IGCSE Biology key terms and definitions (0610)
219 key terms from the Glide Biology notes, grouped by chapter in syllabus order. Learn the wording: mark schemes reward the precise definition.
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Characteristics & Classification
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- Metabolism
- All the chemical reactions that take place inside the cells of an organism.
- Dry mass
- The mass of an organism's tissue once all its water has been removed.
- Species
- A group of organisms that can reproduce to produce fertile offspring.
- Genus
- A group of closely related species; the first word of a scientific name. Panthera leo (lion) and Panthera tigris (tiger) share one.
- Dichotomous key
- A series of paired statements; each choice leads to another pair or to a name.
- Base sequenceExtended
- The order of the bases along one strand of a DNA molecule.
- Vertebrate
- An animal with a backbone.
- Arthropod
- An animal with jointed legs, a segmented body and a hard exoskeleton.
- Exoskeleton
- A hard covering on the outside of the body that supports and protects it.
- Kingdom
- The largest group into which organisms are classified.
- ProkaryoteExtended
- A single-celled organism whose cell has no nucleus.
- CotyledonExtended
- A seed leaf: part of the embryo inside a seed.
Cell Structure & Organisation
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- Organelle
- A structure inside a cell that carries out a particular job.
- Cell
- The basic unit of living organisms.
- Cell sap
- The watery solution inside a vacuole, holding dissolved sugars, salts and other substances.
- Plasmid
- A small ring of DNA in a bacterial cell, separate from the main DNA loop.
- Prokaryote
- An organism whose cells have no nucleus; bacteria are the main example.
- Specialised cell
- A cell with a structure that suits it to one specific function.
- Surface area
- The total area of a surface exposed to the surroundings; a long thin shape has a larger surface area compared with its volume than a round one.
- Tissue
- A group of similar cells working together to do one job.
- Organ
- A group of different tissues that work together to do a job.
- Organ system
- A group of organs working together to carry out a major function.
- Magnification
- How many times larger an image is than the real specimen.
- MicrometreExtended
- One thousandth of a millimetre; written µm.
Movement into and out of Cells
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- Diffusion
- The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, caused by their random movement.
- Concentration gradient
- The difference in concentration between two regions.
- Rate
- How fast something happens; a faster rate means less time taken.
- Solvent
- A liquid that dissolves other substances; water is the solvent in living things.
- Partially permeable membrane
- A membrane that lets some particles through but not others, for example water but not larger solutes.
- OsmosisExtended
- 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.
- Percentage change in mass
- (final mass − initial mass) ÷ initial mass × 100.
- Turgor pressureExtended
- The pressure of the cell contents pushing outwards against the cell wall.
- TurgidExtended
- A plant cell with a high turgor pressure; firm.
- FlaccidExtended
- A plant cell that has lost turgor pressure; soft or limp.
- PlasmolysisExtended
- The membrane and cytoplasm pulling away from the cell wall when the cell loses much water.
- Active transport
- The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration, against a concentration gradient, using energy from respiration.
Biological Molecules
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- Element
- A substance made of only one kind of atom, such as carbon, hydrogen, oxygen or nitrogen.
- Macromolecule
- A very large molecule made by joining many small molecules together.
- Glucose
- A small sugar molecule; the unit from which starch, glycogen and cellulose are built.
- Amino acid
- A small molecule that is the unit of proteins; many amino acids joined in a chain make a protein.
- Fatty acid
- A small molecule that joins with glycerol to make fats and oils.
- Reducing sugar
- A type of sugar, such as glucose, that gives a colour change with Benedict’s solution on heating.
- DNAExtended
- The molecule that carries genetic information; two strands coiled together as a double helix.
- BaseExtended
- One of four chemicals, A, C, G and T, carried by the strands of DNA.
Enzymes
- Catalyst
- A substance that increases the rate of a chemical reaction and is not changed by the reaction.
- Enzyme
- A protein that functions as a biological catalyst.
- Substrate
- The substance that an enzyme acts on.
