Cambridge IGCSE Biology glossary

141 key terms from the Cambridge IGCSE Biology notes, A to Z. Each definition links to the note that teaches it.

A

Absorption: The movement of nutrients from the intestines into the blood.Revise it: Organs of the digestive system
Accommodation Supplement: Changing the shape of the lens to focus on near or distant objects.Revise it: Accommodation
Active immunity Supplement: Defence against a pathogen by antibody production in the body.Revise it: Antigens, antibodies and active immunity
Active site: The region of the enzyme where the substrate fits. Its shape is complementary to the substrate.Revise it: How enzymes work
Active transport: The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (i.e. against a concentration gradient), using energy from respiration.Revise it: Active transport
Adaptation Supplement: The process, resulting from natural selection, by which populations become more suited to their environment over many generations.Revise it: Natural selection and adaptation
Adaptive feature: An inherited feature that helps an organism to survive and reproduce in its environment.Revise it: Adaptive features
Aerobic respiration: the chemical reactions in cells that use oxygen to break down nutrient molecules to release energyRevise it: Aerobic respiration
Allele: An alternative form of a gene.Revise it: Chromosomes, genes and alleles
Alveoli: Tiny air sacs at the ends of the bronchioles where gas exchange takes place.Revise it: The breathing system
Anaerobic respiration: the chemical reactions in cells that break down nutrient molecules to release energy without using oxygenRevise it: Anaerobic respiration
Anomalous result: A result that does not fit the pattern of the other results.Revise it: Evaluating experiments: errors, anomalies and improvements
Antibody Supplement: A protein that binds to an antigen, leading to direct destruction of the pathogen or marking it for destruction by phagocytes.Revise it: Antigens, antibodies and active immunity
Antigen Supplement: A molecule on a pathogen. Each pathogen has its own antigens with specific shapes.Revise it: Antigens, antibodies and active immunity
Artificial insemination (AI) Supplement: Sperm is collected and placed into a female by people, without natural mating.Revise it: Endangered species and how to conserve them
Asexual reproduction: A process resulting in the production of genetically identical offspring from one parent.Revise it: Asexual reproduction
Assimilation: Uptake and use of nutrients by cells.Revise it: Organs of the digestive system

B

Balanced diet: A diet that contains all the nutrients in the correct proportions and gives the right amount of energy for the person.Revise it: A balanced diet and the main nutrients
Bias: When the way a sample is chosen makes some results more likely than others, for example picking the largest leaves.Revise it: Sampling: random sampling, sample size and avoiding bias
Binomial system: An internationally agreed system for naming species. The scientific name has two parts: the genus, then the species.Revise it: Classification, species and binomial names
Biodiversity: The number of different species that live in an area.Revise it: Biodiversity and habitat destruction
Blind spot: Where the optic nerve leaves the eye. There are no receptors there.Revise it: Sense organs and the eye

C

Carnivore: An animal that gets its energy by eating other animals.Revise it: Producers, consumers and decomposers
Catalyst: A substance that increases the rate of a chemical reaction and is not changed by the reaction.Revise it: Enzymes as biological catalysts
Cell: The basic unit of living things; cells are the building blocks of all organisms.Revise it: Cells, tissues, organs and organ systems
Central nervous system (CNS): The brain and the spinal cord.Revise it: The nervous system and neurones
Cervix: A ring of muscle at the opening of the uterus.Revise it: The male and female reproductive systems
Chemical digestion: The breakdown of large insoluble molecules into small soluble molecules.Revise it: Chemical digestion and digestive enzymes
Chlorophyll: a green pigment found in chloroplasts that transfers energy from light into energy in chemicals, for the synthesis of carbohydratesRevise it: Photosynthesis and chlorophyll
Circulatory system: A system of blood vessels with a pump and valves to ensure one-way flow of blood.Revise it: Single and double circulation
Codominance Supplement: A situation in which both alleles in heterozygous organisms contribute to the phenotype.Revise it: Codominance and ABO blood groups
Community: All of the populations of different species in an ecosystem.Revise it: Populations, communities and ecosystems
Consumer: An organism that gets its energy by feeding on other organisms.Revise it: Producers, consumers and decomposers
Continuous variation: Variation that results in a range of phenotypes between two extremes, for example body length and body mass.Revise it: Continuous and discontinuous variation
Control experiment: A set-up that is identical except that the factor being tested is missing or inactive, for example boiled enzyme or no plant. It shows that any change is caused by the factor being tested.Revise it: Planning an investigation: variables, controls, range and repeats
Controlled (constant) variables: Other variables that could affect the dependent variable, so they are kept the same in every test.Revise it: Planning an investigation: variables, controls, range and repeats
Coronary heart disease: Blockage of the coronary arteries by fatty deposits, reducing blood flow to the heart muscle.Revise it: Coronary heart disease
Cross-pollination Supplement: The transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species.Revise it: Self-pollination and cross-pollination

