Whole of Unit/Module 7 - genetics, populations, evolution and ecosystems for AQA A level Biology based on class notes, specification, textbooks, websites, videos and revision sessions. Summarised into bullet point notes that are quick and to the point with just information you need for the exam.
What is a species? group of organisms with similar characteristics that can interbreed to produce
fertile offspring
What is a population? all the individuals of a particular species in a particular place
What is a community? all the population of different species in a particular place
What is a habitat? the place where an organism lives
What is an ecosystem? a mix of different communities and habitats and how they interact based on
abiotic and biotic factors
What is ecological niche? an organisms role/position in an ecosystem – in terms of its interaction
with abiotic and biotic factors
Why can 2 different species not occupy the same ecological niche? interspecific competition will
take place for the limiting factors/resources (abiotic & biotic factors) – better adapted species will
out compete the other = competitive exclusion principle
How to sample plant species over a large area?
obtain a map of the area
divide the map into grids
select a large number of coordinates using a running mean
select a random set of coordinates using a random number chart
in each coordinate place a quadrat
measure abundance of the plant species in each quadrat = frequency or percentage cover
calculate average for the whole area
How to sample plants species along a path?
use a transect
place a tape along the path, count number of plants touching tape (Line Transect)
or
place a tape along the path, at regular intervals along the tape place a quadrat, measure
abundance within the quadrat (Belt Transect)
How to sample animal species in an area?
mark-release-recapture technique
set a trap
capture the animal species [Sample 1]
mark them (tag or fluorescent marker – ensure its non-toxic and not harmful)
release them
after some time (sufficient time for them to mix with the whole population), replace the
trap
count number in 2nd set [Sample 2] and count the number marked
estimate population size by: number in sample 1 x number in sample 2
marked in sample 2
, Assumptions of Mark-release-recapture technique?
no births or deaths
no immigration or emigration
marked animals mix evenly with population
mark is not toxic
mark does not come off
large population
What are the 3 stages of population growth?
slow/lag phase: species becomes adapted to new environment
rapid/log phase: species adapted, abundant resources, doubling with reproduction,
birth rate>death rate
stationary phase: resources become limited, intraspecific competition occurs,
birth rate = death rate
How are resources/limiting factors grouped?
abiotic (non-living): light, temperature, water, O2/CO2, minerals, pH, living space
biotic (living): predator, prey, mates, competition, disease
What is competition? when organisms compete for resources (abiotic and biotic)
What are the 2 types of competition?
intraspecific: occurs between organisms of the same species, only occurs when resources
become limited, leads to natural selection and adaptation
interspecific: occurs between organisms of different species, can happen at any time
even if resources are not limited, leads to formation of climax communities
Describe the predator/prey relationship?
prey increases in number
more food available for predator
predator increases in number (more energy available for reproduction & growth)
predator eats more of the prey
prey decreases in number
less food available for predator
predator decreases in number
less of the prey are eaten
prey increases in number [cycle repeats]
What is succession? how an ecosystem changes over time (change in species diversity and habitat
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