AQA Biology A2 Unit 4 definitions

It's the definitions for Unit 4 AQA bio.

Self-contained unit made up of the biotic and abiotic factors in an area
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A group of individuals of the same species in a habitat
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The organisms of all species that live in the same area
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The place where an organism normally lives
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All the conditions and resources required for an organism to survive and reproduce (its ‘role’)
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Random sampling
Sampling a population to eliminate bias e.g. grid square and co-ordinates
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Systematic sampling
Regular sampling across an area e.g. along a straight line transect
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Method of estimating population size of animals (number in first sample x number in second sample) / marked animals in second sample)
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Abiotic facors
Concerned with the non-living part of the environment
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Biotic factors
Concerned with the living organisms in the environment
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Interspecific competition
Competition between organisms of different species
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Intraspecific competition
Competition between organisms of the same species
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The ability to do work
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The process of adding a phosphate group (e.g. ADP -> ATP)
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Light dependant reaction
Stage of photosynthesis in which light energy is required to produce ATP and reduced NADP
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Light independant reaction
Stage of photosynthesis which does not require light energy directly, but does need the products of the light dependent reaction to reduce CO2 and form carbohydrate
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Loss of electrons, combining oxygen with a substance
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Gain of electrons, loss of oxygen from a substance
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Electron carrier molecule
A chain of carrier molecules along which electrons pass, releasing energy in the form of ATP as they do so
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Photolysis of water
Light energy splits water molecules, yielding electrons, hydrogen ions and oxygen (light-dependent reaction)
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Calvin cycle
A biochemical pathway (part of the light-independent reaction) where CO2 is reduced to form carbohydrate CO2 + RuBP -> GP -> TP -> Glucose or RuBP
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Limiting factor
A variable that limits the rate of a chemical reaction
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First part of cellular respiration in which glucose is broken down (in the cytoplasm) to 2 molecules of pyruvate
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Link reaction
Process linking Glycolysis to the Krebs Cycle (in the matrix of the mitochondria), where the 2 molecules of pyruvate are converted to CO2 and acetylcoenzyme A
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Krebs cycle
Introducing acetylcoenzyme A into a cycle of oxidation-reduction reactions (in the matrix of the mitochondria) that yield some ATP and a large number of electrons
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Electron transport chain
Use of electrons from the Krebs Cycle to synthesise ATP via a series of oxidation-reduction reactions
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Anaerobic respiration
Releasing energy from glucose without oxygen (produces lactate in animals and ethanol in plants and some micro-organisms)
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Trophic level
Each stage in a food chain
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An organism that obtains its energy by feeding on other organisms
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Gross production
Total quantity of energy that the plants in a community convert to organic matter
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Net production
Gross production – respiratory losses
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Energy transfer
(Energy available after the transfer / energy available before the transfer) x 100)
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Pyramid of number
A pyramid drawn with bar lengths proportional to the numbers of organisms present
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Pyramid of biomass
A pyramid drawn with bar lengths proportional to the mass of plants/animals
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Pyramid of energy
A pyramid drawn with bar lengths proportional to the energy stored in organisms
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Biological control
Controlling pests by introducing predators
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Selective breeding
Breeding of organisms by human selection of parents for certain characteristics
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Saprobiotic microorganisms
(Saprophyte) An organisms that gets it food from the dead or decaying remains of other organisms
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Greenhouse gases
Gases such as methane and CO2 which trap more heat energy, raising the Earth
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Production of ammonia from e.g. urea and proteins
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Converting ammonia into nitrites and then nitrates
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Nitrogen fixation
Conversion of nitrogen gas into nitrogen-containing compounds
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Process by which nutrients are washed from the soil into watercourses
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Consequence of an increase in nutrients in watercourses that leads to a decrease in biodiversity
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The changes in an ecosystem, over time, of the species that occupy it
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Pioneer species
A species that can colonise bare rock or ground
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Climax community
The stable, final, community that exists in a balanced equilibrium
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Management of the Earth’s natural resources in such a way that maximum use can be made of them in the future
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The genetic composition of an organism
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The characteristics of an organism (often visible), resulting from its genotype and the environment
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A length of DNA that codes for a polypeptide
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One form of a gene
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Homologous chromosomes
A pair of chromosomes that have the same gene loci and determine the same features
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An allele that is always expressed in the phenotype
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An allele that is only expressed in the phenotype when there is another identical allele
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When the alleles are different for a particular gene
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When the alleles are the same for a particular gene
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Sex linkage
Any gene that is carried on the X or Y chromosome
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Both alleles are equally dominant and are both expressed in a phenotype
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Gene pool
All the alleles of all the genes of all the individuals in a population at any one time
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Allelic frequency
The number of times the allele occurs within a gene pool
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Stabilising selection
Selection that favours average individuals
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Directional selection
Selection that favours individuals at one extreme
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The evolution of new species from existing species
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Geographical isolation
When a physical barrier prevents two populations from breeding with one another
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Other cards in this set

Card 2


A group of individuals of the same species in a habitat



Card 3


The organisms of all species that live in the same area


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Card 4


The place where an organism normally lives


Preview of the back of card 4

Card 5


All the conditions and resources required for an organism to survive and reproduce (its ‘role’)


Preview of the back of card 5
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