D

Deamination Supplement: The removal of the nitrogen-containing part of amino acids to form urea.Revise it: The liver, deamination and urea
Decomposer: An organism that gets its energy from dead or waste organic material.Revise it: Producers, consumers and decomposers
Denaturation: A permanent change in the shape of an enzyme's active site, so the substrate no longer fits and the enzyme no longer works.Revise it: Investigating temperature and pH
Denitrification Supplement: Denitrifying bacteria change nitrates in the soil into nitrogen gas.Revise it: The nitrogen cycle
Dependent variable: The variable that is observed or measured in a scientific experiment. It may change based on changes made to the independent variable.Revise it: Planning an investigation: variables, controls, range and repeats
Dichotomous key: A series of paired statements that leads you to the identity of an organism, using identifiable features.Revise it: Constructing and using dichotomous keys
Diffusion: The net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement.Revise it: Diffusion
Digestion: The breakdown of food.Revise it: Organs of the digestive system
Diploid nucleus Supplement: A nucleus containing two sets of chromosomes.Revise it: Gene expression, haploid and diploid
Discontinuous variation: Variation that results in a limited number of phenotypes with no intermediates, for example ABO blood groups.Revise it: Continuous and discontinuous variation
Dominant allele: An allele that is expressed if it is present in the genotype.Revise it: Key genetic terms
Drug: Any substance taken into the body that modifies or affects chemical reactions in the body.Revise it: Drugs and antibiotics

E

Ecosystem: A unit containing the community of organisms and their environment, interacting together.Revise it: Populations, communities and ecosystems
Egestion: The removal of undigested food from the body as faeces.Revise it: Organs of the digestive system
Enhanced greenhouse effect: Extra infrared radiation trapped by raised CO₂ and methane levels, warming the Earth and causing climate change.Revise it: Methane, carbon dioxide and climate change
Enzyme: A protein that functions as a biological catalyst.Revise it: Enzymes as biological catalysts
Enzyme-substrate complex Supplement: The temporary structure formed when the substrate is bound to the active site.Revise it: How enzymes work
Excretion: the removal of the waste products of metabolism and substances in excess of requirementsRevise it: The seven characteristics of living organisms

F

Fertilisation: The fusion of the nuclei of gametes.Revise it: Sexual reproduction
Fertilisation (in plants): The fusion of a pollen nucleus with a nucleus in an ovule.Revise it: Pollination and fertilisation
Flaccid cell Supplement: A plant cell that has lost water and turgor pressure, so it is soft.Revise it: Turgor, flaccid cells and plasmolysis
Food chain: Shows the transfer of energy from one organism to the next, beginning with a producer.Revise it: Food chains and food webs
Food web: A network of interconnected food chains.Revise it: Food chains and food webs

G

Gene: A length of DNA that codes for a protein.Revise it: Chromosomes, genes and alleles
Genetic modification: Changing the genetic material of an organism by removing, changing or inserting individual genes.Revise it: What genetic modification is
Genotype: The genetic make-up of an organism and in terms of the alleles present.Revise it: Key genetic terms
Golden rice: Rice genetically modified to improve its nutritional quality (more vitamin A precursor).Revise it: What genetic modification is
Gravitropism: A response in which parts of a plant grow towards or away from gravity.Revise it: Phototropism, gravitropism and auxin
Growth: a permanent increase in size and dry massRevise it: The seven characteristics of living organisms

H

Haploid nucleus Supplement: A nucleus containing a single set of chromosomes.Revise it: Gene expression, haploid and diploid
Herbivore: An animal that gets its energy by eating plants.Revise it: Producers, consumers and decomposers
Heterozygous: Having two different alleles of a particular gene. Example: Tt.Revise it: Key genetic terms
Homeostasis: The maintenance of a constant internal environment.Revise it: Homeostasis and negative feedback
Homozygous: Having two identical alleles of a particular gene. Example: TT or tt.Revise it: Key genetic terms
Hormone: A chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs.Revise it: Hormones and endocrine glands
Hydrophyte Supplement: A plant adapted to live in water or very wet places, for example a water lily.Revise it: Hydrophytes and xerophytes

