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Aqa a level biology definitions
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A-Level Biology Key DefinitionsActive immunity: when immune response of the body is stimulated to produce own antibodies upon
detection of a pathogen. (Takes longer than passive but is longer lasting).
Passive immunity: by the introduction of antibodies into the body. (Foetus gets from placenta).
Resolution: The ability to distinguish two different points in a specimen.
Pulmonary artery: The artery that carries deoxygenated blood from the heart to the lungs.
Pulmonary vein: The vein that brings oxygenated blood to the heart.
Renal artery: The artery that carries oxygenated blood to the kidneys from the heart.
Renal vein: The vein that carries deoxygenated blood away from the kidneys back to the heart.
Classification: The organisation of organisms into groups.
Directional selection: A type of selection that occurs when environment changes, acts against one of
extremes.
Gene: A section of DNA on a chromosome that codes for the production of one or more polypeptide
chains.
Gene pool: Set number of alleles in a species. Bigger gene pool=greater variation.
Genetic diversity: The number of different alleles in a population. Can be investigated by comparing
observable characteristics.
Genome: The complete set of genes in a cell.
Homologous chromosomes: A pair of chromosomes which contain the same genes in the same
place.
Independent segregation: The random separation of homologous chromosomes in meiosis 1 that
produces genetic variation.
Natural selection: The process by which the frequency of ‘advantageous’ alleles gradually increases
in a population’s gene pool over time.
Phylogenetic classification: A type of classification that divides organisms into groups based on
evolutionary relationships. It uses a hierarchy in which smaller groups are contained within larger
groups, with no group overlap.
Species: A group of organisms with similar characteristics that are able to breed with one another to
produce fertile offspring.
Species diversity: A measure of the number of different species and the abundance of individuals in
each of these species within a community.
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