AQA Biology Unit 4 Key Definitions

just a sheet that i've made with all the key definitions from unit 4 on it, hope you find it helpful

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  • Created on: 11-12-12 20:19
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Emma Wayne A2 Biology
Key Definitions
Ecosystem- all the organisms living in a particular area and all the non-living (abiotic) conditions e.g. a
freshwater ecosystem such as a lake.
Population- a group of interbreeding organisms in one species in a habitat e.g. population of green
woodpeckers in a woodland.
Community- all the populations of different organisms living and interacting in a particular place at the same
Habitat- the place where an organism lives. Within one ecosystem there are many habitats.
Niche- describes how an organism fits into the environment and its role e.g. what is does, where it lives, what
it eats etc. No two species will have exactly the same niche.
Abiotic Conditions- the non-living features of an ecosystem.
Biotic Conditions- the living features of an ecosystem
Adaptation- A feature that members of a species have that increases their chance of survival and
Intraspecific Competition- when organisms of the same species complete with each other for the same
Interspecific Competition- when organisms of different species compete with each other for the same
Population Growth- population growth = (births + immigration) - (deaths + emigration)
Population Growth Rate-
population change during the period
% population growth rate (in a given period) =
population change at the start of the period ×100
number of births per year
Birth Rate- total population in the same year ×100
number of deaths per year
Death Rate- total population in the same year ×100
Life Expectancy- the age at which 50% of the population are still alive
Producers- photosynthetic organisms that manufacture organic substances using light energy, water and
carbon dioxide.
Consumers- organisms that obtain their energy by feeding on other animals rather than using the energy of
sunlight directly.
Decomposers- a group of organisms that break down dead producers and consumers. In doing so they
release valuable minerals and elements in a form that can be absorbed by plants and so contribute to
Trophic Level- each stage in a food chain

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Emma Wayne A2 Biology
Phenotype- actual appearance of an organisms, result of the genotype and environment.
Genotype- the genetic composition of an organism.
Allele- different forms of the same gene.
Gene- a section of DNA that codes for a polypeptide chain (protein).
Dominant- expresses itself even when present with the recessive allele of the same gene.
Recessive- expresses itself only in the presence of another identical allele.
Co-dominant- if both alleles contribute to the phenotype.…read more


Josh Rigby

Thanks, I'm sure this will help my revision run a lot smoother! :) 

Rebecca Rolph

Thanks this was so helpful!! :)


With both birth rate and death rate it's x1000 not x100 otherwise great :D

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