- Active site
- The part of the enzyme with a shape complementary to its substrate.
- Enzyme-substrate complexExtended
- The enzyme with its substrate bound in the active site.
- Optimum temperature
- The temperature at which an enzyme is most active.
- Denaturation
- A permanent change in the shape of an enzyme, so that it can no longer work.
- Optimum pH
- The pH at which an enzyme is most active.
- Independent variable
- The one factor you change in an investigation.
- Dependent variable
- The factor you measure to see the effect.
- Rate
- How fast a reaction happens; calculated as 1 ÷ time taken.
Plant Nutrition
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- Photosynthesis
- The process by which plants make carbohydrates from raw materials, using energy from light.
- Chlorophyll
- A green pigment found in chloroplasts that transfers energy from light into energy in chemicals.
- Nitrate ions
- Mineral ions taken up by roots; the plant uses them to make amino acids.
- Magnesium ions
- Mineral ions taken up by roots; the plant uses them to make chlorophyll.
- Control
- A set-up that is the same as the test except for the one factor being investigated, so that the effect of that factor can be seen.
- Rate of photosynthesis
- How fast a plant carries out photosynthesis; measured, for example, by the volume of oxygen released in a set time.
- Limiting factorExtended
- The factor in shortest supply, which sets the rate of photosynthesis.
- Hydrogencarbonate indicator
- A solution that changes colour with the concentration of carbon dioxide in it.
- Dicotyledonous plant
- A flowering plant whose seed has two seed leaves; the leaf structures here are those of a dicot.
- Adaptation
- A feature of a structure that helps it carry out its function.
Human Nutrition
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- Balanced diet
- A diet that contains all the nutrients the body needs, in the correct proportions, for its age, sex and activity.
- Scurvy
- A deficiency disease caused by a lack of vitamin C; gums bleed and wounds heal slowly.
- Rickets
- A deficiency disease caused by a lack of vitamin D (or calcium); bones are soft and may bend.
- Ingestion
- The taking of substances, such as food and drink, into the body.
- Digestion
- The breakdown of food.
- Absorption
- The movement of nutrients from the intestines into the blood.
- Assimilation
- The uptake and use of nutrients by cells.
- Egestion
- The removal of undigested food from the body as faeces.
- Physical digestion
- The breakdown of food into smaller pieces without chemical change to the food molecules.
- Chemical digestion
- The breakdown of large insoluble molecules into small soluble molecules.
- MaltoseExtended
- A sugar made of two glucose units; the product of amylase digestion of starch.
- MaltaseExtended
- The enzyme that breaks down maltose to glucose, on the membranes of the epithelium lining the small intestine.
- Absorption
- The movement of nutrients from the intestines into the blood.
- Alimentary canal
- The tube from the mouth to the anus through which food passes.
Transport in Plants
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- Xylem
- The tissue that transports water and mineral ions, and also gives support.
- Phloem
- The tissue that transports sucrose and amino acids.
- Root hair cell
- A cell of the root epidermis with a long, thin extension that takes up water and mineral ions from the soil.
- Stain
- A coloured dye used to make a structure visible; here, a dye that is carried in the xylem.
- Transpiration
- The loss of water vapour from leaves.
- Potometer
- Apparatus that measures how quickly a cut shoot takes up water; used to compare rates of transpiration.
- Transpiration pullExtended
- The pull on the column of water in the xylem caused by evaporation of water from the leaf.
- WiltingExtended
- The drooping of a plant when its cells lose turgor because water loss exceeds uptake.
- TranslocationExtended
- The movement of sucrose and amino acids in the phloem from sources to sinks.
- SourceExtended
- A part of the plant that releases sucrose or amino acids.
- SinkExtended
- A part of the plant that uses or stores sucrose or amino acids.
Transport in Animals
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- Circulatory system
- A system of blood vessels with a pump and valves to ensure one-way flow of blood.
- Coronary arteries
- The arteries on the surface of the heart that supply the heart muscle with blood.
