concentration.
Glucagon: a hormone that raises blood glucose concentration.
ADH: a hormone that increases water reabsorption in the kidneys.
Negative feedback: control in which a change triggers responses that oppose it and restore the normal range.
Adrenaline: a hormone released by the adrenal glands in response to stress; prepares the body for fight or flight.
Thyroxine: a hormone from the thyroid gland that controls basal metabolic rate.
Testosterone: the main male sex hormone, produced by the testes; responsible for male secondary sex characteristics and sperm production.
Oestrogen: the main female sex hormone, produced by the ovaries; controls female secondary sex characteristics and the menstrual cycle.
Progesterone: a female reproductive hormone (produced by the corpus luteum after ovulation) that maintains the uterus lining.
FSH (follicle-stimulating hormone): a pituitary hormone that stimulates follicle development and egg maturation.
LH (luteinising hormone): a pituitary hormone that triggers ovulation.
Ovulation: the release of a mature egg from the ovary; occurs around day 14 of the menstrual cycle.
IVF (in vitro fertilisation): a fertility treatment in which eggs and sperm are combined in a laboratory and resulting embryos are transferred into the uterus.
Basal metabolic rate: the body's minimum rate of energy use at rest; controlled partly by thyroxine.
Fight-or-flight response: the set of physiological changes triggered by adrenaline in response to perceived danger.

Plant Hormones ¶

Auxin: a plant hormone (e.g. IAA) produced in shoot and root tips that controls directional growth by affecting cell elongation.
Phototropism: a growth response to light; positive = towards light, negative = away from light.
Gravitropism: a growth response to gravity; positive = towards gravity (downward), negative = away from gravity (upward).
Rooting powder: a product containing auxins that encourages root development on plant cuttings.
Selective weedkiller: a herbicide containing synthetic auxin that causes rapid uncontrolled growth and death in target weed species.
Gibberellin: a plant hormone that breaks seed dormancy, promotes cell elongation, and can stimulate flowering and fruit development.
Ethene: a gaseous plant hormone that promotes fruit ripening and causes leaf shedding.
Parthenocarpy: the development of fruit without fertilisation; can be induced by gibberellins to produce seedless fruit.
Coleoptile: the protective sheath covering the shoot tip in cereal seedlings; used in classic auxin experiments.
Tropism: a directional growth response of a plant to an environmental stimulus.

Inheritance, Variation and Evolution¶

Reproduction ¶

Gamete: a sex cell with half the normal number of chromosomes (haploid).
Meiosis: cell division that produces four genetically different haploid gametes.
Allele: a different version of the same gene.
Genome: the complete set of genetic material in an organism.
Dominant: describes an allele expressed when only one copy is present.
Recessive: describes an allele expressed only when two copies are present.
Codominance: when both alleles are expressed simultaneously in the phenotype.
Homozygous: having two identical alleles for a gene (e.g. DD or dd).
Heterozygous: having two different alleles for a gene.
Genotype: the combination of alleles an organism possesses.
Phenotype: the observable characteristics of an organism; determined by genotype and environment.
Carrier: an individual who has one copy of a recessive disease allele but shows no symptoms.
Polydactyly: an inherited condition causing extra digits; caused by a dominant allele.
Cystic fibrosis: an inherited condition causing thick mucus; caused by a recessive allele.
Sickle cell anaemia: an inherited condition causing sickle-shaped red blood cells; caused by a recessive allele.
Punnett square: a grid diagram used to predict the probability of different genotypes and phenotypes in offspring.

Variation and Evolution ¶

Variation: differences between individuals of the same species.
Natural selection: the process by which advantageous inherited characteristics become more common over generations.
Selective breeding: choosing parents with desired traits so those traits appear more often in offspring.
Genetic engineering: changing an organism by inserting a useful gene from another organism into its DNA.
Clone: an organism or cell that is genetically identical to another.
Mutation: a random change in DNA that can create a new allele.
Restriction enzyme: an enzyme that cuts DNA at specific base sequences; used to isolate genes in genetic engineering.
Ligase enzyme: an enzyme that joins DNA strands together; used to insert genes into plasmids in genetic engineering.
Plasmid: a small circular loop of DNA in bacteria, separate from the main chromosome.
Continuous variation: a range of phenotypes between two extremes with no distinct categories (e.g. height).
Discontinuous variation: distinct categories with no intermediates (e.g. blood group).
Inbreeding depression: reduced fitness in a population due to the accumulation of harmful recessive alleles from selective breeding.
Tissue culture: growing new plants or animal cells from small tissue samples in a sterile growth medium.
Adult cell cloning: cloning an organism by inserting an adult cell nucleus into an enucleated egg cell.

The Development of Understanding of Genetics and Evolution ¶

Evolution: the change in inherited characteristics of a population over time.
Fossil: the preserved remains or traces of an ancient organism.
Extinction: the permanent loss of a species when no individuals remain.
Antibiotic resistance: the ability of some bacteria to survive antibiotic treatment due to a resistance mutation; spreads by natural selection.
Natural selection: the process by which advantageous inherited characteristics become more common over generations.
Speciation: the formation of a new species when populations become reproductively isolated and diverge over time.
Lamarck's theory: the now-disproved idea that characteristics acquired during an organism's lifetime can be inherited by offspring.
Mendel: the 19th-century scientist whose pea plant experiments laid the foundations of genetics; discovered dominant and recessive inheritance.
Hominid: a member of the great-ape family, including humans and their extinct relatives.
Pentadactyl limb: a limb with five digits, found across many vertebrate groups; evidence of common ancestry.
MRSA: Methicillin-resistant Staphylococcus aureus; an example of a bacterium that has evolved antibiotic resistance.

