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OCR A-Level Biology Ecosystems Summary

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Handwritten Summary by an Oxford Medical Student which covers all content necessary for an A* in Ecosystems at OCR Biology A-Level.

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Biotic factors food
Living factors that affect an ecosystem space competition breeding partners
:
, ,
,




Abiotic factors Non-living factors that offect an ecosystem
:





Light temperature water/oxygen availibility edaphic factors
, , ,




Biomass mass of
living
material present
:




↳ Biomass at a no
trophic level biomass present =
x .


organisms
measuring biomass Water must be discounted :

so
dry samples (dead) are often uses


Efficiency of biomass transfer Only:
a small proportion of food is converted to biomass
↳ Producers Not used for photosynthesis energy lost
au solar
energy is in reactions,
limiting factors
:


,



↳ Consumers Not all :
biomass (bones) is eaten , metabolic waste in heat and excretions

Ecological Efficiency :
Biomass available after transfer/biomass availible before transfer



Nitrogen Fixation Nitrogen fixing bacteria ie
:
· .




aztobacter and Rhizobium convert Ne-NH3
·
Nitrification :



Nitrifying bacteria is .
Nitrosomonas
and Nitrobacter Convert NHz-NO ? -
NO
·
Denitrification :

Anaerobic conditions NO ?-N2 :




·
Ammonification Decomposers :
convert
nitrogen
rich molecules into ammonium compounds




Photosynthesis Converts CO2 to molecules
:
·




containing carbon in plants
Respiration Releases CO2 gas to the atmosphere
·
:




feeding Carbon molecules transferred from producers
·
:
are

to consumers
·

Decomposition :
CO2 is released

fluctuations in CO2 No :



photosynthesis at
night and
increased human activity causes CO2 levels to fluctuate

Primary succession Bare
newly formed rock
Secondary succession Soil but no
organisms
:

or
:




Pioneer Arrives seeds ie lichen
Community or
Algae
as
spores or
:




.Reproduce
↳ nitrogen withstand harsh conditions , can fix
quickly photosynthesise , ,




Intermediate community Species that thrive on the rich soil produced by decomposed pioneer species
:




Climax Community Stable community displaying little change over time
:




Plagiodimax Artificially deflected :

succession is by human activity

Document information

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Uploaded on
October 11, 2023
Number of pages
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Written in
2023/2024
Type
Summary
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