81 terms

IGCSE BIOLOGY DEFINITIONS

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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
reproduction
the processes that make more of the same kind of organism
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
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
a 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
a substance that increases the rate of a chemical reaction and is not changed by the reaction
enzymes
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
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.
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
a synapse
a junction between two neurones
sense organs
groups of receptor cells responding to specific stimuli: light, sound, touch, temperature and chemicals
a 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 explaining that homeostasis is the control of internal conditions within set limits and the control by negative feedback
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
a 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
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
aerobic respiration
the chemical reactions in cells that use oxygen to break down nutrient molecules to release energy
gene
a length of DNA that codes for a protein
a haploid nucleus
a nucleus containing a single set of unpaired chromosomes, e.g. in gametes
a 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
allele
a version of a gene
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 if it is present
recessive
an allele that is only expressed when there is no dominant allele of the gene present
a sex-linked characteristic
a characteristic in which the gene responsibleis 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
adaptive feature
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
the process of adaptation
the process, resulting from natural selection, by which populations become more suited to their environment over many generations
a food chain
showing the transfer of energy from one organism to the next, beginning with a producer
trophic level
the position of an organism in a food chain, food web, pyramid of numbers or pyramid of biomass
a 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
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
a 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
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