Classification of Living Organisms ¶

Classification: the organisation of living organisms into groups based on shared features and evolutionary relationships.
Species: a group of organisms that can interbreed to produce fertile offspring.
Genus: the classification level immediately above species; organisms in the same genus are closely related.
Binomial system: the two-part naming system where each species is given a genus name and a species name in Latin.
Kingdom: the broadest level of classification in the Linnaean system; the five kingdoms are animals, plants, fungi, protists and prokaryotes.
Phylum: the classification level below kingdom and above class.
Domain: the level of classification above kingdom, introduced by Carl Woese; the three domains are Bacteria, Archaea and Eukaryota.
Archaea: a group of ancient prokaryotes with biochemical features distinct from true bacteria, forming their own domain.
Evolutionary tree: a branching diagram showing evolutionary relationships between organisms through common ancestors.
Molecular phylogenetics: the use of DNA and protein sequences to determine evolutionary relationships.
Carl Woese: the scientist who proposed the three-domain system based on ribosomal RNA comparisons.
Convergent evolution: the independent evolution of similar features in unrelated organisms due to similar environmental pressures (e.g. streamlined body in dolphins and fish).

Ecology¶

Adaptations, Interdependence and Competition ¶

Habitat: the place where an organism lives.
Population: all the organisms of one species in a habitat at the same time.
Community: all the interacting populations of different species in a habitat.
Ecosystem: a community of organisms interacting with the non-living components of its environment.
Abiotic factor: a non-living physical or chemical factor that affects organisms in an ecosystem.
Biotic factor: a living factor — the effect of other organisms — that affects a population.
Adaptation: an inherited feature that increases an organism's fitness (ability to survive and reproduce) in its environment.
Structural adaptation: a physical feature of the body suited to the environment.
Behavioural adaptation: a behaviour pattern that improves survival or reproduction.
Physiological adaptation: an internal biochemical or metabolic feature suited to the environment.
Extremophile: an organism adapted to survive in extreme environmental conditions.
Interdependence: the way in which organisms in a community depend on one another for survival.
Mutualism: a relationship between two species where both benefit.
Parasitism: a relationship where one organism (parasite) benefits at the expense of another (host).
Intraspecific competition: competition between individuals of the same species.
Interspecific competition: competition between individuals of different species.

Organisation of an Ecosystem ¶

Ecosystem: a community of organisms interacting with the non-living components of its environment.
Decomposer: a microorganism (bacterium or fungus) that breaks down dead organic matter and waste, releasing minerals.
Decay: the breakdown of dead material by decomposers.
Compost: decomposed organic material used to enrich soil.
Biogas generator: a sealed vessel in which organic waste is broken down anaerobically by bacteria to produce methane-rich biogas.
Transpiration: the loss of water vapour from plant leaves.
Precipitation: water falling from the atmosphere as rain, snow, hail or sleet.
Detritivore: an organism (e.g. earthworm, woodlouse) that feeds on dead organic material, physically breaking it into smaller pieces.

Biodiversity and the Effect of Human Interaction on Ecosystems ¶

Biodiversity: the variety of different species in an ecosystem or across the planet.
Deforestation: the large-scale removal of trees, reducing habitat and increasing atmospheric CO₂.
Eutrophication: the process by which excess nutrients in water cause algal growth, oxygen depletion and death of aquatic organisms.
Global warming: the long-term rise in Earth's average temperature due to increased greenhouse gas concentrations.
Greenhouse gas: a gas (e.g. CO₂, methane, water vapour) that traps heat in the atmosphere.
Acid rain: rain made acidic by dissolved SO₂ and NOₓ from burning fossil fuels; damages plants and acidifies water bodies.
Conservation: protecting and managing species and habitats to prevent loss of biodiversity.
Seed bank: a store of seeds at low temperature and humidity, used to preserve plant genetic material.
Peat bog: a waterlogged, anaerobic wetland ecosystem that accumulates peat and stores large amounts of carbon.
Indicator species: a species whose presence, absence or abundance reveals information about environmental quality (e.g. pollution levels).
Bioaccumulation: the increase in concentration of a toxic substance in organisms at higher levels of the food chain.
Ecotourism: tourism that promotes appreciation of natural environments while funding their conservation.

Trophic Levels in an Ecosystem ¶

Trophic level: a feeding position in a food chain.
Producer: an organism that makes its own food, usually by photosynthesis.
Consumer: an organism that gets food by eating other organisms.
Biomass: the mass of living material in organisms.
Pyramid of biomass: a diagram showing the biomass present at each trophic level, drawn to scale.
Pyramid of numbers: a diagram showing the number of organisms at each trophic level.

Food Production ¶

Food security: having reliable access to enough safe and nutritious food.
Selective breeding: choosing parents with desired traits so those traits appear more often in offspring.
Sustainable fishery: a fishery managed so that fish populations can continue to replace themselves.
Biotechnology: the use of living organisms or biological processes in industrial or food production.
Mycoprotein: food made from fungal biomass grown in industrial fermenters.
Monoculture: growing only one crop species across a large area.
Hydroponics: growing plants in mineral-enriched water rather than soil.
Biological pest control: using living organisms to reduce pest populations rather than chemical pesticides.
Crop rotation: the practice of growing different crops in a field in successive seasons to maintain soil health and reduce pest build-up.
Fishing quota: a legal limit on the quantity of fish that may be caught from a population in a given period.

GCSE Biology Key Terms Glossary¶

How To Use This Glossary¶

Cell Biology¶

Organisation¶

Infection and Response¶

Bioenergetics¶

Homeostasis and Response¶

Inheritance, Variation and Evolution¶

Ecology¶

Connected Pages¶