Definitions IGCSE Flashcards
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
The 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
Organs
A structure made up of a group
of tissues, working together to perform specific
functions
Organ systems
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
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 molecule
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
The 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
The 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
Nerve impulse
An electrical signal that passes along nerve cells called neurones
Synapse
A junction between two neurones
Sense organ
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
Fertilization
The fusion of gamete nuclei to form a diploid zygote
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 disease
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 if it
is present
Recessive
An allele that is only expressed
when there is no dominant allele of the gene
present
Sex linked characteristic
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
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
Process of adaption
The process, resulting from natural selection, by which
populations become more suited to their environment over many generations
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
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
Decomposers
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
Genetic engineering
Changing the genetic material of an organism by removing, changing or inserting individual genes
Sustainable resource
A source 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
