AQA BIOLOGY ALEVEL definitions, ALevel
AQA Biology, AQA ALEVEL BIOLOGY
VERIFIED A+ 2026
• Species -✓✓A group of similar organisms that can reproduce to give fertile offspring
• Population -✓✓A group of organisms of the same species living in a particular area at
a particular time
• Gene pool -✓✓The complete range of all the alleles of all the genes of all the
individuals present within a population at a given time
• Allele frequency -✓✓How often / how many times an allele occurs in a population
• Variation -✓✓The differences that exist between individuals
• Selection Pressure -✓✓Anything that affects an organisms chance of survival and
reproduction
• Evolution -✓✓A change in allele frequencies over time
• Stabilising selection -✓✓Where individuals with alleles for characteristics towards the
middle of the range are more likely to survive and reproduce
• Directional selection -✓✓Where individuals with alleles for characteristics towards one
end of the range are more likely to survive and reproduce
• Disruptive selection -✓✓Where individuals with alleles for characteristics towards both
ends of the range are more likely to survive and reproduce
• Speciation -✓✓The development of a new species from an existing species
• Geographical isolation -✓✓Individuals are completely separated by a physical barrier
• Allopatric speciation -✓✓Speciation due to geographical isolation
• Sympatric isolation -✓✓Speciation that does not require geographical isolation
• Reproductive isolation -✓✓Individuals from different populations have changed so
much that they can no longer breed with one another to give fertile offspring
,• Genetic drift -✓✓When chance rather than environmental factors dictate which
individuals survive breed and pass on their genes
• Gene -✓✓A sequence of bases on a DNA molecule that codes for a polypeptide
• Allele -✓✓A different version of a gene
• Genotype -✓✓The alleles an organism possesses
• Phenotype -✓✓The expression of the genotype of an organism - an organisms
characteristics
• Dominant -✓✓An allele whose characteristic is expressed in the phenotype even if
there is only one copy
• Recessive -✓✓An allele whose characteristic only appears in the phenotype if there
are two copies present
• Codominant -✓✓Two dominant alleles that are both expressed in the phenotype
• Locus -✓✓The fixed position of a gene on a chromosome
• Carrier -✓✓A person carrying an allele which is not expressed in their phenotype but
can be passed onto offspring
• Sex-linked genes -✓✓Genes carried on the sex chromosomes
• Autosome -✓✓Any chromosome that isnt a sex chromosome
• Epistasis -✓✓One gene affects / masks the expression of another gene
• Chi-squared test -✓✓A statistical test used to see if the results of an experiment
support a theory
• Habitat -✓✓The place where an organism lives
• Population -✓✓All the organisms of one species in a habitat
• Community -✓✓Populations of different species in a habitat
• Ecosystem -✓✓A community and all the abiotic conditions in the area which it lives
• Abiotic -✓✓The non living features of an ecosystem
, • Biotic -✓✓The living features of an ecosystem
• Niche -✓✓The role of a species within its habitat, such as what it its and when and
where it feeds
• Adaptation -✓✓A feature that members of a species have that increase their chances
of survival and reproduction
• Physiological adaptations -✓✓Adaptations that change the physical processes inside
an organisms body
• Behavioural adaptaions -✓✓Adaptations that change the way an organism acts
• Anatomical adaptations -✓✓Adaptations that change the structural features of an
organisms body
• Population size -✓✓The total number of organisms of one species in a habitat
• Carrying capacity -✓✓The maximum stable population size of a species that an
ecosystem can support
• Interspecific competition -✓✓Competition between different species for the same
resources
• Intraspecific competition -✓✓Competition within a species for the same resources
• Predation -✓✓Where an organism kills and eats another organism
• Dynamic -✓✓Constantly changing
• Primary succession -✓✓Occurs on land thats been newly formed or exposed, starts
when a new species colonise a new land surface
• Secondary succession -✓✓Happens on land thats been cleared of all the plants but
where soil remains - happens in the same was as primary succession but starts at a
later stage, with larger plants as there is already a soil layer
• Climatic climax -✓✓The climax community for a particular climate
• Plagioclimax -✓✓The climax community when succession is stopped artificially
• Conservation -✓✓The protection and management of ecosystems in a sustainable