I

Independent variable: The variable that is changed in a scientific experiment by the scientist. Changing an independent variable may cause a change in the dependent variable.Revise it: Planning an investigation: variables, controls, range and repeats
Ingestion: The taking of substances, e.g. food and drink, into the body.Revise it: Organs of the digestive system
Inheritance: The transmission of genetic information from generation to generation.Revise it: Key genetic terms
Interpolation: Reading a value from a graph between the plotted points.Revise it: Drawing graphs and charts the Cambridge way
IVF Supplement: Fertilisation of eggs by sperm outside the body; embryos are then placed into a female to develop.Revise it: Endangered species and how to conserve them

L

Limiting factor Supplement: The factor in shortest supply, which stops the rate of photosynthesis from increasing.Revise it: Rate of photosynthesis and limiting factors

M

Mitosis Supplement: Nuclear division giving rise to genetically identical cells.Revise it: Mitosis
Monoculture: Growing a single crop plant on a large area of land.Revise it: Monocultures and intensive livestock production
Movement: an action by an organism or part of an organism causing a change of position or placeRevise it: The seven characteristics of living organisms
mRNA Supplement: Messenger RNA: a copy of a gene, made in the nucleus, that moves to the cytoplasm.Revise it: How genes control proteins
MRSA Supplement: A bacterium that is resistant to many antibiotics.Revise it: Limiting antibiotic resistance
Mutation: Genetic change. It is the way in which new alleles are formed.Revise it: Mutation and sources of genetic variation

N

Nitrification Supplement: Nitrifying bacteria change ammonium ions into nitrate ions.Revise it: The nitrogen cycle
Nitrogen fixation Supplement: Nitrogen gas is changed into nitrogen compounds, by lightning and by nitrogen-fixing bacteria.Revise it: The nitrogen cycle
Nutrition: the taking in of materials for energy, growth and developmentRevise it: The seven characteristics of living organisms

O

Organ: A structure made up of a group of tissues, working together to perform specific functions.Revise it: Cells, tissues, organs and organ systems
Organ system: A group of organs with related functions, working together to perform body functions.Revise it: Cells, tissues, organs and organ systems
Organism: A whole living thing. It may be a single cell (e.g. a bacterium) or many cells organised into tissues, organs and organ systems that work together.Revise it: Cells, tissues, organs and organ systems
Osmosis Supplement: The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane.Revise it: Water potential
Osmosis using water potential Supplement: The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane.Revise it: Water potential
Oxygen debt Supplement: The extra oxygen needed after vigorous exercise, caused by lactic acid building up in muscles and blood.Revise it: Lactic acid and oxygen debt

P

Passive immunity Supplement: Short-term defence against a pathogen by antibodies acquired from another individual.Revise it: Passive immunity
Pathogen: A disease-causing organism.Revise it: Pathogens and how they are transmitted
Peripheral nervous system (PNS): The nerves outside of the brain and spinal cord.Revise it: The nervous system and neurones
Phenotype: The observable features of an organism.Revise it: Key genetic terms
Photosynthesis: the process by which plants synthesise carbohydrates from raw materials using energy from lightRevise it: Photosynthesis and chlorophyll
Phototropism: A response in which parts of a plant grow towards or away from the direction of the light source.Revise it: Phototropism, gravitropism and auxin
Physical digestion: The breakdown of food into smaller pieces without chemical change to the food molecules.Revise it: Physical digestion and teeth
Plasmid: A small ring of extra DNA found in bacterial cells.Revise it: Bacterial cells
Plasmolysis Supplement: The cell membrane and cytoplasm pulling away from the cell wall after water leaves the cell by osmosis.Revise it: Turgor, flaccid cells and plasmolysis
Pollination: The transfer of pollen grains from an anther to a stigma.Revise it: Pollination and fertilisation
Population: A group of organisms of one species, living in the same area, at the same time.Revise it: Populations, communities and ecosystems
Producer: An organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis.Revise it: Producers, consumers and decomposers

