Edexcel IGCSE Biology Double Award Vocabulary

Comprehensive vocabulary flashcards covering the key terms, definitions, and physiological concepts across all units of the Edexcel IGCSE Biology Double Award specification.

Eukaryotic

Describes an organism whose cells contain membrane-bound organelles, such as a nucleus and mitochondria.

Prokaryotic

Describes an organism whose cells lack membrane-bound organelles (such as a distinct nucleus, mitochondria, or chloroplasts), exemplified by bacteria.

Pathogen

A microorganism that causes disease.

Saprotrophic Nutrition

The mode of feeding where digestive enzymes are secreted extracellularly onto dead matter to break it down, carried out by fungi.

Organelle

A specialised structure found inside a cell that performs a specific function.

Cell

A group of organelles working together to perform the same function; the basic unit of life.

Tissue

A group of similar cells working together to perform the same function.

Organ

A structure composed of a group of different tissues working together to perform the same function.

Organ System

A group of organs working together to carry out a particular bodily function.

Zygote

The single diploid cell formed immediately following the fertilisation of a male and female gamete.

Lipid

A biological molecule composed of carbon, hydrogen, and oxygen, structured from $1$ glycerol molecule joined to $3$ fatty acid chains.

Ethanol Emulsion Test

A chemical food test for lipids where ethanol and water are added to a sample and shaken; a positive result produces a milky white emulsion.

Biuret Test

A chemical food test for protein where Biuret reagent is added to a sample; a positive result turns the solution from blue to purple.

Benedict's Test

A chemical food test for reducing sugars (glucose) where Benedict's solution is added to a sample and heated in a water bath at $80\text{--}95\,^\circ\text{C}$ for $5\,\text{minutes}$; a positive result turns the solution from blue to brick red.

Iodine Test

A chemical food test for starch where iodine solution is added to a sample; a positive result turns from brown to blue/black.

Enzyme

A biological catalyst that speeds up the rate of a chemical reaction without being consumed or altered in the process.

Active Site

The specific region on an enzyme where the complementary substrate molecule binds to form an enzyme-substrate complex.

Denature

The alteration of an enzyme's shape (caused by high temperatures or extreme pH) such that the active site is deformed and can no longer bind its substrate.

Metabolism

The overall rate at which all chemical reactions take place inside the body, catalysed by enzymes.

Diffusion

The net movement of particles from an area of higher concentration to an area of lower concentration down a concentration gradient.

Active Transport

The net movement of particles from an area of lower concentration to an area of higher concentration against a concentration gradient, requiring energy from ATP.

Osmosis

The net movement of water from an area of higher water potential to an area of lower water potential across a partially permeable membrane.

Turgid

The firm, swollen condition of a plant cell when water enters by osmosis, supported by the cell wall preventing bursting.

Plasmolysis

The condition of a plant cell placed in a solution of lower water potential where water leaves by osmosis and the cell membrane pulls away from the cell wall.

Photosynthesis

The endothermic reaction converting light energy into chemical energy in plants: $6CO_2 + 6H_2O \rightarrow 6O_2 + C_6H_{12}O_6$.

Limiting Factor

An environmental condition in a reaction that is in the shortest supply and directly prevents the rate of the reaction from increasing further.

Balanced Diet

A diet that provides all essential nutrients in the correct proportions required to support life processes and maintain good health.

Peristalsis

The wave-like contraction and relaxation of circular and longitudinal muscles in the gut wall that pushes a food bolus along the alimentary canal.

Bile

An alkaline substance produced by the liver and stored in the gall bladder that neutralises hydrochloric acid and emulsifies large lipid droplets into smaller droplets.

Ingestion

The process of taking food into the body through the mouth.

Digestion

The chemical and mechanical breakdown of large, insoluble food molecules into small, soluble molecules for absorption.

Absorption

The movement of small, soluble food molecules through the wall of the small intestine into the bloodstream.

Assimilation

The process where absorbed small food molecules are incorporated into body cells to build larger biological molecules (e.g. glycogen and proteins).

Egestion

The removal of undigested food and faeces from the body via the anus.

Excretion

The removal of waste products of metabolism, toxic materials, and substances in excess of requirements from an organism.

Aerobic Respiration

The complete breakdown of glucose to release energy using oxygen, carried out inside mitochondria: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$.

Anaerobic Respiration

The incomplete breakdown of glucose to release a small amount of ATP without using oxygen.

Oxygen Debt

The volume of oxygen required after strenuous anaerobic exercise to completely oxidise and break down accumulated lactate in the liver.

