AQA A2 Biology Notes Populations

My notes taken from the AQA A2 Biology text book on the populations chapter, no copyright intended, please dont copy my notes you may use them but please dont reproduce

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  • Created on: 04-01-13 15:04
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1.1 Populations and ecosystems
Ecology is the study of inter-relationships between organisms and their
Abiotic ­ non-living components (Rain, Temperature)
Biotic ­ living components (Organisms, Competition)
Biosphere ­ layer of land, air and water that surrounds the earth
Ecosystems and self-contained functional units, Two major components;
AQA Biology A2 Notes

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Flow of energy
Cycling of elements
Population ­ group of interbreeding organisms of a species in a habitat
Boundaries of a population can be difficult to define
Populations of different species make up a Community
A community can be defined as all the populations of different species living or
interacting at the same time in a same place
Habitat ­ place where a community lives
In an ecosystem there are many habitats
In a habitat there are microhabitats
AQA Biology A2 Notes…read more

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Niche ­ describes how an organism fits into its environment
Niche refers to where the organism lives and what it does there (Predator or
No two species can occupy the same niche
1.2 Investigating Populations
To study a habitat you need to count the number of species in a given space
Small samples are studied as its impossible to count all species in a large area.…read more

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Number of quadrats in the study area ­ larger number will give more reliable
results but recording can be time consuming. Balance needed between the
time and the validity. Greater number of species being recorded the greater
number of quadrats needed to get valid results.
Position of each quadrat within the study area ­ random sampling needed to
be used.
Random sampling used to avoid bias in collection of data.
Ensures data is valid.…read more

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Obtain a series of coordinates by using random numbers taken from table or
generated by a computer.
Place quadrat at the intersection of each pair of coordinates and record
species within.
More informative to measuse abundance systematically rather than randomly.
Stages of zonation shown well when using transects
Line transect consists of tape stretched along the ground in straight lines, organism
under it is recorded
Belt transects two tapes a meter wide species within the belt are recorded.…read more

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Frequency ­ likelihood of particular species appearing in the quadrat. Gives a quick
idea of species present. Doesn't provide information about density or distribution
Percentage cover ­ estimate of area within quadrat that particular plant/species
appears. Useful when abundance is difficult to count. Data collected rapidly. Less
useful when species overlap.
Necessary to ensure that the sample size is large, mean of all samples is used.…read more

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Estimate population size = total number of individuals on first sample x total number
of individuals in second sample/ number of marked individuals recaputed
Proportion of marked to unmarked is second sample is same as proportions of
marked to unmarked as a whole population
Marked individuals released first distributed themselves evenly amongst the
Population has a definite boundary no immigration
Few deaths and births in population
Method of marking isn't toxic, doesn't make individual more conspicuous
Mark isn't rubbed off during investigation.…read more

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Data has to be analysed and interpreted.
Present the data in form of table or graph
1.…read more

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A period population growth declines, its size remains stable. Due to food supply
limiting factors.
Many factors affect the overall size of the population. Changes in factors change the
overall size.
Abiotic factor ­ concerned with the non-living part of environment
Biotic factor ­ concerned with the activities of living organisms and include
competition and predation
Abiotic conditions that affected population size;
Temperature ­ each species has optimum temperature that is best for it to
survive.…read more

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Plants and cold-blooded animals, below optimum temp enzymes
work slower and metabolic rate slows. Temp to high, enzymes denature
population grows slower. Warm blooded animals can maintain a constant
temperature. Further temperature gets from optimum more energy
organisms use to keep normal body temperature. Leaves less energy for
growth and reproductive rates slow population size gets smaller
Light ­ source of energy for ecosystems. Rate of photosynthesis increases
as light intensity increases. Greater rate of photosynthesis faster plants grow,
more seeds produced population increases.…read more


ali wasi


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