GCSE & IGCSE Biology key terms

207 terms with short definitions you can learn for the exam. Type to filter the list.

Command words 32

Add/Label: Add something to a diagram, table or graph you are given, for example labels on a diagram or units in a table.
Analyse the data/graph to explain IGCSE: Look closely at the data or graph and use the patterns in it to give an explanation.
Assess GCSE: Weigh up all the relevant factors, decide which matter most and reach a judgement.
Calculate: Work out a number, showing your working. Include the unit if there is one.
Comment on: Bring together several pieces of data or information to form a judgement.
Compare GCSE: Give similarities or differences between two or more things. Every point must refer to all of the things being compared. No conclusion is needed.
Compare and contrast GCSE: Give similarities and differences. You must include at least one similarity and at least one difference.
Complete: Fill in the missing parts of a table or diagram.
Deduce: Reach a conclusion from the information you are given.
Describe: Give an account of something, with linked statements. You do not need to give reasons.
Design IGCSE: Plan a procedure, using scientific ideas you already know.
Determine: Get an answer that uses numbers from the data you are given, or show how the answer can be reached using numbers.
Devise GCSE: Plan or invent a procedure, using scientific ideas you already know.
Discuss: Pick out the issue being asked about and explore all sides of it, using reasoning.
Draw: Produce a diagram, using a ruler or freehand.
Estimate: Find an approximate value from a diagram, from data or by a calculation.
Evaluate: Review the information (such as data or a method), consider strengths and weaknesses and come to a supported judgement.
Explain: Give a reason for each point you make. Your answer must include reasoning or justification, which can be mathematical.
Give a reason/reasons: A statement has been made; just give the reason or reasons why.
Give/State/Name: These mean the same: recall one or more facts. No explanation is needed.
Identify: Select the key information from the material you are given.
Justify: Give evidence that supports a statement, either one in the question or an answer you gave earlier.
Measure GCSE: Find a length or angle from a diagram using a ruler or protractor.
Plot: Mark points accurately on a grid from the data, then draw a line of best fit. Choose a sensible scale and label the axes if they are not given.
Predict: Give the result you would expect.
Show that: Prove that the value or statement in the question is correct, showing every step.
Sketch: Draw freehand. For a graph, draw the line and label the axes and important features; the axes do not need a scale.
State and explain GCSE: Make a point, then give the reasoning that justifies it.
State what is meant by: Give the meaning of a term. There may be more than one acceptable way to say it.
Suggest IGCSE: Use what you know to propose an answer in a situation you have not met before.
What, Why, Which IGCSE: Direct question words used in multiple-choice questions.
Write GCSE: Write an equation.

Key terms 147

Abiotic factor: A non-living factor that affects a community, such as temperature, light, water or pollutants.
Active site: The part of an enzyme where the substrate fits and the reaction happens. Its shape is specific to one substrate.
Active transport: Movement of substances from a lower to a higher concentration, against the concentration gradient, using energy from respiration.
ADH: Anti-diuretic hormone, released by the pituitary gland. It makes the collecting ducts more permeable so more water is reabsorbed into the blood.
Adrenaline: A hormone from the adrenal glands that prepares the body for fight or flight, for example by raising heart rate.
Aerobic respiration: Respiration using oxygen: glucose + oxygen gives carbon dioxide + water, releasing a lot of energy. It happens in mitochondria.
Allele: A different form of the same gene.
Alveoli: Tiny air sacs in the lungs where gas exchange happens. They have a large surface area, thin walls and a rich blood supply.
Anaerobic respiration: Respiration without oxygen. In animals glucose gives lactic acid; in plants and yeast it gives ethanol and carbon dioxide. It releases less energy than aerobic respiration.
Antibiotic GCSE: A medicine that kills bacteria or stops them growing. Antibiotics do not work on viruses.
Antibody: A protein made by lymphocytes that binds to a specific antigen on a pathogen.
Antigen: A molecule, usually a protein, on the surface of a cell or pathogen that triggers an immune response.
Artery: A blood vessel that carries blood away from the heart at high pressure. It has thick muscular and elastic walls.
Aseptic technique GCSE: Methods used to stop unwanted microorganisms contaminating a culture, such as sterilising equipment and working near a Bunsen flame.
