Comprehensive IGCSE Biology Revision Guide

Vocabulary practice flashcards covering core biological terms, systems, and definitions from the 2026 Fifths Revision Trials Exam Checklist.

Pathogen

A biological agent that causes disease, which may be a fungus, bacterium, protoctist, or virus.

Levels of Organisation

The structural hierarchy within living organisms arranged in order: organelles, cells, tissues, organs, and systems.

Cell Differentiation

The development process by which unspecialised cells become specialised in structure and function to perform specific roles.

Stem Cells

Undifferentiated cells with the potential to develop into specialised cell types, used in medicine but with associated ethical and practical advantages and disadvantages.

Peristalsis

The wave of muscular contractions along the wall of the gut that forces food through the alimentary canal.

Bile

An alkaline substance produced by the liver and stored in the gall bladder that neutralises stomach acid and emulsifies lipids.

Amylase and Maltase

Digestive enzymes that catalyse the breakdown of starch into maltose and then into glucose.

Proteases

Digestive enzymes that catalyse the breakdown of proteins into basic sub-units called amino acids.

Lipases

Digestive enzymes that break down large lipid molecules into smaller sub-units of fatty acids and glycerol.

Villus

A finger-like projection of the inner lining of the small intestine that increases surface area for the absorption of digestion products.

ATP (Adenosine Triphosphate)

The chemical energy currency molecule released during respiration that provides usable energy directly for cellular processes.

Plasma

The liquid component of blood that transports carbon dioxide, digested food, urea, hormones, and heat energy around the body.

Phagocytes

A type of white blood cell that defends the body by engulfing and ingesting pathogenic microorganisms.

Lymphocytes

White blood cells that respond to disease by producing and releasing specific antibodies targeted to a pathogen.

Platelets

Cell fragments in the blood involved in blood clotting, which prevents blood loss and blocks the entry of microorganisms.

Memory Cells

Cells manufactured in response to vaccination or infection that allow subsequent antibody production against the same pathogen to happen sooner, faster, and in greater quantity.

Fertilisation

The process involving the fusion of a male and a female gamete to produce a zygote that undergoes cell division and develops into an embryo.

Transpiration

The evaporation of water from the surface of a plant, primarily through the leaves.

Phloem

Vascular tissue in plants responsible for transporting sucrose and amino acids between the leaves and other parts of the plant.

Xylem

Vascular tissue in plants responsible for transporting water and mineral salts from the roots up to other parts of the plant.

Auxins

Plant growth regulators (hormones) responsible for mediating directional growth responses, including the positive phototropism of stems.

Placenta

An organ providing nutritional and gas exchange support to the developing embryo from the maternal circulation.

Amniotic Fluid

The fluid surrounding the developing embryo inside the amnion that cushions and protects it from mechanical damage.

Nitrogen-Fixing Bacteria

Bacteria involved in the nitrogen cycle that convert free atmospheric nitrogen into nitrogenous compounds usable by plants.

Nitrifying Bacteria

Bacteria that oxidise ammonium compounds into nitrites and subsequently into nitrates in the soil.

Denitrifying Bacteria

Bacteria that break down soil nitrates, converting them back into atmospheric nitrogen gas.

Population

All the individuals of one particular species living together in a specific habitat at the same time.

Community

All the populations of different species that live and interact together in the same area or habitat.

Habitat

The specific place or environment where a plant, animal, or microorganism naturally lives and thrives.

Ecosystem

A distinct biological community formed by all living organisms interacting with each other alongside the abiotic non-living components of their environment.

Biodiversity

The amount of variety and range of living organisms present within a particular habitat or ecosystem.

Greenhouse Gases

Gases in the atmosphere that absorb infrared radiation and contribute to the greenhouse effect, including water vapour, carbon dioxide, nitrous oxide, methane, and CFCs.

Eutrophication

The process whereby mineral ions (such as nitrates) leach from fertiliser into aquatic habitats, causing rapid algal growth and subsequent depletion of oxygen.

Lactobacillus

A genus of bacteria utilised in food production, specifically for fermenting milk into yoghurt.

Genome

The entire complementary set of genetic material (DNA) present within an organism.

Gene

A specific section of a DNA molecule that contains the chemical code required to produce a particular protein.

Allele

An alternative version or form of a single gene that gives rise to inherited differences in characteristics.

Polygenic Inheritance

A form of genetic control where a phenotypic characteristic is determined by the combined effect of multiple separate genes rather than a single gene.

Mutation

A rare, spontaneous, and random alteration in the sequence of genetic material that can be inherited by offspring.

Codominance

A genetic inheritance pattern where both alternative alleles of a gene are fully expressed in the phenotype of a heterozygous individual.