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IGCSE Biology Key Terms (0610)
IGCSE Biology Key Terms
Cambridge IGCSE Biology (0610) | Essential Definitions & Equations
Based on official Cambridge syllabus 2026-2028
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Diffusion
Net movement of particles...
Osmosis
Net movement of water molecules...
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1. Characteristics of Living Organisms (MRS GREN)
Movement An action by an organism or part of one causing a change of position or place
Respiration Chemical reactions inside cells that break nutrient molecules down, releasing energy for metabolism
Sensitivity Detecting changes inside the organism or in its surroundings, and responding to them
Growth A permanent increase in size and dry mass
Reproduction The processes by which organisms produce more of their own kind
Excretion Removing metabolic waste and any substances beyond what the organism needs
Nutrition Taking in of materials for energy, growth and development
Classification:
Species A group of organisms able to breed together and have fertile offspring
Binomial system An internationally agreed way of naming species: each scientific name has two parts, one for the genus and one for the species
2. Cell Structure
Cell membrane Controls what enters and leaves the cell; partially permeable
Nucleus Contains genetic material (DNA); controls cell activities
Cytoplasm Where chemical reactions take place
Mitochondria Site of aerobic respiration; releases energy
Ribosomes Site of protein synthesis
Plant cells:
Cell wall Made of cellulose; provides support and prevents bursting
Chloroplasts Contain chlorophyll; site of photosynthesis
Vacuole Contains cell sap; maintains water pressure inside the cell; the term is turgor pressure (Extended)
Levels of organisation:
Cell The basic unit of an organism, e.g. a red blood cell or a root hair cell
Tissue Cells with similar structures working as a group on one shared function, e.g. palisade mesophyll
Organ A structure of several tissues working together to carry out specific functions, e.g. the stomach
Organ system Organs with related functions that cooperate to carry out body functions, e.g. the digestive system
Organism A whole living thing, e.g. a plant or an animal
Magnification: image size ÷ actual size
3. Movement of Substances
Diffusion
Particles move randomly, giving a net movement from a region of higher concentration to a region of lower concentration, down a concentration gradient
Osmosis
Water diffusing through a partially permeable membrane; water enters and leaves cells this way, through the cell membrane
A net movement of water molecules across a partially permeable membrane, from the dilute solution (higher water potential) to the concentrated solution (lower water potential) (Extended)
Active transport
Particles are moved across a cell membrane against a concentration gradient, from lower concentration to higher concentration, using energy from respiration
Key difference: Diffusion & osmosis = kinetic energy of the particles; Active transport = energy from respiration
4. Food Tests
| Nutrient | Reagent | Method | Positive Result |
|---|---|---|---|
| Starch | Iodine solution | Add drops | Blue-black |
| Reducing sugars | Benedict's solution | Heat in water bath | Orange/brick-red |
| Protein | Biuret reagent | Add and shake | Purple/lilac |
| Fats/oils | Ethanol + water | Shake, add water | White emulsion |
| Vitamin C | DCPIP | Add drops | Colourless |
5. Enzymes
Catalyst: A substance that speeds up a chemical reaction without being changed by it
Enzyme: A protein involved in all metabolic reactions, acting as a biological catalyst that speeds them up without being used up
Denaturation: Permanent change in enzyme shape due to high temperature or extreme pH; active site no longer fits substrate
Active site Part of enzyme where substrate binds; its shape is complementary to the substrate
Substrate The molecule that the enzyme acts upon
Optimum Temperature/pH at which enzyme works fastest (~37°C for human enzymes)
Tip (Extended): Enzymes are specific — the active site only fits a substrate with a complementary shape
6. Photosynthesis
Definition:
The process by which plants make carbohydrates using light energy, carbon dioxide and water, releasing oxygen as a by-product
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (Extended)
(requires light and chlorophyll)
Word equation:
carbon dioxide + water → glucose + oxygen
Requirements: Light, chlorophyll, CO₂, water
Factors affecting the rate: Light intensity, CO₂ concentration, temperature; the term is limiting factors (Extended)
Uses of carbohydrates: Starch as an energy store, cellulose for cell walls, glucose for respiration, sucrose for transport in phloem, nectar to attract insects
Factors affecting the rate: Light intensity, CO₂ concentration, temperature; the term is limiting factors (Extended)
Uses of carbohydrates: Starch as an energy store, cellulose for cell walls, glucose for respiration, sucrose for transport in phloem, nectar to attract insects
7. Human Nutrition
Balanced diet A diet with all the nutrients in the correct proportions: carbohydrates, fats and oils, proteins, vitamins, mineral ions, fibre and water