ATP IGCSE: The molecule that carries energy released in respiration to the processes in cells that need it.
Auxin: A plant hormone that controls growth. In shoots it causes cell elongation on the shaded side, so the shoot bends towards light.
Benedict's test: Test for reducing sugars such as glucose: heat with Benedict's reagent and a positive result turns from blue to green, yellow or brick red.
Bile IGCSE: A fluid made by the liver and stored in the gall bladder. It neutralises stomach acid and emulsifies fats.
Biodiversity: The variety of living organisms in an area.
Biological control IGCSE: Using a natural predator, parasite or pathogen of a pest to control it.
Biotic factor: A living factor that affects a community, such as food, competition, predators or pathogens.
Biuret test: Test for protein: biuret reagent turns from blue to purple (lilac) if protein is present.
BMI GCSE: Body mass index: mass in kg divided by (height in m) squared. Used as one indicator of whether a person is underweight or overweight.
Bowman's capsule IGCSE: The cup-shaped start of a nephron that surrounds the glomerulus and collects the filtrate.
Capillary: The smallest blood vessel. Its wall is one cell thick so substances can be exchanged with tissues.
Cardiac output GCSE: The volume of blood pumped by the heart per minute: stroke volume × heart rate.
Chlorophyll: The green pigment in chloroplasts that absorbs light for photosynthesis.
Chromosome: A long coiled molecule of DNA carrying many genes, found in the nucleus.
Clinical trial GCSE: Testing a new medicine on people: first small doses on healthy volunteers, then on patients, often double-blind with a placebo.
Clone IGCSE: An organism that is genetically identical to its parent.
Codominance IGCSE: When both alleles in a heterozygote are expressed in the phenotype, such as the IA and IB alleles in blood group AB.
Communicable disease: A disease caused by a pathogen that can be passed from one organism to another.
Community: All the populations of different species living in the same habitat.
Competition: When organisms need the same limited resource, such as light, water, food, space or mates.
Decomposer: An organism, such as a bacterium or fungus, that breaks down dead material and waste, releasing nutrients.
Denatured: When the shape of an enzyme's active site changes, for example from high temperature or the wrong pH, so the substrate no longer fits.
Diabetes (type 1) GCSE: A condition in which the pancreas does not produce enough insulin, so blood glucose can rise too high. Treated with insulin.
Diabetes (type 2) GCSE: A condition in which body cells no longer respond properly to insulin. Linked to obesity; managed by diet, exercise and medication.
Differentiation: The process by which a cell becomes specialised for a particular job.
Diffusion: The net movement of particles from a higher to a lower concentration. It is passive and needs no energy from respiration.
Diploid: A cell with two sets of chromosomes. In humans, 46 chromosomes.
DNA: Deoxyribonucleic acid: a double helix of two strands of nucleotides that carries the genetic code. Bases pair A with T and C with G.
Dominant allele: An allele that is expressed even when only one copy is present.
Ecosystem: A community of organisms and the non-living parts of their environment, interacting together.
Effector: A muscle or gland that brings about a response.
Endocrine gland IGCSE: A gland that releases hormones directly into the blood.
Endothermic GCSE: A reaction that takes in energy from the surroundings, such as photosynthesis.
Enzyme: A protein that acts as a biological catalyst.
Eukaryotic organism IGCSE: An organism whose cells have a nucleus: plants, animals, fungi and protoctists.
Eutrophication: When extra nutrients such as nitrates enter water, causing algal growth, plant death, more decomposers using up oxygen, and the death of fish.
Evolution: The change in the inherited characteristics of a population over time, through natural selection.
Exothermic GCSE: A reaction that releases energy to the surroundings, such as respiration.
Fermenter IGCSE: A large vessel in which microorganisms are grown in controlled conditions to make a product.
Fertilisation: The fusion of a male and a female gamete nucleus to form a zygote.
FSH GCSE: Follicle stimulating hormone, from the pituitary gland. It causes an egg to mature in the ovary.
Gamete: A sex cell (sperm, egg, pollen nucleus or ovule nucleus). It is haploid.
Gene: A section of DNA that codes for a specific protein.
Genetic engineering: Changing an organism's genome, often by inserting a gene from another species, using restriction enzymes, ligase and a vector.