- Pulse rate
- The number of times per minute that the pulse is felt in an artery, equal to the heart rate.
- Coronary heart disease
- A disease in which the coronary arteries are blocked by fatty deposits, reducing the blood supply to the heart muscle.
- Lumen
- The hollow space inside a tube, through which the blood flows.
- Haemoglobin
- A red pigment in red blood cells that combines with oxygen to carry it around the body.
- Phagocytosis
- The engulfing and digesting of pathogens by a white blood cell.
Diseases and Immunity
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- Pathogen
- A disease-causing organism.
- Transmissible disease
- A disease in which the pathogen can be passed from one host to another.
- AntigenExtended
- A molecule on the surface of a pathogen that the body recognises as foreign.
- AntibodyExtended
- A protein that binds to an antigen.
- Memory cellExtended
- A cell made when lymphocytes respond to an antigen. It stays in the body and gives long-term immunity.
- Passive immunityExtended
- Short-term defence against a pathogen by antibodies acquired from another individual.
- CholeraExtended
- A disease caused by a bacterium that is transmitted in contaminated water.
Gas Exchange in Humans
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- Gas exchange surface
- A surface where oxygen passes into the blood and carbon dioxide passes out.
- Ventilation
- The movement of air into and out of the lungs.
- Limewater
- A clear solution that turns milky when carbon dioxide is bubbled through it.
- Rate and depth
- Rate is the number of breaths per minute; depth is the volume of air in each breath.
- Goblet cellExtended
- A cell in the lining of the airways that makes mucus.
- Ciliated cellExtended
- A cell in the lining of the airways with tiny hair-like projections called cilia.
Respiration
- Respiration
- The chemical reactions in cells that break down nutrient molecules to release energy.
- Aerobic respiration
- The chemical reactions in cells that use oxygen to break down nutrient molecules to release energy.
- Anaerobic respiration
- The chemical reactions in cells that break down nutrient molecules to release energy without using oxygen.
- Oxygen debtExtended
- The extra oxygen needed after vigorous exercise to break down the lactic acid that has built up.
Excretion in Humans
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- Excretion
- The removal from organisms of toxic materials, the waste products of metabolism and substances in excess of requirements.
- CortexExtended
- The outer region of the kidney.
- MedullaExtended
- The inner region of the kidney.
- NephronExtended
- A tiny tube in the kidney that, with its blood vessels, filters the blood and forms urine.
- DeaminationExtended
- The removal of the nitrogen-containing part of amino acids to form urea.
- AssimilationExtended
- The movement of digested food molecules into the cells of the body, where they are used and become part of the cells.
Nervous System and the Eye
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- Neurone
- A nerve cell that carries electrical impulses.
- Reflex action
- An automatic and rapid response, which integrates and coordinates a stimulus with the response of an effector (a muscle or gland).
- Synapse
- A junction between two neurones.
- Sense organ
- A group of receptor cells that respond to a specific stimulus.
- Antagonistic musclesExtended
- A pair of muscles whose actions are opposite, so that when one contracts the other relaxes.
- FoveaExtended
- A small area of the retina where the cones are packed closely, giving the sharpest vision.
Hormones, Homeostasis and Tropisms
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- Hormone
- A chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs.
- Adrenaline
- The hormone secreted by the adrenal glands in ‘fight or flight’ situations.
- Homeostasis
- The maintenance of a constant internal environment.
- Negative feedbackExtended
- A change is detected and a response reverses it, bringing the value back to the set point.
- GlycogenExtended
- A storage carbohydrate made from glucose in the liver.
- Fatty tissueExtended
- A layer under the skin that acts as insulation.
- VasodilationExtended
- Widening of the arterioles that supply the skin surface capillaries.
- Phototropism
- A response in which parts of a plant grow towards or away from the direction of the light source.
- Gravitropism
- A response in which parts of a plant grow towards or away from gravity.
- AuxinExtended
- A plant growth substance made in the shoot tip that stimulates cell elongation.