Ingestion Taking substances such as food and drink into the body
Digestion Breaking food down
Absorption Nutrients moving out of the intestines and into the blood
Assimilation Cells taking up nutrients and using them
Egestion Undigested food being removed from the body as faeces
Physical digestion Breaking food into smaller pieces without chemically changing the food molecules
Chemical digestion Breaking large insoluble molecules down into small soluble ones
8. Transport in Plants
Xylem
- Transports water & mineral ions; gives support
- From roots → leaves
- Dead, hollow tubes (Extended)
- Lignified walls (Extended)
Phloem
- Transports sucrose & amino acids
- From sources to sinks (Extended)
Transpiration: Loss of water vapour from leaves through stomata
Translocation (Extended): Sucrose and amino acids being moved through the phloem, from sources to sinks
Source (Extended): A plant part that releases sucrose or amino acids
Sink (Extended): A plant part that uses or stores sucrose or amino acids
Tip: Starch is NOT transported (insoluble) — sucrose is what moves through the phloem
9. Circulatory System
Circulatory system: Blood vessels, a pump and valves that keep blood flowing in one direction
Arteries
Away from heart
Thick walls
High pressure (Extended)
Thick walls
High pressure (Extended)
Veins
To heart
Thin walls
Have valves
Thin walls
Have valves
Capillaries
Exchange
One cell thick
Permeable (Extended)
One cell thick
Permeable (Extended)
Blood flow: Right atrium → Right ventricle → Lungs → Left atrium → Left ventricle → Body
Blood clotting (Extended): Fibrinogen is converted to fibrin, forming a mesh
Coronary arteries: Supply heart muscle with blood
Septum: Wall dividing left and right sides
Coronary heart disease: Coronary arteries become blocked. Risk factors include smoking, stress, diet, lack of exercise, age, sex and genetic predisposition; diet and exercise can reduce the risk
10. Diseases and Immunity
Pathogen An organism that causes disease
Transmissible disease A disease whose pathogen can pass from one host to another
Active immunity (Extended) The body makes its own antibodies to defend against a pathogen
Antibodies (Extended) Proteins that bind to antigens, then either destroy pathogens directly or mark them for phagocytes to destroy
Passive immunity (Extended) Short-term protection from a pathogen by antibodies that came from another individual, e.g. across the placenta or in breast milk
Cholera (Extended) A disease caused by a bacterium that is passed on in contaminated water
11. Gas Exchange
Gas exchange: Oxygen diffuses into blood, carbon dioxide diffuses out, across the alveoli walls
Features of alveoli for efficient gas exchange:
- Large surface area — many alveoli
- Thin walls — one cell thick, short diffusion distance
- Good blood supply — maintains concentration gradient
- Good ventilation with air
Pathway: Nose/mouth → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
12. Respiration
Definition:
Chemical reactions inside cells that break nutrient molecules down, releasing energy for metabolism
Aerobic Respiration (with oxygen):
Chemical reactions inside cells that use oxygen to break nutrient molecules down, releasing energy
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O (Extended)
glucose + oxygen → carbon dioxide + water
Anaerobic Respiration (without oxygen):
Chemical reactions inside cells that break nutrient molecules down, releasing energy, without using oxygen
In muscles:
glucose → lactic acid
In yeast:
glucose → alcohol + carbon dioxide
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (Extended)
Tip: Aerobic releases MORE energy; happens in mitochondria
13. Excretion
Excretion: Removing metabolic waste and any substances beyond what the organism needs
Kidneys excrete: Urea, excess water, excess ions
Lungs excrete: CO₂
Urea formation (Extended): Excess amino acids → deamination in liver → urea
Deamination (Extended): Taking the nitrogen-containing part off amino acids, forming urea
Remember: Egestion (faeces) is NOT excretion — it's undigested food, not metabolic waste
14. Coordination and Response
Reflex action Automatic, rapid integration and coordination of stimuli with responses from effectors (muscles and glands)
Synapse The junction between two neurones
Sense organs Groups of receptor cells that respond to particular stimuli: light, sound, touch, temperature and chemicals
Hormone A chemical made by a gland and carried in the blood; it changes how one or more specific target organs work
Adrenaline The hormone released in 'fight or flight' situations; it increases breathing rate, heart rate and pupil diameter
Homeostasis Maintaining a constant internal environment
Gravitropism A plant response in which parts grow towards gravity or away from it
Phototropism A plant response in which parts grow towards a light source or away from it
15. Drugs
Drug Any substance which, once taken into the body, changes or affects its chemical reactions
16. Reproduction
Asexual reproduction One parent producing genetically identical offspring
Sexual reproduction The nuclei of two gametes fuse to form a zygote; the offspring are genetically different from each other