Genome: All of the DNA of an organism.
Genotype: The alleles an organism has, for example Bb.
Germination IGCSE: When a seed starts to grow. It needs water, oxygen and a suitable temperature.
Glomerulus IGCSE: A knot of capillaries in the kidney where ultrafiltration happens.
Glucagon GCSE: A hormone from the pancreas that raises blood glucose by causing the liver to break down glycogen into glucose.
Glycogen: The storage carbohydrate in animals and fungi, made from many glucose molecules.
Greenhouse gas IGCSE: A gas that traps heat in the atmosphere, such as carbon dioxide, methane, water vapour, nitrous oxide and CFCs.
Haemoglobin: The red protein in red blood cells that binds to oxygen.
Haploid: A cell with one set of chromosomes, such as a gamete. In humans, 23 chromosomes.
Heterozygous: Having two different alleles of a gene, for example Bb.
Homeostasis: Keeping the internal conditions of the body constant, such as temperature, water content and blood glucose.
Homozygous: Having two identical alleles of a gene, for example BB or bb.
Hormone: A chemical messenger carried in the blood to a target organ.
Hydrogencarbonate indicator IGCSE: An indicator that turns yellow when carbon dioxide concentration rises and purple when it falls.
Hyphae IGCSE: Thread-like structures that make up the body (mycelium) of a fungus.
Hypothalamus GCSE: Part of the brain that monitors blood temperature and controls thermoregulation.
Indicator species GCSE: A species whose presence or absence shows the level of pollution, such as lichens for air quality.
Insulin: A hormone from the pancreas that lowers blood glucose by making cells take in glucose and the liver store it as glycogen.
Interdependence GCSE: The way species in a community depend on each other, for food, shelter, pollination or seed dispersal.
Iodine test: Test for starch: iodine solution turns from orange-brown to blue-black.
Lactic acid IGCSE: The product of anaerobic respiration in animal muscle cells.
LH GCSE: Luteinising hormone, from the pituitary gland. It triggers ovulation.
Limiting factor: The factor in shortest supply, which stops the rate of a process such as photosynthesis going any faster.
Lymphocyte: A white blood cell that makes antibodies. Some become memory cells.
Magnification GCSE: How many times bigger an image is than the real object: image size ÷ real size.
Meiosis: Cell division that makes four genetically different haploid gametes.
Memory cell: A lymphocyte that stays in the blood after an infection or vaccination and quickly makes antibodies if the same pathogen returns.
Meristem GCSE: Plant tissue at the tips of roots and shoots containing stem cells that can divide and differentiate.
Micropropagation IGCSE: Growing many identical plants from small pieces (explants) on a sterile medium with plant hormones.
Mitochondria GCSE: Organelles where aerobic respiration happens.
Mitosis: Cell division that makes two genetically identical diploid cells, for growth, repair and asexual reproduction.
Monoclonal antibodies GCSE: Identical antibodies made by clones of one hybridoma cell, which all bind to the same specific antigen.
Motor neurone: A neurone that carries impulses from the central nervous system to an effector.
Mutation: A change in the base sequence of DNA.
Mutualism GCSE: A relationship between two species in which both benefit.
Natural selection: Individuals with alleles that make them better adapted are more likely to survive and reproduce, so those alleles become more common.
Negative feedback: A control mechanism that reverses a change, bringing a level back towards normal.
Nephron IGCSE: A kidney tubule where blood is filtered and useful substances are reabsorbed.
Nitrogen fixation GCSE: Turning nitrogen gas into nitrogen compounds such as ammonium, by bacteria in soil or root nodules, or by lightning.
Non-communicable disease: A disease that cannot be passed between people, such as cardiovascular disease or many cancers.
Nucleotide: The unit DNA is made of: a sugar, a phosphate group and one of four bases.
Oestrogen: A hormone made by the ovaries. It builds up the uterus lining and causes female secondary sexual characteristics.
Osmosis: The net movement of water molecules from a dilute solution to a more concentrated solution across a partially permeable membrane.
Parasitism GCSE: A relationship in which one organism (the parasite) lives on or in another (the host) and harms it.
Pathogen: A microorganism that causes disease, such as a bacterium, virus, fungus or protist.
