IGCSE Biology definitions (Extended)

Movement,

an action by an organism or part of an organism causing a change of position or place

Respiration,

the chemical reactions in cells that break down nutrient molecules and release energy for metabolism

Sensitivity,

the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses

Growth,

a permanent increase in size and dry mass by an increase in cell number or cell size or both

Excretion,

removal from organisms of the waste products of metabolism (chemical reactions in cells including respiration), toxic materials, and substances in excess of requirements

Nutrition,

taking in of materials for energy, growth and development; plants require light, carbon dioxide, water and ions; animals need organic compounds and ions and usually need water

Reproduction,

the processes that make more of the same kind of organism

Species,

a group of organisms that can reproduce to produce fertile offspring

Binomial system of naming species,

an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and species

Tissue,

a group of cells with similar structures, working together to perform a shared function

Organ,

structure made up of a group of tissues, working together to perform specific functions

Organ system,

a group of organs with related functions, working together to perform body functions

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

Osmosis,

the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane

Active transport,

the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration

Catalyst,

substance that increases the rate of a chemical reaction and is not changed by the reaction

Enzymes,

as proteins that function as biological catalysts

Photosynthesis,

the process by which plants manufacture carbohydrates from raw materials using energy from light

Limiting factor,

Something present in the environment in such short supply that it restricts life processes

Ingestion,

the taking of substances, e.g. food and drink, into the body through the mouth

Mechanical digestion,

the breakdown of food into smaller pieces without chemical change to the food molecules

Chemical digestion,

as the breakdown of large, insoluble molecules into small, soluble molecules

Absorption,

the movement of small food molecules and ions through the wall of the intestine into the blood

Assimilation,

the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells

Egestion,

the passing out of food that has not been digested or absorbed, as faeces, through the anus

Transpiration,

loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata

Translocation,

the movement of sucrose and amino acids in phloem: - from regions of production (source) - to regions of storage OR to regions where they are used in respiration or growth (sink)

Pathogen,

a disease-causing organism

Transmissible disease,

a disease in which the pathogen can be passed from one host to another

Active immunity,

defence against a pathogen by antibody production in the body

Passive immunity,

Short-term defence against a pathogen by antibodies acquired from another individual, e.g. mother to infant

Aerobic respiration,

the chemical reactions in cells that use oxygen to break down nutrient molecules to release energy

Anaerobic respiration,

the chemical reactions in cells that break down nutrient molecules to release energy without using oxygen

Deamination,

the removal of the nitrogen-containing part of amino acids to form urea

Synapse,

a junction between two neurones

Sense organs,

groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals

Hormone,

a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs

Homeostasis,

the maintenance of a constant internal environment

Gravitropism,

a response in which parts of a plant grow towards or away from gravity

Phototropism,

a response in which parts of a plant grow towards or away from the direction from which light is coming

Drug,

any substance taken into the body that modifies or affects chemical reactions in the body

Asexual reproduction,

a process resulting in the production of genetically identical offspring from one parent

Sexual reproduction,

a process involving the fusion of the nuclei of two gametes (sex cells) to form a zygote and the production of offspring that are genetically different from each other

Fertilisation,

the fusion of gamete nuclei

Pollination,

the transfer of pollen grains from the anther to the stigma

Self-pollination,

the transfer of pollen grains from the anther of a flower to the stigma of the same flower or different flower on the same plant

Cross-pollination,

transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species

Sexually transmitted infection,

An infection that is transmitted via body fluids through sexual contact

Inheritance,

the transmission of genetic information from generation to generation

Chromosome,

a thread-like structure of DNA, carrying genetic information in the form of genes

Gene,

a length of DNA that codes for a protein

Allele,

a version of a gene

Haploid nucleus,

a nucleus containing a single set of unpaired chromosomes, e.g. in gametes

Diploid nucleus,

a nucleus containing two sets of chromosomes, e.g. in body cells

Mitosis,

nuclear division giving rise to genetically identical cells

Meiosis,

reduction division in which the chromosome number is halved from diploid to haploid resulting in genetically different cells

Genotype,

the genetic make-up of an organism in terms of the alleles present

Phenotype,

the observable features of an organism

Homozygous,

having two identical alleles of a particular gene

Heterozygous,

having two different alleles of a particular gene

Dominant,

an allele that is expressed (in the phenotype) if it is present

Recessive,

an allele that is only expressed when there is no dominant allele of the gene present

Sex-linked characteristic,

a characteristic in which the gene responsible is located on a sex chromosome and that this makes it more common in one sex than in the other

Variation,

differences between individuals of the same species

Gene mutation,

a change in the base sequence of DNA

Mutation,

genetic change

Adaptive feature,

an inherited feature that helps an organism to survive and reproduce in its environment or the inherited functional features of an organism that increase its fitness

Fitness,

the probability of an organism surviving and reproducing in the environment in which it is found

Process of adaptation,

the process, resulting from natural selection, by which populations become more suited to their environment over many generations

Evolution,

the change in adaptive features of a population over time as the result of natural selection

Food chain,

Diagram showing the transfer of energy from one organism to the next, beginning with a producer

Food web,

a network of interconnected food chains

Producer,

an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis

Consumer,

an organism that gets its energy by feeding on other organisms

Herbivore,

an animal that gets its energy by eating plants

Carnivore,

an animal that gets its energy by eating other animals

Decomposer,

an organism that gets its energy from dead or waste organic material

Trophic level,

the position of an organism in a food chain, food web, pyramid of numbers or pyramid of biomass

Population,

a group of organisms of one species, living in the same area, at the same time

Community,

all of the populations of different species in an ecosystem

Ecosystem,

a unit containing the community of organisms and their environment, interacting together, e.g. a decomposing log, or a lake

Genetic engineering,

changing the genetic material of an organism by removing, changing or inserting individual genes

Sustainable resource,

one which is produced as rapidly as it is removed from the environment so that it does not run out.

Sustainable development,

development providing for the needs of an increasing human population without harming the environment

Balanced diet,

one which contains the right amount of each nutrient to meet the needs of the individual without causing malnutrition.

Diarrhoea,

the loss of watery faeces

Circulatory system,

a system of blood vessels with a pump and valves to ensure one-way flow of blood

Coronary heart disease,

Disease caused by the blockage of coronary arteries: possible risk factors include diet, stress, smoking, genetic predisposition, age and gender

Lymphatic system,

a system of lymphatic vessels and lymph nodes that are involved in the circulation of body fluids(lymph) and the protection of the body from infection

Blood clotting,

The conversion of fibrinogen to fibrin to form a mesh preventing blood loss and preventing the entry of pathogens

Nerve impulse,

an electrical signal that passes along nerve cells called neurones

Reflex action,

a means of automatically and rapidly integrating and coordinating a given stimuli with the specific responses of particular effectors (muscles and glands)

Adrenaline,

the hormone secreted in 'fight or flight' situations which causes an increase in breathing and pulse rate, widened pupils and an increase in blood glucose concentration.

Antibiotics,

Drugs used for the treatment of bacterial infection (have no effect on viruses)

Stem cells,

unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions