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Biology AQA Unit 4 Notes

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  A2-LevelBiology Revision Pack  Unit 4: Populations & The Environent  !ae: Teacher:    Section 1.1 – Populations and ecosystems Ecology The stu#y o$ inter-relationships %eteen organiss an# their environent Abiotic  ' non living coponents Biotic  ' living coponentsThe supporting layers o$ lan#( air an# ater that surroun#s the earth is calle# the  %iosphere) Ecosystems *a#e up o$ all the interacting a%iotic an# %iotic $eatures o$ a speci$ic area+pecies are a#e up o$ any groups o$ in#ivi#uals calle# populations) Populations A population is a#e up o$ all the inter%ree#ing organiss o$ one species in a ha%itatBoun#aries o$ populations can %e #i$$icult to #e$inePopulations o$ #i$$erent species $or a counity Community A counity is a#e up o$ all the #i$$erent populations o$ #i$$erent species living an# interacting in a given place at a given tie) Habitat A ha%itat is a place here a counity o$ organiss live) Ecological niche ,escri%es ho an organis $its into its environent Re$ers to here an organiss lives an# hat it #oes therenclu#es all %iotic an# a%iotic re.uireents $or an organis to live !o to species ill occupy the e/act sae niche  Section 1.2 – Investigating Populations ,ue to tie constraints an# collateral #aage( only sall areas ithin a ha%itat are stu#ie# in #etail0 these saples represent the population as a hole) The larger the nu%er o$ saples( the ore representative o$ the counity the results ill %e) Random sampling  ' 1ua#rat Systematic sampling  ' Transect Size of quadrate  ' Larger .ua#rats are use#to easure larger species) $ the speciesoccurs in groups( a large nu%er o$ sall.ua#rats shoul# %e use#) Number of quadrats  ' reater nu%er o$ species( greater nu%er o$ .ua#rats Position of quadrats  ' Ran#o Systematic Sampling ine transect  ' use# to illustrate a transition along hich counities o$  plants3anials change) E)g) onationProvi#es a ay o$ %eing a%le to clearly visualise the changes taking placeAny organis over hich the line passes is recor#e#) Belt transect !  provi#es in$oration o$ the #ensity o$ a species) $ #etaile# #ensity is re.uire# a %elt transect shoul# %e use#) Abundance  ' !u%er o$ species in a given space requency ! chance o$ a particular species occurring ithin a .ua#rat Percentage co#er  ' Estiate o$ the area ithin a .ua#rat that a species occupies To easure the a%un#ance o$ a o%ile species: Estimate of population $ no% indi#iduals caught in first sample & no% caught in second sample No% recaptured Assumptions' ã Proportion o$ arke#3unarke# in#ivi#uals is the secon# saple is the sae $or the hole population ã n#ivi#uals in the $irst saple #istri%ute theselves evenly ã The population has a #e$inite %oun#ary) 5no iigration3igration6 ã Birth3,eath is lo ã *arking etho# is not to/ic3 conspicuous ã *arking is not lost  Section 1.3 – Variation in population size Population gro(th cur#es roth curves o$ populations usually have three ain phases:7)6A perio# o$ slo groth #ue to the $act that there is only a liite# nu%er o$ inter%ree#ing species2)6A perio# o$ rapi# groth(cause# %y the ever increasein organiss that are a%leto repro#uce) 8or eachinterval o$ tie the population si9e #ou%les)6Population si9e %egins tolevel o$$ as there areliiting $actors on the population groth such asavaila%ility o$ resources) Population size  !o population groth ill continue in#e$initely) This is %ecause in tie there ill eventually %e liiting $actors that ill liit the population si9e)The various $actors that liit population si9e can %e o$ to types( a%iotic an#  %iotic) Abiotic ã )emperature  ' Each species has an optiu teperature at hich they survive %est at) The $urther a group o$ organiss are aay $ro this teperature( the saller there groth rate ill %e) $ they are %elo the teperature( eta%olic rate ay%e loer i$ they are col# %loo#e#) ;oever i$ they are aals( they ill pro#uce heat #uring respiration( at lo teperatures ore energy is use# to aintain a sta%le %o#y teperature an# less is use# $or groth) ã ight  ' Light is the ultiate source o$ energy $or an ecosyste) $ light intensity is greater in plants( the ore energy they can use to create spores an# see#s an# so they repro#uce .uicker) ã pH  ' A$$ects the $unction o$ en9yes) En9yes ork %est at #i$$erent p; levels an# so i$ an organis e/ists soehere here there are ore appropriate p; levels then they ill likely have a larger population) ã *ater and hui#ity ' hui#ity a$$ects transpiration rates in plants an# the rate o$ evaporation o$ ater $ro anials)

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