Phagocyte: A white blood cell that engulfs and digests pathogens.
Phenotype: The characteristics an organism shows, produced by its genotype and the environment.
Phloem: Living plant tissue that carries sucrose and amino acids around the plant in both directions (translocation).
Photosynthesis: The process in which plants use light energy to make glucose and oxygen from carbon dioxide and water.
Placebo GCSE: A dummy treatment with no drug in it, used in clinical trials to compare against the real drug.
Placenta IGCSE: The organ that lets oxygen and nutrients pass from mother to fetus and wastes pass back.
Plasmid: A small ring of DNA found in bacteria, often used as a vector in genetic engineering.
Platelets: Cell fragments in the blood that help the blood to clot.
Pollination IGCSE: The transfer of pollen from an anther to a stigma.
Population: All the organisms of one species living in a habitat.
Progesterone: A hormone made by the ovaries that maintains the uterus lining.
Protoctist IGCSE: A microscopic, single-celled eukaryotic organism, such as Amoeba, Chlorella or Plasmodium.
Punnett square: A grid used to show the possible genotypes of the offspring of a genetic cross.
Quadrat: A square frame of known area used to sample organisms.
Receptor: A cell or group of cells that detects a stimulus.
Recessive allele: An allele that is only expressed when two copies are present.
Reflex: A fast, automatic response to a stimulus that does not involve the conscious part of the brain.
Relay neurone: A neurone in the central nervous system that passes impulses from a sensory neurone to a motor neurone.
Resolution GCSE: The ability of a microscope to show two close points as separate. Higher resolution shows more detail.
Respiration: An exothermic reaction in all living cells that releases energy from glucose.
Restriction enzyme: An enzyme that cuts DNA at a specific base sequence.
Saprotrophic nutrition IGCSE: Feeding by secreting digestive enzymes onto food outside the body and absorbing the products, as fungi do.
Selective breeding: Humans choosing parents with desired characteristics and breeding them over many generations.
Selective reabsorption IGCSE: Taking useful substances, such as all the glucose, back into the blood from the nephron.
Sensory neurone: A neurone that carries impulses from a receptor to the central nervous system.
Stem cell GCSE: An unspecialised cell that can divide and differentiate into other cell types.
Stomata: Pores, mostly on the underside of leaves, that let gases in and out. Guard cells open and close them.
Surface area to volume ratio: Surface area divided by volume. Larger organisms have a smaller ratio, so they need exchange surfaces and transport systems.
Synapse: The gap between two neurones, crossed by chemical neurotransmitters.
Thyroxine GCSE: A hormone from the thyroid gland that controls the metabolic rate. Its level is controlled by negative feedback.
Transect GCSE: A line across a habitat along which quadrats are placed at intervals, to show how distribution changes.
Transgenic IGCSE: Containing genes transferred from another species.
Transpiration: The loss of water vapour from the leaves of a plant, mainly through the stomata.
Trophic level IGCSE: The position of an organism in a food chain, such as producer or primary consumer.
Ultrafiltration IGCSE: Filtering small molecules out of the blood under high pressure in the glomerulus.
Vaccination: Giving a dead, weakened or harmless form of a pathogen (or its antigens) so the body makes memory cells without becoming ill.
Vasoconstriction: Narrowing of blood vessels supplying the skin, so less heat is lost.
Vasodilation: Widening of blood vessels supplying the skin, so more heat is lost.
Vector: Something that carries a gene into a cell (such as a plasmid or virus), or an organism that spreads a pathogen (such as a mosquito).
Vein: A blood vessel that carries blood back to the heart. It has thin walls, a large lumen and valves.
Villi IGCSE: Finger-like projections lining the small intestine that give a large surface area for absorbing digested food.
Virus: A non-living particle made of genetic material in a protein coat. It can only reproduce inside a host cell.
Xylem: Dead, hollow plant tubes strengthened with lignin that carry water and mineral ions up from the roots.
Zygote IGCSE: The diploid cell formed when two gametes fuse at fertilisation.

Key equations and calculations 28

Aerobic respiration (2.37) IGCSE: Word: glucose + oxygen → carbon dioxide + water. Symbol: C_{6}H_{12}O_{6} + 6O_{2} → 6CO_{2} + 6H_{2}O.
