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Summary Notes
The Biosphere - How it Works
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A habitat is the place where an organism lives.
A population is all the animals or plants of one species living in a
particular habitat.
A community is all the plants and animals in a particular habitat.
An ecosystem is the habitat together with all the plants and
animals (communities).
A food chain is a diagram which shows simple feeding relationships
Clover
Rabbit
Fox
The arrows in a food chain show the direction of the flow of
energy
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sparrow
ladybird
greenfly
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wolf
weasel
sheep
rabbit
grass
clover
If the sheep are removed there may be a decrease in the size of the
wolf population as one of their food sources has been removed. There
may be a decrease in the rabbit and weasel populations as they will
have increased predation by wolves. There may be more clover as less
will be eaten by sheep. (C)
Energy can be lost from a food chain as heat, in faeces or when it
is used for movement.
A pyramid of numbers is a diagram that shows the number of organisms
at each stage in a food chain. (C)
A pyramid of numbers is usually a pyramid shape but may have a
diamond shape in the case of a large single producer (like a tree). (C)
A pyramid of biomass is a diagram that shows the total mass of
organisms at each stage in a food chain. (C)
A pyramid of biomass is always a pyramid as the mass of producers will
always be greater than the mass of consumers. (C)
The growth rate of any population will depend on the birth rate
and the death rate.
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Under ideal conditions the growth curve of a population will look like:
a)
c)
b)
Little growth as there are few
individuals to reproduce
b) Rapid growth as there is
plentiful food and a lack of
predators
c) Growth slows and stops as food
a)
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supplies or space run out and
there is a build up of waste
products
The growth of a population can be limited by: predation, lack of
food or water, disease, build up of toxic wastes and lack of space.
Competition occurs when 2 or more individuals need a resource (like
food or shelter) that is in short supply.
When 2 species compete for a resource the result will be a
reduction in the population size of the poorer competitor.
Nutrients like carbon and nitrogen need to be recycled so they are
available for new growing organisms.
Nitrogen is an element required to make protein (C)
Plants can only take nitrogen in the form of nitrate. (C)
The protein in dead plants and animals is converted by bacteria into
ammonium compounds then to nitrites and then to nitrates. (C)
Nitrogen fixation is when nitrogen-fixing bacteria convert nitrogen gas
into nitrates. It occurs in the soil and in the root nodules of legumes
(like clover, peas and beans). (C)
Denitrification is when denitrifying bacteria convert nitrites back in
to Nitrogen gas.(C)
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(C)
(C)