Ventilation

The physical movement of air into and out of the lungs via the action of the diaphragm and intercostal muscles.

Phloem

Vascular plant tissue consisting of sieve tube elements and companion cells that transports sucrose and amino acids both up and down the stem.

Xylem

Hollow, continuous plant vessels reinforced with lignin that transport water and dissolved mineral ions upwards from roots to leaves.

Phagocyte

A type of white blood cell featuring a multi-lobed nucleus that engulfs and digests foreign pathogens through phagocytosis.

Lymphocyte

A white blood cell with a large nucleus that recognises specific antigens and produces complementary antibodies and antitoxins.

Homeostasis

The maintenance of a constant internal environment (such as body temperature and water content) despite external environmental changes.

Tropism

The growth response of a plant towards or away from a directional stimulus (e.g. light or gravity).

Auxin

A plant growth hormone/signal molecule produced in shoot tips that stimulates cell elongation on the shaded side of stems.

Central Nervous System (CNS)

The division of the nervous system consisting of the brain and spinal cord, linked to sense organs by sensory and motor nerves.

Synapse

The junction or physical gap between two neurones across which chemical neurotransmitters diffuse.

Accommodation

The reflex changes in the eye involving the ciliary muscles and suspensory ligaments that alter lens curvature to focus on objects at varying distances.

Vasodilation

The widening of arterioles supplying skin capillaries to increase blood flow near the skin surface and increase heat loss when body temperature is high.

Vasoconstriction

The constriction of arterioles supplying skin capillaries to decrease blood flow near the surface and minimise heat loss when body temperature is low.

Pollination

The transfer of pollen grains from the anther of a flower to the receptive stigma.

Germination

The resumption of growth of a seed embryo using stored food reserves, requiring water, oxygen, and warmth.

Genome

The entire DNA and genetic material of an organism.

Gene

A section of DNA on a chromosome that codes for a specific sequence of amino acids to produce a protein.

Allele

An alternative or distinct form of the same gene that gives rise to different characteristics.

Genotype

The specific combination of alleles possessed by an organism for a given gene (e.g. $BB$, $Bb$, or $bb$).

Phenotype

The observable physical characteristics or traits of an organism resulting from its genotype and environmental influences.

Dominant Allele

An allele that is always expressed in the phenotype, even if only one copy is present.

Recessive Allele

An allele that is only expressed in the phenotype when two copies are present and no dominant allele is present.

Homozygous

Having two identical alleles for a particular gene (e.g. $BB$ or $bb$).

Heterozygous

Having two different alleles for a particular gene (e.g. $Bb$).

Haploid

A cell or nucleus containing a single unpaired set of chromosomes ($n$, e.g. $23$ in human gametes).

Diploid

A cell or nucleus containing two complete sets of homologous chromosomes ($2n$, e.g. $46$ in human body cells).

Mitosis

A type of nuclear cell division that produces two genetically identical diploid daughter cells for growth, tissue repair, and asexual reproduction.

Meiosis

A type of reduction division occurring in reproductive organs that produces four genetically distinct haploid gametes.

Mutation

A rare, random change in the DNA base sequence of an organism that can be inherited.

Natural Selection

The process whereby organisms better adapted to their environment tend to survive, reproduce, and pass on their advantageous alleles to offspring.

Ecosystem

A biological community of interacting organisms and their physical, non-living (abiotic) environment.

Community

All the populations of different species living and interacting together in a particular ecosystem.

Population

All the individuals of a single species living in a specific habitat at the same time.

Habitat

The specific place or physical environment where an organism resides.

Trophic Level

The specific feeding position that an organism occupies within a food chain or food web.

Biomass

The total dry mass of living biological material in an organism or trophic level.

Eutrophication

The process whereby leached mineral fertilisers enter waterways, leading to algal blooms, light blockage, death of aquatic plants, and severe oxygen depletion caused by respiring decomposers.

Biological Control

The deliberate introduction of a natural predator or parasite to control the population of a specific agricultural pest.

Fermenter

A sterilised, temperature-controlled vessel used to culture microorganisms under optimum conditions to produce biological products on a commercial scale.

Restriction Enzyme

An enzyme used in genetic engineering to cut double-stranded DNA molecules at a specific recognition base sequence.

DNA Ligase

An enzyme used in genetic engineering to join cut fragments of DNA together by repairing the sugar-phosphate backbone.

Vector

A vehicle (such as a bacterial plasmid or bacteriophage virus) used to transfer foreign genetic material into a host organism.

Transgenic Organism

An organism that contains functional recombinant DNA introduced from a different species.