Fertilisation Gamete nuclei fusing, e.g. the nuclei of a sperm and an egg cell
Pollination Pollen grains being transferred from an anther to a stigma
Self-pollination (Extended) Pollen grains move from an anther to a stigma of the same flower, or of another flower on the same plant
Cross-pollination (Extended) Pollen grains move from an anther to a stigma on another plant of the same species
Sexually transmitted infection (STI) An infection passed on through sexual contact
17. Genetics & Inheritance
Gene A length of DNA that codes for a protein
Allele An alternative form of a gene
Haploid nucleus (Extended) A nucleus with one set of chromosomes
Diploid nucleus (Extended) A nucleus with two sets of chromosomes
Inheritance Genetic information being passed from one generation to the next
Genotype An organism's genetic make-up, in terms of the alleles it has (e.g., Bb, BB, bb)
Phenotype An organism's observable features
Dominant Allele that is expressed when present (capital letter)
Recessive Allele only expressed when no dominant allele of the gene is present (lowercase)
Homozygous Two identical alleles of one gene (BB or bb)
Heterozygous Two different alleles of one gene (Bb)
Codominance (Extended) In a heterozygous organism, both alleles contribute to the phenotype
Sex-linked characteristic (Extended) A feature whose gene sits on a sex chromosome, making it more common in one sex than the other
Mitosis (Extended): Nuclear division giving genetically identical cells (growth, repair, replacement of cells, asexual reproduction)
Stem cells (Extended): Unspecialised cells that divide by mitosis; their daughter cells can then specialise for specific functions
Meiosis (Extended): Reduction division halving the chromosome number from diploid to haploid, giving genetically different cells (involved in producing gametes)
18. Variation and Selection
Variation Differences among individuals of one species
Continuous variation A range of phenotypes lying between two extremes, e.g. body length and body mass
Discontinuous variation Phenotypes fall into a limited number of types with no intermediates, e.g. ABO blood groups, and seed shape or seed colour in peas
Mutation A genetic change
Gene mutation (Extended) A random change in DNA's base sequence
Adaptive feature An inherited feature that helps an organism survive and reproduce where it lives
Natural selection Populations show genetic variation and produce many offspring, which struggle to survive and compete for resources. Better-adapted individuals are more likely to reproduce, so their alleles reach the next generation
Selective breeding Humans pick individuals with desirable features, cross them, then pick offspring showing those features. Repeated over many generations as artificial selection, this improves crop plants and domesticated animals
Adaptation (Extended) The process by which natural selection makes populations better suited to their environment over many generations
19. Organisms and Their Environment
Food chain Shows energy passing from one organism to the next, starting with a producer
Food web A network of linked food chains
Producer Organism making its own organic nutrients by photosynthesis, usually with energy from sunlight
Consumer An organism that feeds on other organisms for its energy
Herbivore An animal that eats plants for its energy
Carnivore An animal that eats other animals for its energy
Decomposer An organism whose energy comes from dead or waste organic material
Trophic level An organism's position in an ecological pyramid, food chain or food web
Population A group of organisms of one species sharing an area at the same time
Community The populations of all the different species in an ecosystem
Ecosystem A community of organisms and their environment, interacting as a unit
20. Human Influences on Ecosystems
Biodiversity How many different species live in an area
Sustainable resource A resource produced as fast as it is taken from the environment, so it does not run out
21. Biotechnology and Genetic Modification
Genetic modification Altering an organism's genetic material by removing, changing or inserting individual genes
© LumiExams.com | IGCSE Biology Key Terms Sheet | Based on Cambridge IGCSE Biology 0610 Syllabus (2026-2028)
Frequently Asked Questions
What definitions do I need to memorize for IGCSE Biology?
Key IGCSE Biology definitions include: diffusion, osmosis, active transport, enzymes, photosynthesis, respiration, homeostasis, and inheritance terms like genotype, phenotype, dominant, and recessive. You should also know MRS GREN (characteristics of living things) and the food tests.
What is MRS GREN in Biology?
MRS GREN is a mnemonic for the 7 characteristics of living organisms: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition. All living things exhibit these characteristics.
What food tests do I need to know for IGCSE Biology?
IGCSE Biology requires you to know: Benedict's test (reducing sugars - blue to orange), Iodine test (starch - brown to blue-black), Biuret test (protein - blue to purple), Ethanol emulsion test (fats/oils - cloudy white emulsion), and DCPIP test (vitamin C).
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