Drugs
- Drug
- Any substance taken into the body that modifies or affects chemical reactions in the body.
- Antibiotic
- A drug that kills bacteria but does not affect viruses.
- Resistant
- Not killed by an antibiotic. Some bacteria are resistant to antibiotics.
- MRSAExtended
- A strain of bacteria resistant to many antibiotics, so infections are difficult to treat.
Reproduction in Plants
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- Asexual reproduction
- A process resulting in the production of genetically identical offspring from one parent.
- Fertilisation
- The fusion of the nuclei of gametes.
- Haploid and diploidExtended
- Haploid: one set of chromosomes (gamete nuclei). Diploid: two sets (zygote nucleus).
- Carpel
- The female part of a flower: stigma, style and ovary.
- Stamen
- The male part of a flower: filament and anther.
- Pollination
- The transfer of pollen grains from an anther to a stigma.
- Wind-pollinated flower
- A flower with its anthers and stigmas hanging outside the petals, adapted for pollen to be carried by the wind.
- Self-pollinationExtended
- Transfer of pollen from an anther to the stigma of the same flower, or of a different flower on the same plant.
- Cross-pollinationExtended
- Transfer of pollen from an anther to the stigma of a flower on a different plant of the same species.
- Fertilisation (plants)
- A pollen nucleus fuses with a nucleus in an ovule.
- Germination
- The start of growth of a seed into a seedling.
Human Reproduction, Hormones and STIs
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- Testis
- The organ that produces sperm.
- Ovary
- The organ that produces egg cells.
- Fertilisation
- The fusion of the nuclei of a male gamete (sperm) and a female gamete (egg cell).
- Amniotic fluid
- The fluid in the amniotic sac that protects the developing fetus.
- Menstrual cycle
- The monthly cycle of changes in the ovaries and in the lining of the uterus.
- FSH and LHExtended
- Hormones that control the ovaries: FSH causes egg cells to mature; LH triggers ovulation.
- STI
- An infection that is transmitted through sexual contact.
Chromosomes, Genes and Cell Division
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- Gene
- A length of DNA that codes for a protein.
- Allele
- An alternative form of a gene.
- X and Y chromosomes
- Females have two X chromosomes (XX). Males have one X and one Y chromosome (XY).
- Protein shapeExtended
- The sequence of amino acids determines the shape of a protein.
- mRNAExtended
- Messenger RNA: a copy of a gene, made in the nucleus, that carries the information to the ribosomes.
- Gene expression (term)Extended
- Genes whose protein the cell makes are said to be expressed.
- MitosisExtended
- Nuclear division giving rise to genetically identical cells.
- Stem cellsExtended
- Unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions.
- MeiosisExtended
- A reduction division in which the chromosome number is halved from diploid to haploid, resulting in genetically different cells.
Monohybrid Inheritance
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- Genotype
- The genetic make-up of an organism, in terms of the alleles present.
- Phenotype
- The observable features of an organism.
- Dominant allele
- An allele that is expressed if it is present in the genotype.
- Recessive allele
- An allele that is only expressed when there is no dominant allele of the gene present.
- Punnett square
- A grid that shows every possible combination of the gametes of the two parents.
- Phenotypic ratio
- The ratio of the different phenotypes among the offspring, such as 3 : 1 or 1 : 1.
- Pedigree diagram
- A family tree that shows how a characteristic is inherited through generations.
- Test crossExtended
- A cross between an organism showing the dominant phenotype and a homozygous recessive organism, used to find an unknown genotype.
- CodominanceExtended
- Both alleles in a heterozygous organism contribute to the phenotype.
- ABO blood groupsExtended
- The phenotypes are A, B, AB and O. The alleles are IA, IB and Io.
- Sex-linked characteristicExtended
- A feature in which the gene responsible is located on a sex chromosome, making the characteristic more common in one sex than in the other.
Variation and Selection
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- Variation
- Differences between individuals of the same species.