way
AQA Biology, AQA ALEVEL BIOLOGY
VERIFIED A+ 2026
• Species -✓✓A group of similar organisms that can reproduce to give fertile offspring
• Population -✓✓A group of organisms of the same species living in a particular area at
a particular time
• Gene pool -✓✓The complete range of all the alleles of all the genes of all the
individuals present within a population at a given time
• Allele frequency -✓✓How often / how many times an allele occurs in a population
• Variation -✓✓The differences that exist between individuals
• Selection Pressure -✓✓Anything that affects an organisms chance of survival and
reproduction
• Evolution -✓✓A change in allele frequencies over time
• Stabilising selection -✓✓Where individuals with alleles for characteristics towards the
middle of the range are more likely to survive and reproduce
• Directional selection -✓✓Where individuals with alleles for characteristics towards one
end of the range are more likely to survive and reproduce
• Disruptive selection -✓✓Where individuals with alleles for characteristics towards both
ends of the range are more likely to survive and reproduce
• Speciation -✓✓The development of a new species from an existing species
• Geographical isolation -✓✓Individuals are completely separated by a physical barrier
• Allopatric speciation -✓✓Speciation due to geographical isolation
• Sympatric isolation -✓✓Speciation that does not require geographical isolation
• Reproductive isolation -✓✓Individuals from different populations have changed so
much that they can no longer breed with one another to give fertile offspring
,• Genetic drift -✓✓When chance rather than environmental factors dictate which
individuals survive breed and pass on their genes
• Gene -✓✓A sequence of bases on a DNA molecule that codes for a polypeptide
• Allele -✓✓A different version of a gene
• Genotype -✓✓The alleles an organism possesses
• Phenotype -✓✓The expression of the genotype of an organism - an organisms
characteristics
• Dominant -✓✓An allele whose characteristic is expressed in the phenotype even if
there is only one copy
• Recessive -✓✓An allele whose characteristic only appears in the phenotype if there
are two copies present
• Codominant -✓✓Two dominant alleles that are both expressed in the phenotype
• Locus -✓✓The fixed position of a gene on a chromosome
• Carrier -✓✓A person carrying an allele which is not expressed in their phenotype but
can be passed onto offspring
• Sex-linked genes -✓✓Genes carried on the sex chromosomes
• Autosome -✓✓Any chromosome that isnt a sex chromosome
• Epistasis -✓✓One gene affects / masks the expression of another gene
• Chi-squared test -✓✓A statistical test used to see if the results of an experiment
support a theory
• Habitat -✓✓The place where an organism lives
• Population -✓✓All the organisms of one species in a habitat
• Community -✓✓Populations of different species in a habitat
• Ecosystem -✓✓A community and all the abiotic conditions in the area which it lives
• Abiotic -✓✓The non living features of an ecosystem
, • Biotic -✓✓The living features of an ecosystem
• Niche -✓✓The role of a species within its habitat, such as what it its and when and
where it feeds
• Adaptation -✓✓A feature that members of a species have that increase their chances
of survival and reproduction
• Physiological adaptations -✓✓Adaptations that change the physical processes inside
an organisms body
• Behavioural adaptaions -✓✓Adaptations that change the way an organism acts
• Anatomical adaptations -✓✓Adaptations that change the structural features of an
organisms body
• Population size -✓✓The total number of organisms of one species in a habitat
• Carrying capacity -✓✓The maximum stable population size of a species that an
ecosystem can support
• Interspecific competition -✓✓Competition between different species for the same
resources
• Intraspecific competition -✓✓Competition within a species for the same resources
• Predation -✓✓Where an organism kills and eats another organism
• Dynamic -✓✓Constantly changing
• Primary succession -✓✓Occurs on land thats been newly formed or exposed, starts
when a new species colonise a new land surface
• Secondary succession -✓✓Happens on land thats been cleared of all the plants but
where soil remains - happens in the same was as primary succession but starts at a
later stage, with larger plants as there is already a soil layer
• Climatic climax -✓✓The climax community for a particular climate
• Plagioclimax -✓✓The climax community when succession is stopped artificially
• Conservation -✓✓The protection and management of ecosystems in a sustainable
way
