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Summary iGCSE Biology Pearson Edexcel Topic 4 Ecology and the Environment Complete Notes
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iGCSE Biology Pearson Edexcel Topic 4 Ecology and the Environment Complete Notes
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IGCSE BIOLOGY – TOPIC 4ECOLOGY AND THE ENVIRONMENT
a) THE ORGANISM IN THE ENVIRONMENTS
• POPULATION – a group organisms of one species, living in the same area
at the same time
• COMMUNITY – all populations of different species living in the same area
• HABITAT – the place where living organisms live
• ECOSYSTEM – the community of organisms and the habitat they live in
• PRACTICAL – investigate the population size of an organism in two
different areas using quadrats
o Place quadrat randomly within sampling area
o Count the number of an organism of the same species within the
quadrat
o Repeat this numerous times within sampling area using the same
size quadrat
o Calculate the estimate of the population size of an organism using
the equation:
Population Size = (Total Area / Sampled Area) x Number of
Organisms Found
o Repeat the process in a different area and compare results to see
if population size differs between areas
Always say to use a random
o A QUADRAT IS A SQUARE FRAME OF WIRE
number generator to find
SPLIT INTO FURTHER SQUARES – IT IS coordinates if use measuring
USUALLY RANDOM TO AVOID BIASED tape on a field!
RESULTS
This is a QUADRAT
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, • BIODIVERSITY – a measure of how many different species of organisms
live in an ecosystem – it is the number of species, not the number of
organisms!
• PRACTICAL - investigate the distribution of organisms in their habitats
and measure biodiversity using quadrats – similar to previous but now
count NUMBER OF DIFFERENT SPECIES within quadrat
• ABIOTIC FACTORS – non-living factors that can affect the size and
distribution of populations
o LIGHT INTESNITY –plants require different amounts of
sunlight, affecting whether plants choose to grow in the
shade or in direct light
o MOISTURE LEVELS – plants require different amounts of
moisture/water – some are not drought tolerant and prefer
boggy conditions
o TEMPERATURE – animals and plants grow optimally at
specific temperatures and these affect the growth and
reproduction of species
o OXYGEN LEVELS – organisms need different amounts of
oxygen to survive – aquatic organisms require clean water
with high oxygen levels
o Others include pH, carbon dioxide levels and wind intensity
• BIOTIC FACTORS – living factors that can affect the size and distribution
of populations
o AVAILABILITY OF FOOD – areas that are not rich and diverse in
food have less animals as these areas cannot provide for the
animals
o PREDATORS – predators prevent prey populations increasing out
of control, having an effect on the numbers in a population
o PATHOGENS – introduction of a new pathogen to a population can
cause widespread disease through the population
o COMPETITION FOR FOOD, WATER OR SHELTER – animal compete
for their needs so they can survive in their ecosystem
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