- Environmental influence
- A condition outside the organism, such as diet, that can change its phenotype.
- Mutation
- A genetic change.
- Gene mutationExtended
- A random change in the base sequence of DNA.
- Adaptive feature
- An inherited feature that helps an organism to survive and reproduce in its environment.
- HydrophyteExtended
- A plant adapted to live in water or very wet places.
- XerophyteExtended
- A plant adapted to live in very dry places.
- Natural selection
- The process in which individuals better adapted to their environment have a greater chance of reproducing and passing on their alleles.
- AdaptationExtended
- The process, resulting from natural selection, by which populations become more suited to their environment over many generations.
- Selective breeding (artificial selection)
- Selection by humans of individuals with desirable features, crossing them, and selecting offspring that show the desirable features.
Energy Flow and Food Webs
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- Energy flow
- The movement of energy through living organisms, from the Sun, as light energy, to chemical energy in organisms, and eventually to the environment.
- Food chain
- A chain that shows the transfer of energy from one organism to the next, beginning with a producer.
- Producer
- An organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis.
- Food web
- A network of interconnected food chains.
- Trophic level
- The position of an organism in a food chain, food web or ecological pyramid.
- Overharvesting
- Taking so many individuals of a food species that its numbers fall.
- Pyramid of numbers
- A diagram showing the number of organisms at each trophic level.
- Pyramid of biomass
- A diagram showing the mass of living material at each trophic level.
- Pyramid of energyExtended
- A diagram showing the energy at each trophic level, in a given area over a given time.
- Energy transferExtended
- The passing on of energy from one trophic level to the next.
Nutrient Cycles and Populations
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- Carbon cycle
- The movement of carbon between the air, living organisms and fossil fuels.
- Decomposition
- The breakdown of dead organisms and waste by decomposers.
- Nitrogen cycleExtended
- The movement of nitrogen between the air, the soil and living organisms.
- NitrificationExtended
- The change of ammonium ions to nitrate ions, carried out by microorganisms.
- DenitrificationExtended
- The change of nitrate ions to nitrogen gas, carried out by microorganisms.
- Population
- A group of organisms of one species, living in the same area, at the same time.
- Community
- All of the populations of different species in an ecosystem.
- Ecosystem
- A unit containing the community of organisms and their environment, interacting together.
- Population growth
- An increase in the number of organisms in a population.
- Sigmoid curve
- An S-shaped graph of population growth in an environment with limited resources: it levels off, and falls if resources run out.
- Limiting factorExtended
- A factor that limits the growth of a population, such as a resource that is in short supply.
Human Influences on Ecosystems
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- Food production
- The amount of food, from crop plants and livestock, that is produced.
- Monoculture
- The large-scale growing of a single crop plant in an area.
- Intensive livestock production
- Keeping large numbers of animals in a small area, to produce as much food as possible.
- Biodiversity
- The number of different species that live in an area.
- Habitat destruction
- The removal or damage of the places where organisms live.
- Deforestation
- The removal of large areas of forest, so that the land can be used for other purposes.
- Untreated sewage
- Human waste water that has not been cleaned before it enters a river or sea.
- EutrophicationExtended
- The process in which extra nutrients in water lead to a fall in dissolved oxygen and the death of aquatic organisms.
- Non-biodegradable
- Not able to be broken down by decomposers.
- Enhanced greenhouse effect
- The extra warming of the Earth caused by increased amounts of greenhouse gases such as methane and carbon dioxide in the air.
Questions
How do I use a key terms list to revise?
Cover the definition, say it out loud, then check it. Cambridge mark schemes reward the precise wording, so learn the definitions as they are written here rather than paraphrasing them.
Which terms are Extended only?
Terms marked Extended are Extended-tier content. If you are sitting the Core papers you can skip them.
Does this cover the whole 0610 syllabus?
It covers the chapters published so far in the Glide Biology notes. New chapters are added to this page automatically as they are published.
Test yourself on real questions with Biology past papers, and see the practicals guide for the food tests and investigations.
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