R

Recessive allele: An allele that is only expressed when there is no dominant allele of the gene present in the genotype.Revise it: Key genetic terms
Recombinant plasmid Supplement: A plasmid containing DNA (a gene) from another organism, joined in by DNA ligase.Revise it: How bacteria are modified to make a human protein
Reflex action: A means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands).Revise it: Reflex actions and reflex arcs
Repeats: Doing the same test again, so that anomalous results can be spotted and a mean calculated.Revise it: Evaluating experiments: errors, anomalies and improvements
Replicates: Several identical set-ups tested at the same time, such as five seeds in each dish.Revise it: Evaluating experiments: errors, anomalies and improvements
Representative sample: A sample that has the same features as the whole population or area it comes from.Revise it: Sampling: random sampling, sample size and avoiding bias
Reproduction: the processes that make more of the same kind of organismRevise it: The seven characteristics of living organisms
Respiration: the chemical reactions in cells that break down nutrient molecules and release energy for metabolismRevise it: The seven characteristics of living organisms

S

Seed bank: A store of seeds of rare plants, kept so plants can be grown if wild populations are lost.Revise it: Endangered species and how to conserve them
Self-pollination Supplement: The transfer of pollen grains from the anther of a flower to the stigma of the same flower or a different flower on the same plant.Revise it: Self-pollination and cross-pollination
Sense organ: A group of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals.Revise it: Sense organs and the eye
Sensitivity: the ability to detect and respond to changes in the internal or external environmentRevise it: The seven characteristics of living organisms
Set point Supplement: The normal level of a factor, such as blood glucose or temperature. Negative feedback returns the level to it.Revise it: Homeostasis and negative feedback
Sex-linked characteristic Supplement: A feature in which the gene responsible is located on a sex chromosome, which makes it more common in one sex than in the other.Revise it: Sex linkage and colour blindness
Sexual reproduction: A process involving the fusion of the nuclei of two gametes to form a zygote and the production of offspring that are genetically different from each other.Revise it: Sexual reproduction
Simple random sampling: Choosing samples so that every individual or position has an equal chance of being chosen, for example using random numbers.Revise it: Sampling: random sampling, sample size and avoiding bias
Sink Supplement: a part of the plant that uses or stores sucrose or amino acidsRevise it: Translocation, sources and sinks
Source Supplement: a part of the plant that releases sucrose or amino acidsRevise it: Translocation, sources and sinks
Source of error: Something in the method or apparatus that makes the measured values differ from the true values.Revise it: Evaluating experiments: errors, anomalies and improvements
Species: A group of organisms that can reproduce to produce fertile offspring.Revise it: Classification, species and binomial names
Stem cell Supplement: An unspecialised cell that divides by mitosis to produce daughter cells that can become specialised for specific functions.Revise it: Stem cells
Sustainable resource: A resource which is produced as rapidly as it is removed from the environment so that it does not run out.Revise it: Sustainable resources: forests and fish stocks
Synapse: A junction between two neurones.Revise it: Synapses

T

Test cross Supplement: Crossing an organism of unknown genotype with a homozygous recessive one to identify the unknown genotype.Revise it: The test cross
Tissue: A group of cells with similar structures, working together to perform a shared function.Revise it: Cells, tissues, organs and organ systems
Translocation Supplement: Movement of sucrose and amino acids in the phloem from sources to sinks.Revise it: Translocation, sources and sinks
Transmissible disease: A disease in which the pathogen can be passed from one host to another.Revise it: Pathogens and how they are transmitted
Transpiration: The loss of water vapour from leaves.Revise it: Transpiration
Transpiration pull Supplement: The pull on water in the xylem caused by evaporation from the leaves. It draws up a column of water.Revise it: Transpiration pull and wilting
Trophic level: The position of an organism in a food chain, food web or ecological pyramid.Revise it: Trophic levels
Turgid cell Supplement: A plant cell full of water, with the cell contents pressing on the cell wall (turgor pressure).Revise it: Turgor, flaccid cells and plasmolysis

V

Variation: Differences between individuals of the same species.Revise it: Continuous and discontinuous variation
Vasoconstriction Supplement: Narrowing of the arterioles supplying skin surface capillaries, so less blood flows near the surface and less heat is lost.Revise it: The skin and temperature control
Vasodilation Supplement: Widening of the arterioles supplying skin surface capillaries, so more blood flows near the surface and more heat is lost.Revise it: The skin and temperature control

Test yourself on these terms with the Cambridge IGCSE Biology flashcards, or tick them off on the specification checklist.