Aerobic respiration (word equation) GCSE: glucose + oxygen → carbon dioxide + water (energy released).
Anaerobic respiration (2.38) IGCSE: Animals: glucose → lactic acid. Plants and yeast: glucose → ethanol + carbon dioxide.
Anaerobic respiration (word equations) GCSE: Animals: glucose → lactic acid. Plants and yeast: glucose → ethanol + carbon dioxide.
Area of a clear zone (5.19B) GCSE: area = πr^{2}, where r is the radius (half the diameter) of the clear zone or culture. Unit mm^{2} or cm^{2}.
BMI GCSE: BMI = mass (kg) ÷ (height (m))^{2}. Unit kg/m^{2}.
Cardiac output GCSE: cardiac output = stroke volume × heart rate. For example 70 cm^{3} × 72 beats per minute = 5040 cm^{3} per minute.
Efficiency of energy transfer IGCSE: efficiency (%) = energy passed to the next trophic level ÷ energy in the level below × 100. Usually about 10%.
Energy in food (1.14B) GCSE: energy transferred (J) = mass of water (g) × 4.2 × temperature rise (°C). Energy per gram = energy ÷ mass of food burned. 1 cm^{3} of water has a mass of 1 g.
Energy in food (2.33B) IGCSE: energy (J) = mass of water (g) × 4.2 × temperature rise (°C); energy per gram = energy ÷ mass of food.
Fick's law (8.5B) GCSE: rate of diffusion ∝ (surface area × concentration difference) ÷ thickness of membrane.
Genetic ratios IGCSE: Aa × Aa gives 3 : 1 dominant to recessive phenotypes (25% recessive). Aa × aa gives 1 : 1 (50% recessive).
Inverse square law for light (6.6) GCSE: light intensity ∝ 1 ÷ distance^{2}. Doubling the distance from the lamp makes the light intensity one quarter.
Magnification (1.6) GCSE: magnification = image size ÷ real size. Rearranged: real size = image size ÷ magnification. Put both sizes in the same unit first. Magnification has no unit, write it as ×400.
Mean and percentage IGCSE: mean = total ÷ number of values (leave out anomalies). Percentage change = change ÷ original value × 100.
Mean and percentage change GCSE: mean = total ÷ number of values (leave out anomalies). Percentage change = change ÷ original value × 100.
Percentage change in mass IGCSE: percentage change = (final mass - initial mass) ÷ initial mass × 100. Used in osmosis practicals.
Percentage change in mass (1.17) GCSE: percentage change = (final mass - initial mass) ÷ initial mass × 100. A negative answer means the tissue lost mass (water left by osmosis).
Photosynthesis IGCSE: Word: carbon dioxide + water → glucose + oxygen. Symbol: 6CO_{2} + 6H_{2}O → C_{6}H_{12}O_{6} + 6O_{2}, using light energy and chlorophyll.
Photosynthesis (word equation) GCSE: carbon dioxide + water → glucose + oxygen (light energy absorbed by chlorophyll).
Population estimate (4.2) IGCSE: estimated population = mean number per quadrat × (total area ÷ area of one quadrat).
Population estimate (9.6) GCSE: estimated population = mean number per quadrat × (total area ÷ area of one quadrat).
Rate from a change IGCSE: rate = change in amount ÷ time, for example cm^{3} of oxygen per minute or bubbles per minute.
Rate from a time IGCSE: rate = 1 ÷ time taken, for example for an enzyme to digest all the starch. A shorter time means a faster rate. Unit s^{-1}.
Rate of decay (9.19B) GCSE: rate = change in mass (or other measurement) ÷ time taken, for example g per day.
Rate of enzyme activity (1.11) GCSE: rate = amount of product made (or substrate used) ÷ time. If you only have a time, rate = 1 ÷ time, unit s^{-1}.
Units of size (1.5) GCSE: 1 mm = 1000 µm; 1 µm = 1000 nm. milli = 10^{-3}, micro = 10^{-6}, nano = 10^{-9}. Going to a smaller unit, multiply by 1000.
Waist to hip ratio GCSE: waist:hip ratio = waist measurement ÷ hip measurement (same units). A higher ratio is linked to a higher risk of cardiovascular disease.

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