IGCSE Biology Glossary
Definition questions are the cheapest marks on the paper. But only if you write the exact wording the mark scheme pays for. Each term below gives you the examiner-ready definition plus a note on how it is actually marked.
32 terms · Cambridge IGCSE Biology 0610 / 0970 · reviewed by our Biology specialists
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.
Aerobic respiration
The chemical reactions in cells that break down glucose using oxygen to release energy. Word equation: glucose + oxygen → carbon dioxide + water.
Allele
An alternative form of a gene, found at the same position on a chromosome. For example, the gene for seed shape has a round allele and a wrinkled allele.
Alveoli
The tiny air sacs in the lungs where gas exchange takes place. Oxygen diffuses into the blood and carbon dioxide diffuses out.
Anaerobic respiration
The chemical reactions in cells that break down glucose without oxygen, releasing much less energy than aerobic respiration. In muscles: glucose → lactic acid. In yeast: glucose → alcohol + carbon dioxide.
Antibody
A protein produced by lymphocytes that binds to specific antigens on a pathogen, marking it for destruction or causing pathogens to clump together.
Denaturation
A permanent change in the shape of an enzyme's active site, caused by high temperature or unsuitable pH, so the substrate no longer fits and the enzyme stops working.
Diffusion
The net movement of particles from a region of their higher concentration to a region of their lower concentration, down a concentration gradient, as a result of their random movement.
Dominant allele
An allele that is expressed in the phenotype when only one copy is present (in the heterozygous condition).
Double circulation
A circulatory system in which blood passes through the heart twice for each complete circuit of the body. Once in the pulmonary circuit (to the lungs) and once in the systemic circuit (to the rest of the body).
Ecosystem
A unit containing the community of organisms and their environment, interacting together. For example, a decomposing log, a pond, or a rainforest.
Enzyme
A protein that functions as a biological catalyst. It speeds up a chemical reaction without being changed or used up by the reaction.
Eutrophication
The over-enrichment of water with nutrients (from fertiliser run-off or sewage), causing an algal bloom that blocks light, the death and decomposition of plants and algae, oxygen depletion by decomposer respiration, and the death of aquatic animals.
Food chain
A diagram showing the transfer of energy from one organism to the next, beginning with a producer. For example: grass → grasshopper → frog → snake.
Genotype
The genetic make-up of an organism. The combination of alleles it carries for a characteristic, written as letters (e.g. RR, Rr or rr).
Homeostasis
The maintenance of a constant internal environment in the body. For example, keeping core temperature and blood glucose concentration within narrow limits.
Meiosis
Reduction division in which the chromosome number is halved, producing four genetically different gametes from one parent cell.
Mitosis
Nuclear division that produces two genetically identical daughter cells with the same number of chromosomes as the parent cell. Used for growth, repair of damaged tissue, replacement of cells, and asexual reproduction.
Natural selection
The process by which individuals with variation better suited to the environment are more likely to survive and reproduce, passing on their alleles, so the favourable feature becomes more common over generations.
Negative feedback
A control mechanism in which a change in a condition triggers a response that reverses the change, returning the condition to its set point. The basis of homeostasis.
Osmosis
The net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane.
Pathogen
A disease-causing organism. For example, bacteria, viruses, fungi or protoctists that cause transmissible diseases.
Phenotype
The observable features of an organism that result from its genotype and its environment. For example, round seeds or brown eyes.
Photosynthesis
The process by which plants synthesise carbohydrates from carbon dioxide and water, using energy from light trapped by chlorophyll. Word equation: carbon dioxide + water → glucose + oxygen, in the presence of light and chlorophyll.
Recessive allele
An allele that is only expressed in the phenotype when two copies are present (in the homozygous condition).
Reflex arc
The nerve pathway of a reflex action: receptor → sensory neurone → relay neurone (in the spinal cord) → motor neurone → effector, producing a fast, automatic response that protects the body.
Translocation
The movement of sucrose and amino acids in the phloem, from regions of production (sources, e.g. leaves) to regions of storage or use (sinks, e.g. roots and fruits).
Transpiration
The loss of water vapour from the leaves of a plant, mainly through the stomata, as water evaporates from the surfaces of mesophyll cells.
Trophic level
The position of an organism in a food chain, food web or pyramid. Producer, primary consumer, secondary consumer, and so on.
Tropism
A growth response of a plant in which the direction of growth is determined by the direction of the stimulus. Phototropism responds to light, gravitropism to gravity.
Vaccination
Giving a weakened or dead pathogen (or its antigens) to stimulate lymphocytes to produce antibodies and memory cells, so a later infection by the real pathogen triggers a faster, stronger immune response.
Variation
Differences between individuals of the same species. Continuous variation (e.g. height) shows a complete range and is affected by many genes and environment; discontinuous variation (e.g. blood group) has distinct categories and is usually controlled by genes alone.