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A2 Biology Unit 4 Key Terms and DefinitionsMake sure you use these terms when answering exam questions!Chapter 1 – PopulationsBook RefKey TermDefinition1.1EcosystemSelf-contained unit made up of the biotic and abiotic factors in an area1.1PopulationA group of individuals of the same species in a habitat1.1CommunityThe organisms of all species that live in the same area1.1HabitatThe place where an organism normally lives1.1NicheAll the conditions and resources required for an organism to survive and reproduce (its ‘role’)1.2Random SamplingSampling a population to eliminate bias e.g. grid square and co-ordinates1.2Systematic SamplingRegular sampling across an area e.g. along a straight line transect1.2Mark-Release-RecaptureMethod of estimating population size of animals (number in first sample x number in second sample) / marked animals in second sample1.3Abiotic FactorsConcerned with the non-living part of the environment1.3Biotic FactorsConcerned with the living organisms in the environment1.4Interspecific CompetitionCompetition between organisms of different species1.4Intraspecific CompetitionCompetition between organisms of the same speciesChapter 2 – ATPBook RefKey TermDefinition2.1EnergyThe ability to do work2.1PhosphorylationThe process of adding a phosphate group (e.g. ADP ATP)Chapter 3 – PhotosynthesisBook RefKey TermDefinition3.1Light Dependent ReactionStage of photosynthesis in which light energy is required to produce ATP and reduced NADP3.1Light Independent ReactionStage of photosynthesis which does not require light energy directly, but does need the products of the light dependent reaction to reduce CO2 and form carbohydrate3.2OxidationLoss of electrons, combining oxygen with a substance3.2ReductionGain of electrons, loss of oxygen from a substance3.2Electron Carrier MoleculesA chain of carrier molecules along which electrons pass, releasing energy in the form of ATP as they do so3.2Photolysis of WaterLight energy splits water molecules, yielding electrons, hydrogen ions and oxygen (light-dependent reaction)3.3Calvin CycleA biochemical pathway (part of the light-independent reaction) where CO2 is reduced to form carbohydrateCO2 + RuBP GP TP Glucose or RuBP3.4Limiting FactorA variable that limits the rate of a chemical reactionChapter 4 – RespirationBook RefKey TermDefinition4.1GlycolysisFirst part of cellular respiration in which glucose is broken down (in the cytoplasm) to 2 molecules of pyruvate4.2Link ReactionProcess linking Glycolysis to the Krebs Cycle (in the matrix of the mitochondria), where the 2 molecules of pyruvate are converted to CO2 and acetylcoenzyme A4.2Krebs CycleIntroducing acetylcoenzyme A into a cycle of oxidation-reduction reactions (in the matrix of the mitochondria) that yield some ATP and a large number of electrons4.3Electron Transport ChainUse of electrons from the Krebs Cycle to synthesise ATP via a series of oxidation-reduction reactions4.4Anaerobic RespirationReleasing energy from glucose without oxygen (produces lactate in animals and ethanol in plants and some micro-organisms)Chapter 5 – Energy and EcosystemsBook RefKey TermDefinition5.1Trophic LevelEach stage in a food chain5.1ConsumersAn organism that obtains its energy by feeding on other organisms5.2Gross ProductionTotal quantity of energy that the plants in a community convert to organic matter5.2Net ProductionGross production – respiratory losses5.2Energy Transfer(Energy available after the transfer / energy available before the transfer) x 1005.3Pyramid of NumberA pyramid drawn with bar lengths proportional to the numbers of organisms present5.3Pyramid of BiomassA pyramid drawn with bar lengths proportional to the mass of plants/animals5.3Pyramid of EnergyA pyramid drawn with bar lengths proportional to the energy stored in organisms5.5Biological ControlControlling pests by introducing predators5.6Selective BreedingBreeding of organisms by human selection of parents for certain characteristicsChapter 6 – Nutrient CyclesBook RefKey TermDefinition6.1Saprobiotic Micro-organism(Saprophyte) An organisms that gets it food from the dead or decaying remains of other organisms6.2Greenhouse GasesGases such as methane and CO2 which trap more heat energy, raising the Earth6.3AmmonificationProduction of ammonia from e.g. urea and proteins6.3NitrificationConverting ammonia into nitrites and then nitrates6.3Nitrogen FixationConversion of nitrogen gas into nitrogen-containing compounds6.3DenitrificationConversion of soil nitrates into mitrogen gas6.5LeachingProcess by which nutrients are washed from the soil into watercourses6.5EutrophicationConsequence of an increase in nutrients in watercourses that leads to a decrease in biodiversityChapter 7 – Ecological SuccessionBook RefKey TermDefinition7.1SuccessionThe changes in an ecosystem, over time, of the species that occupy it7.1Pioneer SpeciesA species that can colonise bare rock or ground7.1Climax CommunityThe stable, final, community that exists in a balanced equilibrium7.2ConservationManagement of the Earth’s natural resources in such a way that maximum use can be made of them in the futureChapter 8 – Inheritance and SelectionBook RefKey TermDefinition8.1GenotypeThe genetic composition of an organism8.1PhenotypeThe characteristics of an organism (often visible), resulting from its genotype and the environment8.1GeneA length of DNA that codes for a polypeptide8.1AlleleOne form of a gene8.1Homologous ChromosomesA pair of chromosomes that have the same gene loci and determine the same features8.1Dominant An allele that is always expressed in the phenotype8.1RecessiveAn allele that is only expressed in the phenotype when there is another identical allele8.1HeterozygousWhen the alleles are different for a particular gene8.1HomozygousWhen the alleles are the same for a particular gene8.3Sex LinkageAny gene that is carried on the X or Y chromosome8.4Co-dominanceBoth alleles are equally dominant and are both expressed in a phenotype8.4Multiple AllelesMore than 2 possible alleles for a particular gene8.5Gene PoolAll the alleles of all the genes of all the individuals in a population at any one time8.5Allelic FrequencyThe number of times the allele occurs within a gene pool8.6Stabilising SelectionSelection that favours average individuals8.6Directional SelectionSelection that favours individuals at one extreme 8.7SpeciationThe evolution of new species from existing species8.7Geographical IsolationWhen a physical barrier prevents two populations from breeding with one another ................
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